First Time Using OSB for Shed Walls – Paint or Treat It First?

[Sam James]

Hi everyone,

I’m currently working on a small garden shed project, doing most of it DIY to keep costs down. I’ve used OSB (Oriented Strand Board) for the walls and roof sheathing, but I’m unsure what the best next step is in terms of protection. I've read mixed things online about whether you should paint it directly, treat it first, or even use a membrane over it.

I’m planning to paint the exterior eventually, but not sure if I need to use a primer, a sealant, or some sort of breathable membrane in between. I don’t want to mess it up and have the boards swell or rot after the first wet season!

Has anyone here used OSB externally on a shed or outbuilding? What worked well for you?

Any advice would be appreciated!

Cheers

[Conor]

OSB3 is already treated to be moisture resistant. It won't rot to quickly.

 

However, it's not water proof. It will absorb water, swell, and flake apart eventually.

 

Painting will help somewhat, but not stop it. You need a proper waterproof membrane on the roof, and a treated cladding on the sides. 

 

Does your roof have an overhang? Od felt the roof, batten the sides, and add t&g or shiplap treated 12mm boards. It'll add another couple hundred to your costs, but the shed will last for decades.