insulating dormers?

[fla 9]

My dad's house is a 1948 build and has some dormers in the upstairs. Due to an overenthusiastic local authority he has not been allowed to carry out an extensive rebuild of the house (a brown envelope is nneded, but thats another story...) The loft has some insulation (rockwool) but the roof slopes do not. These also come into all four of the bedrooms. In addition there is a dormer to each side upstairs that has absolutely nothing in it. Consequently in winter the radiators can be boiling hot but the rooms just about warm. Whats the best way to insulate these withought resorting to pulling off all the inner skins and shoving rolls of insulationin there? I've been told that you can get some polyester foam that can be injected and is meant to be much more efficient than mineral wool.

[swiftkid 1]

I'm not exactly sure what you mean here... if the roof/ceiling is insulated then the roof slopes don't need to be. As you know, heat rises so once it gets to the ceiling the insulation SHOULD stop it going any further. What size insulation is there at the moment? 100mm is about standard-ish for older houses but you will find if you put another layer of 150mm rockwool over the ceiling joists (to stop thermal bridging) it should retain a lot of the heat.

 

If you are after some planning advice, I used to be a Planning Officer (well technician, but I dealt with applications) so could take a look for you.

[Storm Guy 0]

Yes there is insulation you can spray on / in, that seals and insulates but without a proper survey and proper installer wouldn't recommend it. Not sure of your ceiling heights but you may want to consider an insulated plasterboard lining throughout if you have no problem with headheight (which may be the case for a 1948 house). Otherwise I'd do a strip and proper job, though of course cost and practical issues come into play.

[Kevin Bacon 5]

/\ Yep.

 

Hasan, my house is a 1960s bungalow with an upstairs, I think they're called 'Chalet bungalows' or something? Anyway, the main bedroom has a dorma window and also a small bathroom in the eves opposite. Like you, I find it's F'in freezing up there!! The only way really is rip the inner linings off (plaster board usually), line it all properly with the up-to-date building regs approved stuff, the board it up again.

 

In the loft I had to line the eves with that space blanket stuff as well as over a foot thick of normal insulation in the joists, but it's still nowhere near as warm as a purpose built 2 story house with seperate roof. It's one of the downsides of this design of house unfortunately!

[daves16v 1]

I can relate to this as my house is of a similar design and yes the upstairs rooms do suffer a little, not a huge problem but it's evident.

 

I have a theory at least in my house and it's this -

 

Lofts have to be ventilated, so the air comes in through the eaves into the loft where it then travels down the sloped uninsulated roof space and finds it's way between bedroom floorboards and ground floor ceiling. I know this because the carpets around the skirting have become a slight dirty grey where drafts have been blowing in. I can also feel the drafts.

 

No doubt drafts are finding their way in through the slopped roof itself too.

 

A cheap fix would be most welcome but that's wishful thinking I reckon.

[dragon green 5]

I have skeilings in all my upstairs rooms,these were uninsulated,I got some 75mm Celotex (kingspan)solid insulation and cut it to fit the rafters,and carefully pushing it down between them,making sure it doesn't drop out into the eaves,fastening with a screw.Don't fill the rafter all the way up to your underfelt,as you need an inch of airflow !

The only way to do dormers is to strip the plasterboard off !

[fla 9]

really useful comments. Appreciated. On ours the slopes form part of the room, ie there is the inner skin, the joists to which it is attached the water proofing membrane (black sheeting felt) and then the tiles. Its the void created by the joists which i am hoping to fill with Celotex. IN fact i was hoping to be able to just stuff some insulation in from the loft down the sloping portion, but i'm sure there would be too much friction to allow that.

 

You're right Storm Guy, the practical issues fo clearing everything out are what concerns me. The issue is really between ventilation and insulation and achieving the best compromise.

[Storm Guy 0]

As dragon green states above, best option in this scenario may be to use the Celotex solid board (of appropriate thickness depending on your void to allow ventilation). Cut it into lengths dependant on how much space you have to work with in the loft area - You should be able to slide the pieces down, cut to suit the rafter spacings. Use a stiff wire/rod with a simple L shape bend at the end to allow you to either push them gently in place, or stop the first one falling all the way to the eaves. Carefully turn the wire/rod to remove, always checking that you stay away from the felt. Unless roof work has been carried out, the felt may be very fragile. Test a piece but hopefully there shouldn't be too much friction, dependant on the upper surface of the ceiling board (not exactly sure what the make up was back in '48!). The wire will allow you to gauge length. Ideally screw some dowels or similar at the lowest end of the slope (and skim to finish as appropriate etc) to retain the boards. Or simply anchor the first (lowest boards with screws).

[aide 0]

you either remove the plastrboard/ lathe & plaster and 75% cut and fill the joists with cavity insulation bats as Dragon Green has outlined, or you reline the entire space, either with insulation bats as before or with joists & rockwool, and then plasterboard over thus reducing space and headroom. AS DG says you must leave an air gap to reduce damp through condensation. Bear in mind you may need to extend wiring, at at 60yr old wiring will be well past its best.

 

blown insulation is typically used for spaces which can be filled completely, i.e. a brick/ block cavity, i've never filled a timber cavity using blown insuation.

Edited February 6, 2012 by aide
as Storm Guy says too!

[jamiehamy 0]

As dragon green states above, best option in this scenario may be to use the Celotex solid board (of appropriate thickness depending on your void to allow ventilation). Cut it into lengths dependant on how much space you have to work with in the loft area - You should be able to slide the pieces down, cut to suit the rafter spacings. Use a stiff wire/rod with a simple L shape bend at the end to allow you to either push them gently in place, or stop the first one falling all the way to the eaves. Carefully turn the wire/rod to remove, always checking that you stay away from the felt. Unless roof work has been carried out, the felt may be very fragile. Test a piece but hopefully there shouldn't be too much friction, dependant on the upper surface of the ceiling board (not exactly sure what the make up was back in '48!). The wire will allow you to gauge length. Ideally screw some dowels or similar at the lowest end of the slope (and skim to finish as appropriate etc) to retain the boards. Or simply anchor the first (lowest boards with screws).

 

This is on my summer list now!Just need to find a long enough and flexible enough pusher/puller that will allow twisting. I'm in an 1890 sandstone tenement. Got the loft space done, but the gaps I'd never done. Now I've read this, I feel motivated to do it! :)