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Workshop on a slope 2

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ptomharper

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Name
Patrick
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Hi all

I'm not sure if anyone remembers but I came here to ask for advice on my workshop on a slope. I had the ground levelled and ordered the 75m line pump for concrete. So glad I went for the slab over a timber floor construction as suggested.

Now looking to order materials, my next question comes with the roof construction. It will be a dual pitched roof spanning 4.8m. I want to insulate between the rafters so I get the full height inside, therefore I don't need any ceiling joists for a ceiling but is it still necessary to tie in the roof on every rafter or could I use 2 or 3 hefty ties (8x2's?) evenly spaced along the building to tie in the walls? I hope this makes sense. Any help is greatly appreciate!

P.s excuse the drawing
 

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Somewhere in here, the forum, @Mike G describes a 'structural ridge' which does not require ties, I think.

I certainly used that design for my 'shop build. I dis put three ties in at each end, but used them for storage.IMG_1125.JPG
 
ptomharper said:
Just what I was thinking too. Would be some handy storage.
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If you are going to use your ties for storage, then you'll need to use 250 x 50s, or, 200x50 with hangers (from the ridge). If you don't intend loading the ties, you could use 10 or 12m steel rod, supported in the middle by something hanging from the ridge (usually more of the same rod). You'll need plates welded on the end to screw securely to the wall plates.
 
Mike G said:
If you are going to use your ties for storage, then you'll need to use 250 x 50s, or, 200x50 with hangers (from the ridge).
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250x50s fixed with bolts and square washers through the rafters?

How would hangers from the ridge work? On vertical timbers between the ridge and 200x50 tie?
 
ptomharper said:
250x50s fixed with bolts and square washers through the rafters?
Click to expand...

Yes.

ptomharper said:
How would hangers from the ridge work? On vertical timbers between the ridge and 200x50 tie?
Click to expand...

You drop a vertical timber down from the side of the ridge to a joist, and you wrap some universal galv ms banding around the joist to connect the two. If it's more convenient, instead of having a hanger for each joist, you can run a 6x1 binder along between hangers, supporting 2 or 3 joists (again, on universal strapping). All parts of that arrangment are in tension, hence the straps.
 
Mike G said:
Yes.



You drop a vertical timber down from the side of the ridge to a joist, and you wrap some universal galv ms banding around the joist to connect the two. If it's more convenient, instead of having a hanger for each joist, you can run a 6x1 binder along between hangers, supporting 2 or 3 joists (again, on universal strapping). All parts of that arrangment are in tension, hence the straps.
Click to expand...
Got you. Thanks a lot. Before any of this though I will be building a brick plinth not having laid a brick before. Looking forward to it!
 
You could look into making scissor trusses. My shop uses them and they give me an open ceiling.

Pete
 
Hello. I need to order insulation, anyone have advice or experience using PIR board or Rockwool in the walls of a workshop? As it is just a workshop could I go down to 70/80mm thickness rather than 100mm?

Another thing to add is my studs are about 108mm wide (I ripped lots of big roof rafters in half) so should I push the insulation to the inside or outside of the studs?


Appreciate anyones input on this.

Patrick
 
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I find it hard to justify the cost of PIR (Celotex, Kingspan etc) in an outbuilding. It's a lot cheaper with fibreglass/ Rockwool. PIR is approximately twice as effective as mineral wool, but as you say, this is a workshop, not a house, and will only be intermittently heated.

The question of voids in the wall, though, is more important. Can you describe the build-up of your wall from the inside face to the outside.
 
Hi Mike, thanks for replying.

PIR is looking very expensive even from a insulation seconds website.

This is my build up. I may take away the OSB to the outside walls. I was originally going to only OSB the outside for now and ply the inside down the line but if it makes sense to omit the OSB and ply the inside face when I build the walls I may do that. Would be cheaper.
26252.jpg
 
OK, there's a couple of things there. Firstly, you absolutely should not leave any voids. Interstitial condensation is a real danger. What you've got are vapour barriers on BOTH sides of the wall, which is never a good idea. Any water vapour within the wall can't get out, and will condense when the temperature falls. Ideally, you'd put the OSB on the inside, and just have a membrane on the outside.....saving quite a lot of ply.
 
Mike G said:
OK, there's a couple of things there. Firstly, you absolutely should not leave any voids. Interstitial condensation is a real danger. What you've got are vapour barriers on BOTH sides of the wall, which is never a good idea. Any water vapour within the wall can't get out, and will condense when the temperature falls. Ideally, you'd put the OSB on the inside, and just have a membrane on the outside.....saving quite a lot of ply.
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Ok. So I'll go for the ply on the inside only. Would you do the same on the roof? Ply the inside, membrane and battens for metal roofing on the outside. As for the voids in the walls. If I push whatever insulation I use up tight to the internal ply will a void between outside face of insulation and the breather membrane on the outside be an issue?
 
ptomharper said:
If I push whatever insulation I use up tight to the internal ply will a void between outside face of insulation and the breather membrane on the outside be an issue?
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Yes. You need to avoid voids. Compressing additional fibreglass in would be my approach........or ripping the studs down to the same thickness as the insulation.
 
ptomharper said:
Would you do the same on the roof? Ply the inside, membrane and battens for metal roofing on the outside......
Click to expand...

Yes......with the caveat that metal roofing sheets require ventilation underneath. Good airflow is critical, because you will get condensation on the underside, which needs to dry off before it pools somewhere. Check the manufacturer's details carefully.

Again, I would suggest OSB rather than ply. Firstly, it's cheaper. Secondly, if it is shuttering ply you are intending to use, then OSB can be a lot flatter. It only needs to be 10mm thick, unless you are intending hanging stuff (shelves, racks, units etc) directly on the sheathing, rather than screwing through to the studs.
 
Mike G said:
Yes. You need to avoid voids. Compressing additional fibreglass in would be my approach........or ripping the studs down to the same thickness as the insulation.
Click to expand...
I'll do that. No way am I ripping any more timbers
 
Mike G said:
Yes......with the caveat that metal roofing sheets require ventilation underneath. Good airflow is critical, because you will get condensation on the underside, which needs to dry off before it pools somewhere. Check the manufacturer's details carefully.

Again, I would suggest OSB rather than ply. Firstly, it's cheaper. Secondly, if it is shuttering ply you are intending to use, then OSB can be a lot flatter. It only needs to be 10mm thick, unless you are intending hanging stuff (shelves, racks, units etc) directly on the sheathing, rather than screwing through to the studs.
Click to expand...
Airflow on the roof is something I won't overlook. I was going to use hardwood ply. I have nothing against osb I just much prefer the look of ply for all the walls inside as that will be the finish.
 
ptomharper said:
...... I have nothing against osb I just much prefer the look of ply for all the walls inside as that will be the finish.
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Paint it, though. A few hours of painting is transformative. Makes it feel light and airy, rather than like a cave.
 
Mike G said:
Paint it, though. A few hours of painting is transformative. Makes it feel light and airy, rather than like a cave.
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There is that option. It's cheaper too, quite a bit cheaper. I assume both ply and OSB have the same properties to suffice as a vapour barrier though? Full of glue.
 
Oh yeah, I bet. Thanks for answering my questions, appreciate it. I'm sure there will be more to come!
 
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