Roof insulation.

[dobbslc]

I'm installing 70mm Kingspan insulation in between the roof rafters in a bedroom is a 1" air gap ok between the Kingspan and the tiles?
It's repacing the fiberglass and bubble wrap! already there. I'm then going to over board it with insulated plaster board.
Sound ok?

 

[brightspark]

was led to believe its 50mm below the underfelt /some ive seen are when fitting dowwnlighters in to it

 

[addjunkie]

Mine is roughly a 2" gap...8 iinch joist, 150mm kingspan, and 30 mm insulated plasterboard. But if you have 1 inch with ventilated sofit, should be fine IMHO.

Though the dormers only have 50mm of kingspan. Building inspector was happy.

 

[garethp]

50mm airspace is the norm but I think that covers everything from flat roofs to steep pitches. Is there a breathable membrane under the tiles or standard felt?

 

[dobbslc]

Looks like tar/felt. To me certainly not anything modern.
Wish I'd got the 50mm stuff now!!!

 

[garethp]

I wouldn't worry about it, what's the ventilation like top and bottom of the air gap?

 

[dobbslc]

Top vents into the top loft space (chalet bungalow) the bottom the lower roof space.

 

[gaz1]

if you can add a spacer to bottom of rafters before you board over that will give you what space is needed

 

[dobbslc]

I was thinking that! ^^^
Last thing I want to do is "improve" the roof and then get damp!
Should have thought of getting the thinner Kingspan and saved a few quid

 

[Hitch]

Just done mine with 50mm air gap, continuous vented eaves already and fitted vented ridge tiles 1500 approx centres.
Building control was happy with that. 75mm Cellotex between, with 25+12 moisture barrier plasterboard over the top.
Slightly under spec'd but building controll was happy.

Its supposed to be 50mm gap if its old sytle felt, if its a breathable membrane i believe it can go right up.

 

[garethp]

I think it'll be ok at 25mm and decent ventilation a bonus. Our last house was built circa 1890 with a bedroom in the roof and the gap between the ceiling and roof stuffed with rock wool about 40 years ago - no signs of rot in timber when we refurbed it about 10 years ago.

The current house is a bungalow which sounds the same roof style as yours, built in the 70's with rockwool insulation and no air gap or any ventilation in the loft space . No sign of damp or rot.

However the plan is to improve the insulation in the next few years and there will be 50mm ventilation gap.

As gaz1 said you could put a 25mm batton on the rafters so you can pull the insulation back a bit, might be worth it for peace of mind?

 

[dobbslc]

Well I got some 2x1" batten and dropped the Kingspan so I now have a 50mm air gap.

Hopefully that will sort it.

 

[gaz1]

erm a bit of advice here dont know what you have planned

but using 3x2 lower than the beam and then a piece on its side to the roof would be better than what your doing there on the nearest ones much easier to board up and also fasten your corner angle on it as well

makes it easier to plaster up afterwards as well

 

[dobbslc]

I know what you mean but this side of the beam is very close to the door lining so I can't have more than a layer of plaster board on it otherwise I'd have run a decent sized batten along the bottom edge, bit of a faff but when needs must!