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By Woody2Shoes
#1300549
DomD wrote:Will that require thinner roll insulation (e.g. 100mm) between the 150mm rafters?
Thanks


Yes - normally you'd expect an air gap of about 50mm. Exciting to see progress, cheers, W2S
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By MikeG.
#1300553
Yes. I would allow a 25mm sag, min, so if you can get 120/ 125 thick insulation, then use that. Otherwise, 100mm. You could push 25mm of Celotex into place above 100mm of mineral wool.
By DomD
#1300556
Thanks both of you, I think from my limited research the larger 50mm gap is for vapour impermeable felt and a breather membrane only requires min 10mm. I will see where I can find 125mm loft roll insulation.
I'm also going to try and use a higher quality membrane on the walls as I may need to leave it unclad for some time.
By Woody2Shoes
#1300790
DomD wrote:Thanks both of you, I think from my limited research the larger 50mm gap is for vapour impermeable felt and a breather membrane only requires min 10mm. I will see where I can find 125mm loft roll insulation.
I'm also going to try and use a higher quality membrane on the walls as I may need to leave it unclad for some time.


I think that it's worth following the manufacturers instructions for the particular membrane/underlay you actually buy (if you're lucky, on the label, otherwise on the website). My experience is that they all (perhaps excluding the old-fashioned tar-based felts) shrink to a greater or lesser degree. Cheers, W2S

PS re. unclad walls - the main enemy of the membrane is UV light - a good way to temporarily protect whatever you go with is to cover it with black DPM sheet held on with battens
By DomD
#1300982
Woody2Shoes wrote:PS re. unclad walls - the main enemy of the membrane is UV light - a good way to temporarily protect whatever you go with is to cover it with black DPM sheet held on with battens


I've got spare dpm so will look at using it for that. Any recommendations for the membranes for walls and roof? I was looking at the novia ones as they are fairly low cost.

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Ridge supports up now. I plan to lift the ridge beam into space tommorow.
Last edited by DomD on 19 Aug 2019, 07:42, edited 1 time in total.
By DomD
#1301055
As I have decided not to do raised ties but regular joists sitting on the top plate, does it make sense to do them first?
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By MikeG.
#1301064
There are arguments either way. You could do the joists first and put down some temporary boarding on them to enable easier access to the ridge, then do the ridge, then the rafters. However, you'd have to fix battens etc to the joists such that they were safe from falling over. Or you could do it the orthodox way.........rafters first.
By DomD
#1301065
MikeG. wrote:There are arguments either way. You could do the joists first and put down some temporary boarding on them to enable easier access to the ridge, then do the ridge, then the rafters. However, you'd have to fix battens etc to the joists such that they were safe from falling over. Or you could do it the orthodox way.........rafters first.


That's what I was thinking with the boarding as I have no scaffold and the top plates are at 2.5m. Why would I need to fix battens if I have nailed down the joists?
By DomD
#1301097
Ok I will use some battens I have spare.

Another question: you can see the sheathing here is just short of full height:
Image
The osb at the top will cover part of the gap but I was wondering if it would be acceptable to leave ~1" gap at the bottom to be covered by the skirting board - I am assuming the bricks are vapour impermeable anyway so do not need the osb as a vapour barrier?
Also are there advantages to laying two sheets offset horizontally rather than one sheet vertically?

Thanks again for all your help,
Dom
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By MikeG.
#1301117
It's fine to leave a gap at the bottom and cover it later with a board. The problem laying boards landscape rather than portrait is that the horizontal join might be unsupported (ie no timber behind it). If you've got noggins around the building at the right height then fine, it makes no difference at all.

I don't know if your straps are fixed in place yet, but if they aren't, see if you can move them away from the edges of blocks. They're stronger if they are at least 3 or 4 inches in from the edge of a block.
By DomD
#1301138
MikeG. wrote:It's fine to leave a gap at the bottom and cover it later with a board. The problem laying boards landscape rather than portrait is that the horizontal join might be unsupported (ie no timber behind it). If you've got noggins around the building at the right height then fine, it makes no difference at all.

I don't know if your straps are fixed in place yet, but if they aren't, see if you can move them away from the edges of blocks. They're stronger if they are at least 3 or 4 inches in from the edge of a block.
That makes sense - I'll do vertical then.
Already screwed down unfortunately but quite a few are away from edges and I did a fair amount more than recommended on your diagram.

Currently on the joists putting in the ridge - you can see the gap of three joists:
Image

Dom
By DomD
#1301150
Ridge up! Unfortunately it is fairly bowed with a 4cm difference from eaves to ridge at opposite sides - I suppose I just put the rafters on the short side in first to push it into place?

Regarding rafters, is the best way to cut them just with a circular saw and is there any way to get around having to lift the guard manually when making the seat cut? Should the rafter tail be cut afterwards?

ThanksImageImageImage
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By MikeG.
#1301177
Put the rafters up in pairs, and tap the high one down. They'll soon pull the ridge straight. You will probably find it easiest to use both a circular saw and a hand saw for cutting the rafters. Clearly mark your pattern piece, and wear goggles, because precision circular sawing involves looking at the blade, not the mark on the base, and that means getting a face-full of sawdust.
By DomD
#1301320
Half of the rafters are now up:
Image

I cut them by lifting them onto my saw horses cutting one of the angled sides with my mitre saw and doing the rest with a circular saw. My circular sawing certainly could use some improvement but I think the birdsmouths look reasonable:
Image

The nailing schedule I have used for the roof is:
Joists to top plates: 4x 3.1in toenails
Rafters to top plates 3x 3.1in toenails
Rafters to joists: 3x 3.1in face nails
Rafters to ridge: 3x 3.1in face nails

There is lots of space in the 'attic' area for storage - I'm glad I didn't raise the ties.
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Dom