Types of roof insulation for commercial buildings.

Start with the roof you have. Corrugated steel, a timber deck and a concrete soffit give the installer different surfaces and details to work around. Then ask what you want to improve.

We compare the routes for commercial buildings nationwide across England and Wales, from the roof layers to the working area below. HOLVEM installs beneath sound roofs, walls and soffits, with coatings where the job needs them.

For our roof application routes, read spray foam roof insulation. Where an active leak or structural defect exists, check the roofing or structural work first.

01The types at a glance

The main types at a glance

First, compare the finished roof. A loose roll, board or foam sample leaves out supports, membranes, linings and access. Those are the parts that can change your budget.

The final column shows what makes up the installed job. The method cost table below gives you a starting comparison; written quotes confirm the work for your building.

02Mineral wool and liners

Mineral wool and liners

Mineral wool works within a supported roof assembly. Ask where the liner and vapour-control layer sit and what holds the insulation up. Each component has a job.

In an existing building, purlins, services and rooflights make that detailing more involved. Include them in the quote; a roll price alone won't tell you what a finished liner system costs.

Then check how warm, moist air is kept away from the cold sheet. The vapour-control layer needs continuous seals at the supports and openings, and the roof needs its designed drying route.

The worked example on our condensation risk analysis page, a standing-seam flat roof, combines mineral wool between the joists with closed-cell foam under the deck and a vapour control membrane, each with its own role.

Don't assume that a liner arrangement suits every occupied bay. Identify installation clearance, support details and the effect on services and future maintenance. Agree the internal working area, protection and finished height as part of the proposal.

Where non-combustible insulation is a project requirement, check the classification of the actual specified material. That still leaves the roof's other layers, fixings and lining to be assessed against the fire strategy. A material property is not the complete assembly's result.

03Rigid boards

Rigid boards

Rigid boards suit regular surfaces and designed support systems. That makes them worth comparing during new build or roof renewal, when joints and fixings can be planned into the assembly.

For a retrofit, ask where the boards will sit: between supports, below the deck or above the roof line. That choice affects headroom, moisture and the space the installer needs.

But a corrugated sheet is different from a flat deck. Boards need cutting, fitting and joint details around the profile. Ask how the proposed system will handle those corners.

Your quote should include supports, joints, membranes and finish, with the rooflights and services shown. Then you can compare a fitted board system with a sprayed layer on equal terms.

For a thermal target, the declared conductivity of the selected board feeds the calculation. The completed roof also includes the other layers and thermal bridges. A headline material value should not be used as if it were the roof's U-value.

Boards are not ruled out simply because the roof is commercial. A designed board system can be the suitable route. The choice follows the existing construction, the work already planned and the performance required, with its complete work clear.

04Closed-cell and open-cell

Sprayed foam: closed-cell and open-cell

Sprayed foam forms its insulation layer on the surface. It follows corrugated and curved profiles, which is useful where separate pieces would need fitting around each change of shape. We check the surface and preparation first.

Closed-cell is rigid and vapour-resistant. HOLVEM uses it for suitable direct-bonded cold-sheet applications and concrete soffits, as well as within assessed hybrid constructions. Open-cell is softer and vapour-open, with an acoustic role in suitable assemblies.

That distinction is central to specification. Open-cell should not be substituted directly onto a cold metal sheet because it shares the spray-foam name. A material chosen for a drying or acoustic role is not automatically the material needed at that receiving surface.

The next question is the floor. Can you release a bay, move the stock or protect fixed plant? We'll agree the application zone and re-entry plan with you. Other areas can keep working around that plan.

The layer's work includes its depth, coverage, junctions, exclusions and finish. A fire coating or lining is a specified component, rather than a finish added later without evidence. The handover should show what was applied against that work.

Closed-cell system data and open-cell system data explain the roles. An application recommendation then connects those roles to your roof's layers and operating conditions.

One layer can have several jobs

Thermal resistance, air sealing and the assessed moisture role need to be stated separately. A continuous appearance doesn't mean every thermal bridge has disappeared, and a bonded layer doesn't repair a failed roof covering.

The specified U-value must describe the complete roof or soffit, with the thermal bridges included. For an existing metal roof, supports and fixings remain part of the calculation even when the air path at a detail is sealed.

05Overcladding and panels

Overcladding and insulated panels

Overcladding builds a new roof above the one you have. Your quote needs to show supports, fixings, rooflights, gutters and weathering at the new height, with the old layers still included in the design.

So it buys more than underside insulation. It renews the weather-facing roof. If that is what your building needs, compare a complete overcladding price with the other roof-renewal routes.

Insulated panels can form a new or replacement roof. When the old sheets come off, lifting, access and weather protection become part of the programme as well as the panel itself.

Ask what you will have when the work is finished: the same sheet insulated beneath, a new skin over it, or a completely new roof. That is the comparison that makes the prices useful.

An old roof that is unsuitable to retain needs that finding resolved. Insulation should not be specified as a way to conceal it. The suitable roofing and structural professionals check the repair or replacement work before the insulation decision is settled.

Spray foam versus overcladding explains that comparison. Obtain complete proposals for the building, including access and finish, rather than ranking the routes by a material-only price.

06Choosing by roof type

Choosing by roof type

Profiled and corrugated metal

For profiled metal, check the sheet, leaks, old liners and use of the building. On a sound retained roof, we can bond closed-cell foam to the underside. If the roof needs renewing, a panel or designed liner system may be the route.

A cold sound sheet and a failed outer roof need different work. See profiled metal roof underside and insulating a metal roof.

Fibre-cement and asbestos-cement

Do not identify composition from the roof profile alone. Begin with the dutyholder, a competent asbestos surveyor and HSE guidance, using the material information and roof assessment for the proposed work.

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.

For retained-roof treatment, the chosen face, preparation, depth and finish must be specified. Management of the retained material continues. A sheet left in place beneath treatment should not be described as if it had been removed.

Flat roofs and timber decks

Flat describes the roof form, not its complete construction. Check the external covering, deck, supports, retained insulation, cavities, membranes and lining. A flat metal-deck roof and a timber deck under a vapour-resistant weather layer need different moisture decisions.

Work from inside changes that assembly. Assess condition, drying and vapour control before choosing the insulation position or material. If roof renewal is already required, compare the designed external route as part of that project.

Read flat-roof applications. A timber deck needs a condensation risk analysis of the proposed build-up; do not copy a concrete-soffit specification onto it.

Concrete soffits

A concrete soffit can receive a suitable bonded layer beneath the slab. The specification needs the slab construction, supporting details, junctions, thermal target and finish, together with access around services or the use above.

At The Box, Plymouth, we applied 120 mm closed-cell beneath 787 m² of concrete soffit, to a specified U-value of 0.18 W/m²K. That depth was calculated for that slab; yours is calculated for your construction.

Read soffit insulation. State whether the element is a roof, floor or another interface, so the assessment and intended result are attached to the actual construction.

07Condensation and dew point

Condensation and dew point

The dew point is the temperature at which moisture in the air starts to condense. A cold steel sheet can reach it while the room below still feels warm. We check both the roof layers and the air beneath them.

First establish whether the water is condensation, rain entry or both. Existing leaks go to a roofer first. Insulation beneath the sheet is not a repair to the weather line, and an external repair doesn't automatically settle an underside moisture problem.

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, with a condensation risk analysis where needed.

At TJW Grab Hire, about 505 m² of box-profile steel roof in good condition ran with condensation onto the vehicles and equipment below. 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.

For a liner, board, panel or hybrid roof, ask how the complete build-up handles moisture at the joints and between layers. Your condensation risk analysis checks those details together.

08Fire and assemblies

Fire: compare the applicable assemblies

Fire requirements belong at the start of the comparison. Ask which evidence supports the material, depth, lining and finish in your proposed roof, and how that meets the fire strategy.

The manufacturer's uncoated Class 1 surface-spread-of-flame result to BS 476-7 used 45 to 50 mm on 9 mm plasterboard. Its coated B-s2,d0 assembly used 35 to 40 mm on 9 mm plasterboard with intumescent coating at 0.7 mm wet film thickness. These are tested build-ups, not interchangeable labels for every roof.

The British surface-spread result is not a Euroclass. The coated result is not evidence for foam alone. Establish applicability to the proposed construction, and include the required coating or lining in the quotation and installation records.

For mineral wool, boards or panels, obtain the actual material and assembly classifications too. A broad material category doesn't describe every finish, joint and interface. Read fire performance and coatings for HOLVEM's evidence route.

09Installed costs

Costs: compare the installed roof

Our cost guide publishes installed foam-only bands of £16 to £25/m² + VAT at 25 mm and £22 to £35/m² + VAT at 50 mm. Coated systems and thermal-target depths are priced per project.

To compare them with boards or a liner, include supports, membranes, joints and finish. To compare with overcladding or replacement, include the external roof work and access too.

Programme matters alongside the total. A retained-roof internal application, a new external assembly and an open-roof replacement create different working areas and weathering responsibilities. Ask each contractor to identify restrictions and how the building returns to use.

Compare the installed methods

The table below shows typical costs for each method, from our cost guide. They give you a useful first budget; your roof survey and written quotations settle the actual work.

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.

10Projects and depths

Projects: compare the decision behind the depth

TJW Grab Hire, Bournemouth

A sound steel roof of about 505 m², kept in place and treated with 50 mm closed-cell from below. Steel and metal roofs are the core of our work. Read TJW Grab Hire.

Midlands distribution warehouse

A corrugated metal roof that leaked air, ran with condensation and drummed under rain. We specified 75 mm closed-cell for those problems, applied to the underside in one continuous layer.

The depth was set for that roof's problems, not as a standard. Read the Midlands warehouse.

The Box and Derriford, Plymouth

The Box has a concrete soffit with a specified 0.18 W/m²K at 120 mm. Derriford District Centre has a design U-value of 0.18 W/m²K, with closed-cell bonded to a metal-deck soffit plus open-cell.

Both are calculated figures for different constructions, which is why the depth differs from roof to roof. Read The Box and Derriford.

Black Hangar Studios, Alton

A 4000 m² hangar under a corrugated asbestos-cement roof, sealed from below.

Here the result the studio reported was acoustic. Read Black Hangar Studios.