Renovation + Home Improvement
Apr 20, 2021 2:46 pm
We have a self built all timber home we did in the mid 80's when we were young, immortal and did not feel the cold. Now we are retired, really feel the cold and the house is in the Snowy Mtns. We used to work winters away, but now we live at home we noticed the deficite of insulation in the original design. Photo below.
Our roof is a cathedral ceiling with naked raked oregon rafters, a thin plywood above the rafters, sisalation on that, then battens 70x28mm old hardwood, then tin roofing. No insulation, so it's hot in the summer and freezing in the winter
Our thoughts on solutions:
1/ Piggyback new battens on top of the old ones, say 75 x 45mm treated pine. That gives us then a bigger gap to put batts in.
2/ Piggyback as above, then put 7mm structural bracing ply over the top before securing the tin to that, with or without a new layer of sisalation ?
3/ Remove the old battens, replace with thicker battens.
Note: We dont want to use foam insulation, especially styrene based foams, just batts and sisalation like memberanes if appropiate.
We also do not intend to insulate below the plywood ceiling as that will kill the beautiful natural timber look of the cathedral ceiling, anything we do needs to go on top.
Is piggy backing the battens legal, and if so what sort and frequency of fastenings shoul we do ?
Could we piggy back 2 layers of battens on the old ones, that will give us heaps of room for thick earthwool.
Thanks for all advice:)
Re: Solutions for insulating a raked rafter roof with 30mm g2
Apr 20, 2021 4:06 pm
The most heat escapes through the ceiling and roof so you need to get a lot of insulation up there and seeing as you are in the Snowies which is probably Zone 8- Alpine, I'd be looking at R5 at least and probably better - R6. That means you are going to need much thicker battens. R4 insulation is close to 200mm thick, R5 - 240 and R6 close to 300mm.
Your idea of using another layer of 45mm thick battens on top of the old 28mm ones to give a total depth of 83mm isn't really practical. You would just be able to squeeze R2 batts in there. Hardly sufficient for a cold climate like yours.
If it was me and I was going to go to the trouble and expense of removing the roof to fit more insulation up there, I'd want to make sure it was worthwhile.
Re: Solutions for insulating a raked rafter roof with 30mm g3
Apr 20, 2021 4:28 pm
Thanks for the advice.
So, how would you increase the gap ?
We may never get it perfect, but one layer of earthwool is going to be aheck of a lot better than zip.
Could you use 200 x 50mm and stand them on edge as battens ?
PS: there is no insulation under the suspended timber floor, thats the next thing after the roof. Then we may reclad the walls, when we swap the weatherboards to colourbond and stuff better insulation in there when we do the walls.
Re: Solutions for insulating a raked rafter roof with 30mm g4
Apr 20, 2021 9:02 pm
I'm actually quite astounded that you didn't do any of that when you built the house originally, especially seeing that it is after all in a sub-alpine area. Being an ex-Kiwi with our colder weather and having been in the trade for over 45 years, it was drilled into us even when I was an apprentice about the need for good insulation.
Yes, a 200 x 50 on edge would give you a good depth for decent R-rated batts.
Re: Solutions for insulating a raked rafter roof with 30mm g5
Apr 20, 2021 9:28 pm
If we use the 200 x 50 on edge, should remove the existing battens ?
Fastening the 200 x 50, one or two batten screws per rafter intersection, would have to skew them ?
Re: Solutions for insulating a raked rafter roof with 30mm g6
Apr 21, 2021 8:17 am
Yes, I'd remove the existing. I'd skew nail them but put in blocking every 3m or so to keep them at 90º to your rafters. You may need to strut the lowest batten or second lowest batten off your top plate too to stop it "rolling" depending on my question below. After that the solid blocking will support the others.
What spacing are your existing battens and what pitch is your roof? I'd imagine it would be around 45º?
I'd also think twice about swapping your weatherboards for Colorbond cladding too. The Colorbond would have nil insulation qualities as opposed to the weatherboards. You could always batten the timber framing to get thicker batts in there to compensate. A much easier and cheaper proposition than the roof.
Re: Solutions for insulating a raked rafter roof with 30mm g8
Apr 21, 2021 10:02 am
14º, gee I'm surprised at that. Most of the exposed rafter houses I've seen are a lot steeper than that but that is good for you or anyone else working on the roof.
Re: Solutions for insulating a raked rafter roof with 30mm g11
Apr 22, 2021 10:28 am
Hmm, maybe. I'd put the first 200 x 50 batten in place and skew nail it to the rafters first and see how rigid it was. After you have the second batten in place, block between them which will stiffen the first one up considerably. You may not need any struts.
What size are your rafters and what sort of span are they? I'm just thinking about the extra loading with the increase in batten size.
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