Green Building Forum - OSB vs plywood

OSB vs plywood

Shevek — Fri, 20 Jul 2012 12:02:25 +0100

What are the main differences worth knowing about between OSB and plywood? When should you use one and not the other? Do they have different characteristics with regard to vapour permeability? Is there a price difference? Is one more environmentally friendly than the other?

OSB vs plywood

Peter_in_Hungary — Fri, 20 Jul 2012 13:14:53 +0100

Perhaps include LSB characteristics as well.

OSB vs plywood

Timber — Fri, 20 Jul 2012 13:24:34 +0100

OSB in dry or humid conditions is fine. OSB in wet conditions (or where there is a risk of wetting) is not.

Plywood can be used in most wall and roof applications, but MUST be the correct grade. A propper plywood with a durable timber species and a class 3 glue bond will cost about 3x that of OSB/3

OSB vs plywood

owlman — Fri, 20 Jul 2012 13:53:48 +0100

Heres a current price comparison for a reasonble quantity, for small quantities you'll pay more, all 2440 x 1220;-

18mm FSC OSB3 ..................................Â£14.50
11mm FSC OSB3...................................Â£9.50
15mm FSC OSB2...................................Â£11.90
18mm WISA SPRUCE special ply.................Â£24.00

OSB vs plywood

davidfreeborough — Fri, 20 Jul 2012 13:55:48 +0100

Generally speaking, OSB is more vapour open than plywood as there isn't a continuous unbroken glue layer.

David

OSB vs plywood

jamesingram — Sat, 21 Jul 2012 07:28:55 +0100

OSB is a better use of available resources ?

OSB vs plywood

Sprocket — Fri, 15 Feb 2013 14:53:01 +0000

Advice wanted. Can I try to revive this discussion?
I've been reading various material PR brochures and am now even less confident than before.
I need to choose spec for timber sheathing between Foamglas insulation and silicate board (internal surface).

Stuck between WBP (FSC of course) and OSB3 (either Smartply or Sterling OSB3). Probably 18mm

Slightly favouring OSB3 so far because it looks to have better environmental credentials.
eg. Sterling OSB3 is FSC and even made from UK timber sources. Lots of WBP seems to come from all over the world and selecting decent quality with any confidence looks a bit of a minefield. If there are specific recommended ply brands to be sure of quality that might help me out too.

I am concerned about mold growth. It will be fully enclosed of and _should_ be dry but not being able to see it just makes me more paranoid. I've seen mold growth on WBP surfaces (like my garage) around here already and I don't like the idea of mold behind the panels. So I thought OSB3 rather than regular OSB/2 just in case.

I know the moisture should be kept out but I am just thinking what-if worst-case etc.
There is plenty of anecdotal data of bad mold on OSB (worse than WBP) but little specifically on OSB3. Does the exterior grade resin bonding and moisture tolerant nature of OSB3 mean it is mold resistant?

TIA

OSB vs plywood

Cav8andrew — Fri, 15 Feb 2013 16:45:37 +0000

I had a similar situation and eventually went for WBP on the basis that from previous experience our supply of OSB3 had been very variable in panel thickness, 18mm +/- 2/3mm and I was concerned this would provide a uneven base to which to closely attach the Fermacell. Having said that the sheets of WBP, when the banding was removed, appeared to be trying to mimic a banana, but this was eliminated when fixed to studwork. THINKS, perhaps I should change my timber supplier !

OSB vs plywood

borpin — Fri, 15 Feb 2013 21:40:26 +0000

I had some cheap OSB used as a first floor while the frame went up last Autumn. Got wet continuously for about 2 months - still fine and now the flooring for my loft area! WPB ply - first sight of water and split like a banana!

OSB vs plywood

Timber — Fri, 15 Feb 2013 22:52:03 +0000

WBP as a standard has been superceeded (sp). You should be looking for a plywood with an EN636 class 2 glue bond for humid conditions and class 3 for exterior.

OSB3 will not be as good as a plywood with an EN636 class 3 bond when it comes to exposure to moisture. OSB3 is more like EN636 class 2 plywood.

I agree ply vs OSB when it comes to source of materials - OSB is probably 'better' in that it may very well use UK grown timber and it is normally made in the UK AFAIK (Sterling and Smartply). A lot of ply is imported from other places.

As for plywood brands - use a big name product like Finnforest (Metaswood) or similar.

As for mould growth, the grade of plywood or OSB use has nothing to do with risk of mould growth. Both will grow mould given the correct environment.

I wouldn't say that OSB3 is an exterior grade of board. It will swell and flake if exposed to moisture/exterior environment for long periods of time. OSB3 is no more mould resistant than anything else. Constantly damp surface = risk of mould growth almost regardless of substaight (sp).

Lots of dodgy plywood knocking around though, and I would NEVER by any that is marketed as WBP (see above statement about withdrawn WBP standard).

OSB vs plywood

borpin — Sat, 16 Feb 2013 11:30:18 +0000

As per the other thread on this. I got some class 3 ply and it is falling apart with minimal exposure. I would get a sample and leave it outside before actually using it! As Timber says, lots of dodgy ply around even from reputable merchants.

OSB vs plywood

borpin — Sat, 16 Feb 2013 11:32:12 +0000

BTW Timber, what is 'Marine Ply'.

OSB vs plywood

Shevek — Sat, 16 Feb 2013 12:13:28 +0000

Super handy thread. Big stand out for me: OSB = cheaper and probably more environmentally friendly.

OSB vs plywood

Beau — Sat, 16 Feb 2013 15:09:33 +0000

Posted By: borpinBTW Timber, what is 'Marine Ply'.

I have always believed this means the the glue was WBP and that that the wood used was naturally rot resistant (normally exotic from South America leaving me feeling bad)

As for OSB we had an old shed that the roofing felt blew off leaving the OSB exposed to the elements for 3-4 years until being repaired. The 18mm board was now more like 22mm but was completely intact and when dried out still held screws almost like new.

OSB vs plywood

Timber — Sat, 16 Feb 2013 19:00:35 +0000

^ as above - an EN636 class 3 glue bond with a durable timber used as the ply veneers.

OSB vs plywood

owlman — Sat, 16 Feb 2013 19:58:25 +0000

BS 1088 International standard for marine plywood.

OSB vs plywood

tombuild.com — Sun, 17 Feb 2013 23:33:53 +0000

Read somewhere (will try and locate it) that OSB was distinctly less environmentally damaging than ply as it contains waste wood, and has a lower carbon footprint, I use it instead of ply for green roofing and internal partitioning and find it works fine.

OSB vs plywood

fostertom — Wed, 20 Feb 2013 12:02:53 +0000

If OSB gets wet and swells a bit, its reasonably useful airtightness goes to pot.

OSB vs plywood

nikhoward — Wed, 20 Feb 2013 20:58:47 +0000

OSB gets my vote, normally made in UK from forest thinningss, so less road miles than ply which is normally imported