Making penetrations in a spray foam roof
mackzully
| Posted in Energy, Heating & Insulation on
My roof will be spray foamed (closed-cell), but I’m wondering how hard is it go back and make penetrations in the roof for such things as suntubes, DWV pipes, etc. in the foam. The issue is that I’d like to get the roof foamed in asap, but I’ll certainly not have all the penetrations to the roof finished before the foaming, and I’ve gotten a number of different responses from foamers about doing this. Is it enough to simply cut away the foam with a drywall knife, install the suntube (for example), then seal back around the tube with Touch’n’Foam?
Thanks,
Z
Replies
Mackzully,
Why not just frame in for the things you think you will install later and have the foamers skip those portions. Then you can temporarily insulate with FG. Later when you do install your sun tubes and vents you can go back with some cans of great stuff to fill in around.
The alternative is similar to what you said; you must cut out with a knife...not a utility knife though, a long boning knife is usually a good choice. For pipes, the standard is to sharpen a piece of PVC and twist it through the foam.
Carving through foam is not difficult but can be frustrating, and it is much easier to just plan ahead.
gk
The foam is pretty easy to cut thru. I'm in the south and they only spray about 3" of CC for our climate.
I would just use a 12" sawzall blade from the roof to open up your tunnel access. Take out just 1 piece if possible, rather then smaller chunks. Can foam after install.
If you do install your sun tunnel 1st make sure it's masked off. Even though mine was hanging down 60" they still shot a load of foam up into it. Took 4 hrs to clean--still had the protective wrap on it.
I have to add a water heater vent when my elec. heater craps out. I added gas piping on the remodel and I felt it was easy enough to add later then plan ahead.
Seems to be one issue is getting a good seal around the penetration after the fact. If you use a different product to seal with, I can imagine the possibility of some (probably minor) complications of incompatibilities. Plus perhaps a difficulty reaching some areas.
If you know the locations where you will have vent pipes, etc. why not install them first? You don't have to have the entire DWV system in place to install a vent stub.
mackzully,
That's exactly what I did with my SIP's (which are foam panels with osb on either side) put them in place and then when I get to the mechanical parts I take a long sawzall blade an make as good a cut as I can Once in place I use canned foam to reseal the area.. Normal flashing will provide the water barrier you need.
Thanks all for your recommendations. I think I'll be trying to get as much done before they foam, but the tubular skylights I've picked (10" ODL severe weather model with a spun seamless aluminum flashing) aren't curb mounted, so I'm not sure boxing out will be best for them. Also, being with my work schedule as it is, who the heck knows when I'll get all 6 of them installed, so I might as well enjoy the insulation for as long as possible...Thanks again!
Z
There seems to be some confusion here.You said "roof" All the other replies seemed oriented to this being an insulation job.There is a polyurethene roof material also. could you clear up which you are talking about?
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Piffin-Apologies, I meant I'm having the underside of my roof deck sprayed with closed cell foam. Not having a foam roof installed ;)Z
easy answer then. Cut the hole with the sawzall, then foam from a can around the projection.But watch clearances with any combustion appliance flues!
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Thanks! That's kinda what I thought, but I figure those of you out there will know better and more than any salesdroid I talk to.As for combustibles, the only thing I'll be running hot through the roof will be my dryer vent. Anyone have any preferences for flat roof dryer vent caps? I can't seem to find any...Thanks,
Z
I have never run a dryer vent through a roof.One reason is that you will find a lot of moisture condensing in the flue tha ay and running back down in until it finds a place to look like a roof leak
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Hmm... How would that be different than a regular dryer vent run where the vent runs up a wall then across the ceiling to an an outside wall vent? Don't you get moisture build up in that configuration as well? Especially if the vent is in unconditioned space?Z
That horizontal run across top of ceiling would be pitched down to the outside so condensate drains OUT of the house instead of back down into it. The initial run vertial from dryer is warm enough to not see much cooling/condensation.It is where it gets near exterior that it suddenly cools and vapour turns to water.To be honest, almost every run Ihave ever done went down and under flor then out or straight through the wall and out
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I have never run a dryer vent through a roof.
We did something even worse by giving in to running a dryer vent up from the basement through an exterior 2x5 wall, then through the roof. In fall weather it has condensing problems and I hate to think about the winter.
It was a tough spot since any decent venting location was to be covered with a wrap around deck or exited over a cement sidewalk, both not good places because of ice buildup on the walking surfaces.
I don't know what the fix would be, perhaps a water seperator plumbed to a condensate pump and seamless duct as in a condensing furnace exhaust? Ever heard of such a thing?
Cheers
Beer was created so carpenters wouldn't rule the world.
Not yet!;)
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Dang
Beer was created so carpenters wouldn't rule the world.
There are condensing dryers that don't need to be exhausted. We have the Bosch one, and it seems to work fine. We just drain it into the washing machine drain.
I would ask the guys doing the installation.
The can products are made for insulation rather than for waterproofing. The mix for roofs is denser and probably has UV inhibitors.
You probably could use it and coat over with a polyurethane caulk then paint, but I'd bet my eyeteeth that the same distributor for the product you are buying has a patching filler available that is compatible
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!