Pitched roof insulation for barns, sheds and commercial buildings

If the search results show loft rolls and timber rafters, start again with the roof you can see. Your sheets, steelwork, rooflights and openings need a construction that fits them. The building underneath matters too, whether that is a warehouse aisle, machinery bay or livestock shed.

01Not a loft

A commercial pitched roof is not a loft

First, identify the structure above your floor. A typical sheeted commercial roof has purlins supporting the covering, with the sloping frame members carrying the bay. It does not offer the same timber-rafter cavities or ceiling-joist space assumed by domestic loft advice.

The sheet is both the weather-facing covering and a cold surface above the room. The insulation can sit beneath it, within a designed liner construction, or in a new external roof arrangement. Those positions leave different layers and junctions to complete.

This guide covers pitched roofs. For flat roofs, see our guide to the types of roof insulation.

This guide covers commercial and farm buildings. For a house loft, impartial home energy advice services cover domestic options.

02Why it drips

Why a sheeted pitched roof drips

Once you know the construction, follow the water before choosing insulation. Rain can enter at a failed lap, fixing, sheet or adjoining detail. Condensation forms when moist indoor air reaches a roof surface colder than its dew point. Both causes can be present in the same building.

Note when the drips appear and how far they spread. Water during rain at one detail points the roof inspection towards ingress. Droplets spread across the underside on cold mornings usually point to condensation. Photographs taken safely give the contractor a starting record; the checks establish the cause.

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, with a condensation risk analysis where needed.

If the roof leaks, call a roofer first. HOLVEM is not a roofing contractor, and spray foam is not waterproofing. Read commercial roof repair and roof condensation to keep those jobs in the right order.

03Three routes

Three ways to insulate a pitched sheeted roof

With the cause understood, compare where the insulation goes. The three broad routes are a supported liner construction, an external roof system and a bonded layer beneath the retained sheet. Boards and mineral wool are separate material choices within the liner route.

Typical UK industry figures, 2026. Send photographs or drawings for a free estimate.

For a suitable roof, underside work can be phased around agreed areas of the building. A liner or external assembly has its own access and protection requirements. Ask each contractor which bays remain usable and when, rather than compare a broad promise that the building stays open.

For the step-by-step method on a metal roof, see our guide to insulating a metal roof. This page looks at the pitched construction as a whole.

04The details

The details that decide the job

The main area is only the beginning. Follow the route from the eaves to the ridge and note every rooflight, support and penetration. Your specification should show where the layer continues, where it stops and which openings remain functional.

Purlins and thermal bridges

Steel purlins interrupt the thermal route. Foam can wrap their accessible surfaces, but the steel still passes through the construction as a thermal bridge. The U-value calculation accounts for the purlins as a repeating thermal bridge, rather than treating the whole roof as an uninterrupted insulation slab. Junctions such as the eaves, ridge and roof lights are considered separately.

For a liner or board system, ask the same question about supports and fixing positions. The drawn section and the installed details must describe the same heat-loss path.

Laps and fixings

Check their condition before treating the underside. A failed weathering detail needs repair; a sound detail needs completing within the insulation specification. Put the prerequisite roofing work and its handover into the programme so the new layer goes onto a ready roof.

Rooflights

Mark rooflights before measuring the area and planning protection. At TJW Grab Hire, the polycarbonate rooflights were left uncoated, with the treatment stopped cleanly at their edges. Masking and finishing those boundaries keeps the daylight opening clear.

Rooflights also affect access and fragility. Photograph them from the floor; do not step onto the covering to obtain a closer view.

Ridge and eaves

Keep required ventilation openings working. Identify them in the drawing and the site plan before application. Any proposed change to an opening needs resolving within the ventilation design, rather than being treated as another gap to fill.

That gives the installer clear boundaries. That way the insulation and the ventilation each get on with their own job.

05Barns and livestock

Barns and livestock buildings

In a barn, the use beneath the roof is part of the moisture brief. Animals, bedding and stored material can add moisture to the air. Ventilation removes moisture, but it does not make a cold sheet warm. Insulating the surface and maintaining the required airflow address different parts of the problem.

A new uninsulated sheet can still be cold enough to collect condensation. Before spending on replacement, establish whether the existing roof is suitable to retain and whether the actual problem is rain entry, condensation or both.

Plan the work around the stock and working floor. We agree with you which bays are cleared of stock before we spray. Agree the released areas, protection and handovers before the team starts, while keeping the ventilation required for the building's use.

Our agricultural-building page shows how we work in farm buildings. Send the shed's use and working pattern with the roof information so the proposed programme fits the operation.

06Fibre and asbestos cement

Fibre-cement and asbestos-cement sheets

If the material is fibre cement or suspected asbestos cement, establish its identity and condition before planning work. Use the asbestos survey or register and competent advice. A photograph of a corrugated sheet cannot confirm whether it contains asbestos.

HOLVEM does not test for asbestos or replace roof sheets, and 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.

Treat the covering as fragile until a competent person confirms otherwise. Take enquiry photographs safely from inside and let the contractor plan the inspection and access. Retaining a roof keeps its material records and management requirements in force.

Read fibre-cement encapsulation for the underside method and the fibre-cement/asbestos roof decision for the wider choices. These are material and condition decisions, separate from the free-estimate route.

07Building regulations

Building regulations for pitched roofs

The table shows the 2021 edition (with 2023 amendments), which applies now, and the 2026 edition, which takes effect on 24 March 2027 (24 September 2027 for higher-risk building work), subject to transitional arrangements.

Which row applies depends on the work. Building control confirms compliance; we supply the roof calculation. Do not infer an agricultural exemption or apply a domestic loft detail from this table. Your project adviser confirms the route.

Wales has its own Approved Document L. The English tables do not transfer to a Welsh project. Read building-regulations U-values and U-values and Part L for the edition and project checks.

08How deep

How deep does the insulation need to be?

With the target established, calculate the whole roof. A layer for condensation and a build-up for a required U-value are different specifications. The existing sheet, other layers, junctions and steelwork affect the result.

The condensation depth is typically 25 mm or 50 mm closed-cell, depending on the roof make-up, confirmed before we spray. Where the work needs a calculated U-value, the depth comes from that calculation. The thinner-layer bands are not a building-regulations compliance specification.

See thickness and objective for that distinction. Ask for the layers, conductivity, corrections and target to be recorded with your quotation, so the proposed depth has a clear basis.

09Costs per m²

Costs per m²

Now put the construction and programme beside the cost. Our foam-only rates are £16 to £25/m² + VAT at 25 mm and £22 to £35/m² + VAT at 50 mm. A liner, overcladding or replacement price includes different work, as the route table shows.

Typical UK industry figures, 2026. Send photographs or drawings for a free estimate.

Check each contractor's VAT basis and inclusions. Access, repairs, preparation, protection and finish belong in the total. Extra coatings and a calculated thermal depth need their own project price. The cost guide gives the published foam bands; spray foam versus overcladding compares the two interventions.

10Recorded work

Projects beneath real sheeted roofs

The details above are visible in the project records. At TJW Grab Hire, Bournemouth, about 505 m² of sound box-profile steel received 50 mm closed-cell in two working days. The foam wrapped the purlins and stopped at the polycarbonate rooflights, which stayed clear. The customer reported condensation eliminated.

At Black Hangar Studios, Alton, the 4,000 m² corrugated asbestos-cement roof stayed in place above steel purlins and trusses. It received a 25 mm closed-cell base followed by 150 to 200 mm open-cell, with nothing cut or removed. The studio reported rain-and-wind drumming and resonance virtually eliminated. The acoustic result is the studio's report for that hybrid build-up.

For a curved-roof comparison, the Rolls-Royce Nissen hut record shows 50 mm closed-cell and an intumescent finish on a corrugated steel arch, with lower heat loss and heating/cooling costs reported by the client; see Nissen huts. That arch is a pointer to another construction, rather than pitched-roof proof.

11Getting a price

Getting a price for your roof

Start with photographs of the underside, a rooflight, the ridge and the eaves, taken from safe positions. Add drawings and the building's use if you have them. We can measure and check the roof remotely from aerial imagery alongside what you send, as a virtual survey within the free estimate.

Clear photographs often get you a free, same-day estimate without a site visit. We tell you which next step applies after reviewing them: confirmation on installation day before work starts, or a free survey followed by a firm written quote for larger or complex work. No obligation either way.

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

12Why HOLVEM

Why HOLVEM

Your pitched roof covers stock, machinery or a working floor. Here is why owners hand it to us rather than strip it or clad over it.

We keep a suitable roof on and plan the work bay by bay around the space below. The active bay is released to the team, while the agreed areas remain in use. That avoids a strip-out programme with the roof open to the weather.

Correctly diagnosed and specified, closed-cell spray foam stops roof condensation. Guaranteed to stop condensation when we confirm it is condensation at survey, set the depth, and the roof has no existing leaks.

Your pitched-roof specification includes the roof calculations, with the purlins accounted for, and a QA evidence pack at handover. Surveyors, insurers and buyers can review the construction and completed work.

Backed by a 25 year product and workmanship warranty.

One team takes the job from specification through installation across England and Wales from four depots. Over 500 installs include TJW and Black Hangar, whose records show different briefs beneath sheeted roofs.

Send photographs: the underside, a rooflight, the ridge and the eaves, taken safely, for a free estimate.

13Which route fits

Three questions point to the first step.

Answer the three below. The result names the first step; your photographs confirm the roof and the route.

14Questions, answered

Questions about pitched roof insulation

What is the best insulation for a pitched barn or warehouse roof?

Compare the complete liner, external-roof and underside-foam routes against your construction and intended result. A suitable retained roof is a different starting point from a covering already due for renewal. Include moisture, fire, access and the finish in each proposal.

What are the regulations for pitched roof insulation in England?

Approved Document L Volume 2 gives the new/replacement and renovation routes shown above. The project team confirms which edition and row apply. We supply the roof calculation. Wales uses its own Approved Document L.

Can you insulate a barn with livestock in the building?

We agree with you which bays are cleared of stock before we spray. Agree the work zones and handovers around the shed, with the required ventilation kept working. The programme follows the actual operation and access.

Will insulation stop the barn dripping?

Correctly diagnosed and specified, closed-cell spray foam stops roof condensation. Repair existing leaks first, then specify the depth for the suitable roof. The layer does not replace required ventilation.

Do I have to remove an asbestos-cement roof first?

HOLVEM does not test for asbestos or replace roof sheets, and 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.

Do you keep the rooflights?

The agreed rooflight openings are masked and left clear. TJW's polycarbonate rooflights were uncoated, with the insulation stopped at their edges. Include their positions when showing us the roof.

Can I get a price from photographs?

Yes, a free estimate with a virtual survey, often the same day from clear photographs. Straightforward work can be confirmed on installation day before work starts; larger or complex work follows a free survey and firm written quote. No obligation either way.