Spray foam insulation and building regulations: what applies to a commercial building

The useful first conversation is about your building and the planned work. A condensation treatment, a major roof renovation and a change from unheated storage to a heated workspace are different projects. Agree the regulatory route with the project designer and building control before the specification is fixed.

An Approved Document gives guidance on meeting the requirements in England. It is not a product approval, and a product certificate is not approval for every place that product might be installed.

01New or existing building?

New work or work to an existing building?

Start with what will change on your building: a new roof, a replacement, an insulated layer on an existing element, or a different use for the space. That description gives the project team a basis for deciding which guidance and evidence the work needs.

For England, Approved Document L Volume 2 separates new or replacement elements from renovated and retained elements. Sections 10 and 11 explain the routes for work to existing buildings. A roof already in place does not automatically put the work outside building regulations.

Section 11 includes renovation of thermal elements, material changes of use and changes to energy status. Its renovation guidance identifies work to more than 50% of an individual thermal element, or a major renovation affecting more than 25% of the external building envelope. Those percentages concern defined areas and types of work, not a percentage of the floor you happen to be spraying.

Have the project team establish how that guidance applies to the actual proposal. The same section explains how the area is assessed from inside or outside. Technical and functional feasibility provisions also matter. The building regulations U-values guide holds the detailed element-by-element explanation, rather than repeating its tables here.

A change in use needs equal care. If a previously unheated space becomes part of a heated building, the project team must consider the change to energy status. Do that before choosing insulation from a price list.

02Evidence for each requirement

Which evidence answers which requirement?

Once the work is defined, put each question beside its evidence. This is the structure to use when comparing specifications.

Use the table to keep the evidence together as the design develops. It helps the project team connect each requirement to the proposed insulation. Other requirements can apply to the wider work too, so agree the details through the designer and building-control process.

03Part L: the U-value

Part L: the U-value belongs to the construction

With the work category agreed, establish the thermal target. A U-value describes heat transfer through a complete element. The foam's conductivity is one input; the sheet, deck, existing insulation, supports and junctions affect the result.

In the 2021 edition of Approved Document L Volume 2 incorporating the 2023 amendments, Table 4.2 (“Limiting U-values for existing elements in existing buildings”) gives a threshold of 0.35 W/m²K and an improved value of 0.18 W/m²K for a flat roof or roof with integral insulation. That is one row for one category, not a single figure for every roof. Other roof categories differ.

The distinction between a threshold and an improved value matters. A threshold is not an instruction to spray every roof to that figure. The work category, trigger provisions and applicable qualifications decide the proposal. Keep the detailed comparison on the U-values and Part L page.

The Box in Plymouth shows what a project-specific target looks like. Its published record is 787 m² of concrete soffit at 120 mm closed-cell, to a specified U-value of 0.18 W/m²K. The work included adhesion and thickness checks and site inspection. That figure was calculated for its construction; it is not a universal result for 120 mm of foam.

Read The Box project record for the substrate and verification behind the figure. If you have a target already, send the drawing or specification that sets it.

04Part C: condensation and moisture

Part C: condensation and moisture

A thermal target does not settle the moisture question. Adding insulation changes temperatures within a construction. The proposal must also consider where moisture comes from, how it moves and whether it can accumulate within the layers.

Surface condensation is water forming on a cold exposed face. Interstitial condensation occurs within the construction. A layer can improve the temperature you see from the room while changing conditions elsewhere, so assessment needs the whole build-up.

Approved Document C addresses protection from harmful moisture effects. HOLVEM's condensation risk analysis explains how BS 5250 moisture-management principles and methods such as BS EN ISO 13788 are used for a specified construction. A more detailed assessment is needed where a simple method does not adequately describe the conditions.

Useful inputs include the roof covering and deck, existing insulation, internal use and moisture, temperatures, ventilation and any proposed air and vapour control layer. Process moisture in a factory and moisture in an occupied livestock building belong in that assessment; they are not background details.

Keep required ventilation working. A vapour-resistant foam does not automatically remove the need for an additional air and vapour control layer, and open-cell is not HOLVEM's specified layer directly against cold steel. The analysis decides the arrangement.

Correctly diagnosed and specified, closed-cell spray foam stops roof condensation. The depth is typically 25 mm or 50 mm closed-cell, depending on the roof make-up, confirmed before we spray.

Guaranteed to stop condensation when we confirm it is condensation at survey, set the depth, and the roof has no existing leaks.

Rain entry is different. A roofer repairs existing leaks before insulation; foam does not replace the weather line. Put that repair scope beside the insulation scope so one contractor's work is not mistaken for the other's.

05Part B: fire

Part B: fire follows the tested build-up

Once the thermal and moisture layers are understood, check the required finish. Fire performance depends on the material, its thickness, substrate, coating or lining and the way the assembly was tested.

Our manufacturer's uncoated Class 1 surface-spread-of-flame result to BS 476-7 was tested at 45 to 50 mm on 9 mm plasterboard (BTTG report 27/06605/10/24). No Euroclass is established for that uncoated foam. The coated B-s2,d0 assembly used 35 to 40 mm on 9 mm plasterboard with DC315 at 0.7 mm wet film thickness (BTTG report 27/06638/12/24).

Neither result automatically classifies foam on a metal sheet, concrete soffit or a thicker layer. A description such as coated foam is not enough to identify the tested assembly. The designer or fire engineer sets the requirement for the building, agreed with building control.

Use the fire performance and coatings page for the evidence and the dedicated fire-classification guide for the meaning of the classes. Do not treat a historic national class as a Euroclass equivalent. The applicable Approved Document B edition and transitional arrangements belong in the project's review.

06Materials and workmanship

Materials and workmanship

Next, make the design clear enough for the team on site to follow. The specification should name the system, surface preparation, depth, junctions and finish. It also needs the application conditions, so the installed work can be checked against what was proposed.

We use certified spray foam systems, which we apply as an accredited installer for the manufacturer. The installed work is recorded in the HOLVEM QA evidence pack. Product paperwork establishes the declared material data; the job records show what was applied to your building.

Ask how thickness, coverage and adhesion will be checked and recorded. Ask how rooflights, services and work areas are protected, and which separation, ventilation and re-entry arrangements govern the programme. A promise to finish in a day is not a substitute for those arrangements.

Where asbestos-cement is present, provide the survey or register and competent asbestos advice. HOLVEM does not test for asbestos or replace roof sheets.

HOLVEM never removes asbestos sheets. If the roof is safe to keep, we encapsulate it; if not, removal is a job for asbestos removal professionals, licensed where HSE requires it.

07Is spray foam banned?

Is spray foam banned?

Spray foam insulation is not banned or illegal in the UK. The important questions are suitability, specification and installation to recognised standards. Listed or protected buildings may need consent before installation; check with the local planning authority first.

The official material behind many news stories concerns homes, mainly timber pitched roofs and lofts. It does not provide approval for a particular commercial roof.

The Commons Library briefing and RICS consumer guide explain their domestic context. For a commercial proposal, keep the written specification, calculations, relevant product evidence and QA records together. The label spray foam alone does not answer the project questions.

08What to send building control

What to send building control

Bring that evidence together before booking the work. The project team needs to review one agreed construction, with the documents describing the same layers and details. Start with the information below.

Keep a copy with the building file after handover. A future facilities manager should be able to identify the system and understand why it was installed that way. Where a detail changes on site, it needs checking against the calculations and fire specification before it becomes the installed detail.

09Wales has its own guidance

Wales has its own guidance

For a building in Wales, use the Welsh Approved Documents and the applicable Welsh requirements. Do not carry an England table across simply because the roof construction looks the same.

Our building regulations Wales guide holds the Welsh Part L detail. Send the project location with the brief so the right guidance is used from the start. HOLVEM works across England and Wales.

10Questions, answered

Questions

Does spray foam need building regulations approval?

The answer depends on the building and work being undertaken. New work, renovation of a thermal element and changes of use or energy status need their regulatory route established. Agree that route with the designer and building control before installation; a product certificate does not settle it.

Does spray foam meet Part L?

The complete element needs the applicable thermal calculation. There is no foam depth that answers Part L for every building. The target, existing construction and bridges determine the specified depth, with any applicable qualifications assessed for the project.

Who signs off the condensation risk analysis?

A competent person prepares and takes responsibility for the assessment within the project design process. HOLVEM supplies the assessment and specification for its scope; the designer and building-control process establish what evidence is required and how it is accepted.

Is a fire coating always needed?

The building's fire strategy and the position of the insulation decide the required surface. If a classified build-up is required, the proposed system must have relevant evidence for that arrangement. An uncoated result does not answer a coated-system requirement.

What if the roof is already leaking?

Identify and repair the rain-entry defects first. The roofing work and insulation work need their own written scopes. A condensation analysis does not turn insulation into waterproofing.

11Why HOLVEM

Why HOLVEM

We put the paperwork into the job as it develops. The Box and Derriford records show what that means in practice: a thermal target becomes a particular build-up, with its depth, access and verification recorded.

We connect the proposed insulation to the U-value calculation and moisture assessment the construction needs. Certified spray foam systems, which we apply as an accredited installer for the manufacturer, come with a written scope and HOLVEM QA evidence pack. Fire evidence stays attached to the tested build-up, so a product claim is not mistaken for a classification of your roof.

Suitable photographs and measurements often mean a free, same-day estimate without a site visit. The virtual survey uses aerial imagery alongside your photographs or drawings. Straightforward jobs are confirmed on installation day before work starts; larger or complex jobs get a free survey, then a firm written quote. No obligation either way.

Send photographs or drawings → free, same-day estimate with a virtual survey → confirmed on install, or a free survey and firm written quote for larger jobs.

A binding quotation is issued in writing before work starts, from a survey or from the photographs and drawings you send.

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