Purlin Brace/Strut

[Ian Page]

Am I correct in my belief that purlin braces/struts should be no more that 4' on center and notched (and nailed) to accommodate the rafter spanning purlins? Also can an additional length of lumber, face nailed to the brace and directly under the purlin to effect a 'bearing point, ' take the place of notching?

[chris mcintyre]

Am I correct in my belief that purlin braces/struts should be no more that 4' on center and notched (and nailed) to accommodate the rafter spanning purlins?


Ian, I think you are asking about purlins running perpendicular to the rafters for attaching roof decking? If so I am not aware of any requirement for notching and the spacing is determined by the manufacture of what is being applied, with metal roofing it can be anywhere from 2' up to......




....with 16

” coverage and ribs spaced

8


” apart give this long span, concealed fastener,

standing seam panel a unique style that lends
itself to a wide variety of applications. It can be
used to span purlins spaced up to 7’ apart,....




If you are asking about bracing in an attic I am not sure what California code would be, but the IRC (R802.5.1) says that the braces for the purlin can not be more than 4' apart....no notching required.

[matt faust]

Ian - Good Question.

See IRC R802.5.1

1. Purlins shall be no smaller than the size of the rafters they support.
2. Purlins shall be continuous.
3. Shall be supported by 2"x4" braces - installed to bearing walls
at a slope not less than 45 degrees - from horizontal.
4. Braces spaced not more than 4 feet on center.
5. Unbraced length length of braces shall not exceed 8 ft.

This system is for the original roof - adding tile would totally change the
load and render this system inadequate.

mf.:cool:

[matt faust]

Ian...

Regarding the notching or two piece system.
Both are common in my experience, and I was a framer for 30 years.
Just make sure if it's 2 pieces that they are nailed together well.

With purlin systems look for
1. Lack of purlin bracing.
2. If missing note that there my not have been a bearing wall close enough,
then look for rafter ties as an option.
3. Braces with an angle more severe than 45 degrees.
4. Purlin bracing and collar ties removed to install attic heating systems.
5. And of course, don't forget ridge and hip supports too.
It's very common to see the missing.

mf.:cool:

[David Garton]

Ian, I believe Matt pretty much covered it all, at least this is what I remember to be true when I use to do it

[Ian Page]

Thank you guys - special kudos to Matt - that was exactly what I was looking for. My inspection yesterday dealt with exactly this issue, particularly with regard to the lack of bearing walls for support. The ensuing Mickey Mouse attempt to support the purlin, resulted in any meaningful bracing being 10' and 12' apart. The lack of which, IMO allowed the purlin to twist away from the rafter. I'm not sure if it was original construction or not (1978 duplex), though it looked like it. It's hard to fathom that the roof framing would have passed original inspection with this support system (or lack therof). More recently a new roof - composition in place of original cedar shake and OSB decking - had been installed. The purlins/braces could have been installed at that time, but not likely as this was just one of about 250 units in a complex, all with similar replacement roofs. Fortunately the roof itself (2x6 rafters with no rafter or collar ties) showed little evidence of bowing or sagging but time will tell. Clients advised to seek Structural Engineer's review. Again, many thanks all.

[Scott Patterson]

Thank you guys - special kudos to Matt - that was exactly what I was looking for. My inspection yesterday dealt with exactly this issue, particularly with regard to the lack of bearing walls for support. The ensuing Mickey Mouse attempt to support the purlin, resulted in any meaningful bracing being 10' and 12' apart. The lack of which, IMO allowed the purlin to twist away from the rafter. I'm not sure if it was original construction or not (1978 duplex), though it looked like it. It's hard to fathom that the roof framing would have passed original inspection with this support system (or lack therof). More recently a new roof - composition in place of original cedar shake and OSB decking - had been installed. The purlins/braces could have been installed at that time, but not likely as this was just one of about 250 units in a complex, all with similar replacement roofs. Fortunately the roof itself (2x6 rafters with no rafter or collar ties) showed little evidence of bowing or sagging but time will tell. Clients advised to seek Structural Engineer's review. Again, many thanks all.

With a home built in 1978 I think it has stood the test of time! ;)

[matt faust]

Ian..........

Just a comment on your recommendation for review by a structural engineer.

As Scott mentioned - seems to have stood the test of time.
I find middle ground between yourself and Scott's comment.

In my practice t4h comment would read something like this.

As viewed from the attic, roof framing consists of 2X6 common rafters, purlin
bracing, and continuous OSB sheeting throughout.

CONCERNS
A. Purlin bracing is over spanned without the benefit of typical supporting struts
at approved intervals.
B. Purling bracing has twisted over time and is not in contact with rafters.
C. Rafter ties - have not been utilized as an alternative to purling bracing,
where applicable.
However, no deflection of the common roof rafters was noted at the time of the inspection.
For further expert evaluation of the roof framing consult a qualified, state licensed
professional in the applicable field, prior to the end of the escrow inspection period.

mf.:cool:

[Ian Page]

Matt
Fortunately(?) the prospective purchaser, who is somewhat familiar with construction was present during the inspection. I was able to physically show him and explain my concerns but also explained the lack of any adverse effects to the roofing as a whole (at this time only). My, 'S.E. review' was paraphrased for posting purposes. I fully agree with your advise and comments, however.

Probably, like yourself, I have been on numerous roofs with more bracing and found them to bounce like trampolines. This one showed little effect of the minimally supported rafters. Perhaps a testament to the lumber used at that time, certainly not the workmanship. Again, many thanks.

ip