How should spray foam be installed? What the product approvals require

A product approval is conditional: it assesses one product for particular roof build-ups and covers only the installation it describes, not whether your roof was suitable or the work was done well^[3]. The industry Code of Practice says each approval is specific to one product and one application, and that installation must follow it^[6].

A common claim, repeated in Trading Standards guidance for installers (November 2025), is that an approved product is "considered compliant" with Building Regulations^[8]. The BBA's own explainer lists that belief as a misconception^[3]. The BBA also warns that the regulation statements inside its approvals may be out of date since the 2022 changes^[9]. How to check an approval, and the BBA's current position, are in spray foam product approvals and the BBA suspension.

Approvals differ by product, so the table shows typical conditions, not one rule for every foam: check the approval for your product. Kiwa BAR-20-170 (October 2021) stated a three-year validity and its renewal could not be confirmed^[4]. A low-resistance (LR) underlay is a breathable membrane that lets water vapour pass; a high-resistance (HR) underlay, such as bitumen felt, resists it^[5]; an air and vapour control layer (AVCL) is a sheet on the room side that limits moist air reaching the roof. Other terms are in the spray foam glossary.

The documents do not all agree. The timber limit is 20% in the BBA approval and 19% in the Kiwa approvals, and the industry Code sets none^[1][2][6]. One older BBA approval bans recessed downlights outright, while Kiwa allows them with a 75 mm clearance and hooded fittings^[12][2].

Cables matter because the wiring rules halve the safe current of a cable totally surrounded by insulation for more than 0.5 m^[13].

Most current guidance says not: RICS says most products should not go directly onto tiles or slates, and government-commissioned modelling rated foam sprayed straight onto them high risk, for open- and closed-cell foam, in every scenario it tested^[14][5]. RICS adds that some products must not go onto bitumen felt, warns against unventilated plastic sheets, and says most should not be used to remedy leaks^[14].

BBA product approval 11/4816 (first issued April 2011) was different: it covered existing tiled and slated roofs, including roofs with no underlay, so spraying onto the underside of clay tiles and slates was within its scope; its current status is unknown^[10].

In the modelling, a high-resistance underlay was the main driver of risk: open-cell foam under an HR underlay with no AVCL was high risk in both climates, and bitumen felt was treated as an HR underlay^[5]. Open-cell foam installed to BS 5250:2021 over an LR underlay was low risk^[5]. The Building Safety Regulator stresses this is theoretical modelling of limited scenarios, not an installation guide^[15].

The PCA and RPSA's Sprayed Foam Insulation Inspection Protocol (March 2023) says foam on the roof covering, or on an HR underlay, may be assumed high risk^[16]. More on the research: does spray foam cause condensation or rot roof timbers?.

No: the Insulation Manufacturers Association (IMA) Code of Practice (May 2023) sets out a process and leaves the technical limits to each product approval^[6]. It requires a survey by a competent employee of an approved installer, a product approval, a homeowner pack, a record left in the loft and a copy for the manufacturer, but sets nothing on thickness, timber moisture, ventilation gaps, vapour control, linings, cables, flues or Building Regulations^[6]. What the pack should contain is in what paperwork should you have for spray foam insulation?.

The Trading Standards guide for installers (November 2025) lists a product approval from a body such as the BBA or Kiwa, BS 5250:2021 (moisture in buildings), Approved Documents B, C, F and L, photographs before, during and after, the 14-day cancellation right and the duty of reasonable care and skill^[8]. It says an installer unfamiliar with the Construction (Design and Management) Regulations 2015 is a sign of an unqualified installer^[8].

There is no single agreed answer in the sources: even the Building Safety Regulator's fire consultants wrote about the effects "if" applying foam counts as building work^[17].

• Building Regulations 2010: renovating a "thermal element" is defined to include providing a new layer (reg 2); work that reg 23 requires is "building work" (reg 3(1)(h)); reg 23 applies where more than half of the element is renovated; Schedule 3 lists competent-person schemes for wall insulation only, none for roof or loft insulation^[18].
• Planning Portal: loft insulation must meet the minimum energy efficiency values in the Approved Documents; where more than 25% of a roof is renewed, the insulation must be brought up to standard; eaves ventilation must be kept clear^[19].
• Approved Document L: sets roof U-values (heat loss), not depths; in the 2021 edition the threshold for a renovated roof is 0.35 W/m²K, with a lesser standard allowed where needed to avoid condensation^[20]; the 2026 edition, which takes effect on 24 March 2027, keeps 0.35 as the threshold and 0.16 as the improved value for an existing roof^[21].
• IMA Guide (October 2024): gives a building control or competent-person route for cavity wall foam, but none for roof work^[22].

The 50% and 25% figures are different triggers, and neither settles the question for spray foam. If you are planning work, ask your local authority building control team in writing whether an application is needed, and keep the reply with your paperwork.

Scotland, Northern Ireland and Wales: in Scotland, insulation work is exempt from needing a building warrant but must still meet the building standards; SPICe advises checking with the local authority^[23][24]. In Northern Ireland, insulation work normally needs a building regulations application^[25]. The Commons Library (briefing modified July 2026) says no official Wales-specific guidance on spray foam is available^[26].

Only with listed building consent, and Historic England says foam sprayed to the underside of the roof covering is "likely to harm the fabric of the building and is not easily removed" (Advice Note 18, para 85)^[7][14]. The same note says historic buildings are typically vapour permeable, insulation that traps moisture can speed up decay, and work should be reversible where possible (paras 10, 14, 67 and 68)^[7].

RICS says foam must not go into a listed or protected building without consent, and in its view foam is not reversible and unlikely to obtain consent^[14]. An earlier Historic England guide lists sprayed foam among inappropriate materials for traditional roofs^[27].

A common claim is that spray foam "should not be used" in listed buildings: the sources set a consent requirement rather than a ban, though their direction is clearly against it^[7].

No. For a loft not used as a room, RICS asks why insulate at rafter level when ceiling-level insulation costs less, and advises independent advice, separate from the installer and manufacturer, before foam goes in^[14]. The Energy Saving Trust suggests considering mineral wool first, and says impermeable foam on an old, poorly maintained roof is among the highest-risk options^[28]. See thinking of having spray foam installed?

A mismatch means the installation is outside what the approval assessed; on its own it does not show what condition the roof is in^[3]. The PCA protocol has three possible conclusions: risk not significantly increased, risk increased, or not enough information to say^[16]. The industry Code says departing from the product specification voids the manufacturer's warranty, so check your own warranty's terms^[6]; separately, the Consumer Rights Act 2015 requires services to be performed with reasonable care and skill^[29].

In a PCA survey reported in May 2025, 15 of its 21 register firms reported on more than 500 inspections: 79% of properties diverged from the protocol and 27% needed major works, in homes already under suspicion^[30]. One anonymised case file describes how a 25 mm air gap was designed and sold, but not reliably built.

Gather the paperwork first, then get independent evidence before anyone removes anything: see should I remove spray foam insulation? and your consumer rights.