Insulating rafters

[olimain]

I've started the process of converting a bathroom into a bedroom and while I'm at it want to add some insulation to the sloped part of the ceiling and the purlin wall in the photo below (above the flat part of the ceiling is a new loft conversion with tonnes of insulation already).

The house is Edwardian and has a boarded roof. The rafters / studs are about 100mm wide. Am I right in thinking that after I've pulled off the plaster I should add 50mm of celotex or similar to that sloped part (leaving a 50mm airflow gap on the roof side) and the full 100mm to the purlin wall?

Do I need to add a vapour barrier before plasterboard and should I be thinking about insulated plasterboard on top or is 50mm decent enough?

[olimain]

Anyone?

[olimain]

Thanks, it's only a small area so don't mind the extra cost for insulated PB if we will notice a difference. It's the coldest room in the house

So if we go 50mm in rafters then 1000 gauge polythene then 50mm+12.5 insulated plasterboard we'd be looking pretty good? Is it ok to have the vapour barrier between the two foil surfaces like that?

[olimain]

gizlaroc said:

In an area like that where space is a premium I would consider Superquilt.

Staple over your studwork/rafter, then batten over the top and attach plasterboard

Our posts crossed - this is very interesting and appealing, especially as it sounds so quick! Off to research it now but I assume no need for any sort of vapour barrier with this stuff? Huge time saving not having to put 50mm battens in to maintain the air gap and then sawing all the celotex etc. Almost sounds too good to be true!

[olimain]

Another question - while I have the floors up in that room is it worth insulating those too with rockwool or something? (Kitchen is below)

[olimain]

Spudler said:

Definitely.
Loft insulation would be fine unless you're after acoustic values then isover or rockwool.

Thank you - our kitchen lighting is currently pathetic so while the floor is up I plan to put in downlighters. With LEDs do I still need to use some sort of cap to keep them away from the insulation?

Like these: https://www.amazon.co.uk/ALC274-274x162mm-Downligh...

[olimain]

Spudler said:

Personally I would, even if sparks say no need.
Cut up some soil pipe or downpipe.
For the sake of a small amount of work it's piece of mind.

Haha yeah I wasn't thinking of buying them from there, 12 quid for that seems ridiculous. Plus I can't look at them without thinking hospital bed pan!

Soil pipe sounds good as I have a few m left over from digging in the new stack. just cut a few inches and sit it over the light or does it need some sort of cap/bung on top too?

Edit: in fact I think I get what you mean, open ended length of pipe popped over each light and the insulation snug around the sides but not on top of it?

Edited by olimain on Thursday 19th January 13:44

[olimain]

TA14 said:

Quite: http://www.homebase.co.uk/en/homebaseuk/terracotta... and that one's on the large side

That is genius! Cheap and easy, what's not to like?

[olimain]

Little Lofty said:

Whilst adding extra insulation is a good thing don't forget about ventilation. I'm currently upgrading an old loft, BC are more concerned about the ventilation than getting the maximum amount of insulation squeezed in.
The interior of the dormer was black with mold when we took out the rockwool, there was zero ventilation.

The eaves space behind that wall in the photo is very draughty and the 50mm air gap will be left on the cold side of the rafters to (hopefully!) cover me.

[olimain]

Jambo85 said:

Insulating the space between two occupied rooms seems a bit unecessary to me, as presumably you'll be heating both spaces so what is to be insulated? Comes at a significant cost and makes future plumbing and electrical work a lot harder than it needs to be... Would current building regs require this in a new build?

In our recent loft conversion they definitely insulated the floor - no idea whether it's compulsory on a new build or not. Using loft insulation would be pretty cheap though compared with something like Celotex.

Edited by olimain on Thursday 19th January 15:23