OSB for outside use.

[artie]

There was a thread recently about using osb externally and the consensus was, not a good idea, at least not long term.
I hurriedly roofed a chicken coop one Sunday afternoon with 11mm osb. I think I'll leave it for a few months to see what happens.
The thread, I can't find it again.?? got me thinking about a product available in Canada / USA which is like laminated osb, you can buy flat pack storage sheds in Lowes etc panelled with it.
I haven't seen the like in UK.

 

[Woody2Shoes]

If it's OSB3 you should be fine. Even if it's OSB2 or 2+ you should be fine if you paint it with fence paint or similar. Both options assume no ground contact.

 

[Glitch]

OSB3 is moisture resistant, it's not waterproof. Untreated it will eventually fall apart.

My builder mate reckons it lasts a month before showing signs of weathering but lots of anecdotal stories about OSB3 left in the garden for months without damage. Edges likely to swell first.

I have painted some 'semi-exposed' pieces of OSB with Sikkens Rubbol Satura Plus - Like encasing it in resin .

For a chicken coop why not use roofing felt, or better still get a piece of EPDM?

 

[Woody2Shoes]

OSB3 is moisture resistant, it's not waterproof. Untreated it will eventually fall apart.

My builder mate reckons it lasts a month before showing signs of weathering but lots of anecdotal stories about OSB3 left in the garden for months without damage. Edges likely to swell first.

I have painted some 'semi-exposed' pieces of OSB with Sikkens Rubbol Satura Plus - Like encasing it in resin .

For a chicken coop why not use roofing felt, or better still get a piece of EPDM?

My guinea fowl have been living in an osb2 hutch (painted with fence paint) for the last three years or so - no sign of decay.
PS I'm a builder too

 

[artie]

It was just a rush job I did to keep the rain off the chooks for a day or two until I would make something proper.
But I'm going to leave it unpainted to see how long before it falls apart.

 

[Glitch]

My guinea fowl have been living in an osb2 hutch (painted with fence paint) for the last three years or so - no sign of decay.
PS I'm a builder too

Will last a while when treated but I assume you wouldn't use it externally in a permanent structure?

For the non-builders:
OSB2 is classified for use in dry conditions only. Use Class 1
OSB3 is suitable for 'humid' conditions, Use Class 2 i.e. occasional but not persistent wetting (typically condensation) and not exposed to the weather, particularly rain.
I had the misfortune of looking up the standards to understand how permeable this stuff is. OSB3 is not a good vapour control layer!

 

[Glitch]

It was just a rush job I did to keep the rain off the chooks for a day or two until I would make something proper.
But I'm going to leave it unpainted to see how long before it falls apart.

Be interesting to see how long it lasts. Perhaps long enough not to bother spending money on protecting it.

 

[Woody2Shoes]

Will last a while when treated but I assume you wouldn't use it externally in a permanent structure?

For the non-builders:
OSB2 is classified for use in dry conditions only. Use Class 1
OSB3 is suitable for 'humid' conditions, Use Class 2 i.e. occasional but not persistent wetting (typically condensation) and not exposed to the weather, particularly rain.
I had the misfortune of looking up the standards to understand how permeable this stuff is. OSB3 is not a good vapour control layer!

I use osb in roofing, flooring and sometimes in stud walling. I wouldn't use it in a human-being-house without a proper rain shield or other protection. I also wouldn't rely on its vapour impermeability (although I know some do, in certain situations including MikeG, architect, sometime of this parish) not least because you normally need to leave a 3mm gap between boards. I have used osb for temporary covers etc and a bird house, and as long as it's not in direct contact with the ground it lasts for quite a few years outside - even without a paint or other coating. Let's not forget we're talking about a chicken house here! Osb is absolutely fine for the structure of a hen house - it's cheap and relatively eco-friendly.

 

[Woody2Shoes]

Be interesting to see how long it lasts. Perhaps long enough not to bother spending money on protecting it.

I think that the key will be in the design details - eg overhanging eaves all round, at least 6 ins off the ground etc etc but yes, osb could well last several years untreated, and possibly twice as long or indefinitely if kept painted with the right stuff.

 

[Glitch]

I use osb in roofing, flooring and sometimes in stud walling. I wouldn't use it in a human-being-house without a proper rain shield or other protection. I also wouldn't rely on its vapour impermeability (although I know some do, in certain situations including MikeG, architect, sometime of this parish) not least because you normally need to leave a 3mm gap between boards. I have used osb for temporary covers etc and a bird house, and as long as it's not in direct contact with the ground it lasts for quite a few years outside - even without a paint or other coating. Let's not forget we're talking about a chicken house here! Osb is absolutely fine for the structure of a hen house - it's cheap and relatively eco-friendly.

From what I've read and understood about OSB I totally agree with you. Fine for sheds and hen houses!

I got a bit O(s)bsessed with it because I made a mistake in my shed build and wanted to know how big a mistake it was.

I copied others and used it inside (with a plastic VCL) and outside. MikeG does his OSB inside only and no additional VCL and I can appreciate that allows moisture to pass through the walls better than mine.

I'm not going to stress over my build anymore. Not optimal but should hopefully be enough leakage to avoid major condensation - As long as it lasts as long as a hen house it'll still be standing when we move!

 

[Glitch]

I think that the key will be in the design details - eg overhanging eaves all round, at least 6 ins off the ground etc etc but yes, osb could well last several years untreated, and possibly twice as long or indefinitely if kept painted with the right stuff.

Agreed.
I've got a good overhang, no soffits to help good airflow across the rafters and exposed OSB in the roof is painted in Barn paint. The rest is kept weatherproofed but might have its moisture resistance tested occasionally.