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Looking up at the finished warehouse deck soffit: the cream closed-cell layer filling every corrugation of the steel decking between pale painted beams, a grey steel purlin crossing in front.
Project recordThe deck soffit, into every corrugation

Project record · Concrete deck · New build

New-build warehouse, Ipswich: 300 m² of concrete deck at 135 mm closed-cell.

A new-build warehouse with a concrete slab cast over profiled steel decking, insulated from below. The targets were set at the start: a U-value of 0.18 W/m²K, condensation control in line with BS 5250, and a fire finish to the project specification. We applied 135 mm of closed-cell straight to the deck, into every corrugation, across 300 m² in four days, and finished it with an intumescent coating.

300m²
Concrete deck, into the corrugations
135mm
Closed-cell, bonded to the deck
0.18W/m²K
U-value target, set at the start
4days
Two spray rigs

01The building

A new warehouse with a concrete deck over profiled steel, and three targets to meet from below.

A new-build warehouse in Ipswich. Its concrete slab was cast over profiled steel decking, which left a corrugated steel soffit on the underside: a cold, high-mass deck above a working floor. The insulation had to go on from below, to a U-value of 0.18 W/m²K, with condensation controlled in line with BS 5250 and a fire finish to the project specification.

Why the deck mattered. A concrete slab on steel decking has high thermal mass and stays cold. Under a conditioned floor that means continuous heat loss through the slab, and a condensation risk wherever humid air reaches the cold steel.

Why boards were out. Board systems, PIR or mineral wool, need fixings, tapes and cut detailing across a profiled deck. That leaves gaps at junctions and penetrations and slows the programme. Sprayed closed-cell bonds to the deck and fills the profile in one continuous layer, which acts as insulation and vapour control together, with no separate membrane.

The brief. 0.18 W/m²K through the deck, condensation control in line with BS 5250, a fire finish to the project specification, and the depth checked across the deck before the work was offered for inspection.

Building
Warehouse, new build
Location
Ipswich, Suffolk
Substrate
Concrete slab on profiled steel deckingInsulated from below, into the corrugations
Area
300 m²
Application
135 mm closed-cell
Targets
U-value 0.18 W/m²K; condensation control to BS 5250; fire finish to specification
Programme
Four days, two spray rigs
Checks
Thickness gauge across the deck; final visual inspection

02What we specified, and why

135 mm of closed-cell bonded straight to the deck, filling the profile, then an intumescent coating over the cured foam.

A U-value target sets the depth. 0.18 W/m²K through this deck with this product is a 135 mm layer, built up in passes, bonded to the steel and carried into every corrugation, then checked for depth before the fire finish went on.

  • The system: closed-cell, at 135 mm. Low-emission closed-cell foam sprayed in two to three passes of 40 to 70 mm, bonded straight to the profiled steel deck. Thermal conductivity 0.027 W/mK aged is the product figure the calculation used. Concrete soffits, the application.
  • Why closed-cell on a profiled deck. It bonds, sets rigid and fills the profile, so the layer is continuous and fixing-free, and it acts as insulation and vapour control together. The foam has a declared water vapour resistance factor (μ) of 62, which goes into the condensation check in line with BS 5250.
  • Why the depth is checked, not assumed. A U-value target is only met if the depth the calculation set is actually on the deck. Thickness was checked with a gauge across the deck, and the whole soffit inspected for full, consistent coverage, before the coating went on. U-values and Approved Document L.
  • Why no primer. The surfaces were clean, dry and free of oil and debris. On the deck profile no primer was needed; the foam bonds to the prepared steel.
Product
Closed-cell spray foam, low-emission
Depth
135 mm, in two to three passes
Substrate
Profiled steel decking, prepared, no primer
U-value
0.18 W/m²K, the target set at the start
Fire finish
Intumescent coating at 0.8 mm wet film thickness
Checks
Thickness gauge; final visual inspection
The finished warehouse soffit in its white intumescent finish, the corrugations of the deck still readable through the coating, with ductwork, cable tray and pipework fixed beneath it.

Coated, with the services back in. The intumescent finish over the cured foam, the profile of the deck still readable through it, and the building's services fixed beneath. Project record.

Photographs · Project record

The bare deck, the rig on the floor, the layer at depth, the finish.

The profiled steel soffit and the frame before the work, a spray rig set up on the deck, the closed-cell layer carried into every corrugation, and the soffit coated with the services going back in.

Before: the new warehouse frame with the bare profiled steel decking exposed on the underside of the mezzanine deck, pale painted beams and columns below it.
Project recordBefore: bare profiled steel deck
During: a spray rig and its heated hose set up on the concrete deck, an operative in protective clothing feeding the hose over the edge rail, the profiled steel soffit above.
Project recordDuring: the rig on the deck
After: the cream closed-cell layer filling every corrugation of the deck soffit between the painted beams.
Project recordAfter: into every corrugation
After: the soffit in its white intumescent finish, insulated ductwork and pipework fixed beneath it.
Project recordAfter: coated, services in

Photographs from the job, as it ran. Labelled Project record because they are.All project records

03How the work ran

Prepare, set up two rigs, spray in passes, gauge, inspect, coat.

A new build on a programme, with 300 m² of profiled deck to cover from below in four days. Two spray rigs, the depth built up in passes and checked with a gauge, and the fire finish applied once the foam had cured.

  1. Preparation

    Clean, dry, free of oil and debris.

    The profiled steel soffit prepared for adhesion across the whole deck. No primer was needed on the profile; the foam bonds to the prepared steel.

  2. Set-up

    Two spray rigs on the deck.

    Two rigs working the 300 m² in parallel, the hoses run up to the deck, so the depth could be built in a four-day programme.

  3. Application

    135 mm in two to three passes of 40 to 70 mm.

    Closed-cell foam sprayed straight to the deck, each pass bonding to the last, carried into every corrugation so the layer is continuous across the profile.

  4. Checks and finish

    Gauged, inspected, then coated.

    Depth checked with a thickness gauge across the deck and the whole soffit inspected for full, consistent coverage, then an intumescent coating applied over the cured foam at 0.8 mm wet film thickness.

04The outcome

135 mm across all 300 m², into every corrugation, in four days.

One continuous layer, bonded to the deck, with no boards, fixings, tapes or separate membrane, set to the 0.18 W/m²K target and finished with an intumescent coating.

Concrete deck treated

300m²in four days

The whole deck, including full coverage into the corrugations, with two spray rigs.

Depth, bonded to the deck

135mmtwo to three passes

One continuous layer, 40 to 70 mm a pass, checked with a thickness gauge across the deck.

U-value target

0.18W/m²Kset at the start

The depth the calculation needed for this deck and this product, applied and gauged.

Fire finish

Intumescent0.8 mm wet film

Intumescent coating over the cured foam, to the project specification.

Where this record comes from

Calculated and applied, not metered. A U-value is calculated for the build-up to BS EN ISO 6946 by a competent person and met by applying the depth it needs. HOLVEM supplies the calculation and gauges the depth; the assessor holds the compliance position.

Yours will differ. A different deck, target or exposure gives a different depth. How thickness follows the objective.

05Where this record leads

If this looks like your building.

The application this record used, the building family it belongs to, and the fire finish it carries.

Your next step

Your building.
Your brief.
A specialist.

If you already know the U-value or thickness you need, tell us and we price to it. If you do not, tell us what you know about the building and the problem, and we work it out with you. Someone who does this every day reads it and comes back to you.

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