Undersized purlin bracing in older homes?

I come across these T&G boards used for purlin bracing and collar ties in attics, especially in retirement homes built in the 70’s. Is there a standard for purlin bracing size? For some reason I think I saw 2x4 minimum. I called these out as undersized because there was some minor sagging of the roof in this area, though the whole rafter structure had these installed. Same with the collar ties. It also looks like the purlin braces are incorrectly tied to the ceiling joists?

In older homes, it matters more what is working than anything else. The problem I have with the above photo is purlins and purlin bracing typically match the size of the rafter. The bracing is smaller which is ok if it is a 2x4. Also, the bracing (strut) does not appear to be attached to the purlin but rather directly attached to the rafter which is odd. I think collar ties are ok if they are 1x4 or larger.

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Agreed, it seems incorrectly installed and I called it out as such. The purlin is 2x8 and the rafters are 2x6, so I guess it’s ok as long as it’s at least as big? The collar ties are (3/4) 1" thick, more like T&G wood siding board, as I’ve seen in a few places around this age.

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It will work out. Undersized or unconventional materials used as collar ties and purlin bracing with some roof sagging observed. That should do it.

And no, I do not think oversized purlins is a problem.

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R802.4.5 Purlins

Installation of purlins to reduce the span of rafters is permitted as shown in Figure R802.4.5. Purlins shall be sized not less than the required size of the rafters that they support. Purlins shall be continuous and shall be supported by 2-inch by 4-inch (51 mm by 102 mm) braces installed to bearing walls at a slope not less than 45 degrees (0.79 rad) from the horizontal. The braces shall be spaced not more than 4 feet (1219 mm) on center and the unbraced length of braces shall not exceed 8 feet (2438 mm).

R802.4.6 Collar Ties

Where collar ties are used to connect opposing rafters, they shall be located in the upper third of the attic space and fastened in accordance with Table R602.3(1). Collar ties shall be not less than 1 inch by 4 inches (25 mm × 102 mm) nominal, spaced not more than 4 feet (1220 mm) on center. Ridge straps in accordance with Table R602.3(1) shall be permitted to replace collar ties.

A 1" board is 3/4" so the t&g board is fine.


Ahh…good thinkin’ :wink:

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Ok, that’s what I thought I remembered reading. I did think about the T&G thickness after I typed that last response. Thanks!

This is what matters - Is is performing as intended? I let a lot of “minor” stuff go but it all depends on your comfort level and what you see. We’re not there to redesign the roof framing the way we would do it. We’re there to observe and report if it’s working. If it’s not, write it up and stand behind it.


I am confused. What purlins?
I see struts secured to ceiling joists with an conventual beam strut layout under rafters.

Looks ok to me…

I see 1x roof bracing elements all the time. They sure look floppy, but they’re on homes that have stood for 100 years and are doing fine.
And if there’s an effective truss element involved, know if it’s a tension or compression element.

I’d focus on any sagging, not the cause.