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Old 11-01-2009, 02:05 PM   #1
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


Hi,

We've got a 3' deep/wide cantilevered space on our upper level, with hot water baseboard running on the far end (along the entire wall of that living room space), meaning that the hot water pipes drop down into the cantilevered space at the far end of the cantilever. We are starting some (retrofit) insulation work on the concrete-block walls of the tuck-under garage, which is under the living room that has the cantilever (so, one side-wall of the garage is the point from which the cantilever extends out above), and realize that we should try to address the cantilever, if possible, at this point as well. We opened the ceiling drywall of the garage in two places along the wall with the cantilever, and see that 1) there's no blocking above the foundation/garage wall to air seal/insulate from the cantilever... and 2) the cantilever appears to not be properly air sealed or insulated from down-below -- I can feel metal (soffit?) on the bottom, with cold air coming up in places. There's fiberglass in the cantilever cavities, with facing towards the bottom, but as described, it's not air sealed very well.

My question is how to best address the worst of the cantilever situation, in terms of air-sealing and insulation, without tearing out the soffit from outside (which we're not ready to do at this point), and without creating problems with freeze-ups for those pipes at the far end of the cantilever?

My first thought is to add rigid foam sections (sealed w/caulk) above the garage/foundation wall, to act as block between the cantilever space and the rest of the floor/ceiling space. My concern is that that method could pose more problems for the cantilever pipes (if it would be blocking heat from getting out there - which I know isn't energy-efficient, but possibly has been happening thus far, as the garage is heated space (it's on the downstairs loop, which also runs into the downstairs living space - bad layout, I know). Any suggestions on how to (better) insulate/air seal the cantilever from the side (accessing from the garage ceiling, not from below by removing the soffit covering), taking into consideration the pipes out there? I've been warned by more than one plumber to NOT use spray foam insulation right up to the pipes, as it makes it darn near impossible to get to/work on them, if/when needed... so, in my mind that would rule out spraying in foam that way (am I correct in this assumption?). Can I just leave the cantilever as-is for now (w/ fiberglass in there, but poorly air-sealed) and add the foam blocking, and then later address the actual cantilever space (from below by removing the soffit), or is that a bad idea in terms of the cantilever pipes?

[Forgot to mention earlier, but there hasn't been an issue w/ pipes freezing out there -- once, years ago (previous owner), but no problems in the 3+ years we've owned the home.]

Thanks in advance for your feedback/suggestions -- I'm new to this (but learning)!

Katie
Anchorage, AK (currently in the teens!)

NOTE - added photos, showing cantilever from outside, then the opening in garage ceiling showing no blocking (and inadequate fiberglass insulation - not filling entire cavity, and facing down against metal soffit, rather than against the subfloor, which is I think how it should be -- am I correct?)
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?-dsc07503.jpg   How to (retrofit) insulate/air seal cantilever with hot water pipes in it?-dsc07490.jpg   How to (retrofit) insulate/air seal cantilever with hot water pipes in it?-dsc07493.jpg   How to (retrofit) insulate/air seal cantilever with hot water pipes in it?-dsc07502.jpg  


Last edited by KatieAK; 11-03-2009 at 05:32 PM. Reason: adding photos/note
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Old 11-03-2009, 04:03 PM   #2
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


Pipes in cantilevers in Florida are fine. They should never have been put there in Alaska. Open the area, remove the pipes and use closed cell spray foam to seal the space.
Ron

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Old 11-03-2009, 05:17 PM   #3
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


Hi Ron,

Thanks for the response. Yes, I know, the design behind this is hardly logical for the climate, and ideally, we'd be able to do a proper fix by removing them. However, I imagine that rerouting that pipe (I think it's only one) is not an option, as it is for/from the hot water baseboard that runs along the majority of that wall in the living room (the cantilevered space), and there's no other wall to put that baseboard on (the opposite wall already has baseboard, and the far/end wall is short, and mostly taken up by a sliding glass door.

So, assuming we're stuck with the piping being out there, what's the best case scenario for how to insulate around the piping, without making the pipes inaccessible for repair (if needed)? I like the idea of spray foam for its air seal and insulation value in one, but I know we don't want to bury the pipes in that foam.... Is there a way to 'block off' the piping, and spray foam around that blocking? Would that still make the pipes in effect inaccessible though? I've read about a two-fold approach, using spray foam and fiberglass -- spraying a thinner layer of foam just on the top of the cantilever cavity (directly on the subfloor?), and then filling the rest of the cavity with unfaced batt. I'm wondering if that might be worth considering in our situation -- and then putting rigid foam board on to cap off & air seal the bottom (above the metal soffit), as then the batting could be removed for pipe access if need be, and only ~ 1-2" at the top of the cavity would be spray foamed. Any experience with such an approach, anyone?

I'm adding a few photos to the original post now, for some visual help. The current fiberglass in the cavities is facing down, which I'm reading is not correct (supposed to be facing directly against the above subfloor, right?), and clearly it's not filling the full space either, which is bad from an air flow perspective, correct? Clearly it needs 'remediation'....

Thanks much for the feedback,
Katie
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Old 11-03-2009, 07:25 PM   #4
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


You are looking at the pipe problem with an inexperienced eye and discounting a solution based on it.
I would suggest you call in someone who does this for a living. Leaving the pipes where they are will bite you in the kiester one day.
Ron
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Old 11-03-2009, 07:51 PM   #5
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


Yes, I definitely admit I'm not experienced on the plumbing side. We do have a trusted plumber who's worked on the system for years coming out in a few weeks for a different job (moving those pipes out from the garage walls in the photo so we can insulate and sheetrock), so I'll certainly consult with him further then. He is the one who thawed the freeze-up out in the cantilever bay many years ago (prev. owner). Not sure if it was against his suggestion that they left the plumbing out there or not (I'm guessing it was a cost issue that had them leave it where it was).

In the meantime, I'm trying to brainstorm ways that we would be able to at least better air seal/insulate, with the current piping configuration. Any suggestions on that front?

Thanks,
Katie
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Old 11-03-2009, 08:07 PM   #6
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


I would cover the pipes with a pipe insulating sleeve and then seal it in foam. If there's an issue, you can cut through the foam and peel the sleeve away leaving a clean surface to work on. If you leave it where it is, I would insulate it as much as possible. Easy access would not be a concern considering the consequences of a burst pipe.
Ron
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Old 11-04-2009, 12:24 AM   #7
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


Great idea, with the pipe insulation sleeve before spraying in foam. Would you recommend hiring a professional to spray in the foam, or could we use a small rental kit (the total cantilevered space is about 35'x3') for this type of job? One more question -- would we need to install a blocking at the bottom of each cavity before spraying in foam, since it's only metal soffit at the bottom now? Thanks again for your feedback!
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Old 11-04-2009, 08:10 AM   #8
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How to (retrofit) insulate/air seal cantilever with hot water pipes in it?


Quote:
Originally Posted by KatieAK View Post
Great idea, with the pipe insulation sleeve before spraying in foam. Would you recommend hiring a professional to spray in the foam, or could we use a small rental kit (the total cantilevered space is about 35'x3') for this type of job? One more question -- would we need to install a blocking at the bottom of each cavity before spraying in foam, since it's only metal soffit at the bottom now? Thanks again for your feedback!
I don't know what the capacity of the rental foam cannisters are. You would need to speak to someone more familiar with this. The rental place would know, based on what they sell.
What you need to do is based on the structural setup of the house. You would need to post photos to get a worth while opinion. The foam depth is only going to be 3-4" for a closed cell foam. The joists for a 3' cantilever should be 3x12", 12" on center. The blocking might be needed depending on the pipe location.
Ron

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