Structural Engineering: RE: Reattaching a subpurlin to a diaphragm

I would recommend you have the roof surveyed with one of those "moisture detectors" (sorry, I don't know proper terminology - but they can detect moisture below the roof membrane). If there is a lot of moisture, then there is little choice as to the next step.

Bob Garner, S.E.

From: FSRahbar@aol.com [mailto:FSRahbar@aol.com]
Sent: Friday, July 10, 2009 10:42 AM
To: seaint@seaint.org
Subject: Re: Reattaching a subpurlin to a diaphragm

I agree with S.Macie. If the moisture damaged the hanger, it would most likely damage the plywood as well.

Farzin S. Rahbar, SE
David C. Weiss Structural Engineer & Associates, Inc.
(818) 227-8040 Ex. 13 Fax: (818) 227-8041

In a message dated 7/10/2009 10:38:06 A.M. Pacific Daylight Time, ECVAl3@aol.com writes:

Clips & Screws (1/2" long) might work but, if there was a leak, It might be prudent to open the roofing to inspect for further damage to the plywood or the framing members.

S.Macie, P.E.

In a message dated 7/10/2009 10:33:03 A.M. Pacific Daylight Time, rhkratzse@aol.com writes:

Does the subpurlin "figure" without composite action with the sheathing? If it does, would gluing (purely for lateral restraint) be adequate for a single purlin repair?

Ralph

Sent from my iPhone 3G

On Jul 10, 2009, at 10:19 AM, "Bill Allen" <t.w.allen@cox.net> wrote:

I am looking at some roof repairs (yeah, I've finally made the "Big Time") at a commercial structure. It is a typical panelized roof with 2X4 sub purlins spaced at 24" spanning 8'-0". These sub purlins are attached to the purlins with FN hangers. Somewhere along the line, moisture got between the roofing membrane and the insulation foil which allowed corrosion to attack the FN hangers. Recently, one sub-purlin failed. Fortunately, no one was in the space at the time.

The question I have is regarding the attachment of the replacement sub purlin to the existing roof diaphragm. Of course, the owner would rather not remove the existing roofing to re-nail from above. However, considering that the diaphragm is probably only 1/2" thick, I really don't see any other way. Some of the sub purlins are attached at the panel edge some are not but the only way to know that is to remove the roofing.

Does anyone have any ideas?

TIA,

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
V (949) 248-8588 • F(949) 209-2509

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