News Article

Loft and Room in Roof Insulation

Energy Saving Trust

Thinking about loft or room in roof insulation?

As the building industry has evolved, so has the requirement for ever more exacting standards of insulation. Not only has the requirement for increased insulation requirements changed but so too has the cost of living space.

In New Build there has been an increased trend to make use of all the available space within a building’s structure. An obvious wasted area has traditionally been the roof space so houses these days are more often than not being designed with rooms in the roof occupying what would previously been an empty void.

House prices have soared along with the cost of moving home, so more and more households are upsizing by extending. A relatively cheap and effective way of doing this is to convert that empty space in the loft into living accommodation. This is particularly popular where the availability of land space surrounding the property is limited.

The combination of these issues often poses challenges to specifiers and builders foremost of which being how to insulate to building regulations and keep the depth of build of construction to a minimum particularly in loft conversions where headroom may be limited. These challenges have meant that loft and room in roof insulation has become increasingly important.

Isothane’s Duratherm OS foam insulation offers an ideal solution. It is both KIWA and LABC accredited and due to it’s structure allows headroom to be maximised whilst still improving the thermal efficiency of the property.

Duratherm LABC


Duratherm is an onsite spray applied closed cell foam. It can be applied direct on to sarking materials in a pitched roof such as breather membranes, standard felt and sarking boards with no need for an air gap. This translates into an immediate saving in headroom versus other room in roof insulation products. It can be installed to meet the u values required under building regulations.

By sealing and adhering to the timbers Duratherm eliminates air leakage which can otherwise tend to significantly compromise insulation efficiency and poses a major problem when trying to cut board insulation between timbers.

Duratherm typically has a ‘K’ value or thermal resistance of 0.025W/mK and therefore an application of just over 150mm depending upon the design will achieve a U value of 0.18W/m2K. Where in existing buildings there is insufficient timber depth, either the timbers can be extended by battening down or the application can be overlaid with foam backed plasterboard with the knowledge that behind it, the Duratherm has already saved headroom and eliminated any air leakage issues.

A vapour control layer should be installed on the underside of the timbers so that this combined with the closed cell properties of the foam eliminate the risk of interstitial condensation. Beneath this conventional plasterboard can be fixed to the timbers.

Duratherm can also be used to insulate both flat and pitched roof dormers and the application can be extended to include dormer walls and ‘cheeks’.

This combined with the main roof application will extend the advantages of Duratherm to the whole structure making for a thermally efficient living space free from air leakage. In the case of New Build, where air pressure testing is now a requirement, Duratherm becomes a major contributor to ensuring a favourable result.

For advice on how, where and when to specify Duratherm or for U value calculations and Condensation Risk Analyses contact our technical support team.


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