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Internal Wall

When refurbishing period properties one of the key challenges faced is how to upgrade its thermal performance.

In many cases it is not possible to install an External Wall Insulation system as the building may be listed or the owners do not wish to lose the character and feel of the existing facade. In these instances designers have to look at what Internal Wall Insulations systems are available.

Utilising traditional PUR insulations internally could mean loosing a significant loss of useable internal floor area, which could have detrimental effects on the comfort of the property and also reduce the saleable floor space value. 

With a thermal conductivity value of 0.0038W/mK (Design Value - 0.007W/mK) Vacuum Insulation Panels (VIPs) offer high levels of insulation performance with minimum thickness. Using Vacuum Insulation Panels can offer up to a 5-times reduction in thickness when compared with traditional PUR.

As good as the performance of Vacuum Insulation Panels is, should a panel be punctured then up to 80% of its insulation performance will be lost. Taking this into account, using this technology as an Internal Wall Insulation takes a great deal of thought as the likelihood of a fixing being driven into the panels at a later date could be high.

In order to overcome this issue it is prudent to include a void in the design between the internal room surface and the vacuum panels. This would allow fixings to be put into the wall at a later date without the fear of puncturing the panels. 

In a recent project in Kensington, London the architect designed the following vacuum panel wall construction which would give him both a high performing insulation system with minimum build-up, but also ensure there was minimum chance of the VIPs being punctured at a later date.

The wall construction was as follows - 

Existing Wall / 15mm VIP with 10mm EPS backing / 60mm Gyproc Stud / 12mm Plywood Boarding / 12.5mm Plasterboard / 3mm Skim Coat.

This construction creates an 87mm gap between the Vacuum Insulation Panels and new internal room surface.


When evaluating the effectiveness of this Vacuum Insulation Panel system the Architect carried out an analysis which showed a comparable performing PUR system would have equated to a wall build-up of 158mm. The Kevothermal system comprised of a 113mm total thickness, a saving of 45mm.

By reducing the wall build-up thickness by 45mm this amounted to a total gain of 4.2m2 (45ft2) of floor space. With the value of the property being so high (approximately £3,500 per sq. ft.) the Architect was able to achieve an estimated extra £160,000 of saleable floor space.