The short answer
What is spray foam insulation? It is polyurethane insulation sprayed as a liquid that expands and sets into a continuous layer bonded to the roof, wall or soffit. On commercial buildings, closed-cell foam is rigid, seals laps and fixings and, correctly specified, stops condensation on cold metal sheets; open-cell foam is softer and vapour-open, used for thermal and acoustic insulation in suitable breathable build-ups.
If you're looking up at a cold warehouse roof, the question is what you need the insulation to do. Stop drips? Keep heat in? Quiet the rain? A profiled sheet, a concrete soffit and a timber deck need different answers.
HOLVEM is a commercial building-performance company. We establish what is happening in the building first, then specify what should change beneath the surface. Our own teams survey, specify and install nationwide across England and Wales, with coatings where the work needs them.
So let's start with the material, then work through the checks for your building. If you're ready to discuss a job, see our commercial spray foam insulation service.
01What it is and how it goes on
What it is and how it is applied
From roof to quote, in order
- 01Show us the roofPhotographs, drawings and the layers already there.
- 02Tell us the problemA wet underside, a cold work area, rain drumming or a U-value target.
- 03We check and calculateThe construction, the layers and the depth.
- 04Agree the resultA quote for the complete work, with the finish.
Two liquid components meet as they are sprayed, expand on the surface and set into polyurethane insulation. Because the layer forms there, it follows the roof profile instead of leaving you to fit separate boards around every corrugation.
That is useful on a curved steel arch or an irregular concrete soffit. We can follow the shape and seal the agreed details. In a hybrid roof, the foam works alongside other insulation, membranes and linings, each with its own job.
But the surface has to be ready. We check old finishes, dirt, corrosion and damage before setting the preparation. If the roof leaks, a roofer fixes it first. Spraying underneath a live leak only hides the problem.
Spraying underneath a live leak only hides the problem.
Your quote should say where the layer starts and stops, how thick it will be and what finish it needs. Rooflights stay clear; services that need future access are identified before we spray.
Then we plan the floor below. You may need to move stock or vehicles, or release a bay while we protect machinery. We'll agree access, ventilation, separation and re-entry with you before the team arrives.
Insulation, an air seal and the complete building
Insulation slows heat transfer through the treated roof, wall or soffit. A continuous layer also seals the air paths it covers. Open doors and untreated wall junctions still matter, so tell us where you feel the draughts as well as where you see the water.
Tell us what you need the building to do. A wet underside, a cold work area, rain drumming on the roof and a written U-value target are different starting points. You can bring more than one problem; we'll give each one a place in the proposal.
Afterwards, keep the specification, thickness checks, coverage photographs, calculations and finish records with your building file. When someone asks what went on the roof, you have the answer.
The sequence is simple: show us the roof, tell us the problem and agree the result. We check the construction, calculate the layers and quote the complete work. You can see what you are buying.
02Closed-cell and open-cell
Closed-cell and open-cell compared
Closed-cell foam is rigid and vapour-resistant. Open-cell is softer and vapour-open, with an acoustic role in suitable constructions. They are not interchangeable roof treatments.
| Question | Closed-cell | Open-cell |
|---|---|---|
| General character | Rigid, bonded and vapour-resistant | Softer, vapour-open and sound-absorbing |
| Appropriate commercial roles | Suitable cold metal, retained roof surfaces and concrete soffits; assessed hybrid constructions | Suitable acoustic and vapour-open assemblies, including specified roof build-ups |
| What decides suitability? | Substrate, moisture design, objective and complete construction | Drying path, substrate, moisture design, acoustic objective and complete construction |
| Directly on a cold metal sheet? | The specified foam type for the suitable direct-bonded treatment | Not a substitute for closed-cell directly on that cold sheet |
| Does its name check the roof's U-value? | No; calculate the complete element | No; calculate the complete element |
| Does its name establish fire compliance? | No; tested assembly and fire strategy decide | No; tested assembly and fire strategy decide |
For open cell vs closed cell spray foam, ask where moisture can go and what each layer needs to do. On a cold steel sheet, we need a rigid, vapour-resistant layer bonded to the metal. In an acoustic build, softer open-cell foam can play a different role.
Sometimes both belong in one roof. That is a designed hybrid: each material does a job, and the layers are checked together. It isn't a matter of spraying whichever foam is available.
Closed-cell system data and open-cell system data explain HOLVEM's material roles. Use the declared data for the selected system and assess its behaviour with the layers already in the building.
What the project examples show
At The Alban Arena in St Albans, we used open-cell and closed-cell in the roof of a working venue. Across more than 29 schools in Hampshire and Berkshire, we applied open-cell to single-storey flat roofs. Those are practical examples of the different roles.
Each new building gets its own specification.
A sample tells you how the material feels. Your roof drawings tell us where it belongs. We need both the existing layers and the required finish to design the new build-up.
03On a commercial roof
What it does on a commercial roof
A profiled or curved roof has plenty of awkward corners for a fitted insulation system. A sprayed layer follows those contours and bonds to the surface. That is why it works beneath corrugated sheets, curved arches and irregular soffits.
Foam thickness is only part of the thermal answer. The sheet, old insulation, cavities and steel bridges all count, so we calculate the whole roof. The foam's declared conductivity feeds that calculation; it isn't the roof's U-value.
The same care applies at junctions and penetrations. Sealing the air path around steel helps with draughts, while the steel itself still conducts heat. Your calculation needs to include both.
A · Across the profile
B · Along the slope, at a purlin
- Profiled metal sheetRetained in place; the sprayed layer follows its contours.
- Closed-cell layerRigid and vapour-resistant, bonded to the metal. The survey sets the depth.
- LapClosed-cell foam seals laps and fixings.
- FixingThrough the sheet into the purlin, sealed by the bonded layer.
- Steel purlinSealing the air path around steel helps with draughts, while the steel itself still conducts heat. The calculation includes both.
Heat conducted through the steel
Condensation on a cold metal roof
Correctly diagnosed and specified, closed-cell spray foam stops roof condensation. Zero call-backs for condensation. The depth is typically 25 mm or 50 mm closed-cell, depending on the roof make-up, confirmed before we spray. We use a condensation risk analysis where needed. Existing leaks go to a roofer first.
At TJW Grab Hire in Bournemouth, about 505 m² of box-profile steel roof in good condition ran with condensation onto the vehicles and equipment beneath it. We sprayed 50 mm closed-cell to the underside. The customer reported that the condensation was eliminated.
Backed by our 25 year HOLVEM workmanship warranty, plus the manufacturer's 25 year product warranty issued directly to you.
The survey sets the depth for your roof. Read TJW Grab Hire.
Heat loss and rain noise need their own answers
If your designer has set a U-value, send it with the drawings. We'll calculate the complete roof, wall or soffit against that target. A layer chosen to stop condensation can be shallower than one needed to meet a thermal requirement.
Rain noise is another job. Open-cell has a sound-absorbing role in suitable builds; at Black Hangar Studios, the studio reported that drumming and resonance from rain and wind were virtually eliminated.
Read thickness and objective for the depth decision and rain noise and acoustics for that separate building problem.
04Fire and coatings
Fire performance and coatings
For fire performance, ask which build-up was tested. The substrate, foam depth and coating or lining belong with the result. We'll check that evidence against your project's fire strategy.
The manufacturer's fire evidence includes an uncoated Class 1 surface-spread-of-flame result to BS 476-7 at 45 to 50 mm on 9 mm plasterboard. Its coated B-s2,d0 assembly was tested at 35 to 40 mm on 9 mm plasterboard, with an intumescent coating at 0.7 mm wet film thickness. These are results for those tested assemblies.
Keep those two tests separate: Class 1 is a British surface-spread result; B-s2,d0 is the coated assembly's Euroclass. Your fire strategy decides which construction and finish you need.
Ask what coating or lining is included, how it is applied and what evidence you get at handover. An exposed soffit and a layer behind a ceiling can need different finishes. Your quote should make that clear.
Read fire performance and coatings. HOLVEM is an accredited installer for the manufacturer of the spray foam systems we apply.
05The wrong choice
Where it is the wrong choice
Sometimes the survey points to another trade first. That's useful: you want to know about the failed sheet or wet deck before you pay to cover it.
| Building finding | What happens before an insulation proposal |
|---|---|
| Active roof leak | A roofer establishes and repairs the water entry |
| Unsound roof or supporting structure | A roofing or structural professional assesses it and sets the work needed |
| Surface unsuitable for adhesion | We set the preparation or a different construction; we never cover the defect |
| Timber build-up with an uncertain moisture route | Assess retained layers, vapour control and drying before choosing insulation |
| Fire strategy requiring a different assembly | Select a construction with applicable evidence and the required finish |
| Working area can't be controlled | Agree suitable access and site plan before installation |
| Roof already due for replacement | Compare the designed new assembly with a separate internal retrofit work |
At The Regis School in Bognor Regis, one of two steel containers had a live leak, so we did not spray it. Insulating from inside never repairs an active leak.
Asbestos-containing or suspected materials need the dutyholder, a competent asbestos surveyor and HSE guidance involved in the assessment. 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.
Timber roofs need their own moisture decision
With timber, we need to know what is above and below the deck: weather covering, old insulation, membranes, cavities and lining. Those layers decide how moisture moves and how the timber can dry.
So we check the proposed roof before choosing the foam. Ventilation and access for future inspection stay in the design; they aren't details to sort out after the timber is covered.
For a home loft, use the RICS consumer guide and an independent adviser who can inspect that dwelling.
06Compare the complete work
Costs: compare the complete work
Our cost guide gives HOLVEM's published prices. Its installed foam-only ranges are £16 to £25/m² + VAT at 25 mm and £22 to £35/m² + VAT at 50 mm. Deeper applications and coated systems are priced for the project.
Your quote should name the area, depth, preparation, access, protection, finish and programme. That way a foam-only price is easy to distinguish from a complete coated system.
Now compare the finished work. A board system may need supports and a lining; sprayed foam may need high-level access and a fire coating. Ask each contractor to show what is included.
Tell us about working hours and fixed machinery at the start. Clearing one bay for a continuous run is different from short access windows around live plant. We'll price the plan your building actually needs.
Compare the installed methods
| Method | Typical installed cost per m² | What you are buying |
|---|---|---|
| Closed-cell spray foam, 25 mm | £16 to £25 + VAT | Foam only on a sound, prepared surface; the roof stays in place |
| Closed-cell spray foam, 50 mm | £22 to £35 + VAT | Foam only, with depth confirmed for your roof at survey |
| PIR or rigid boards | £30 to £50 installed | A fitted board system; compare supports, joints and finish |
| Mineral wool and liner | £20 to £30 installed | Insulation with its supporting liner and vapour-control details |
| Roof overcladding | £60 to £90 | A new weather-facing roof system over the retained roof |
| Insulated panels or replacement | £100 to £160 + VAT | A new insulated roof, with removal and access checked in the quote |
These are the method figures in our cost guide, not a quote for your building. The guide does not state a VAT basis for the board, mineral-wool and overcladding rows, so ask the contractor to confirm it. Added coatings and external foam systems are priced per project. Compare what is included before you compare the totals.
07Commercial projects
Commercial projects: different reasons to specify
Black Hangar Studios, Alton
A 4000 m² hangar under a corrugated asbestos-cement roof, insulated from below with closed-cell and open-cell foam, with nothing cut or removed. The studio reported that the drumming and resonance from rain and wind were virtually eliminated. Read Black Hangar Studios.
The Alban Arena, St Albans
Read The Alban Arena: 100 mm of open-cell and 25 mm of closed-cell in the roof of a working venue.
If your building stays in use, the programme belongs beside the technical design. We agree which areas you release, what needs protection and when work can take place.
School flat roofs
Across more than 29 schools in Hampshire and Berkshire, we applied open-cell foam to single-storey flat roofs. Read the schools programme.
TJW Grab Hire, Bournemouth
TJW's sound steel roof was running with condensation, not leaking, so it took 50 mm closed-cell to the underside.
Steel and metal roofs are the core of our work. Our own teams survey, specify and install from four depots: Weybridge, Bedford, Manchester and Exeter.
