Best approach to insulating skylight shaft

headtheball14

Hoping for some help.
I have an old skylight .the skylight itself seems ok when I got someone to look at it .But the shaft was completely uninsulated . I have propped some insulation up around the exposed areas and this helped a bit but I know the shaft is letting a lot of the warm air escape. What are the easiest/ best ways of insulating this myself. I'm not particularly handy.

Should I just tie fibre glass around it. I also put some polyesterene in the gap between the shaft and stud frame Is this a good or bad idea?

I could probably get some ply and put this around the exterior of the fibre glass without compressing it. Or would I just get some insulated boards. Should they go inside the stud frame in that case?
Or should I see if someone could just spray foam the shaft and if so any tips would be appreciated

10-10-20

Photos would help us to visualise it better.
Does it suffer from moisture buildup, and how is it vented?

headtheball14

10-10-20 wrote: »

Photos would help us to visualise it better.
Does it suffer from moisture buildup, and how is it vented?

Sorry I thought I had replied yesterday.
It's not vented to my knowledge. There's no moisture buildup. I had a leak a couple of years ago and asked about replacing the skylight itself at that time but they said it looked solid at the time.
I'll try to get photos up in a bit. The shaft is the only non insulated element in my attic. The rest has fibreglass double layers on it.
I was reading the following and trying to follow it
It seems to be fibreglass followed by a layer of rigid insulation boards.
https://www.finehomebuilding.com/2013/11/07/insulated-skylight-shaft

10-10-20

That's an interesting method of insulation in that link. Is your attic also a cold-roof - in that the insulation is on the attic-floor as opposed to being in the attic ceiling?

If you have a cold-roof then you can follow the method provided as it appears to be 90% of what you might need, but they seem to use plasterboard within the attic space and that's not needed. You could just use glass wool where they specify "cavity insulation" and then a rigid PIR (polyisocyanurate) board (without the plasterboard) and seal it with expanding foam at the edges.
But you need to pay attention to ensure that there are no leaks of air from the shaft into the cold void of the attic.

But if you are looking for a simpler method, I'd recommend wrapping it with some layers of glass wool and support the insulation using some twine, lightly wrapped around to keep the wool in place. If you want to go green, use sheeps' wool in place of the glass wool. https://www.sheepwoolinsulation.com/

headtheball14

Thanks , Yes, it is cold roof, currently insulation only on the attic floor .
I had bought earth wool before to add an extra 200 mm to floor of the existing layer of insulation. That helped a lot but there have been issues with the skylight shaft and I can feel the cool air draft when I’m under it.
I am just going to head to builders providers now and see if I can price some rigid pir.
I also wasn’t sure if I should put pir inside in the void or outside. I think even as you say if I just secure the fiberglass around the shaft that should improve things a lot.
Thanks again

10-10-20

If you go down the PIR route, the PIR would be most optimal directly on the shaft where the temperature difference is greatest and then glass wool around that, if needed. But that mightn't be easy to complete if the shape of the shaft is not regular with large exposed panels. So glass then PIR might be the better option.

headtheball14

Just an update.
I can understand why the shaft has not been insulated before. It's painful enough. Much worse than rolling insulation .
I bought 3 25mm pir boards. I've been trying to cut and fit it. The battens on the shaft are all different sizes so I've been measuring and cutting the boards started with saw, then breadknife. Now using small knife.
.
The water tank is right beside the shaft which means I can't get boards on one side of the shaft. I'm trying to fit as much as I can but will still have gaps .
Cutting in the attic is a pain. Getting to the final side of shaft is tricky. There are a couple of pipes blocking access resulting in me scurrying over and under the pipes like a cat burglar.
I managed to fit 3 but not very well. They are just wedged or propped in currently.

10-10-20

Three down, good job. Get as much PIR as close to the plasterboard as possible. Use expanding foam if you really need to fill the small gaps; look for low-expansion foam unless you want a party in the shower underneath. Then wrap it all in glass-wool.
Also, is that water tank covered?

headtheball14

10-10-20 wrote: »

Also, is that water tank covered?

Yes,Water tank has a fairly battered cover over it. Not that ken to get pir boards too near the water.