Home Construction Question

[ChevyHDGert]

My contractor has spec'ed out OSB Techshield for the roof decking and CDX plywood sheathing on the corners of the house and asphalt impregnated fiberboard sheathing everywhere else on the exterior walls.

Is there any real need to plywood sheath the entire exterior?

 

[Raspy]

The exterior sheathing is great for siesmic strength and just general stiffening of the structure because it adds a tremendous amount of diagonal bracing. It also acts as a backing to the siding, adds some additional nail holding and acts as additional blocking for the studs. It's a good idea, but probably not absolutely necessary. If you do leave it out you'll have to add some kind of diagonal bracing. Probably straps.

I am definately doing it on my new place and I'll be using the same siding material as you. It will make the building better.

By the way, I've been told by inspectors that OSB is actually stronger than plywood for sheathing. Plus it's cheaper and consistant. CDX is really poor quality with a lot of voids.

 

[sweettractors]

I agree with Raspy 100%. Added structural strength, alone, is worth a little extra cost. Ken Sweet

 

[/pine]

the plywood on the corners adds lateral bracing...(as mentioned)

an alternative is "let in" corner bracing...without one or the other there is nothing to prevent a wall from racking over...without plywood or cut in bracing there is nothing to permanently lock the walls into a plum/square position...

You did not mention the type of siding that is going to be used...if it is solid siding (like Hardy Board etc.) it should be fine although I would rather see a foam board with higher "R" value than "beaver board"...

If the siding is vinyl...I would want solid sheathing all the way around the structure as the beaver board or foam board offers very little protection from flying projectiles in extreme wind/storm conditions...

 

[ChevyHDGert]

Some walls will be sided with stone but mostly brick.

 

[/pine]

masonry (brick,stone etc.) are great...but if it was my home I would look at the "R" values of the asphalt impregnated fiberboard and compare the difference in prices with something that offers more insulation value...

 

[nickel plate]

The exterior sheathing is great for siesmic strength and just general stiffening of the structure because it adds a tremendous amount of diagonal bracing. It also acts as a backing to the siding, adds some additional nail holding and acts as additional blocking for the studs. It's a good idea, but probably not absolutely necessary. If you do leave it out you'll have to add some kind of diagonal bracing. Probably straps.

I am definately doing it on my new place and I'll be using the same siding material as you. It will make the building better.

By the way, I've been told by inspectors that OSB is actually stronger than plywood for sheathing. Plus it's cheaper and consistant. CDX is really poor quality with a lot of voids.

In wood frame construction the components of an engineered structural panel shearwall are evaluated and applied in exterior and interior wall areas from the top plate to the bottom plate with no breaks (windows, doors, etc.) in between. If you have a wall run with a lot of windows then metal "X" or "V" bracing that reaches under the widow and to the bottom plate is quite helpful to the wall's stability.
Three types of metal wall straps come to mind: The "T", the "L" and the flat strap. Several years ago I quit specing the "T" and "L" braces because the framers would often cut the required groove too deep into the studs causing more damage than good. Changed over to the flat strap but had to educate the framers as how to apply because I was finding most of them nailed up with extreme amounts of strap sag between the studs as they were nailing from one end of the strap to the other. To do it right, you start your nailing in the middle of the strap, the first nail then creates a "propeller" effect so you can locate the proper angle from the bottom plate to the top plate and start nailing out and away in each direction from the center. The result will be a tight and twangy to the touch diagonal metal wall brace.

 

[Raspy]

nickel,

On my new place the entire frame is steel and the design calls for diagonal rod bracing and steel straps of 3" X 1/8". This is for an open design with no sheathing on the roof or sides.

I'm eliminating most of the strapping and rods because it will all be sheathed and the straps are right where some windows go. I know it sounds stupid to remove bracing to accommodate a window, but there is enough strength to over compensate for this. It also has rigid frame bracing.

Installing the bracing initially to get the rough steel inspection did cause some consideration because it had to remain floppy to retain the proper post alignment. The idea was to tighten it up later, after the sheathing is on.

 

[Alan L.]

I am no construction expert at all. Forty years ago when I was in construction with my dad, we put something called gyplap on the exterior of the studs, not much different from sheetrock really. The corners were braced diagonally.

Everything around here nowadays has OSB all around which probably adds considerable strength. This change probably happened because its a material that is relatively cheap and was not available back then. Regular plywood would be more expensive.

If it were me, right now, I'd put the OSB all the way around.

My house, built in 2007, has OSB all around, then 1/2 inch styrofoam insulation on the outside of that, it adds some R value to the wall. Then an air space, then brick veneer with ties every so often. The back porch is cedar, in that area its Tyvek housewrap on OSB - no styrofoam on that part, then the ceder nailed to that.

We have the OSB techshield on the roof decking. Seems like at the time that was about $9 a sheet and regular OSB 7/16" (its really closer to 1/2") was only about $5 or $6 a sheet.

 

[75H2]

Are the walls framed with 2X4 or 2X6? When we were looking ar builders a few years ago one spec'd out 2X4 walls with osb in the corners and a blue "styrofoam" on the other outside walls. The builder we went with framed in 2X6 with OSB all around. I questioned the first builder, the salesperson's canned answer was that the deper walls didn't do anything for R value. My issue is that there was little keping the outside out other than siding & shetrock. I like the idea of more substantial construction. That's just my .02