Wednesday, October 17, 2007

and yet another

Subject: RE: roof connections
Date: 8/29/2007 9:37:13 A.M. Eastern Daylight Time
Reply To:

Mr Koenig, it looks like you have discovered something significant.

There is more literature on connection strength and toe-nailed connections. Split wood reduces the strength of toe-nailed connections. The only way to determine if the connection is adequate if the wood is seriously split, would be strength testing of similarly nailed joints.

While, toe-nails are still allowable in some codes, hurricane prescriptive standards have not allowed them. Straps or clips are more reliable. Screw, if done properly, would be better than nails, but if the wood is split, the best solution would be a wrap around strap. I think you could make an argument for straps as the solution for all split wood connections. Otherwise, it would seem the builder would have to do testing to show adequacy.

How are the main trusses connected to the wall frame. What windspeeds were they designed to? What building code was in effect when the houses were built.

I would try to get the builder to go back and put in clips or straps. Or, if the builder is correct in that toe nails are adequate, and your engineer confirms that to be the case, then perhaps your association could negotiate a cost for them to put in straps instead of screws. That is, the builder will have expense of going back into each house, and if a homeowner wanted to have straps, then the homeowner would only have to pay the incremental cost.

If the code doesn’t allow toe nails in your area, then you have a legal case to get straps put in.

If they used the wrong size nails, that is also a problem.

If the wood is split, I would think you could force them to use straps to ensure the integrity of the joint. Putting screws into split wood may not be adequate.

Other considerations for your association---Do you have impact resistant shutters on your glazed openings. That is something you should consider for your home.

Soffits are another problem these days. Gable vents and other roof vents are also pathways to get water in the house. Windows and doors are very leaky and water intrusion is another common problem.

We hope to update the study you quoted as there has been a lot of research since 2001. We have recently completed a new series of wind tunnel tests that will hopefully be used to improve the loads on roofs within a few years.

Lawrence A. Twisdale, Jr. PhD. PE
Applied Research Associates, Inc.
8540 Colonnade Center Drive
Raleigh, N.C. 27615
Fax 919-582-3401

A March 2002 report written by Dr. Lawrence Twisdale, PhD, PE for the state of Florida entitled Development of Loss Relativities for Wind Resistive Features for Residential Structures states that: (1) hurricane clips have been an industry standard since the mid 1960s; (2) toe nail roof connections shouldn't be used in hurricane-prone areas; and (3) a hurricane clip is more than twice as strong as a three nail toe nail connection. (Pulte's spec calls for two nails). The full report can be downloaded at

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