Insulation into eaves

[mfarrow]

Hi

Currently trying to give our loft a thermal makeover, including undoing the previous owner's 'enhancements'.

After making the loft hatch bigger, and boarding up the roof of the airing cupboard (this was removed to give better access to the roofspace when a new boiler was put in the garage) I'm now ready to start insulating.

most of it seems straightforward (a bit of rockwool here, a smattering of celotex there) but I can't figure out how best to insulate the sloping ceilings at the front/back of the house where the rafters come down to the first wall plate.

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I was thinking about either 50mm celotex or rockwool in the gap between the plasterboard and the felt, the problem with rockwool being that it's not as good as celotex, but if I push celotext down I'll be left with a gap where the rafters tie to the joists.

I feel like I'm between a rock and a hard place. Can someone please help me figure this one out?

Thanks

 

[Johnboy54]

This reply may jog your post a bit so I'll impart my understandings.
Down at the eaves, you need an air flow otherwise condensation forms in the loft and rots your roof.
This can be overcome by replacing the felt with breathable felt.
Problem being you already have a roof, which means major surgery and lots of expense to re-tile and re-felt the roof.
So,you still need an airfow between your plasterboard and the felt/celotex/rockwool.
I dare say if you look at other houses in your area with similar conversions, you'll see tiles have been replaced with several flat/currogated tiles that allow air to flow between the roof trusses.
How many per metre etc I have no idea. I just know you need them, and your local building regs dept will tell you.
Problem being, if you don't have planning permission, building regs may not be so helpfull, which is where this forum comes in.
I do know you can't just block off the air flow at the eaves without replacing it by some other means.
I can see you've already started with plasterboards.
But, on Ebay there's a foam you can buy and spray yourself that seals between the trusses and does away with the need for airflow, whilst providing the thermal insulation.
So it says in the specs.
Not sure now of the name but if you type in loft insulation it will come up with it.
Over to the experts.
John

 

[mfarrow]

Thanks John for the comprehensive reply.

I'm aware of the need to have some airflow still (did a search and found lots of condensation topics), but thought this would be OK if I left 50mm (the rafters are 100mm)???

The plasterboard was put in with the house.

 

[Johnboy54]

Not sure what you mean about the gap being left?
Looking at the pic it seems a simple enough job to cut the celotex to suit down at the eaves?
Also, as you say, 2" celotex would leave you with an airflow, but rockwool would fill the 4" inch truss in and stop the airflow.
Forget the rockwool.
Good luck.
John