H-clips - required?

[psiposs]

Steep roof, 2 foot on center rafters. No H-clips on OSB. Are they required for new construction (in WA)?

[Jeffery L. Haynes]

Either clips or block it.

[lfoster]

There is usually stamping on the interior side that state if sheathing should allow for expansion. Most I have seen say 1/8 inch on the 8 foot side.

[James F. McKee]

how thick is the osb?

[psiposs]

Not able to see the thickness of the OSB. Did not see or look for any notation about spacing etc.

[psiposs]

If its thick it may not require H-clips?

[dhelm]

In Washington, most OSB roof decking is 7/16 and requires H clips midway between trusses/rafters if 24 inch OC spacing (and most are 24 inch)

[Chuck Evans]

I think it is generally up to the manufacturers. APA "recommends" 1/8 inch expansion gap at all edges unless mfr states otherwise. Also tongue and groove or panel clips where required.

If the are not present and I reference the APA recommendation and let the builder try to demonstrate that the mfr says it's not required.

[Joe Funderburk, CMI]

IRC 2009 (and 2006) Table R503.2.1.1(1) gives the maximum spans for roof sheathing based on:

1) the thickness of the sheathing.
2) whether or not the sheathing has clips.
3) live and total loads

OSB/plywood is allowed to span 60" maximum with clips (7/8” thick sheathing) and 48” maximum without clips (7/8” thick sheathing).

3/8" is the thinnest that can span 24 inches with clips.
7/16" is the thinnest that can span 24 inches without clips.

In summary, 7/16" wood structural panels can span 24 inches without clips (live load <= 40 lbs/sf & total load <= 50 lbs/sf).

Note: 7/16" live load increases to <= 100 lbs/sf at 16" spans.

[Nick Gromicko]

http://www.nachi.org/h-clips.htm

[Bruce A. King]

Many code inspectors will not allow 7/16 OSB with "24 inch" span unless clips are used. Its just too spongy and weak. Actually, trusses that are 24 on center leave a 22.5 inch sheathing span but it's referred to as "24 inch" usually.

I never see 24 inch without clips unless they just missed a few here and there.

I did find a 32 inch span the other day using 7/16 OSB with clips that the builder is digging for answers on now. Since the OSB has a 24/16 rating I don't see how it can be right even if their engineer signs off on it.

I found a lot of discussion online where builders say 7/16 is too weak even with 24 inch span and clips. Its funny how you can find the good builders online discussing things but the code minimum ones are scarce. Same with inspectors too, most of my competition is not participating on here.

[Joe Funderburk, CMI]

Bruce, if the live load maximum for 7/16 at 24" OC is 40 lbs/sf, how could anyone but a child walk on it? Seems like there could be no walking whatsoever on such a roof.

Anyone know how the weight of a person is distributed on a roof? For example, how is the weight of a 200 lb man distributed on a roof per sq. ft?

Where do they come up with 40 lbs/sf max on live loads? Wouldn't that necessarily prohibit anyone from ever re-roofing the structure?

[Bruce A. King]

It gets into "durations", short duration vs long duration.

Good question, needs more research.

[Kenton H. Shepard, CMI]

H-clips are an architects or engineer's call, not a code requirement.

7/16" OSB very commonly spans rafters 24" on center without clips. Not required by most residential codes unless your area has special requirements.

Don't call missing clips a defect unless you know for a fact that they were required when the home was built. Don't recommend that they be retrofit. It's cost prohibitive. If you think the sheathing is over-spanned, recommend evaluation by an engineer.

When clips are installed every 24", the roof sheathing panels are touching every 24". I have seen OSB and plywood with clips installed buckle at the clips after panels swelled with moisture. Spaces between panels are typically created by tacking 8d nails above the last course before installing the subsequent course. The tacked nails are pulled after sheathing is nailed.

[Joe Funderburk, CMI]

Originally Posted by kshepard

H-clips are an architects or engineer's call, not a code requirement.

7/16" OSB very commonly spans rafters 24" on center without clips. Not required by most residential codes unless your area has special requirements.

Kenton, I beg to differ. It most certainly IS a code requirement. See: IRC 2009 (and 2006) Table R503.2.1.1(1). How can you say it isn't a code requirement when it clearly specifies the need for end supports (clips being the most commonly used method) in the IRC???

Anyone installing 7/16" OSB or plywood on 24 inch spans without end supports (clips) is in violation of "commonly accepted building standards" (the IRC) unless your jurisdiction has chosen to exclude that requirement by law.