Hoping for some advice on loft insulation...
I'd like to create a warm loft by insulating between and in front of the rafters, so that the roof space stays warmer than insulating above ceiling level. I know that I need a vapour barrier inside of the insulation to stop the cold rafters then getting damp.
My question is - I've got a really annoying roof truss design, like this:
What do I do when the diagonals of the truss would likely go through where I want to insulate / have a vapour membrane? Do I need to do a sealed penetration detail with tape etc? And do I need to worry about the diagonals "cold bridging"? Or am I missing a trick here? Is it even possible to have a warm loft with roof trusses...?
our old house had trusses like that, and the only usable space was between the inner part. So how about only insulating that section, then you don't need to worry about cold bridging?
...it looks like I'll have to move the light wiring as well...
Do you have a specific reason why you want to do this? Given that with the design of loft (like mine) you cant actually use the space as a usable room so I think you want as much ventilation around the roof and trusses as possible. As soon as you start closing stuff up you restrict the flow of air and that is where rot and damp can set in.
☝️ this.
If it's not being used as a room then what are you trying to achieve?
It's much easier to insulate at ceiling level and then have a healthy breeze blowing through the loft keeping it well ventilated.
Doesn't stop you from storing stuff up there.
Hmm. Well I want to insulate it to keep upstairs warmer / save on heating. And I figured I might as well have a warm storage space up there that's more usable for things that might be affected by cold... If I get a loft ladder it becomes a semi usable space
Well I want to insulate it to keep upstairs warmer / save on heating.
Well it's MUCH easier to insulate at ceiling level and you could put much more insulation there also.
As already stated.... A loft doesn't have to be warm to store stuff in it/have a loft ladder.
Well. To insulate between the rafters you need to leave AT LEAST 50mm air gap from the underside of the felt. Also, that felt isn't breathable so you'd be potentially creating a problem.
If you absolutely must insulate the pitch of the roof, use a dense foam (Kingspan, Celotex etc) and screw it to the underside of the rafters to guarantee the air gap isn't compromised. This will be what can only be described as a colossal pain in the arse due to all the trimmers and additional timbers you have in the way. Inevitable gaps will mean heat escapes, you're not gonna get a good fit/finish.
You will get a MUCH better solution by insulating over the ceiling, then putting a chipboard 'floor' on stilts down to maximise your storage space. You can still store whatever up there and it will be clean and dry.
I was going to do what the OP proposes, for much the same reasons, and also have a trussed rafter roof. I had vents fitted in the ridge and hips to allow air from the eaves to flow above the insulation. When I actually came to work out the details, it was too complex. I put extra insulation on the ceiling and left it as a cold loft. Even that was bad enough, cutting the OSB floor boards round all the bracing.
The diagonal bracing on the bottom of the rafters, in the plane of the roof, is also a nuisance if you want to insulate between the rafters. It is required by building regs, despite looking temporary.
Thanks all... sounds like cold roof it is. Grr. Wish the builders hadn't been so cheapskate in the first place!
Have a similar roof structure to yours, I topped up the insulation at ceiling level and got the added bonus of much quieter bedrooms.
Well I want to insulate it to keep upstairs warmer / save on heating. And I figured I might as well have a warm storage space up there that’s more usable for things that might be affected by cold… If I get a loft ladder it becomes a semi usable space
Lots and lots of work for little benefit.
Get lap spreaders, seal the loft hatch and get soffit spacers so that ventilation is maintained. A cold roof condenses more moisture so ventilation becomes more important.
I would be putting it on the ceiling, that way the heat from downstairs isn’t heating empty loft space too ie taking longer to heat the spaces you want heating
Our house has a roof void with insulation in the roof where you are suggesting putting it. Last year I put insulation on the ceiling and it made a massive difference to how warm the useable rooms got
What about rockwool in-between rafters then superfoil stretched and stapled?
