I thought my only real choice was OSB or plywood. In our wet climate I'm heavily leaning toward plywood over OSB b/c of its better ability to handle moisture.

I've just read about this stuff: http://bpcan.prod.alogient.com/en-CA/products/insulation-and-structural-boards/composite-insulation-panels/excel-west-/ "breathable structural insulated sheathing" In reading the product info, it appears this is structural sheathing that has a membrane that is vapour permeable but not air permeable (air barrier). What is the advantage of such a product as opposed to plywood (which I thought was an air barrier itself, so long as the joints are properly sealed)?

They list 3.63 perms. In a moist environment, plywood is about 10 perms.

OSB deteriorates much faster when wet than does plywood. ZIP sheathing, very common today, is OSB with a special paint coating. We're moving to Fir plywood on the exterior of our double stud houses because it is much more resilient than OSB, and we'll tape it with SIGA Wigluv tape. You're better off budget wise to separate the sheathing from the insulation. IMO those materials are for cheapo builders who want a quick inexpensive material to meet some code.

Hi there Bob, are you familiar with Magnesium Oxide Fiber Ceramic (MgO) board? I market a very new US invented and manufactured for the 1st time, MgO board that is water, mold, fungus, bug/termite, fire and hurricane resistant. It takes the place of drywall but weighs only 40-42 lbs and goes up just like drywall. It comes in 4x8 sheets and will eventually, in my opinion, take the place of toxic drywall. I've been in the new home sales industry here in the Atlanta area and have seen quite a lot of damaged due to mold from wet drywall. Let me know if you would like more info. Maggie Steck [email protected] 678-908-7095 P.S. I'm all all about building "healthy" homes.

The solution is to stop building houses that rot, not start using materials that allow the rot but are not damaged. We know how to do this & hundreds of builders across the country are building this way. My understanding is that MgO board is very expensive, but that is an issue that you can address easily: what is the cost of MgO board?
What are the uses other than replacing all drywall? It cannot be used for structural sheathing, right? I have not used this material but I'm sure there are places where it may be a good substitute for current methods.

Posted By Bob I on 26 Jul 2015 04:32 PM
The solution is to stop building houses that rot, not start using materials that allow the rot but are not damaged. We know how to do this & hundreds of builders across the country are building this way.

So what does that entail in terms of sheathing?

IMO, something like ZIP, which can be taped, or Fir CDX; there are others. But the material isn't the important thing here; it is the fact that rotting houses are becoming so common that they have created a specific marketing opportunity for these folks. They may sell an excellent product, but the larger point is that builders have to smarten up and build better houses. We know how. (By the way: if the studs are rotting, does it matter that the drywall is intact?)

I believe the answer is the time-tested method of using concrete/masonry. It has worked for thousands of years and is time tested. It can get wet repeatedly and will not rot. Add insulation to it (ICF, SCIP) and you have a winning combination.

Go to places like Europe, Middle East, Russia, Asia, etc, and you will see how concrete/masonry structures are still standing and being utilized today. Those that haven't been bombed during WWII are still standing. Houses were built with the intention to last centuries, not decades. 

Thank you, Bob. I'm leaning towards plywood myself. And by Fir, if you mean douglas fir, well that grows like dandelions around here so sounds good to me! ;-)

Anyone else want to put in their 2 cents about plywood vs OSB for structural sheathing?

Posted By walleygirl on 27 Jul 2015 12:03 AM


Anyone else want to put in their 2 cents about plywood vs OSB for structural sheathing?

When it comes to plywood vs AdvanTech OSB, the OSB wins, hands down.

They've tested plywood against AdvanTech OSB and the OSB won on all weather tests. It can take a year in the rain and elements and no swelling, splitting, rot or delamination. They even offer a 500-day weather exposure warranty. AdvanTech OSB

Best thing is to price out plywood with AdvanTech OSB.

Unless you looks at perms - then it's a poor second.