Spray foam glossary: the terms surveyors, lenders and installers use

Terms A–Z

Air and vapour control layer (AVCL)

A sheet fitted on the warm, room side of the insulation to limit moist indoor air and vapour reaching the roof. In the government-commissioned modelling, adding an AVCL brought the felt-underlay scenarios down to low or medium risk^[1]. Read more: condensation and roof timbers

Approved Document B

The government guidance on fire safety that accompanies the Building Regulations. Fire research published by the Building Safety Regulator in December 2025 found it gives no guidance on the fire class of the surfaces lining a roof space^[2]. Read more: is spray foam a fire risk?

Approved Document C

The government guidance on moisture, including condensation, that accompanies the Building Regulations. Approved Document L leaves roof ventilation gaps to it, and allows a lower insulation standard where that is needed to comply with Part C^[3]. Read more: condensation and roof timbers

Approved Document L

The government guidance on conserving fuel and power. It sets U-values rather than insulation depths; the 2021 edition gives 0.35 W/m²K as the threshold for a renovated roof and 0.16 as the improved figure, and the 2026 edition (in force from 24 March 2027) keeps both figures^[3][4]. Read more: how spray foam should be installed

BBA (British Board of Agrément)

A body that describes itself as an independent product-approval, testing and inspection body, not a trade body^[5]. UKAS suspended its recognition of the BBA from 26 February 2026; existing BBA approvals stay valid until their expiry date (as at 15 June 2026)^[6]. Read more: product approvals and the BBA suspension

"BBA certificate"

What many people call a BBA product approval. The BBA itself lists the belief that an approved product automatically complies with Building Regulations as a misconception^[7]. Read more: product approvals explained

Bitumen felt

A traditional roofing underlay that resists water vapour, which the government-commissioned modelling treats as a high-resistance underlay^[1]. RICS advises against spraying foam onto bitumen felt^[8]. Read more: what was the foam sprayed onto?

Blowing agent

The gas that makes the foam expand. UK open-cell foams are water-blown and give off carbon dioxide^[9], while closed-cell foams moved from HFC to HFO gases after new foams containing HFCs with a global warming potential of 150 or more were banned from 1 January 2023^[10]. Read more: what is spray foam insulation?

Breathable (said of foam)

A word often used for open-cell foam because it lets water vapour through easily. It does not make open-cell automatically safer: the government-commissioned modelling found open-cell foam high risk over a felt-type underlay with no vapour control layer^[1]. Read more: is open-cell safer than closed-cell?

Breather membrane

Another name for a breathable, low-resistance roof underlay. The manufacturers' Code of Practice lists a pitched tiled roof with a breather membrane as one of its standard roof types^[11]. Read more: how spray foam should be installed

BS 5250:2021

The British Standard code of practice for managing moisture in buildings, which replaced the 2011 edition^[12]. The modelling for the Building Safety Regulator found low risk for open-cell foam installed to it^[1]. Read more: condensation and roof timbers

BS EN 15026

The standard for the more detailed moisture simulation that BBA product approvals call for where a simpler condensation check finds a risk^[9]. The 2007 edition cited in the government-commissioned modelling has since been revised^[1]. Read more: condensation and roof timbers

BS EN ISO 13788

The standard behind the simpler condensation calculation (the Glaser method) that BBA 23/7062, for example, requires before spraying^[9]. The government-commissioned modelling warns that this method may underestimate the risk^[1]. Read more: condensation and roof timbers

Building Regulations

The legal rules for building work, with guidance in the Approved Documents; Trading Standards guidance for spray foam installers lists Approved Documents B, C, F and L as relevant^[13]. Schedule 3 of the 2010 regulations lists competent-person schemes for wall insulation but none for roof or loft insulation^[14]. Read more: how spray foam should be installed

Building Safety Regulator (BSR)

The building safety regulator within HSE. It published government-commissioned modelling of moisture risk in spray-foamed roofs in March 2024 and fire research in December 2025; neither is government policy or installation guidance^[1][2]. Read more: what the government has said

Closed-cell foam

A dense, rigid spray foam, typically 28.8–36 kg/m³ in the UK product approvals checked, that insulates better per millimetre than open-cell and strongly resists water vapour^[15]. The government-commissioned report describes it as giving a degree of vapour control, not as vapour-proof^[1]. Read more: open-cell vs closed-cell

Cold roof

A pitched roof insulated at ceiling level, on the loft floor, rather than along the rafters^[16]. Read more: condensation and roof timbers

Condensation risk assessment

A calculation of whether moisture is likely to condense within the roof once it is insulated. BBA 23/7062, for example, requires one to BS EN ISO 13788 before spraying, while the manufacturers' Code requires one but names no method^[9][11]. Read more: what paperwork you should have

Consumer Contracts Regulations 2013

The rules that give a 14-day right to cancel a contract made in your home. If the trader did not give you the cancellation information, or started work within the 14 days without your express request, then if you cancel you may pay nothing for that period^[17]. Read more: your consumer rights

Consumer Rights Act 2015

The law that requires a service, such as an installation, to be carried out with reasonable care and skill. Where it is not, the remedies include having the work redone or a price reduction^[18]. Read more: your consumer rights

Counter-batten

A batten laid over the underlay, beneath the tile battens, that leaves an air gap above the underlay; BS 5250:2021, as summarised in the government-commissioned report, uses that gap as one option for breathable underlays^[1]. BBA 23/7062 allows foam to be sprayed directly onto the underlay only where counter-battens sit above it^[9]. Read more: how spray foam should be installed

Density

The weight of foam per cubic metre, which separates the two types: typically 7–9 kg/m³ for open-cell and 28.8–36 kg/m³ for closed-cell in the UK product approvals checked; the government modelling used 7 and 42^[9][15][1]. Read more: open-cell vs closed-cell

Digital Markets, Competition and Consumers Act 2024 (DMCCA)

The law, in force since 6 April 2025, that bans unfair commercial practices such as misleading actions, misleading omissions and aggressive selling^[19]. The sections giving consumers their own rights of redress were still shown as not yet in force (as at October 2026)^[20]. Read more: your consumer rights

Drape

The slight dip of a flexible underlay between rafters. BS 5250:2021, as summarised in the government-commissioned report, adds a 15 mm drape allowance to a 25 mm ventilated gap under a high-resistance underlay^[1]. Read more: how spray foam should be installed

DRN

The reference on a published Financial Ombudsman Service decision, for example DRN-5667884, in which the ombudsman stressed that each case turns on its own merits^[21]. Read more: Section 75 and the Financial Ombudsman

Eaves ventilation

Openings at the lower edge of the roof that let air into the roof space. Product approvals say existing vents and ventilation gaps must be kept clear and not covered with foam^[22][23]. Read more: condensation and roof timbers

ECO4 (Energy Company Obligation)

A government home-energy scheme for eligible households, whose installers must be TrustMark-registered^[24]. It was extended to 31 December 2026 (as at 20 October 2026)^[25]. Read more: spray foam history and schemes

Euroclass

The European reaction-to-fire rating under BS EN 13501-1. The current UK spray foam approvals checked record Euroclass E, from a small-flame test, and RICS describes the foam as combustible^[9][15][8]. Read more: is spray foam a fire risk?

Financial Ombudsman Service

The service that decides complaints against banks and lenders, including Section 75 claims about spray foam. In two published spray foam decisions, the ombudsman found a report from the firm that went on to remove the foam could be doubted as not independent, and that removing the foam first left too little evidence^[21][26]. Read more: Section 75 and the Financial Ombudsman

Great British Insulation Scheme (GBIS)

A government insulation scheme that ran from April 2023 until it closed on 31 March 2026^[27]. Its delivery guidance (v2.1, December 2025) lists pitched-roof insulation but does not mention spray foam^[28]. Read more: spray foam history and schemes

Green Homes Grant

A voucher scheme in England that opened on 30 September 2020 and closed to applications on 31 March 2021^[29][30]. It did not specify which types of insulation could be installed^[31]. Read more: spray foam history and schemes

Handover pack

The documents an installer should give you after spraying. The manufacturers' Code lists the installer, date, product type and batch, product approval, photographs, pre-installation survey, condensation risk analysis and any warranty, with a short version left in the loft^[11]. Read more: what paperwork you should have

High-resistance (HR) underlay

An underlay that lets little water vapour through, such as bitumen felt, modelled at an Sd value of 5 m^[1]. The government-commissioned modelling found this kind of underlay the main driver of risk when foam is sprayed beneath it^[1]. Read more: condensation and roof timbers

IMA Code of Practice

The Insulation Manufacturers Association's Code of Practice for installing spray foam in domestic roofs, Issue 1, May 2023. It sets survey and paperwork steps but no technical limits such as moisture levels, ventilation gaps or fire linings, which come from the product approvals^[11]. Read more: how spray foam should be installed

Insurance-backed warranty

A warranty backed by insurance, meant to give cover if the installer stops trading. Ministers direct people with scheme-funded installations to claim on their warranty where the installer has gone^[32]. Read more: installer gone bust?

Isocyanate (MDI)

The reactive chemical in one of the two foam components. HSE says spraying isocyanate products is a significant cause of occupational asthma, and the manufacturers' Code says that since August 2023 anyone using them must complete mandatory training under UK REACH^[33][11]. Read more: spray foam fumes and health

Kiwa

A product approval body whose BDA Agrément approvals cover some spray foams; those approvals carry a stated validity of three years^[15][22]. Read more: product approvals explained

Lambda (λ)

Thermal conductivity, in W/mK: how readily a material conducts heat, so lower insulates better. Typical figures in the UK approvals checked are 0.038–0.039 for open-cell and 0.025–0.028 for closed-cell^[9][22][15]. Read more: open-cell vs closed-cell

Low-resistance (LR) underlay

A breathable roof underlay that lets water vapour pass, modelled at an Sd value of 0.04 m^[1]. The current approval BBA 23/7062 covers open-cell foam in pitched roofs with this kind of underlay only^[9]. Read more: what was the foam sprayed onto?

Moisture content

How much water timber holds, as a percentage by mass. Approvals require timber below 20% (BBA) or 19% (Kiwa) before spraying, and the government-commissioned modelling used 20% for solid timber and 18% for timber-based products as decay thresholds^[9][15][1]. Read more: condensation and roof timbers

Moisture meter

A hand-held instrument that gives a moisture reading for timber at the point tested. It can only read what it reaches: RICS notes that timber can give a low reading on its visible face and be wet behind the foam^[8]. Read more: condensation and roof timbers

Mortgage valuation

The lender's assessment of a property's value as security for a loan. RICS says spray foam may affect the surveyor's opinion of value, and that the surveyor follows the lender's instructions and may ask for an independent specialist report^[8]. Read more: spray foam and mortgages

Mu (μ)

The vapour resistance factor: how strongly a material resists water vapour compared with still air. The government-commissioned modelling used 3.3 for open-cell foam and 61.12 for closed-cell^[1]. Read more: open-cell vs closed-cell

Off-gassing

The release of chemicals from foam into the air after spraying. A 2020 RICS journal article says it is usually temporary, while a US government agency says the potential for it is not fully understood^[34][35]. Read more: spray foam fumes and health

Open-cell foam

A soft, light spray foam, typically 7–9 kg/m³ in the UK product approvals checked, that lets water vapour through easily and is now the most commonly applied type^[9][1]. It is not automatically lower risk than closed-cell; see "Breathable" above. Read more: open-cell vs closed-cell

PAS 2030 and PAS 2035

BSI specifications for installing individual energy efficiency measures (PAS 2030) and for whole-house retrofit (PAS 2035), required for work under ECO4 and the former GBIS^[36]. PAS 2035:2023 took effect on 30 March 2025 and requires a qualified Retrofit Coordinator on every project^[37]. Read more: how spray foam should be installed

PCA (Property Care Association)

A trade association whose members include specialists trained to assess spray foam in roofs^[38]. In August 2026 it announced, as reported in the trade press, a membership category for removal contractors, described as a benchmark rather than regulation of the market^[39]. Read more: should you remove spray foam?

PCA protocol

The industry's non-invasive, visual inspection method for spray-foamed roofs, published in March 2023. It reaches one of three conclusions (risk not significantly increased, risk increased, or insufficient information) and sets no moisture percentage or gap size^[40]. Read more: for professionals

PIR and PUR boards

Factory-made rigid insulation boards, not spray foam. The standard for sprayed foam, BS EN 14315-1, covers foam formed in place and excludes factory-made products^[41]. Read more: is it spray foam or boards?

Product approval

A document from a body such as the BBA or Kiwa assessing one product for one application, on conditions about how it is installed^[11]. It is not a warranty and does not cover whether the product suited your roof or was installed properly^[7]. Read more: product approvals explained

Purlin

A horizontal beam that supports the rafters partway up a roof slope. Read more: condensation and roof timbers

Rafter

One of the sloping timbers that form a pitched roof. Spray foam under a roof can cover the rafters, so their condition cannot be seen^[42]. Read more: what is spray foam insulation?

Re-occupancy time

How long to stay out of the space after spraying. No UK regulator sets a time: one BBA approval says only that sufficient time must pass, while the manufacturers' Code says 24 h, or 2 h with forced ventilation of at least 30 air changes an hour^[23][11]. Read more: spray foam fumes and health

"Removal certificate"

A phrase people search for, but the sources checked for this guide found no official document of that name. The government's spray foam research does not deal with removal, and the HomeOwners Alliance says it cannot recommend removal firms because no standard exists^[1][43]. Read more: after spray foam removal

RICS Home Survey levels

The three levels of home survey in the RICS Home Survey Standard, each with its own extent of roof-space inspection. The standard's most detailed level does not mention spray foam, so how it is reported depends on the surveyor^[44]. Read more: buying a house with spray foam

Roof stabilisation

Spraying rigid foam under tiles or slates to re-fix them when their nails are failing. The one UK approval found, BBA 10/4771 Product Sheet 2 (2010), makes no claim to strengthen the roof structure and requires sound timbers first^[45]. Read more: what spray foam does and does not do

Sarking

The layer fixed over the rafters beneath the tiles or slates; the sources use the word for felts, membranes and timber boards^[8][11][46]. RICS warns that some products must not be sprayed onto bitumen sarking felt^[8]. Read more: how spray foam should be installed

Sd value

A layer's resistance to water vapour, expressed in metres and taking its thickness into account: the higher the figure, the more it holds vapour back. The government-commissioned modelling used 0.04 m for a breathable underlay, 5 m for felt and 20 m for foil backing^[1]. Read more: condensation and roof timbers

Section 56

Part of the Consumer Credit Act 1974 that makes what a supplier said before the contract the responsibility of the lender providing the finance^[47]. Read more: Section 75 and the Financial Ombudsman

Section 75

Part of the Consumer Credit Act 1974 that makes the credit provider equally liable with the supplier for misrepresentation or breach of contract, where a single item has a cash price over 100 pounds and up to 30,000 pounds^[48]. Read more: Section 75 and the Financial Ombudsman

Spray foam insulation

Insulation made on site by spraying two liquid components that react, expand and set, usually under a roof^[11]. It comes in two main types, open-cell and closed-cell^[49]. Read more: what is spray foam insulation?

TA6

The Law Society's Property Information Form, which sellers must answer truthfully; the 6th edition is mandatory for Conveyancing Quality Scheme firms on instructions from 30 March 2026^[50]. No question on the form names spray foam, but question 5.1(h) asks about insulation works and 6.1(h) about insulation warranties (6th edition specimen, October 2025)^[51]. Read more: selling a house with spray foam

TrustMark

The scheme the Commons Library calls the government-backed quality scheme, with which ECO4 installers must be registered^[52][24]. TrustMark cannot help if the business has ceased trading or lost its registration^[53]. Read more: installer gone bust?

U-value

A measure of how much heat passes through a whole built-up element, such as a roof, where lower is better; it describes the construction, not a single material^[3]. Read more: how spray foam should be installed

UKAS

The UK's national body that recognises the testing and approval bodies behind product approvals. It suspended its recognition of the BBA on 26 February 2026, at the latest until 25 November 2026, and says existing BBA approvals stay valid until they expire^[6]. Read more: product approvals and the BBA suspension

Vapour control layer (VCL)

A layer on the warm side of the insulation that limits water vapour passing into the roof; an AVCL also limits air movement. Approvals differ: one open-cell approval requires a VCL unless a BS 5250 assessment shows otherwise, while a closed-cell approval says the foam must not be sprayed onto one^[22][15]. Read more: condensation and roof timbers

Wall plate

The timber along the top of an outside wall on which the rafters sit, at the eaves. Read more: condensation and roof timbers

Warm roof

A pitched roof insulated along the line of the rafters, as with spray foam under the roof^[16]. A new-home warranty body's technical standards, citing BS 5250:2021, say a warm roof with a breathable underlay needs no ventilation under the underlay, while under a high-resistance underlay the minimum clear ventilation path is 25 mm^[16]. Read more: how spray foam should be installed

Workmanship warranty

A warranty that covers the quality of the installation work, not just the product. RICS warns that some warranties cover only the material, not workmanship or design^[8]. Read more: installer gone bust?