Insulating an old pitched roof

[MD01]

I've searched and cannot find the answer so I'm hoping someone can advise:

I have a large pitched roof with a couple of rooms within the pitch. So, the walls of the room are sloping, leading up to a flat ceiling. They have velux windows. There is attic space above the flat ceiling part of the rooms.

The roof is slate tiles with NO felt or other membrane on the inside.
The flat area of the attic is insulated with loose boards over the top.

When I look down inside the pitch from inside the attic, I can see the back of the plasterboard (which forms the bedroom wall). there is no insulation at all - just an empty space.

I want to insluate this and my question is this: Given what I have described above, particularly the lack of felt or other membrane, do I still need to leave a gap between the insulation and the tiles. My plan is to push insluation down with a broom - it works, I've tried it. But I am concerned about the ventilation.

I have been avised that it doesnt matter as the slates have gaps and the area will be ventilate...the house is over 50 years old.

Any advice or comments would be appreciated.

Many thanks,

mike

 

[markie]

MD01

you can put it down but you will have to maintain a air gap to allow air to flow freely

you should have at least 50mm gap from insulation and slates.
What size are your rafters ?
The reason why i ask is, if the rafters have been beefed up, as in timber has been nailed/bolted a long side of the original rafters, this would give you a 6-7 inch gap, if so you could put kingspan down in between the rafters it's a bit more exspensive then loft insulation but it will be warmer in the winter,
the regs say it should be 90mm thickness, but even if you put 60mm in it's better than nothing

 

[MD01]

thanks - rafters haven't been beefed up but they are all around 170mm, so just over 6.5 inches. So I could put thinner insulation down and leave a gap.

I tried it with 150mm knauf space blanket but this doesn't leave any gap at all as it bunched up. Looks like I need to go thinner then.

Will this allow the house to remain cool in the summer

thanks

Mike

 

[markie]

Cooler in the summer, warmer in the winter.

 

[MD01]

Sorted. Cut the 150mm space blanket into 3 foot sections and pushed down each one gently, measuring carefully so as not to push it too far. Now insulated, with a 50mm ventilation gap and room is significantly warmer.

Job done

thanks

 

[davebwithane]

Hello I have a similar setup to what you have described and I am wondering if you have had any problems since using the space blanket in the voids ? ie. the soffit to joist gap ? I think that is what you were referring to ??
Thanks
Dave

 

[MD01]

...no problems at all. There is still a space all the way down as I measured each length and pushed it down the exact distance required, so no bunching.

Short lengths worked better due to friction. i.e. trying to push down an 8 foot length was near imposible. Also, once in they expanded and with the shorter lengths it was easier to check there was a sufficient space before putting the next lenght down.

Other problem was the occasional screw that stuck through the plasterboard. I just pushed past these. I also taped over the end of the spaceblanket to keep the foil covering in place.

good luck.

 

[davebwithane]

thanks for the reply. Has the space blanket become soggy ? I'm thinking og using celotex instead as I only have a 100mm space.

 

[MD01]

...not that I have noticed, though I haven't taken it out to inspect...