Concrete Soffit Insulation

Most recent project – ULCCO, Liverpool – Click here for more details

Are you building an office block or car park and using flat concrete for the roof, though struggling to find the best form of insulation that will also eliminate condensation, and will even bond straight to the concrete without the hassle of fitting insulated panels?

Our sprayed insulation service is the solution you are looking for, available in both Class One & Class Zero fire ratings.

‘Webtherm’ and ‘Pirthane’ are both rigid polyurethane foam systems designed for spraying onto the underside of concrete, and can be applied astonishingly neatly, ideal if the roof will be open and seen by the general public etc.


We are one of the market leaders currently applying the Pirthane system, and come strongly recommended by the suppliers, Isothane Ltd, based in Accrington, Lancs. The Pirthane concrete insulation system gives a fire protection rating of class zero, achieved by first applying a layer of Pirthane HR foam followed by two coats of an Intumescent coating available in either White or Light Grey, to also give an aesthetically pleasing finish to the surface.

Imagine the hassle of cutting and fitting insulated boards to the underside of particularly large spans of flat concrete, not to mention the wastage involved, when compared to our highly trained and experienced engineers simply turning up, and spraying the insulation in place to any desired thickness, to achieve a near perfect flat finish, we think you’ll agree with us when we say spray foam concrete insulation is the way to go.

Foam Thickness (mm)
K – Value
U – Value

Besides Pirthane we offer our standard product, which is the WebTherm class one rigid foam concrete insulation, sprayed in the same way except obviously being rated at class one, not class zero. The colour of the foam is almost magnolia, though we can quote for applying almost any coating underneath the foam, from simple matt emulsion right up to impermeable chlorinated rubber coatings, available in a wide range of colours.

If the insulation is to be left exposed inside a roof or wall space, do not worry, our insulation can be painted in water based emulsion to all RAL numbers. This is a service Websters Insulation can quote for and is applied by our own highly skilled engineers.

With a portfolio boasting the likes of IKEA (Coventry), ASDA (Harlow, ESSEX), Carillion (Doncaster Lakeside Keepmoat Stadium, Glamorgan County Cricket Club, Cardiff), Balfour Beatty (Metronet Rail Depot, London), Banner Holdings (Arundel Gate office block, Sheffield), you can be sure our experience will benefit you above all competition. See the case studies below for problems that were presented to, followed by our solution.

Below are before and after photographs taken from a contract in London. Websters Insulation insulated three separate residential apartment blocks above a car park / beneath living accommodation to eliminate cold bridging through the concrete soffit.

Case Studies…

Case Study One: IKEA, Coventry

We were contacted by a company called Underwood Carpenter, with the task of quoting for and applying the Pirthane Class 0 system to the underside of over 1500 square metres of flat Bison concrete planks, located in numerous places on site.

The bulk of the work lay in insulating the soffits, to which we first applied a coat of PVA concrete bonding primer followed by a 55mm thickness of Pirthane HR Foam and two coats of water based intumescent FPC as part of the Pirthane system. The result was an astonishingly neat finish that met the specification perfectly, and also led to us doing more work within the same building, both insulation work and specialist paint coatings (applying an intumescent ‘egg shell’ coat to much of the surrounding steelwork).

Case Study Two: ASDA, Harlow, Essex

We were approached by DCI Refrigeration who were in a small predicament. An underground concrete roof at the ASDA store in Harlow was seriously condensating, and a large amount of black mould had formed as a result of this condensation.

Our solution to this was to totally scrape off and remove the mould, which we did ourselves, and subsequently apply a 50mm thick layer of Class One Webtherm insulation to all underside areas of the newly cleaned flat concrete. Besides adding a decent level of insulation, this method is also guaranteed to eliminate condensation for the life of the building.

Case Study Three: Osborne Developments, Granville House, Surrey

We were contacted by Osborne Developments, who were building a large pool house from concrete and required the whole underside of the flat concrete ground floor roof insulating. Not won over by the idea of panels, they called us for advice, and we came up with the following solution:

We firstly applied a layer of PVA concrete primer to the whole underside of the roof area, then a vapour check barrier using a chlorinated rubber coating followed by 50mm of Class one Webtherm spray foam and a final vapour barrier, again using the chlorinated rubber coating. The system we proposed worked perfectly, and ensured water vapour given off from downstairs couldn’t come into contact with the concrete ceiling, and the insulation prevented any cold bridging through the concrete. We also insulated the steel uprights to prevent condensation forming once they’d been cladded over.