Insulating a Mansard Roof - any experiences?

Olga_da_Polga

Hi all

this is my first post here, hope it's in the right place.

I live in the upper half of a terraced house which has been converted into 2 flats. The roof is a mansard style - flat roof at the top, with sloping slated sides front & back (if that isn't clear - draw a square, cut off the top 2 corners at an angle & that's what the cross section looks like).

My problem is, it was freezing last winter and there's no loft to insulate - my bedroom is directly under the roof, the lower part of the bedroom wall is vertical but the upper part slopes in as it follows the underside of the roof (hope that makes sense!). We are having a roof overhaul done soon and I wondered about having insulation put in, but the only way I can see this being possible is if the insulation is put in from the outside (plastered walls on the inside!).

Does anyone have any experience of doing this, or any suggestions of how else to minimise all the warmth escaping to the outside?

thanks all
OdP

Doozergirl

Multi-foil insulation such as tri iso super 10. It's not cheap to buy but it's very quick and easy to install. Pretty sure it can be laid both over and under rafters. You need ventialtion gaps but the key is that it has very little depth to it so won't take up masses of space up there.

http://www.actis-isolation.com/pdf/11pdf13.pdf

Olga_da_Polga

Thanks Doozergirl, that looks really useful, and brilliant to give me such a quick reply. I'll go over it in detail but it definitely looks like it would be an improvement on the horsehair felt which is currently the only lining between the sarking boards and the slates! (roof about 100yrs old apparently...)

ormus

what height do you have in the rooms?
if you have enough height to play with, you can pull off the PB and insulate. then re plasterboard it.

Olga_da_Polga

Room height is fine, so I could do that. Not sure it's plasterboard though - this could be original plastering. I've certainly found other walls in the house which are old lath & plaster construction - discovered when drilling holes in an attempt to put in rawl plugs :¬(

baldelectrician

Another way to go is to have insulated plasterboard (you get plasterboard with 40mm or 60mm foam stuck to the back).

I had to use it when I dis my extension, we had some kingspan sheets left so I did under the floor on the existing part of the house- it made a major difference to the heating.
I am paying the same / slightly less to heat my house + 2 storey extension than I was before the extension.

The insulated board and kingspan for below the floor cost aroung £400-£500 for the whole area, but it has been worth it.

ormus

Olga_da_Polga wrote: »

Room height is fine, so I could do that. Not sure it's plasterboard though - this could be original plastering. I've certainly found other walls in the house which are old lath & plaster construction - discovered when drilling holes in an attempt to put in rawl plugs :¬(

doesnt really matter what the construction is. it maybe PB or the old lathes.
i just thought with it being a flat conversion job, the ceilings would be PB.