DIY Doctor UK DIY Forums

Hi there!

I'm trying my hand at insulating one of the rooms on the top floor of my house that will become a small office. I'm in the process of undertaking the challenging job of fitting PIR between the pitched ceiling joists, and the joists are a little bit tipsy!

My concern is that because the joists are a tad wonky that when the insulation is in the front of the PIR boards won't meet on the same plane, and then for when I cover them with plasterboard there will be some small gaps underneath. Someone suggested I put a thin sheet of insulation over the top of the PIR and the rafters to avoid bridging, but will that be enough?

Thanks in advance for your time!

Regards,
Luke

Hi diy_luke,
Screw 50x25 battens to the underneath of the rafters, use packing pieces to give an even surface across the rafters.
Regards S

Hi S,

Thanks for your guidance! I assume i'd only screw the batons to some of the rafters, i.e. not the protruding one?

And what do you mean by 'packing pieces'?

Thanks for your help! :)

Hi diy_luke,
Unless you have an exceptionally bad roof you will need to add a batten to every rafter, you can buy packs of plastic packing pieces (various thicknesses) do screw through these to keep them in place.
Start with the lowest rafter, screw on a batten with no packers and work away from it using battens and packers to give you a flat surface.
Regards S

Thanks for the guidance S :)

Hi S,

As I have now found time to get back to this project, I wanted ask for some additional advice.

The joists are around 35mm thick. I'm assuming I should be okay then to use battens that are 30mm wide? This seems obvious, but for the fact i'll be leaving a slight gap. My thinking is that it will be minor anyway and can be covered over by the foil tape when I insulate the roof, but welcome your own thoughts.

Thanks,
Luke