Insulating external wall

[JoeJoe]

See diagram here:

of the wall in our spare bedroom has no insulation at all. It is in fact the lower half of the wall (top half is a window) that is made up of plasterboard over vertical studs and the back of the boards is exposed to the roof tiles - hence the wall becomes very cold.

I can access the back of the un-insulated wall through a small door and want to attempt to put some insulation against it. The space under the eaves is very small (triangular shapes - height ~ 60cm, width at widest point), but I can just about crawl there.

There is no chance of maneuvering anything rigid (i.e. kingspan) there into position, so my plan is to put some glass wool (say 100mm) between the studs, and secure it in place with some sort of a mesh nailed to the studs.

Any thoughts?

[Roger Mills]

Yes, remove and replace the plasterboard. While it's off, fix Kingspan between the studs. Also, put lots of fibre matting between and over the joists in order to benefit the room below.

[Stuart Noble]

Not long finished a similar shaped attic room in a Victorian house. I did use celotex but you need one person outside cutting while the other poor sod is on his back trying to position the stuff.

Rockwool will probably stay up without the mesh, and the odd batten here and there would suffice. The only problem is that if the roof felt isn't breathable, you're supposed to have a 50mm gap between it and the insulation. From that point of view, 50mm Rockwool slabs might be better. Easier to work with than foam and less likely to get in your eyes when working overhead.

What about the roof above the window? I took the lath and plaster ceiling down, which wasn't much fun, but there didn't seem much point in doing the walls and then leaving the key area .

[JoeJoe]

I am talking about insulating the wall, not the roof. Do you mean that I nee to make sure I leave a gap where the insulated wall meets the roof?

Flat roof was done up properly last year (insulation and all).

[Doctor Drivel]

Insulate between and over the wooden studs to prevent cold bridging. Don't block any vents that create air flows that might be there. Keep the insulation as thick as possible.

A friend did this two years ago as there was no a piece of insulation in the loft conversion done in the 1970s. The attic room was far warmer in winter and cooler in summer too. Heating bills remained the same (he had a condensing boiler fitted at the same time), when bills went up on average about 1/3. So a saving of a bout 1/3 in fuel.

[fred]

In article , JoeJoe writes

Could you use Kingspan cut to the width of the stud gap then cut horizontally into sections to get it into place, seal gaps with the purpose made foil tape or larger/uneven gaps with expanding foam.

[Stuart Noble]

No, ventilation shouldn't be an issue with the walls

[JoeJoe]

Could work, although the access could be smaller than I estimated. I'll have to investigate 1st.

Thanks for the tip.

[Davy]

I tackled a similar job on my last house. Rolled fibre blanket (glass or mineral) into the gap between the studs - the roughness of the studs held it in place. Very simple job. I wanted to use the eaves space for storage so then boarded over the insulation with hardboard stapled to the studs. Whilst you are at it insulate the floor of the eaves space so the room below gets the benefit. Make sure that the insulation blocks the entrance to the floor space under the spare bedroom or wind will blow through this and remove the heat coming from the room below. Conversely, don't insulate any sloping ceiling in the spare bedroom cos it will prevent cross ventilation of the loft.

Davy