Roof insulation: Rafters or Ceiling?

I've searched the forums and SEI but didn't find anything specific on whether ceiling- or rafter-based insulation would be a better option for my detached house.

I use the attic for storage/running computer equipment etc (about 50% of it is already floored) with about 120mm of existing fibre insulation. A family member had their roof sprayed with an expanding foam and he said it made a huge difference to the heat retention in the house, though it was messy.

Are there other alternatives? We probably won't be converting the attic for living space as the roof is double-hipped and low-set (about 182cm in the center).

Many thanks!

does the attic have a rad / heater??? is it connected to the house system or stand alone?

sydthebeat said:

does the attic have a rad / heater??? is it connected to the house system or stand alone?

Click to expand...

No, just the standard cold water tank and a tank for the hot water system. There is also some piping from the roof into an additional system for the solar panels.

I guess if I go for rafter insulation, I'd be spending additional money heating a space I'm rarely in!

when insulating across the ceiling joists theres a few things to look out for.
1. if using quilted material, dont squash it down, ie if your joists are 125mm and you put in 200mm quilt, you cant squash this down to 125mm as the end result will simply be 125mm insulation.

2. it you put in insulation higher than the joist, you will need to construct a 'secondary joist floor' over the existing.. ie 100 x 44 over the existing... this will give you 225mm to play with....

3. if you dont want to do this, what id suggest is to take up the quilted material, cut 100mm sheets of PU foam board and squeez into space between joists.... try to get these as tight as possible... and the come along after and relay the 125mm quilted material.. the main purpose of the quilt would thn be to cover any possible gaps...

That's really useful! THanks for the tips.