Protecting Glulam Beams from Water
Wunderbar
| Posted in General Questions on
Ive got a few exterior exposed glulam beams and wondering any advice on the best way to protect them. I was thinking id install some drip edge flashing on the top acting as a mini “roof” and roll on a sealer. Or maybe paint on some of that rubber roofing membrane on the top?
Thanks!
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It would help to have a sketch or picture of the beams you want to protect. My first thought is to detail the beams similarly to what you'd do with an exterior header for a deck, but exactly what you want to do very much depends on exactly what you're trying to protect, and how that beam you want to protect is tied into the rest of the structure.
Bill
My 50 year old house has glulams that hold the house up and then run outside and support the deck. They thought tar paper would be a good idea
Not so much
After repairing them I coated the top edge with westsystem, a layer of ice and water, then copper flashing bent down on the sides and end, ice and water, then the deck boards. The ice and water in my case was to try to seal the nail holes
In my case it was also necessary to flash up the wall as water splashed up the wall and would undermine the wall.
Anyway, probably more complicated than what you are facing. If I had beams extending out as an architectural detail I would want metal on top
Thanks, yes its similar to what yours are. They are cantilevered out holding up a balcony deck. im thinking ill treat them and put metal on top
Glulam holding up a roof or overhang sure. Exposed, holding up a deck is a bad idea overall, I would build this as a flat roof with a floating deck over it.
Structural beams are next to impossible to replace without taking your house apart, you want it protected properly.
Remember pressure treated eats aluminum, so copper is king. IF you keep the bends less than 90 then water doesn't run down the face of the beams
Stainless steel sheet also works, and is often cheaper than copper. You can use pretty thin sheet, so no need to get heavy stuff and spend more money. I would use 304 or 316 alloy here.
Bill
Well, finding it in roll easily might make the PITA factor higher than the price of copper
IF you isolate from the PT you might get away with aluminum, but I would not try it
Ive got some extra drip edge flashing from the metal roof that I was going to use, was thinking id just do a strip of tar paper in between any PT and flashing? Any issues with doing that?
You note above that the glulams are cantilevered out, supporting a balcony deck. Are they treated for rot resistance? If not, I would be extremely concerned about long-term safety. That design always fails eventually. If the beams don't rot, they direct water into the wall where it causes problems. I have done it once in my career, on a project designed by others, and I used pressure treated lumber, capped the top with copper, added multiple drip kerfs to keep water from traveling back and I still say it will fail prematurely.
As for a coating, nothing clear will stick around for long. I would paint them.
I agree this is a dumb thing to do but disagree that it is destined to fail
So , 53 year old house, ~400 square feet of deck supported by 1970 glulams.
4x16 of the master is cantilevered
Initial install: 1970 mindless.
The upside?
The glue is waterproof
I removed the top lamination on every single beam with my hands. The rot literally stopped at the glue line.
The beams were sized for twice the span so plenty left to support the deck[yes I did the math]
I am going to say that 40 years of survival with a really piss poor install bodes well for the lifespan of a thoughtful install.
Again, not a good plan to start with, but PT is relatively new and many houses still stand after hundreds of years.
My copper flashing runs several inches up the wall, and is counterflashed. Lowering the deck surface by 1 1/2 inches helped. My deck surface has no exposed fasteners to allow water into the beam. As mentioned the flashing is shaped to prevent water running down the face of the beam
To repeat, probably not what I would have done, but what I was faced with.
Yes, the structural beams are cantilevered out into the elements but there's a large roof overhang that covers the entire balcony. Granted this wont prevent them from seeing some water but its not fully exposed. I could could build out a flat roof with EPDM and a floating deck if that is the best way to go.
If you are at the stage where you can make a different choice, I would do so.
make choices before the siding goes on and doorways installed
Definitely go for the flat roof if you can.
What I have done for this type of install is wrapped the top and sides of the beam in peel and stick and run it up the wall. Floor joist between the beams on joist hangers and tapered sleepers on top before the subfloor. This way the there is a small gap between the beam and the floor so when the EPDM eventually leaks the water won't get trapped and rot the beam.
Watch with peel and stick around EPDM, you only want to use butyl or acrylic adhesive, the mod bitumen ones will turn the rubber into mush if they come in contact.
With most railing hardware, the you need at least two plies on the outside to anchor and these have to be tied back to the beam (ie Simpson DTT). With a flat roof, never put any railing hardware through the membrane, always edge mount with enough gap that you don't need to remove the railing to replace the membrane.
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