Workshop construction.

[Joe Shmoe]

Hi folks,

I'm still a little confused about constructing my workshop walls/roof in a way that won't encourage damp down the line, and the more 'workshop builds' that I read on here, the more confused I get. Here are my current plans of construction:


Walls:

LogLap cladding --- permeable barrier --- 100mm studwork cavity (filled with 60mm Rockwool Flexi-slabs touching inside walls) --- 9mm Ply --- 2 layers plasterboard.

Roof:

Cedar Shingles ---- 19mm Batons --- permeable Barrier ---- 18mm OSB --- 100mm studwork cavity (filled with 60mm Rockwool touching inside walls) --- 9mm Ply --- 2 layers plasterboard.


Couple of questions

1) Is this the correct way of construction?

2) Is it okay to fix the loglap straight to the framework? I figured as the rockwool slabs would be pushed to the inside walls, this would leave a 40mm gap directly behind the loglap to aid drying out?

3) Do I even need the 9mm Ply? (which I added to help protect from moisture). If so, do I have it on the correct side of the plasterboard ?

4) From what I understand, the Cedar shingles are supposed to be fixed to batons so there is airflow underneath to prevent damp/aid drying out. How do you stop wasps etc getting in this cavity, and should the barrier underneath be permeable or non-permeable?


Kind regards
Joe.

 

[MikeG.]

Hi Joe,

the walls are not to bad, but may not be easy to get right........and ther is an issue with the breathable membrane. It is difficult to locate mineral wool in exactly the right place unless you have something to push it up against...........and you wont have.

It would be much better to (inside to outside) fully fill the 100mm studs with insulation, then have your breathable membrane, then run battens down the line of your studs to space the cladding away from the permeable membrane. That would also suit the membrane, which relies on air movement outside it to evaporate any condensate.

On the inside, the ply (or OSB) is there to provide racking resistance for the building. It is an important structural element. If you don't have it you will need to build in a lot of bracing. It is also a decent vapour barrier, and it gives a good fixing for stuff on your workshop walls. You don't need the plasterboard.

The roof is a strange one!

Why the 18mm OSB? You can omit this, put in proper sized battens, and save yourself lots of money. The OSB would require venting below it, in which case the breathable sarking is a waste of money (you may as well use felt).

So, my suggestion for your roof:

-shingles
-25x50 battens
-25x50 counterbattens
-breathable sarking ("Tyvek" or similar)
-rafters fully filled with insulation (100mm rafters makes it sound like a very small building)
-OSB lining inside

Again, I would omit the plasterboard.

I hope this helps.

Mike

 

[OLD]

Cedar shingles are very nice to look at when new but they are expensive.

 

[Joe Shmoe]

Hi Mike, thanks for your words of advice!

If I space the cladding off the frame with batons, what do I use to stop insects/wasps crawling up the 1" gap that is created along the bottom edges of the walls? Would I also need a gap along the top in order for air to flow through ?

I see on some other builds that people have not bothered to use batons. Is this a major error on their part ?

I was looking through workshop builds, and many of them, it seems that people have constructed their workshops how I originally proposed…...without an airgap. They appear to lay OSB sheets over the trusses, and then (usually) lay FELT shingles straight on top. How are their constructions differing from mine - or again, have they made an error too ?

Regards
Joe

 

[MikeG.]

Joe,

there are lots of errors out there! If people have built with no gap behind their cladding, they are asking for trouble in the long run. This gap can be insect proofed with insect mesh, available from Builder's Merchants........but easier is stainless steel thin coat plasterers corner bead.......the mesh type, rather than the one with big round holes. This is L shaped and about 25mm in each dimension.......so easy to use, just by nailing across the ends of your battens, top & bottom, before you fix your cladding.

Rooves often have ply/OSB decking with felt..........but must........must........be ventilated below this if they do.This can mean eaves vents and insulation at joist level, or it can mean eaves and ridge vents and insulation spaced off the underside of the OSB.

Mike

 

[Joe Shmoe]

Hi Mike, I shall take your advice to heart and will be spacing the cladding with batons.


Can anyone tell me if there are any differences between Shiplap and PGTV cladding is, aside from appearance ?

I'm trying to decide which to go for and have even considered log-lap as its not much more expensive. Do any of them offer beneifits over the others ?


Regards
Joe