structural fiberboard sheathing

[marson]

i am about to start framing a superinsulated house. the specs call for

1/2" structural fiberboard sheathing (brace-rite by knight celotex). no osb on the corners. this is not something i chose, but it is on contract so i'm stuck with it. no additional bracing is required.

what do you engineers out there think of this system? i've heard of houses which creak in the wind, but that was not the structural fiberboard. there is no additional bracing specced.

anyone used this much? i'd really really like to sheath my walls before standing them up, but am wondering if this is even possible with this shit. for example, can you even walk on a wall, or will it break between studs? can i cut it with a rotozip?

[PPS]

It's listed as a permissible braced wall product in the IRC (method #4, 1/2" or 25/32" structural fiberboard applied vertically or horizontally, on studs spaced 16" o.c. maximum, and installed per table 602.3(1).

The kicker is it's only certified for 16" OC. [ R602.10.3 (4) ]

For a single story home in SDC (Seismic Design Category) A or B, 100 mph wind or less, it's installed at each in and 25 feet oc (min. of 16% of the wall). For SDC C or wind 110 mpg or less, it's 25% of the wall, for SCD D-1 it's 30% and for SCD D-2 it's 40% of the wall. ((Same as OSB)).

Fastening is 1-1/2" gal roofing nail, 6d common nail (8d if structurally rated) or staple 16 ga. 1-1/2". All fastening is 6" oc field and 3" oc. edge. (man that's a lot of nails.)

Advantages appear to be high permeability rating of 20 and an R-value of 1.3 (yawn). It appears to be ok for up to a 3-story home, no osb on the corners. this is not something i chose, but it is on

[Bob Morrison]

You could always use OSB or plywood over the fiberboard.

[RicodJour]

That's a big expense to cover a building twice - who's supposed to pay for it? If you're talking about just adding the OSB over the fiberboard on the corners, that's going to cause an issue with the siding surface. Please clarify, Bob.

R

[marson]

one of the reasons they are calling for fiberboard is because of its high perm rating. so adding OSB would defeat that purpose.

my main concern is that it provides enough rigidity. after all, this is a half million dollar project, and here we are using a product that is regarded by many as inferior to OSB. well, I guess i'll find out. thanks for the replies.

[Bob Morrison]

If the building is designed for wind load only then the fiberboard product should work fine. The literature I've read allows for up to 150 PLF loading for this product, but only for wind load. I would like to spec this product, but most of my designs are governed by seismic loads and the product has not been tested for that type of loading.

Perhaps I was a little too flip about my earlier answer. For that I apologize -- it has been a tough couple of weeks. I am now thinking you could possibly use either let-in 1x4 wood bracing or perhaps Simpson Wall bracing straps. These would stiffen the house with very little change in perm value.

[marson]

thanks, bob. we don't have seismic loads here (northern mn). here's a question for you--what gives a stiffer frame--sheathing the corners with osb or let in bracing?

at this point after talking to the owner and the architect, i think i am going to try the fiberboard. if it seems to shaky, I'll sheath the corners.

[Bob Morrison]

I'm guessing the OSB will give you a stiffer wall, but I think you will be surprised at how stiff the fiberboard wall is when you are done. Remember, it has a rated capacity of 150 PLF. That's 3000 pounds for a

20-foot long wall. I expect that the most noticeable deflection will occur around openings. There is a way to add horizontal straps to "reinforce" the openings in order to get the wall to be stiffer. I can send you a detail if you contact me off list. See e-mail address below.