Celotex Isover

Loft Insulation

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What is loft insulation?

Loft insulation is any material installed within the joists of a pitched roof space to reduce heat loss from the building below.

Saint-Gobain Insulation UK offers a variety of Celotex and ISOVER products suitable for installation in a loft.

Some old loft insulation installations can easily feature as little as a single layer of around 100mm insulation between the ceiling joists. The most common solution to top-up existing loft insulation levels is to lay glass mineral wool insulation over the top of the existing insulation within the ceiling joists, although if this is in particularly poor condition it may be better to replace this with fresh material

Glass mineral wool is a flexible solution that is easy to fit within the loft with the main point of attention when installing being at the eaves to ensure no roof ventilation is blocked. It is common to see anything upwards of 300mm of glass mineral wool insulation laid at ceiling level to meet the current thermal performance regulations.

Some old loft insulation installations can easily feature as little as a single layer of around 100mm insulation between the ceiling joists. The most common solution to top-up existing loft insulation levels is to lay glass mineral wool insulation over the top of the existing insulation within the ceiling joists, although if this is in particularly poor condition it may be better to replace this with fresh material.

It may be the case that the loft area is to be used for storage, and if so then the loads that the roof construction will be subjected to should be taken into careful consideration.

Assuming the roof construction is able to deal with the intended loads then Celotex PIR foam insulation boards can accommodate typical storage loads without compressing. Timber boarding should be laid over the boards to provide protection and maintain their performance. Screw fixings are typically all that is required to secure a product like Celotex GA4000 or XR4000 in position above the joists.

The insulation is lightweight and does not impose significant weight on existing structural timbers. The rigid boards can be laid over the entire floor of the loft; or they can be used only in the area required for storage, with ISOVER glass mineral wool insulation covering the rest of the floor.

PIR insulation is thermally efficient and can be used as part of a complete refurbishment of the loft floor, or in conjunction with existing insulation laid between the joists, to help improve heat loss from the property and, where necessary, meet the requirements of national building regulations.

Advice should be sought on correct installation practices, including ensuring a well-sealed ceiling below the loft joists. Continuity of insulation at the wall/roof junction should be achieved without blocking eaves vents and while ensuring adequate ventilation of the loft space.

The building detail is for illustrative purposes only. It does not constitute advice and should not be relied upon.


Insulation products to consider
Product Name Thickness Range Sizes Lambda BBA
ISOVER Spacesaver 100-200mm Spacesaver: Width 1160mm, Length 5200-12180mm | Spacesaver Ready-Cut: Width 3x386 or 2x580mm, Length 5200-12180mm | Spacesaver Lite: Width 1160mm, Length: 3500-7000mm 0.044 W/m.K Tick Icon
ISOVER Spacesaver Plus 100-200mm Width 1160mm, Length 3500–7000mm 0.040 W/m.K Tick Icon
Celotex GA4000 50-100mm Width 1200mm, Length 2400mm 0.022 W/m.K Tick Icon
Celotex XR4000 110-200mm Width 1200mm, Length 2400mm 0.022 W/m.K Tick Icon