attic flooring

[Bruce King]

Many new homes around here have trusses 24 on center, most of the attic floors are double thickness OSB (7/16) when furnaces and water heaters are present.

Some have single 7/16 OSB spanning 24" where the attic is only for storage.

The access on all examples is folding stairs or ceiling scuttles.

The single layer 7/16 has a span limit of 16 inches.

Any difference in IRC code because this area is only for storage?

In other words, is 7/16 OSB ever allowed to span 24 inches when used in storage areas without regular access?

[Ted Menelly]

Personally I have always hated the 2 foot span. I am an older fart that use to build 16 on center even with trusses or at the very very least used 5/8 on the roof or walkways in attics.

I can't tell you how many times I stepped on 7/16 in an attic and scruuuuunch, crack. For storage I do not know the code I will have to look it up as well

[Mitchell Toelle]

Beware, any time you see sheathing on top of trusses where there is no mechanical sitting on it. Caution your client to never store any goods in that area. The bottom cord of most roof truss systems are engineered for only live load, not dead load, unless otherwise specified. If that sheathing is for access to work needed areas then it's okay, just for that, but not for storage of goods.

Hope that's helpful.

MPT

[Ted Menelly]

Beware, any time you see sheathing on top of trusses where there is no mechanical sitting on it. Caution your client to never store any goods in that area. The bottom cord of most roof truss systems are engineered for only live load, not dead load, unless otherwise specified. If that sheathing is for access to work needed areas then it's okay, just for that, but not for storage of goods.

Hope that's helpful.

MPT

Yes and that also. Most new homes that builders use trusses on homes there will be a sign on the wall that it is not to be used as storage.

[Steve Frederickson]

Mitchel, I think you misspoke. Storage of goods would be considered live load, not dead load. Dead load is the weight of the building materials. All trusses are designed for dead load. Not all trusses are designed for live load on the bottom chord. However, based on the photo, I can almost guarantee that it was designed as a storage area.

Having said that, the question is above the sheathing. The sheathing should have a span rating stamped on the sheet. The rating would have the maximum span for allowed when used as floor sheathing, and teh max. span allwoed when used as rofo sheathing.

I hope this helps.

[Jerry Peck]

Many new homes around here have trusses 24 on center, most of the attic floors are double thickness OSB (7/16) when furnaces and water heaters are present.

Some have single 7/16 OSB spanning 24" where the attic is only for storage.

The access on all examples is folding stairs or ceiling scuttles.

The single layer 7/16 has a span limit of 16 inches.

Any difference in IRC code because this area is only for storage?

In other words, is 7/16 OSB ever allowed to span 24 inches when used in storage areas without regular access?

Looking at IRC Table R503.2.1(1) for structural panels used for subfloor underlayment or, or for combination subfloor underlayment, I don't see anything less than 23/32 (3/4 inch) listed for a span of 24 inches.

The thinnest I see listed is 7/16 inch where used as a subfloor on 16 inch O.C. supports ... with "subfloor" being key, not to be used by itself 'as the floor'.

I also don't see any exception to the requirements for "floors" either, not for attic storage.

By the way, 2 layers of 7/16 inch does not meet the code either, not unless I am missing something???

I guess, if an engineer designed it with something less and could back it up with "rational analysis", and signed and sealed it, the local AHJ may (would not have to, but 'may') accept it.

[Richard Stanley]

Too often I find 7/16 sheathing used for equipment access flooring in attices. Also the stamp is facing up that says "this side down" and also it is rated for sheathing - not flooring.

[Jerry Peck]

also it is rated for sheathing - not flooring.

It can be rated for sheathing, at those spans in the span rating, and used for "subflooring" at reduced spans - see the table I referenced.

[Herb Scott]

If there is no evidence that the trusses were cut or modified than it is likely that they were designed for storage. I would put in my report that trusses are generally designed for dead loads only and recommend contacting the builder / truss manufacture to confirm that storage is permissible.
However, the bottom cord of the truss appears to be only 2x4 and even if it is 2x6. This means that under the OSB there will be either inadequate insulation, compressed insulation or (more likely) no insulation.
Lite storage on trusses never bothered me but when it affects the insulation you may be better off renting storage space.

[Bruce King]

Picture shows attic flooring over the garage area.
2x4 lower chord, no insulation.

thanks for all the info guy's!