Insulation

How to install Cellotex on vertical studs covering eaves

Anonymous user 09/03/2024 - 3.02 PM

Hi all, I had building control inspector in recently on refurb project of a Victorian terrace and he has told us we need to insulate the triangular eaves space in our two loft rooms. Both sides have vertical walls built with stud just below the main purlins. They are about 0.7m high on one side, 1.2m high the other (which has a dormer). He has requested 270mm quilt on top of the floor in this space, and 100mm PIR boards on the verticals, which is fine. My question is for the PIR boards, should these be cut to match the spaces between the studs (which are 70mm thick so they will stick out the back a bit), or can they be mounted behind the studs in much bigger slabs, which would mean a lot less cutting? If they are in the spaces between studs, are they tacked in place with nails and then the gaps filled with expanding foam? Many Thanks Andy

H&C INSULATIONS LTD

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Nottingham

The Celotex insulation board can be secured to the back of the studding, as you wont be loosing any room space as this area is a dead space anyway, and you will still have enough space for air flow. Secure with screws and washers and be sure to foil tape all joints. The only time we insulate between the roof trusses would be when a insulated plasterboard is to be fitted within the room. Also be sure to insulate behind the studding on the void floor with minimum 270mm loft roll.

Answered13 June 2019

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Right Price Builders

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Plymouth

Although wood is a poor conductor of heat, voids can cause condensation. If the studwork is proud to the insulation then mould will accrue on the plastered surface in time resulting in mould where the timber stud work is . To avoid this one should employ a 1 inch celotex vapour barrier to bridge both voids & stud work. This will minimise spalling & foeing. Total recommended minimum insulation 50mm celotex bats plus 25mm celotex vapour barrier to studwork . Both must be taped & sealed with celotex insulation tape. Best practice is to cut celotex accurately and place between voids and then cover both voids and stud work with 25mm celotex . Vapour barrier must be taped & nailed to studwork then plaster board is affixed to studwork in normal way with drywall screws for maximum integrity.

Answered23 June 2019

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