Roof insulation query
Discussion
I'm about to make a loft in my place habitable.
Head height is marginal (partly as I'm 6'4") so I want to give as much a feeling of "space as we can.
Right now the room has plasterboard attached to the roof rafters, along with a plasterboard ceiling (leaving a void above to the ridge).
What I'm thinking of doing is stripping out all the plasterboard exposing the beams etc and plastering between the rafters - the house is very old so this would look "right" and, I think, give more of an impression of space even if the practical head height isn't much changed (maybe a few cms).
There's absolutely bugger all in the way of insulation up there at the moment. All that's above/around the plasterboard is void and even the odd bit of daylight. I can see a rough black textured shiny plastic material which I suspect is the backside of some felt under the clay tiles?
So the question is...I'm hoping some sort of insulating board could be put between the rafters, against/near the black material, ahead of plastering to give a bit of insulation? I'd want it to be breathable and would likely use lime plaster over the top of it. There's also not much depth to play with - I've seen similar done, but with much deeper rafters. Pretty sure I have less than 70mm. Possibly less than 50mm.
Does anyone have recommendations of the sort of thing I should be looking at? And whether this is a dumb idea...
Head height is marginal (partly as I'm 6'4") so I want to give as much a feeling of "space as we can.
Right now the room has plasterboard attached to the roof rafters, along with a plasterboard ceiling (leaving a void above to the ridge).
What I'm thinking of doing is stripping out all the plasterboard exposing the beams etc and plastering between the rafters - the house is very old so this would look "right" and, I think, give more of an impression of space even if the practical head height isn't much changed (maybe a few cms).
There's absolutely bugger all in the way of insulation up there at the moment. All that's above/around the plasterboard is void and even the odd bit of daylight. I can see a rough black textured shiny plastic material which I suspect is the backside of some felt under the clay tiles?
So the question is...I'm hoping some sort of insulating board could be put between the rafters, against/near the black material, ahead of plastering to give a bit of insulation? I'd want it to be breathable and would likely use lime plaster over the top of it. There's also not much depth to play with - I've seen similar done, but with much deeper rafters. Pretty sure I have less than 70mm. Possibly less than 50mm.
Does anyone have recommendations of the sort of thing I should be looking at? And whether this is a dumb idea...
We had to have a new roof on a project a year or 2 ago. To meet building regs we had to have 75mm Celotex between the rafters + a multifoil (like the TLX) between the tiles and the rafters (with a specified air gap). Our rafters were 75mm so this was the thickest that we could fit without replacing the timber.
If you are going to plaster between the rafters that the tiles sit on top of, and not replace the roof, then where is the insulation going to go?
I guess you wouldn't need to meet building regs for roof insulation as you're not replacing the roof (but that is just a guess).
You could put Celotex or similar between the rafters and replace the plasterboard as it currently is, but that is still going to be fairly poorly insulated with a max of 70mm of celotex + cold bridging at rafters with the head room unchanged.
They do insulation backed plasterboard that you could put onto the rafters as well, but that will obviously be thicker and reduce your head height...
Is it just for your use or will added value at time of sale be important, and hence building regs?
If you go with celotex between the rafters, remember to account for the thickness of the rafters when ordering, I've still got about £200 worth of celotex taking up room in the garage...
If you are going to plaster between the rafters that the tiles sit on top of, and not replace the roof, then where is the insulation going to go?
I guess you wouldn't need to meet building regs for roof insulation as you're not replacing the roof (but that is just a guess).
You could put Celotex or similar between the rafters and replace the plasterboard as it currently is, but that is still going to be fairly poorly insulated with a max of 70mm of celotex + cold bridging at rafters with the head room unchanged.
They do insulation backed plasterboard that you could put onto the rafters as well, but that will obviously be thicker and reduce your head height...
Is it just for your use or will added value at time of sale be important, and hence building regs?
If you go with celotex between the rafters, remember to account for the thickness of the rafters when ordering, I've still got about £200 worth of celotex taking up room in the garage...
jmsgld said:
If you go with celotex between the rafters, remember to account for the thickness of the rafters when ordering,
Also be aware that you either need a ventilated airspace above the Celotex, of at least 50mm (25mm. if breathable roofing felt), or continuous vapour barrier on the inside face (which effectively precludes exposed rafters), otherwise you'll get interstitial condensation that will rot the timbers of the roof structure.Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff