Glulam Beam Rotting from the Inside Out?? 6

[UTvoler]

Hello friends and experts!
A water park facility that I do some consulting work for has some issues with rot in a few glulam beams. The building structure is glulam framing with a transparent panel roof. The beams in question are horizonal girt members located in the eave of the roof, ~16-ft above finish floor. It's a water park, so obviously serious humidity/moisture/chemical issues in general inside the facility. This particular area is located behind a large duct sock, there are no eave vents, and so very stagnant air/little to no air movement.

The roof panels are fastened to the glulam with stainless steel lag bolts, and the interesting thing is that the rot appears to have started internally at the lags. No signs of leaks from the roof, and just a few inches away from the rotted areas the moisture in the wood reads ~6%.

My best guess is the some form of condensation at the lags concentrating moisture in the wood? Recommendation is probably to replace in kind, but not sure on how to address the root cause of the issue.

Any thoughts on cause?

 

[dik]

PWF, in these environs, has added preservative necessitating the incisions.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ChorasDen]

dik, we understand that, such is the nature of treating either Western Hemlock of Douglas Fir. These wood species require incision to increase the (very limited) amount of preservative treatment that these species are able to retain. Southern Pine, available all over the south and eastern part of the U.S., does not require incision, and is not incised prior to treatment. This is due to the shape and structure of the wood cells and how they accept and bind to copper based wood treatments. I image that AWPA and FPL have lots of literature discussing how the structure of Southern Pine differs from western species to allow this to occur.

 

[lexpatrie]

There's NO incising on the wood. C'mon.

NO. NOT all treated wood has incising.

If it isn't incised, it's either a) not DF (or other refractory species) and has a pressure preservative treatment (like southern Pine) that's not got a lot of color to it, or it's AC2 which doesn't have a lot of color to it. Or it's not preservative treated (my vote).

I'd wonder when it was built, but for this to have PPT I'd be surprised. Aluminum and Stainless don't exactly agree on the galvanic chart, but you need water. I think it is water causing the problem, the "bolt" is where the rot appears to be concentrated, but I'm not fully sold it's chlorine related or not. I'd expect corrosion if it were chlorine related. I don't quite see that here.

And yes, the "Chlorine" smell is Chloramines. Usually produced via reaction with uric acid which is in sweat, as well as other sources.

While there seems to be some condensation occurring, it appears limited to water staining of the wood.

Here's what I see - the skylight has an aluminum edge angle that traps any water (as condensation), it looks like there's debris/corrosion there (top photo), admittedly aluminum doesn't "corrode" like that. I wonder if there's a more modern edge treatment that doesn't accumulate/trap water and what looks like blocking underneath it needs to be replaced. Various metal compatibility should be considered in the replacement, but it doesn't look like it's getting wet enough to actually corrode like that. Unless the screws are dramatically corroded, you can't really see from the photo.

 

[WKTaylor]

Recommend submitting this issue to the APA as a question... they seem to be a resource with expertise... and/or maybe this would present a opportunity for study of Your phenomena.

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BTW... Your photo of rotted wood and a 'lag bolt threaded-end' visible. lexpatrie (Structural)13 May 24 16:47

Weird... the photo seems to show a bolt with H28 coarse threads and a relatively 'flat-tip'... typically fastened with a washer/nut... NOT the wood-lag-bolt with pointed-tip on the thread-ends and sharp-piercing widely spaced wood-screw threads I expected to see, thus...

Regards, Wil Taylor
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