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Anthrotectonic Hylodynamics

Coupled Transport and the Biological Boundary Layer of the Building Envelope

Version 1.2 · 1st November 2026

Contents

• Abstract

• Part I · The problem

• Part II · The physical core

• Part III · The biological boundary layer and material physics

• Part IV · The human interface

• Part V · The living envelope in practice

• Part VI · Verification and falsification

• Part VII · The honesty firewall and register of retired claims

• Part VIII · Futures, open data and education

• Part IX · Limitations and referee objections

• Appendix A · Data architecture (illustrative)

• Apparatus · Glossary and symbol index

• References

• Credits

Abstract

Building physics usually treats the external envelope as an inert separator, with fixed material properties and a clean surface. This paper treats the envelope as an open, weather-driven system held away from equilibrium, whose outer surface is colonised by microorganisms and loaded by atmospheric deposits. This is a framing proposition. It assembles established results from transport physics, carbonate chemistry, microbial ecology, crystallisation mechanics, environmental psychology and UK statute. On those it builds one central, testable proposition: that the biological boundary layer measurably changes the surface moisture exchange of a wall, and so contributes to the gap between predicted and measured building performance.

Each claim states whether it is established or a proposition. Retired claims stay visible in a public register. Part VI sets out laboratory and field protocols by which the central proposition can be confirmed, bounded or rejected.

Illustrative figures are labelled as such. No figure is presented as a measurement of a specific building.

Part I · The problem

1.1 The envelope as a driven system

A building envelope separates a controlled interior from a variable exterior. Thermodynamically, a building is an open system. It can hold a locally ordered state only by a continuous throughput of energy and maintenance, exporting entropy to its surroundings, as living systems do (Schrödinger 1944, What is Life?; Prigogine 1977). This is established as physics. Without that throughput, weather, chemistry and biology drive the fabric towards degradation.

The framework calls the gap between the intended stability and this continuous forcing the anthrotectonic rift. The envelope is therefore treated as a slow event, not a fixed object.

1.2 Beyond cosmetic maintenance

Surface soiling, biological growth and efflorescence are commonly treated as appearance problems. The removal method is then chosen for visible effect, not for its effect on the material. I stated this as a proposition, or characterisation of practice.

Some removal methods can damage the substrate. High-pressure water impact, for example, can exceed the tensile strength of soft mortars by orders of magnitude (5.2). This is established physics. This paper treats each intervention as a deliberate change to the surface boundary condition of the wall, to be recorded, justified and, where possible, measured (5.4).

1.3 The performance gap

Innovate UK’s Building Performance Evaluation programme studied around 50 recently completed non-domestic buildings. Average measured carbon emissions were about 3.8 times the design estimate. The programme’s results were widely reported as energy use of about 3.5 times the design prediction. Building services, controls and operation were major contributors (Innovate UK 2016, Building Performance Evaluation Programme: Findings from Non-Domestic Projects, summary). This is established. Results for homes varied widely.

This paper advances a further contributor that current models omit: the moisture state of the external fabric, sustained by its biological surface. This is a proposition, tested in Part VI.

Part II · The physical core

The building envelope is treated here as an open system held away from equilibrium by weather. This is a framing proposition. Every equation in this part is established in its own field. This is established. Their combined application to a weathered, biologically colonised UK façade is the framework’s proposition. This is a proposition.

2.1 Non-equilibrium foundations

Near equilibrium, coupled heat and moisture flows are linear in their thermodynamic forces, and the cross-coefficients are equal (Onsager 1931; de Groot & Mazur 1962). This is established:

J_q = L_qq ∇(1/T) + L_qm(-∇(μ_w/T)), J_m = L_mq ∇(1/T) + L_mm(-∇(μ_w/T)), L_qm = L_mq

The simplified forms commonly written with -∇μ_w/T assume near-isothermal conditions. The cross-effects are thermal diffusion (Soret) and diffusion-thermo (Dufour). This is established.

In the linear regime, entropy production can never be negative. The dissipation function therefore acts as a Lyapunov certificate: the transport subsystem on its own has a stable state. This is established. This certificate applies to transport only. Once biology is active, the system becomes a far-from-equilibrium dissipative structure in the sense of Prigogine (1977). The category is established; its application to biofilms is a proposition.

2.2 Coupled heat and moisture transport

Conduction (Fourier):

q = -λ(u) ∇T

Conductivity rises with moisture content (BS EN ISO 10456 moisture conversion). This is established.

Liquid flow (Darcy 1856; Richards 1931), closed by van Genuchten (1980) and Mualem. This is established:

∂θ/∂t = ∇·[K(h)(∇h + ∇z)]

Coupled balances (Künzel 1995; BS EN 15026). This is established:

(dw/dϕ)(∂ϕ/∂t) = ∇·(D_ϕ∇ϕ + δ_p∇(ϕ p_sat))

(dH/dT)(∂T/∂t) = ∇·(λ(w)∇T) + h_v ∇·(δ_p∇(ϕ p_sat))

Here H includes the enthalpy of the moisture held. Writing ρ c in its place is a linearised simplification. Latent heat h_v = 2.45×10⁶ J/kg.

Saturation vapour pressure (Magnus; BS EN ISO 13788). This is established:

p_sat(T) = 610.78 exp((17.27 T)/(237.3 + T)) Pa

2.3 The exterior boundary: rain, wind and particles

Wind-driven rain. Two routes are used:

• the semi-empirical form of Straube and Burnett (2005), G_wdr = RAF·DRF·U₁₀·R_h·cos θ;

• in the UK, the driving-rain indices of BS EN ISO 15927-3, with exposure per BS 8104.

The catch-ratio form, R_wdr = η R_h, follows Blocken and Carmeliet (2004). This is established.

Wind profile at the boundary (log law, from the RANS treatment of the Navier–Stokes equations). This is established:

U(z) = (u_*/κ) ln(z/z₀)

Particle settling and impaction. This is established. Stokes settling with the Cunningham correction:

v_s = (ρ_p d_p² g C_c)/18μ

Impaction is governed by the Stokes number:

Stk = (ρ_p d_p² U)/(18μ L_c)

At low Stk, particles follow the streamlines. As Stk approaches and exceeds 1, they cross streamlines and impact on edges, sills and reveals.

Deposition velocity (resistance model; Seinfeld & Pandis). This is established:

v_d = v_s + (1/(r_a + r_b + r_a r_b v_s))

2.4 Carbonate chemistry at the pore wall

Rainwater and pore water equilibrate with atmospheric CO₂, forming carbonic acid and bicarbonate. This is established. Calcite dissolution is surface-controlled. It is described by the PWP rate law (Plummer, Wigley & Parkhurst 1978, American Journal of Science 278:179–216). This is established:

R = k₁ a_(H⁺) + k₂ a_(H₂CO₃*) + k₃ a_H₂O - k₄ a_(Ca²⁺) a_(HCO₃⁻)

The solubility product applies to CaCO₃ ⇌ Ca²⁺ + CO₃²⁻.

2.5 The biological boundary layer (bridge to Part III)

The surface exchange in BS EN 15026 is:

g = β (p_v,air - p_v,s) + a_r g_rain

This framework modifies that exchange in two modes. This is a proposition, and it is under test:

• Mode A (thin films): β_bio(t,u), a_r,bio(t,u) and the surface free energy γ_SV.

• Mode B (moss, lichen thalli, crusts): a discrete layer with its own d, sorption isotherm, s_d and D_w.

Both modes also carry orientation-dependent solar absorptance. The correction factors are to be measured on paired fouled and cleaned samples to BS EN ISO 15148, BS EN ISO 12572 and BS EN 16322 (Part V).

Part III · The biological boundary layer and material physics

3.1 Growth kinetics: the cardinal temperature model

The growth rate of the microorganisms in the biological boundary layer responds non-linearly to temperature and pH. It is described by the Cardinal Temperature Model with Inflection (CTMI) and its pH counterpart (Rosso et al. 1995, Applied and Environmental Microbiology 61:610). This is established:

μ = μ_opt τ(T) ρ(pH)

τ(T) = ((T - T_max)(T - T_min)²)/((T_opt - T_min)[(T_opt - T_min)(T - T_opt) - (T_opt - T_max)(T_opt + T_min - 2T)])

Laboratory optima must be rescaled to field conditions. A typical UK autumn surface near 12 °C runs at roughly a quarter of the optimum rate. This is a proposition.

3.2 Mould onset and memory: the VTT model

The VTT model (Viitanen & Ojanen 2007) describes mould development with an index M from 0 to 6. This is established. Growth is possible above a temperature-dependent critical humidity:

RH_crit = -0.00267 T³ + 0.160 T² - 3.13 T + 100, T ≤ 20 °C; 80%, T > 20 °C

When humidity falls below the threshold, the index declines only slowly. Here t is the time in hours since the dry period began, and dM/dt is in index units per hour:

The threshold is about 88% RH at 5 °C and 81% at 12 °C, falling to 80% at 20 °C.

3.3 Substrate classes and soiling: the Sedlbauer isopleths

Sedlbauer (2001) defined isopleth systems for spore germination and mycelial growth, built from the growth data of fungi found in buildings. The lowest curve is the Lowest Isopleth for Mould (LIM). This is established. Building materials fall into four substrate classes:

• Class 0: optimal medium;

• Class I: biodegradable materials;

• Class II: porous mineral materials such as renders;

• Class III: inert materials, for which no isopleth is given.

Sedlbauer adopts a conservative design assumption: “In case of considerable soiling, substrate category I always has to be assumed”. This is established. The applicable LIM for a soiled render is therefore the lower, Class I curve. This is the framework’s scientific link between surface soiling and mould risk.

Germination is tracked as a cumulative tally, where each hour on the isopleth of n_h days contributes 1/(24 n_h) (Sedlbauer & Krus 2002). This is established:

G = Σ (1/(24 n_h)), germination when G ≥ 1

3.4 Fronts, recession and extinction

Fungal growth by hyphal tip extension advances at a near-constant linear rate (Prosser & Trinci 1979). This is established. It forms a pushed front. The classical Fisher–KPP equation (Fisher 1937; Kolmogorov, Petrovsky & Piskunov 1937) gives a minimum pulled speed, v* = 2√(Dr). Degenerate (porous-medium) diffusion gives sharp fronts with finite speed (Sánchez-Garduño & Maini 1994). This is established as mathematics:

∂C/∂t = ∇·(D₀(C/C_max)^m∇C) + r C(1 - (C/C_max)), m ≥ 1

Thin algal films may not behave as pushed fronts. The application of these forms to façades is. This is a proposition.

Reformulated as a moving-boundary (Fisher–Stefan) problem, the front can advance, stall or recede (El-Hachem, McCue & Simpson 2021; Simpson & McCue 2024). This is established as mathematics. If an intervention reduces a colonised patch below a critical dimensionless length (L < π/2, with length scaled by √(D/r)), the population recedes towards extinction. Its application to façades is a proposition. Because the front is pushed, the diffusivity D is never back-calculated from an observed speed.

3.5 Surface chemistry: dissolution, acids and texture

Mineral surfaces dissolve by proton- and ligand-promoted reactions, controlled by the detachment of surface complexes (Furrer & Stumm 1986, Geochimica et Cosmochimica Acta 50:1847). This is established:

R_j = k_j (C_j^S)^n_j

Fungi and lichens excrete organic acids, notably oxalic acid, converting calcite to calcium oxalate (Gadd 2007, Mycological Research 111:3–49). This is established:

CaCO₃ + H₂C₂O₄ → CaC₂O₄·H₂O + CO₂

The acid supply therefore travels with the advancing colony. This is a proposition.

Dissolution rates scale with reactive surface area, so surface area must be known. In soil science it is often estimated from texture using the relation from the PROFILE weathering model (Sverdrup & Warfvinge 1993; Warfvinge & Sverdrup 1995; applied as Eq. 18 in Erlandsson et al. 2016, Chemical Geology 441:1–13):

A_min = 0.3 χ_sand + 2.2 χ_silt + 8.0 χ_clay

Here χ are mass fractions and A_min is in m² per gram of mineral matter. This reproduces the field values reported by Erlandsson et al. (2016), of the order of 10²–10³ m²/kg. That paper’s own parameter table states cm²/kg, which does not match its worked values.

The relation was calibrated on natural soils and assumes area depends on texture alone. Hodson, Langan & Meriau (1998) showed that mineralogy controls surface area as well as texture. This is established. Mortar aggregate and carbonated binder are not soils, so this paper does not use the relation to predict mortar surface area. It is retired for mortars. Reactive surface area is instead measured on the specimens themselves (Part VI):

• specific surface area by gas adsorption (BET method, BS ISO 9277);

• pore-size distribution by mercury intrusion porosimetry (BS ISO 15901-1).

Neither method measures reactive area directly. Both replace a soil-calibrated estimate with measured properties of the actual material.

Two abiotic processes run alongside:

• Dedolomitisation and calcite reprecipitation in dolomitic binders (Štukovnik et al. 2020) make porosity time-dependent. The chemistry is established; the coupling to biofilm transport is a proposition.

• Carbonation. Fresh concrete surfaces have pH values easily exceeding 12 and even 13. Carbonation of portlandite and C-S-H then lowers the surface pH over time, from the surface inward (Stohl et al. 2023, Journal of Building Engineering 76:107201). This is established. Most colonising organisms prefer lower pH, which is consistent with new concrete staying clean while older concrete greens. This is a proposition. Colonisation has, however, been reported above pH 10, so pH modulates growth rather than gating it (Veeger et al., as reviewed by Stohl et al. 2023).

Secondary precipitation grows with the cube of supersaturation, G = G₀(β - 1)³ (Scherer & Bellmann 2018, Cement and Concrete Research 103:226). This is established for C-S-H on calcite; its transfer to renders is a proposition.

3.6 Novel materials

• Plasticised PVC. In a two-year field exposure of pPVC containing dioctyl phthalate and dioctyl adipate (DOA), the sequence was. This is established:

  – Aureobasidium pullulans colonised first, at 25–40 weeks;

  – yeasts and yeast-like fungi followed after about 80 weeks;

  – after 95 weeks the yeasts outnumbered A. pullulans, at about 1,000 against 390 CFU/cm²;

  – no bacterial colonisation was observed.

  Every A. pullulans strain tested could grow on intact pPVC as its sole carbon source, degrade DOA, secrete extracellular esterase and cause weight loss of the material (Webb, Nixon, Eastwood, Greenhalgh, Robson & Handley 2000, AEM 66:3194). This is established. Adhesion to pPVC was up to 280% greater than to uPVC after 4 hours (Webb et al. 1999, AEM 65:3575). This is established.

• Polyurethane. Polyester polyurethane can be degraded by endophytic Pestalotiopsis microspora (Russell et al. 2011, AEM 77:6076). This is established.

• uPVC frames contain no plasticiser and age mainly by ultraviolet photo-oxidation. They are excluded from plasticiser-depletion models.

3.6.1 Seal depletion: an interfacial, supply-limited model

The classical Michaelis–Menten equation (Michaelis & Menten 1913) assumes enzyme and substrate are both dissolved in one well-mixed solution. Neither holds for a gasket. The plasticiser sits inside a solid polymer and must first reach the surface, and the enzyme acts only where it is adsorbed on that surface. The solution-phase form is therefore retired for this purpose (Part VII). It is replaced by two steps in series.

Step 1: supply by diffusion. Plasticiser moves through the polymer by Fick’s second law, with a concentration-dependent diffusivity (Crank 1975; Wei, Linde & Hedenqvist 2019, npj Materials Degradation 3:18). This is established:

∂C/∂t = (∂/∂x)(D(C) (∂C/∂x)), D(C) = D₀ e^(α C)

Step 2: removal at the surface. The flux arriving at the surface (x = 0) equals what leaves it. Plasticiser leaves by evaporation, as in Wei et al. (2019), plus a biological term r_bio. The form is established; the biological term is a proposition:

D(C)(∂C/∂x)|_(x = 0) = F (C_s - C_e) + r_bio

The biological term is interfacial. Enzymes acting on insoluble polymers first adsorb to the surface and then hydrolyse there (Mukai, Yamada & Doi 1993, International Journal of Biological Macromolecules 15:361). When enzyme is in excess over accessible surface sites, the rate saturates in enzyme concentration, not substrate concentration. This is the inverse Michaelis–Menten form (Kari, Andersen, Borch & Westh 2017, ACS Catalysis 7:4904). This is established for cellulases on cellulose, and is a proposition for fungal esterases on pPVC:

r_bio = (k_cat Γ_s [E])/(K_M^inv + [E])

where:

• Γ_s is the areal density of accessible ester sites, taken as proportional to the surface plasticiser concentration C_s;

• [E] is the enzyme concentration at the surface;

• K_M^inv is the enzyme concentration giving half the maximum rate.

Which step controls. Wei et al. (2019) use the dimensionless ratio F L/D for a sample of thickness L to decide between diffusion control and surface control. Extending it to include the biological term. This is a proposition:

Λ = ((F + r_bio/C_s)L)/D

• Large Λ: supply-limited. Mass loss is linear in √t.

• Small Λ: surface-limited. Early mass loss is close to linear in t.

This gives a direct test: the shape of the mass-loss curve shows which regime a colonised seal is in.

Polyester polyurethane has no mobile additive to supply; the polymer itself is hydrolysed at the surface. Only the interfacial term applies, and degradation proceeds as surface erosion (Mukai et al. 1993; Russell et al. 2011). For building sealants, this is a proposition.

Time to failure. T_f is defined as the time for the plasticiser content of the outer layer to fall to an embrittlement criterion P_crit, a framework value of 15% plasticiser loss. This is a proposition. All parameters (D₀, α, F, k_cat, Γ_s, K_M^inv) are unmeasured for building seals. This is under test.

3.7 Salt and frost: one crystallisation physics

A crystal growing in a confined pore exerts the Correns pressure (Correns 1949; Steiger 2005). This is established. Damage is better predicted by a strain-energy criterion that includes pore saturation (Flatt et al. 2014, Nature Communications 5:4823). This is established:

P_c = (RT/V_m) ln(C/C_s)

• Mirabilite (V_m ≈ 220 cm³/mol, 10 °C): about 7.4 MPa at a supersaturation of 2; about 0.7–3.5 MPa at realistic in-wall supersaturations of 1.07–1.39. The form is established; the values are calculated.

• Strengths for comparison: lime mortar tensile strength is about 0.3–1.5 MPa; sandstone about 2–5 MPa. These are established, typical values.

• Ice follows the same form, P = (ΔH_f/V_m)(ΔT/T₀): about 5.6 MPa at 5 K of undercooling. The form is established; the value is calculated.

Where salt crystallises depends on the evaporation Péclet number (Huinink & Pel 2002, Physics of Fluids 14:1389). This is established:

Pe = (v_e L)/(ε D)

• Pe > 1: crystallisation at the surface, as efflorescence.

• Pe < 1: crystallisation within the pores, as subflorescence with microcracking (Nogueira et al. 2020). This is established.

Real walls hold salt mixtures (Godts et al. 2023, Scientific Reports 13:13306). This is established. A biological layer that slows evaporation lowers Pe and may favour subflorescence. This is a proposition, and it is under test.

3.8 Secondary performance modifiers (scope notes)

• Acoustics. Laboratory tests of a modular green wall reported a weighted sound absorption coefficient of 0.40 and a weighted sound reduction index of 15 dB (Azkorra et al. 2015, Applied Acoustics 89:46–56). This is established for that system. Effects of thin biofilms or moss on masonry are unmeasured. This is a proposition.

• Solar absorptance. Light renders are about 0.2–0.4; dark surfaces exceed 0.8. These are established, typical values. Raised rock temperatures beneath Verrucaria nigrescens on limestone have been recorded (Carter & Viles 2004, Geomorphology 62:1–16). This is established. Biological darkening may speed drying on sunlit faces and increase coating thermal cycling. This is a proposition, and it is under test.

• Fire. Reaction to fire is classified for products and systems (BS EN 13501-1; BS 8414 with BR 135; LPS 1181 and FM approvals for insulated panels). This is established. No claim is made that biological layers change fire performance. Cleaning and maintenance must not damage coatings, seals, cavity barriers or fire-stopping. This is an established principle.

Part IV · The human interface

4.1 Systemic building ethnography

A façade is a physical boundary, but it is also a public surface that people read. Ethnographic method, from Boas’s field documentation and Malinowski’s participant observation to Mead’s comparative fieldwork, treats such surfaces as evidence of how a community lives. This is established as method.

Mary Douglas defined dirt as “matter out of place” (Douglas 1966, Purity and Danger). This is established. On that reading, visible soiling and colonisation register socially as a lapse in care, whatever their physical significance. Maintenance can then be read as a ritual that restores order. That it also lowers occupants’ cognitive load is this framework’s interpretation. This is a proposition.

Geertz’s “thick description” (Geertz 1973, The Interpretation of Cultures) sets the standard for the record. A thin record reads “stain washed”. A thick record states:

• the substrate;

• the colonising organism;

• the moisture route;

• the method used;

• why the intervention matters to the people who use the building.

4.2 Physiology, biometeorology and the health firewall

Thermal comfort follows the human heat balance (Fanger 1970; ISO 7730). This is established:

M - W = C + R + E_sk + C_res + E_res + S

where:

• M is the metabolic rate and W is external work;

• C and R are convective and radiant exchange, set in part by internal wall surface temperatures;

• E_sk is evaporation from the skin;

• C_res and E_res are respiratory losses;

• S is heat storage in the body.

Transient response is modelled by the two-node model (Gagge, Stolwijk & Nishi 1971). This is established.

The health firewall. The framework assesses environmental conditions only. It asks whether internal or external surfaces cross the growth thresholds of the Sedlbauer LIM curves or the VTT index (Part III), and it uses those results to guide preventive work. It makes no clinical diagnosis or attribution. Health questions belong to qualified clinicians and to the public-health literature.

4.3 Environmental psychology

• Restorative environments. Attention Restoration Theory (Kaplan & Kaplan 1989, The Experience of Nature) proposes that some environments restore directed attention. This is established as theory. Stress Recovery Theory draws support from Ulrich (1984, Science 224:420), where surgical patients with a window view of trees had shorter post-operative stays than those facing a brick wall. This is established as an observed association in that study.

• Disorder and norms. The “broken windows” idea began as a magazine essay (Wilson & Kelling 1982, The Atlantic) and was not peer-reviewed. Field experiments later showed that visible disorder can increase norm-violating behaviour (Keizer, Lindenberg & Steg 2008, Science 322:1681). This is established for those settings. Systematic observation in Chicago found that disorder and crime largely share common causes rather than disorder directly causing crime (Sampson & Raudenbush 1999, American Journal of Sociology 105:603). This is established. Both findings are reported together.

• Application. That unmanaged colonisation of a façade acts as a negative environmental cue for occupants and passers-by is a proposition. It is consistent with the work above, but has not been tested directly.

Part V · The living envelope in practice

5.1 The perfect wall and the fifth layer

Lstiburek’s “perfect wall” places four control layers in a fixed order (Lstiburek, Building Science Insights BSI-001). This is established:

1. rain, air and vapour control layers, placed on the structure;

2. thermal control, placed outside those layers;

3. cladding, which is mainly a screen against ultraviolet light and physical damage.

The structure then sits warm and dry, inside every control layer.

Most UK solid masonry has no separate membrane. The porous outer masonry is itself the rain-control layer, storing water and releasing it by drying. This is established. The state of that outer surface therefore governs the wall’s moisture balance.

This framework adds a fifth layer: the biological boundary layer on the outer face. Outside to inside, the layers run:

• biological boundary layer;

• cladding or outer masonry;

• thermal control;

• vapour, air and rain control;

• structure.

It acts in two modes (Part II, 2.5):

• Mode A, thin films: these alter surface transfer and wetting.

• Mode B, moss, lichen and crusts: these form a discrete layer with their own storage and vapour resistance.

That this layer measurably changes surface drying is. This is a proposition, and it is under test. On insulated renders over EPS, the effect on outward vapour transmission is also. This is a proposition, and it is under test. The fifth layer is a testable contributor to the performance gap, not a proven cause of it.

5.2 The physics of removal

Pure water and DLVO. Particle adhesion is the sum of van der Waals attraction and electrical double-layer repulsion (Derjaguin & Landau 1941; Verwey & Overbeek 1948). This is established:

V_T = V_A + V_R, κ⁻¹ ≈ (0.304/√I) nm (1:1 electrolyte, 25 °C)

The Debye length κ⁻¹ sets how far the repulsion reaches:

• Lower ionic strength extends repulsion. It releases particles held in the secondary minimum and discourages redeposition (Ryan & Elimelech 1996, Colloids and Surfaces A 107:1). This is established.

• Particles in the primary minimum still need hydrodynamic shear. The size of the effect on façades is. This is a proposition.

• Purified water still conducts. Its theoretical conductivity is about 0.055 µS/cm, and in air it equilibrates to about 1 µS/cm at pH about 5.6. This is established.

• No lysis. Pure water does not lyse walled microbial cells, because the cell wall resists the osmotic load. Removal is by detachment and shear. This is established.

Pressure without cavitation. A free jet in air does not fall below vapour pressure, so cavitation is not a mechanism here (see the register of retired claims). The mechanisms are. This is established:

• stagnation pressure: p = (1/2)ρ v²;

• water-hammer impact pressure: p = ρ c v (Joukowsky 1900; c ≈ 1480 m/s);

• liquid-impact damage modes (Adler 1979), applied to cleaning by Guha, Barron & Balachandar (2011).

Worked example, calculated:

• At 250 bar, the ideal jet speed is about 224 m/s.

• The transient water-hammer pressure is then about 330 MPa.

• Lime mortar has a tensile strength of about 0.3–1.5 MPa, roughly 220–1100 times lower.

• Guha et al. found cleaning effectiveness peaks near about 5 nozzle diameters of stand-off and is lost beyond about 26.

High pressure is therefore unsuitable for soft historic masonry.

Glass thermal stress. The form is established; the values are calculated:

ΔT_crit = (σ_t(1-ν))/(E α)

These values assume E ≈ 70 GPa, ν ≈ 0.22 and α ≈ 9×10⁻⁶ /K.

Operating rule: keep the glass–water temperature difference at or below 30 °C.

5.3 Statutory boundaries (England and Wales)

Water Supply (Water Fittings) Regulations 1999. This is established:

• Schedule 1 defines fluid categories 1–5.

• Schedule 2, paragraph 15, requires a backflow prevention device appropriate to the highest fluid category downstream.

• WRAS guidance rates a Type AA air gap for category 5 against back-pressure and back-siphonage, with a gap of at least 20 mm or twice the inlet bore.

• Pure-water systems filled through a visible Type AA air gap are the simplest compliant arrangement.

Environmental Permitting (England and Wales) Regulations 2016. This is established:

• Regulation 12 requires a permit for water discharge and groundwater activities.

• Regulation 38 creates the offences. These replaced Water Resources Act 1991 s.85 in 2010.

• Empress Car Co v National Rivers Authority [1999] 2 AC 22 governs what counts as “causing” pollution.

• Rinse water carrying removed soil and biomass can be polluting matter even when the source water was pure.

Discharge to sewer. Discharge to a public sewer is trade effluent and needs the sewerage undertaker’s consent (Water Industry Act 1991 s.118). This is established.

Awaab’s Law (SI 2025/1042, in force 27th October 2025), social housing only. This is established:

This section states the law in general terms. It is not legal advice.

5.4 Evidence records

A condition record must let another practitioner see what was observed, separately from what was concluded. Each field is tagged O (observed) or I (inferred, with its basis).

Seven required fields, completed before work begins:

Chain of custody. Each record shows:

• who recorded it, and when;

• the device used;

• a cryptographic hash at capture;

• where it is stored;

• the version history of any edit.

Images are signed as C2PA content credentials at capture where the camera supports it, otherwise at ingest. RAW files and derived images are both hashed. Signing makes alteration detectable; it does not prove a record is correct.

Historic fabric. Work on historic buildings follows BS 7913:2013, Guide to the conservation of historic buildings. Its conservation principles include minimum intervention and, where practicable, reversibility. This is established. Cleaning follows BS 8221-1:2012, which covers natural stone, brick, terracotta and concrete. Any repair that follows cleaning is governed by BS 8221-2:2000. This is established.

Part VI · Verification and falsification

The propositions in this paper must be testable by anyone with access to standard building-physics apparatus. A null result, showing that the biological boundary layer has no measurable effect, is a valid and publishable outcome. Falsifiability follows Popper (1959, The Logic of Scientific Discovery). Lakatos’s account of research programmes, in which auxiliary hypotheses may be adjusted, is acknowledged. For that reason the auxiliary assumptions are fixed in advance here. This is established as epistemology.

6.1 Paired-sample laboratory suite

Specimens come from one wall, at one orientation and elevation, in three arms:

Where coring is not permitted, as on historic fabric, in-situ water absorption is measured by the pipe (Karsten tube) method, BS EN 16302:2013. This is established.

6.1.1 Capillary absorption (BS EN ISO 15148)

The test uses partial immersion, with the exterior (colonised) face as the inflow face. This is established:

Δm/A = A_w√t

Here Δm/A is in kg/m² and A_w in kg/(m²·s^0.5). The reported quantity is A_w,F/A_w,C, with the N arm as reference. A change in absorption is indicated only where the ratio falls outside the pre-registered equivalence bounds. This is a proposition.

6.1.2 Vapour transmission (BS EN ISO 12572)

Dry-cup and wet-cup tests give. This is established:

g = δ_a (Δp_v/s_d), s_d = μ d

where δ_a ≈ 2.0×10⁻¹⁰ kg/(m·s·Pa) is the vapour permeability of still air. The biological layer acts as a resistance in series, so the reported quantity is:

Δs_d,bio = s_d,F - s_d,C

A positive Δs_d,bio shows added surface vapour resistance. This is a proposition. Whether that resistance retains moisture in the wall is a whole-wall question for 6.2 and hygrothermal simulation (BS EN 15026).

6.1.3 Drying (BS EN 16322)

Drying curves are recorded through the constant-rate (capillary) phase and the falling-rate (diffusion-limited) phase. This is established. The test asks whether the biofilm matrix of extracellular polymeric substances lengthens the drying tail under identical air conditions. This is a proposition.

6.2 Field pair: in-situ heat flux and moisture

The two zones are matched in orientation, exposure and construction. One is left colonised and one is cleaned, and both are monitored from October to April.

6.2.1 Thermal transmittance (ISO 9869-1). Heat-flux plates are fixed on the internal face, away from thermal bridges and direct sun. The U-value is found by the average method. This is established:

U = (Σ_j q_j)/(Σ_j(T_i,j - T_e,j))

The method requires at least 72 hours of stable conditions. Its total uncertainty is commonly reported as about 14–28% even when the standard is followed carefully. This is established. Small moisture-related differences on well-insulated walls may therefore fall below what the method can resolve. Solid, uninsulated masonry is tested as well, because surface moisture has its largest thermal effect there. This is a proposition. Recolonisation of the cleaned zone is logged throughout.

6.2.2 Moisture and temperature. Capacitive RH and temperature sensors are placed at set depths. Resistance pins are used for relative trends only, because they are calibrated for timber and distorted by salts. Absolute moisture content is taken from gravimetric drilled samples (BRE Digest 245 method). This is established.

6.3 One-wall photographic record

This is a low-cost record any practitioner can run. This is a proposition:

• Shoot from a fixed tripod position, square to the wall.

• Use RAW capture, locked white balance and a calibrated colour target in frame.

• Shoot at a fixed time of day, preferably under overcast sky.

• Analyse colour in the CIE L*a*b* space.

• Link the images to the nearest Met Office MIDAS Open station record: rainfall, temperature and humidity, plus irradiance where the station records it.

Twelve weeks is a pilot. A full record runs for 12 months.

6.4 Pre-registration and equivalence testing

Before any data are collected, the following are entered in a public registry (Nosek, Ebersole, DeHaven & Mellor 2018, PNAS 115:2600). This is established:

• hypotheses;

• sampling plan and power calculation;

• sensor calibrations;

• analysis plan.

A non-significant difference is not evidence of no effect. Each hypothesis is therefore tested with two one-sided tests (TOST) against equivalence bounds set as the smallest effect of practical interest (Lakens 2017, Social Psychological and Personality Science 8:355). This is established:

If a test can show neither a difference nor equivalence, the result is reported as inconclusive. A rejected hypothesis is retired to the register in Part VII.

Four outcomes of the combined test (Lakens 2017):

Limitation of arm N. A sheltered zone also differs in weather exposure from the exposed zones. Arm N therefore bounds the cleaning effect but does not remove every confounder. This limitation is stated in every report.

Additional controls (Part IX).

• Fouled cores are split in the laboratory and one half is cleaned. This isolates the cleaning effect with no difference in exposure.

• The outer 5 mm of arms F, C and N is tested for pore-size distribution by mercury intrusion porosimetry (BS ISO 15901-1), and for specific surface area by gas adsorption (BET, BS ISO 9277). These are required, not optional. They detect changes in near-surface pore structure and supply the measured surface area used in place of soil-texture estimates (3.5).

• Plasticised seals (3.6.1): mass loss is recorded against both t and √t for paired colonised and sterile specimens, to identify supply-limited or surface-limited loss.

Part VII · The honesty firewall and register of retired claims

7.1 Firewall rules

1. Every claim states whether it is established, a proposition, under test or retired.

2. Every equation has a published origin. No equation is created for this paper.

3. Health: environmental indicators only. No clinical attribution is made.

4. Null and inconclusive results are publishable (Part VI).

5. Internal software and tooling appear only in Appendix A.

6. No commercial claim rests on a. This is a proposition.

7. Every prediction carries a stated uncertainty.

7.2 Register

Each entry gives the claim, its status, the reason, and the replacement with its tier.

7.3 Process

Any reader may propose a retirement, with evidence. Retired entries stay visible and dated, and are never silently deleted.

Part VIII · Futures, open data and education

8.1 The Scholar-Technician: learning outcomes

The Scholar-Technician is a practitioner who treats each intervention on a façade as a recorded, non-destructive material intervention. The proposed learning outcomes fall in three domains. This curriculum design is a proposition:

1. Enclosure physics. Explain coupled heat and moisture transport and hygrothermal simulation (BS EN 15026). Interpret in-situ thermal measurement (ISO 9869-1) and its uncertainty. Explain how salts crystallise near the surface and inside the material (Part III).

2. Biological systems. Recognise the main groups that colonise façades and name them only with catalogued taxa. Apply the Sedlbauer and VTT thresholds. Take samples suitable for DNA identification.

3. Environmental and water law. Apply backflow protection under the Water Supply (Water Fittings) Regulations 1999. Distinguish discharge to surface water or ground (EPR 2016) from discharge to sewer (trade effluent, WIA 1991 s.118).

Condition records are signed as C2PA content credentials (Coalition for Content Provenance and Authenticity). This makes later alteration detectable. It does not prove a record is correct.

8.2 Open data

Data follow the FAIR principles (Wilkinson et al. 2016, Scientific Data 3:160018). This is established:

• Formats: Apache Parquet for analysis, plus CSV with a data dictionary.

• Content: measured coefficients (A_w, s_d), drying curves, growth time series, and their weather sources.

• Licence: CC BY 4.0.

• Data protection: address-linked building records can be personal data under UK GDPR. Release requires a lawful basis, consent where required, and aggregation or anonymisation before publication.

The aim is a shared, citable evidence base on how the building fabric weathers under a changing climate. Its usefulness depends on contributors following Part VI. This is a proposition.

Part IX · Limitations and referee objections

9.1 The linear transport frame and a non-linear surface

Objection. Onsager’s relations are linear and near-equilibrium. The colonised surface is non-linear, far from equilibrium and under solar forcing.

Response. Conceded as to scope. The paper applies the Onsager frame to transport only and treats the biology as a far-from-equilibrium system (2.1). No kinetic certificate is claimed for the biological layer. A full non-linear treatment is future work.

9.2 Surface coefficients without pore data

Objection. If biology alters near-surface pores, adjusting surface coefficients alone is an over-simplification.

Response. Accepted. Part VI now requires measurements on the outer 5 mm of arms F, C and N:

• mercury intrusion porosimetry (BS ISO 15901-1) for pore-size distribution;

• gas-adsorption specific surface area (BET, BS ISO 9277).

The same measurements replace the soil-calibrated texture relation for mortar surface area (3.5). Neither method measures reactive area directly, so this limitation is narrowed, not removed. If pore structure differs between arms, Mode A is extended to a thin altered zone with its own transport functions.

9.3 Is the “fifth layer” only wet-wall physics?

Objection. Any thermal penalty may be ordinary moisture-dependent conductivity, which would make the term redundant.

Response. This is the strongest objection, and largely right. The fifth layer is a boundary condition on moisture, not a new thermal mechanism. Any thermal effect would arise through the established relation λ(w) (BS EN ISO 10456). The proposition is only that biology changes the moisture boundary condition. If the Part VI ratios for A_w, Δs_d and drying are equivalent to no change, the term is retired to Part VII.

9.4 Michaelis–Menten on a solid polymer

Objection. The solution-phase integrated form does not describe enzyme action on an insoluble surface.

Response. Conceded and acted on. The solution-phase form is retired (Part VII, entry 11). Section 3.6.1 replaces it with diffusion supply of plasticiser to the surface, coupled to interfacial kinetics. The interfacial step uses the adsorption–hydrolysis picture of Mukai et al. (1993) and the inverse Michaelis–Menten form of Kari et al. (2017). Its parameters remain unmeasured for building seals.

9.5 Urban wind shielding

Objection. Free-stream Stokes numbers ignore shielding, stagnation and wakes in dense urban form.

Response. Accepted. Stokes-number estimates are indicative only. Site-specific deposition needs exposure factors (BS EN ISO 15927-3; BS 8104) or computational wind modelling of the kind reviewed by Blocken and Carmeliet (2004). Deposition hotspot maps remain. This is a proposition.

9.6 Continuum fronts and stochastic hyphae

Objection. A continuum equation cannot capture discrete, stochastic hyphal branching.

Response. Conceded at hyphal scale. The continuum models describe colony-scale density over centimetres to metres, where branching noise averages out. Hyphal-scale behaviour needs individual-based models. The scale of every claim is stated.

9.7 Measurement resolution on insulated walls

Objection. With in-situ uncertainty of about 14–28%, differences on well-insulated walls will fall inside the error.

Response. Agreed. A result on insulated walls is expected to be inconclusive. That is why solid uninsulated masonry, where surface moisture has the largest thermal effect, is a required test arm (6.2). The equivalence bounds are relative and set by power analysis, not fixed.

9.8 The sheltered control

Objection. A sheltered zone has a different weather history, which confounds arm N.

Response. Accepted and already stated (6.4). A further control is added: fouled cores split in the laboratory, with one half cleaned. This isolates the cleaning effect without any difference in exposure.

9.9 Biofilm-driven subflorescence

Objection. No data show that biofilms push crystallisation inward. A biofilm could equally act as a surface sink for efflorescence.

Response. Accepted. The claim is stated as a proposition under test (3.7). Both directions are predicted outcomes. Salt distribution profiles in paired specimens after wet–dry cycling will decide between them.

9.10 Privacy in open data

Objection. Condition grades with coordinates can re-identify properties, and no anonymisation method is given.

Response. Accepted. Release rules, all. This is a proposition:

• coordinates and full postcodes are removed;

• data are aggregated to postcode sector or coarser;

• any cell with fewer than ten properties is suppressed;

• releases follow the Information Commissioner’s Office guidance Anonymisation and pseudonymisation (2025), including its motivated-intruder test.

Appendix A · Data architecture (illustrative)

This appendix describes a proposed schema for exchanging observed façade states in machine-readable form. It also describes a proposed Model Context Protocol (MCP) interface. Both are design proposals, not public deployments. All identifiers are fictitious placeholders.

A.1 JSON-LD template (Illustrative: observed state only, no prescription)

{

  "@context": {

    "schema": "https://schema.org/",

    "enc": "https://example.org/enclosure#",

    "obs": "https://example.org/observation#"

  },

  "@graph": [

    {

      "@id": "https://example.org/asset/0001",

      "@type": ["schema:Place", "enc:BuildingEnvelope"],

      "schema:identifier": "placeholder-0001",

      "schema:postalCode": "XX1 1XX",

      "enc:elevation": { "@id": "https://example.org/asset/0001/elevation/N" }

    },

    {

      "@id": "https://example.org/asset/0001/elevation/N",

      "@type": "enc:Elevation",

      "enc:orientationDegrees": 0,

      "enc:substrate": "Textured acrylic render",

      "enc:hasObservation": { "@id": "https://example.org/obs/0001-N-2026-11-01" }

    },

    {

      "@id": "https://example.org/obs/0001-N-2026-11-01",

      "@type": "obs:ConditionObservation",

      "schema:dateCreated": "2026-11-01",

      "obs:primaryColoniser": {

        "@type": "obs:Taxon",

        "schema:name": "Trentepohlia aurea",

        "obs:taxonomicAuthority": "AlgaeBase"

      },

      "obs:deltaSdMetres": { "obs:value": 0.12, "obs:uncertainty": 0.03 },

      "obs:uValueUncertaintyPercent": 14.0,

      "obs:weatherSource": "Met Office MIDAS Open (station placeholder)",

      "obs:provenance": "C2PA content credential (placeholder)"

    }

  ]

}

All values are illustrative. Each node has a unique IRI, and each vocabulary has its own namespace.

A.2 Glossary anchor

Anthropogenic cliff face. A building façade treated as an artificial rock habitat, after the urban cliff hypothesis (Larson et al. 2004, The Urban Cliff Revolution). As applied here, this is a proposition.

Apparatus · Glossary and symbol index

Symbol index

Some symbols carry different meanings in different source fields. Each meaning is kept with its section, and the conflicts are flagged (⚑).

⚑ Resolution rule. The source symbol is kept and the meaning is fixed by its section. A subscript is added in the final typeset (μ_air, μ_gr, μ_vap, M_VTT, M_met, α_th, α_s, κ_vK, κ⁻¹_D, G_germ, G_ppt).

Glossary

• Air gap, Type AA. An unobstructed vertical gap between the water inlet and the spill-over level. WRAS rates it for fluid category 5 (5.3).

• Biological boundary layer. The colonised outer surface of a wall, treated as Mode A (thin film) or Mode B (discrete layer). This is a proposition. (2.5).

• BET method. Determination of specific surface area from gas adsorption isotherms (Brunauer–Emmett–Teller), standardised as BS ISO 9277.

• Biomicrite. Limestone of skeletal grains in a micrite (lime-mud) matrix, in Folk’s classification.

• C2PA. Coalition for Content Provenance and Authenticity. Its signed content credentials make later alteration of a record detectable.

• Cardinal Temperature Model with Inflection (CTMI). A growth-rate model using minimum, optimum and maximum temperatures (Rosso et al. 1995).

• Correns pressure. The pressure exerted by a crystal growing from a supersaturated solution in a confined pore.

• Debye length. The distance over which electrical double-layer repulsion acts in an electrolyte solution.

• DLVO theory. Colloid stability as the balance of van der Waals attraction and double-layer repulsion (Derjaguin, Landau, Verwey, Overbeek).

• Equivalent air layer thickness (s_d). The thickness of still air with the same vapour diffusion resistance as the specimen.

• Equivalence testing (TOST). Two one-sided tests, which show whether an effect lies within pre-set bounds (Lakens 2017).

• EPS. Expanded polystyrene. The biofilm matrix is written in full: extracellular polymeric substances.

• Extracellular polymeric substances. The polysaccharide, protein and lipid matrix that microorganisms secrete, binding a biofilm to its surface.

• FAIR. Findable, Accessible, Interoperable, Reusable (Wilkinson et al. 2016).

• Fisher–Stefan model. A reaction–diffusion model with a moving boundary, allowing a population front to advance or recede.

• Fluid category 5. Under Schedule 1 of the Water Supply (Water Fittings) Regulations 1999: fluid representing a serious health hazard because of the concentration of pathogenic organisms, radioactive or very toxic substances.

• Health firewall. The rule that this framework assesses environmental conditions only and makes no clinical attribution.

• Hygrothermal. Relating to coupled heat and moisture transport in building materials.

• Inverse Michaelis–Menten kinetics. A rate law for enzymes acting on insoluble surfaces, in which the rate saturates with enzyme concentration rather than substrate concentration (Kari et al. 2017).

• Lowest Isopleth for Mould (LIM). The lowest temperature–humidity curve, from measured growth data, at which mould germination or growth has been observed for a substrate class (Sedlbauer 2001). Below it, growth is not expected; it is not physically impossible.

• Mercury intrusion porosimetry (MIP). Determination of pore-size distribution from the pressure needed to force mercury into pores (BS ISO 15901-1).

• Péclet number (evaporation). The ratio of advective to diffusive salt transport. It decides whether salts crystallise at the surface or within the pores.

• Perfect wall. Lstiburek’s ordering of rain, air, vapour and thermal control layers, with the structure inside all of them.

• Pushed front. A spreading front whose speed is set by growth behind the leading edge, not at it. It travels faster than the linear (pulled) minimum speed.

• Scholar-Technician. A practitioner who records, justifies and where possible measures every façade intervention (Part VIII).

• Subflorescence. Salt crystallisation within the pores, below the surface, often in hydrated forms (e.g. mirabilite). It can cause scaling and spalling.

• Sulphation crust. A gypsum crust formed when SO₂ reacts with carbonate stone or binder, trapping carbonaceous particles.

• Thick description. Geertz’s term for a record that explains context and meaning, not only the action taken.

• Trade effluent. Liquid produced in the course of a trade or industry at trade premises, excluding domestic sewage (WIA 1991 s.141). Discharging it to a public sewer needs the sewerage undertaker’s consent (s.118).

• Urban cliff hypothesis. The proposal that cities replicate cliff and rock-outcrop habitats, and are colonised accordingly (Larson et al. 2004).

• VTT model. A mould-index model (0–6) with a temperature-dependent critical humidity and slow decline in dry periods (Viitanen & Ojanen 2007).

• Water-hammer pressure. The transient impact pressure of a liquid striking a surface, p = ρ c v (Joukowsky).

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• Sedlbauer, K. and Krus, M. (2002) ‘Biohygrothermal procedure for the prediction of mould growth’, Restoration of Buildings and Monuments, 8(5), pp. 475–494.

• Seinfeld, J.H. and Pandis, S.N. (2016) Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. 3rd edn. Hoboken, NJ: Wiley.

• Simpson, M.J. and McCue, S.W. (2024) ‘Fisher–KPP-type models of biological invasion: open source computational tools, key concepts and analysis’, Proceedings of the Royal Society A, 480(2294), article 20240186.

• Steiger, M. (2005) ‘Crystal growth in porous materials—I: The crystallization pressure of large crystals’, Journal of Crystal Growth, 282(3), pp. 455–469.

• Stohl, L., Manninger, T., von Werder, J., Dehn, F., Gorbushina, A. and Meng, B. (2023) ‘Bioreceptivity of concrete: a review’, Journal of Building Engineering, 76, 107201.

• Straube, J.F. and Burnett, E.F.P. (2005) Building Science for Building Enclosures. Westford, MA: Building Science Press.

• Štukovnik, P., Bokan-Bosiljkov, V. and Marinšek, M. (2020) ‘Alkali-dolomite reaction in air lime mortar: implications for increased strength and water resistance’, Journal of Cultural Heritage, 45, pp. 160–168.

• Sverdrup, H. and Warfvinge, P. (1993) ‘Calculating field weathering rates using a mechanistic geochemical model PROFILE’, Applied Geochemistry, 8(3), pp. 273–283. doi:10.1016/0883-2927(93)90042-F.

• Ulrich, R.S. (1984) ‘View through a window may influence recovery from surgery’, Science, 224(4647), pp. 420–421.

• van Genuchten, M.Th. (1980) ‘A closed-form equation for predicting the hydraulic conductivity of unsaturated soils’, Soil Science Society of America Journal, 44(5), pp. 892–898.

• Verwey, E.J.W. and Overbeek, J.Th.G. (1948) Theory of the Stability of Lyophobic Colloids. Amsterdam: Elsevier.

• Viitanen, H. and Ojanen, T. (2007) ‘Improved model to predict mold growth in building materials’, in Thermal Performance of the Exterior Envelopes of Whole Buildings X. Atlanta: ASHRAE.

• Warfvinge, P. and Sverdrup, H. (1995) Critical Loads of Acidity to Swedish Forest Soils: Methods, Data and Results. Lund: Department of Chemical Engineering II, Lund University.

• Washburn, E.W. (1921) ‘The dynamics of capillary flow’, Physical Review, 17(3), pp. 273–283.

• Webb, J.S. et al. (1999) ‘Plasticizers increase adhesion of the deteriogenic fungus Aureobasidium pullulans to polyvinyl chloride’, Applied and Environmental Microbiology, 65(8), pp. 3575–3581.

• Webb, J.S., Nixon, M., Eastwood, I.M., Greenhalgh, M., Robson, G.D. and Handley, P.S. (2000) ‘Fungal colonization and biodeterioration of plasticized polyvinyl chloride’, Applied and Environmental Microbiology, 66(8), pp. 3194–3200.

• Wei, X.-F., Linde, E. and Hedenqvist, M.S. (2019) ‘Plasticiser loss from plastic or rubber products through diffusion and evaporation’, npj Materials Degradation, 3, article 18. doi:10.1038/s41529-019-0080-7.

• Wilkinson, M.D. et al. (2016) ‘The FAIR Guiding Principles for scientific data management and stewardship’, Scientific Data, 3, 160018.

• Wilson, J.Q. and Kelling, G.L. (1982) ‘Broken windows: the police and neighborhood safety’, The Atlantic Monthly, 249(3), pp. 29–38.

Reports and guidance

• Innovate UK (2016) Building Performance Evaluation Programme: Findings from Non-Domestic Projects. Getting the Best from Buildings. Swindon: Innovate UK.

• Information Commissioner’s Office (2025) Anonymisation and pseudonymisation. Wilmslow: ICO.

• World Health Organization (2009) WHO Guidelines for Indoor Air Quality: Dampness and Mould. Copenhagen: WHO Regional Office for Europe.

Standards

• BRE Digest 245, Rising damp in walls: diagnosis and treatment.

• BS 7913:2013 Guide to the conservation of historic buildings.

• BS 8104 Code of practice for assessing exposure of walls to wind-driven rain.

• BS 8221-1:2012 Code of practice for cleaning and surface repair of buildings. Cleaning of natural stone, brick, terracotta and concrete.

• BS 8221-2:2000 Code of practice for cleaning and surface repair of buildings. Surface repair of natural stones, brick and terracotta.

• BS 8414 with BR 135, fire performance of external cladding systems.

• BS EN 13501-1, fire classification of construction products.

• BS EN 15026, hygrothermal performance: numerical simulation.

• BS EN 16302:2013 Conservation of cultural heritage. Measurement of water absorption by pipe method.

• BS EN 16322, Conservation of cultural heritage. Determination of drying properties.

• BS EN ISO 10456, thermal properties of building materials.

• BS EN ISO 12572, water vapour transmission properties.

• BS EN ISO 13788, surface temperature and interstitial condensation.

• BS EN ISO 15148, water absorption coefficient by partial immersion.

• BS EN ISO 15927-3, driving rain indices.

• BS ISO 15901-1, pore size distribution by mercury porosimetry.

• BS ISO 9277, specific surface area of solids by gas adsorption (BET method).

• ISO 7730, ergonomics of the thermal environment.

• ISO 9869-1, in-situ measurement of thermal resistance and thermal transmittance.

Legislation and case law

• Empress Car Co (Abertillery) Ltd v National Rivers Authority [1999] 2 AC 22 (HL).

• Environmental Permitting (England and Wales) Regulations 2016 (SI 2016/1154).

• Hazards in Social Housing (Prescribed Requirements) (England) Regulations 2025 (SI 2025/1042), known as Awaab’s Law.

• Water Industry Act 1991 (c.56).

• Water Supply (Water Fittings) Regulations 1999 (SI 1999/1148).

Credits

Framework, corpus and direction: Matthew Kenneth McDaid.

Drafting, cross-examination and verification: prepared through a structured exchange between two AI language models: Claude (Anthropic), which held the corpus, drafted and verified citations, and Google AI, which co-drafted and stress-tested the text. All references were checked against published records. Items still marked for verification are flagged in the text.

Correspondence: via the framework’s author.