Ideas how to insulate Velux windows

[Novice Becky]

Any ideas how to insulate my Velux windows? The ceilings below are horizontal with vaulted shafts for the Velux. The bathroom Velux is especially bad. Ignore the orange box attached to bathroom Velux - it's a digital shower processor no longer there

 

Cover what's there with more PIR sheets and tape joins? Would air gaps pose a problem for interstitial condensation? Rip off PIR and start again? Other materials? What thickness of insulation (I know this will depend on thermal conductivity). Thank you.

[Iceverge]

1 minute ago, Novice Becky said:

. The bathroom Velux is especially bad. 

 

In what way? Drafts, condensation mold? 

 

 

[Redbeard]

I take it there is plasterboard on the bathroom side of the 'tunnel'? Does it have a vapour control layer (VCL) on the cold side? If not, rip it out, install a really-well-taped VCL and re-plasterboard. Then build up from the cold side, filling any gaps with *air-tight* foam. Butt up tightly to any timbers, and at least one further layer over them. 150 - 200mm of PIR is not, in my view, too much. Keep all the joints tight, and tape them too, with decent air-tightness tape, not just foil tape. The existing does not seem to terminate very tightly at the top where it meets the rafters and the noggin. Make that bit better, and keep it all as tight as the btm of the proverbial duck.

[nod]

I’ve similar setup in two places I used multi-foil to rap them Then taped the seams 

[Novice Becky]

16 hours ago, Iceverge said:

In what way? Drafts, condensation mold?

Thanks @Iceverge. Condensation and mould. This has been cured by the MVHR going in in December but it will still be a cold bridge (or cold mountain?)

[Novice Becky]

Thanks @nod. Foil wrap sounds quick and straightforward but quite a lot less insulation than the 200mm of PIR suggestion.

 

Thanks @ Redbeard. I didn't quite get the re-plasterboard after VCL. Can you explain please? If I Take off the PIR that's there then there will be the plasterboard exposed. Can I just tape the VCL to the existing plasterboard and timbers and then build up the insulation?

[nod]

6 hours ago, Novice Becky said:

Thanks @nod. Foil wrap sounds quick and straightforward but quite a lot less insulation than the 200mm of PIR suggestion.

 

Thanks @ Redbeard. I didn't quite get the re-plasterboard after VCL. Can you explain please? If I Take off the PIR that's there then there will be the plasterboard exposed. Can I just tape the VCL to the existing plasterboard and timbers and then build up the insulation?

No the 18 layer foil is equivalent to 90 mil of rigid pri and far easier to seal with tape in awkward spaces 

Use two layers 

[Iceverge]

Multifoil........ 

 

Might I suggest you do a quick search of it on the site as to the perception of many........

[Novice Becky]

On 22/03/2024 at 07:34, Iceverge said:

Multifoil........ 

 

Might I suggest you do a quick search of it on the site as to the perception of many....

Thanks @Iceverge. There's always more than one way to do things and this forum is great to read about different experiences.