attic conversion roof insulation questions

[sb1456]

Hi, greatly appreciate any advice on the following:

Im insulating my attic with 100mm kingspan.

1) Do I insulate between the rafter right down to the bottom, nearly down to the wall plate, or do I insulate down the vertical side posts, and leave the void (which will be used as storage space/cupboards) insulation free.

2)Do I insulate right to the top (peak/ ridge board) or only as far as the horizontal top of the roof, again leaving an approx 1m high insulation void space (will obviously insulate the horizontal part of the attic ceiling).

3) There is a 50mm gap created by batons, for ventilation, where the rafters are uninterrupted from top to bottom this is fine, however this air flow if stopped above the Veluxes is this OK?, in other words is air flow essential in this 50mm gap or is it just to stop the insulation boards touching the breathable membrane felt.

Apologies if the questions are a bit daft, and if the terminology used is a bit off.

thanks jon

 

[freddiemercurystwin]

1) Do I insulate between the rafter right down to the bottom, nearly down to the wall plate, or do I insulate down the vertical side posts, and leave the void (which will be used as storage space/cupboards) insulation free.

If you want to use the void for storage then it would be easier to use rigid insulation between the joists and maybe a layer on top across the top of the joists then lay some boards on top ensuring your insulation bubble is complete and meets with the cavity wall insulation if there is any, if practicable to do so.

2)Do I insulate right to the top (peak/ ridge board) or only as far as the horizontal top of the roof, again leaving an approx 1m high insulation void space (will obviously insulate the horizontal part of the attic ceiling).

Just use 3 layers of Rockwool on the flat ceiling.

3) There is a 50mm gap created by batons, for ventilation, where the rafters are uninterrupted from top to bottom this is fine, however this air flow if stopped above the Velux’s is this OK?, in other words is air flow essential in this 50mm gap or is it just to stop the insulation boards touching the breathable membrane felt.

If you have a breathable membrane then it will still allow moisture to escape. Or is it not actually breathable and just traditional felt? Generally BC will accept a 25mm gap if it is a breathable membrane and isn’t too slack.

ps 100mm Kingspan sounds too thin, normally you need more between a good layer under the rafters too.

 

[sb1456]

thanks for the reply, however you didn't answer question 1.

should i insulate between the rafters right down to the wall plate/joists. Or should i insulate to the top of vertical side posts and then carry on the insulation down vertically down the side posts.

Secondly, I was told (maybe incorrectly) by my BC officer. That it was breathable membrane, 50mm air gap, 100mm celotex/kingspan insulation between rafters, then plaster board on top to meet building regs.

Jon

 

[freddiemercurystwin]

You said you wanted to use the void for storage. In which case it would be better to insulate as per my reply. So insulate the rafters down to the wall, then insulate at ceiling level with rigid and then board over.

 

[datarebal]

everything over the building requires insulation.

this does not mean taking it up to apex , as freddy says its acceptable to use rock wool on the flat ceilings, foil board between rafters and under .

I believe 100mm between is not enougth, there should be 40mm on the underside of rafter before plaster board.

your are trying to keep the place warm insulate everywhere.. your heating bill will be reduced amazingly if done properly