Using plywood as ceiling

choppermutt

Renovating interior of old shed. Thinking of using 1/4" plywood as ceiling rather than plasterboard. Purely for aesthetic reasons

I am wondering is plywood permeable to water vapour and if I stain/varnish the plywood - will that effect its permeability?

I have EPS board to use as attic insulation and a breathable membrane under the roof

Esel

Woul it not be a fire hazard?

Lumen

https://www.boards.ie/discussion/2058373810/using-plywood-as-ceiling

I am wondering is plywood permeable to water vapour

Yes, and more so the higher the humidity.

and if I stain/varnish the plywood - will that effect its permeability?

Varnish will reduce it. Stain probably won't have much effect.

What are you trying to achieve? If you want a air/vapour barrier put one between the ply and the insulation.

blackbox

Definitely a fire hazard. If you want a wooden ceiling for aesthetic reasons it should only be a facing on fire resistant plasterboard.

Lumen

https://www.boards.ie/discussion/comment/122709320#Comment_122709320

Yeah, but it's a shed. The point of fire resistance is to give occupants time to escape without the structure falling on their heads or killing them with smoke inhalation, but there are no occupants in a shed.

It's not like the ply is going to spontaneously combust.

choppermutt

I have EPS board insulation which I believe does not need the vapour control layer......is that correct??

blackbox

https://www.boards.ie/discussion/comment/122709411#Comment_122709411

It may have been presumptuous of me, but when the OP said the ceiling was for aesthetic reasons, I thought it might have a high level of occupancy.

Lumen

https://www.boards.ie/discussion/comment/122709791#Comment_122709791

Depends really. What is the shed used for? Is it heated? If so, occasionally or continuously? Is it well ventilated? Does it have any sink or toilet?

EPS is open cell, semi-permeable. In a heated building the vapour drive will mostly be from inside to outside, so without vapour control the vapour can condense in the insulation, which is bad.

Rows Grower

https://www.boards.ie/discussion/2058373810/using-plywood-as-ceiling

!/4 inch ply is not really thick enough I'd imagine.