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KatieAK 10-25-2009 09:03 PM

insulating heated garage(retrofit)- polyiso placement & keeping pipes from freezing?

We've got an attached, heated garage (hot water baseboard) that is currently uninsulated -- bare concrete block walls on the 3 walls not adjacent to house. Two of those walls are above grade, and the third is mostly below grade (except the far front upper corner). The original plan was to use rigid foam (polyiso) affixed to the interior of the concrete block, then furring strips (1x3s?), then sheetrock (for fire code). However, we've got some questions/issues, that I'm hoping we can get feedback on -- first related to the insulation type and placement, and then regarding the plumbing (if/how to work around, prevent freeze-ups, etc.).

Regarding Insulation:
- Is there polyiso foam board that is fire rated so as to not need (sheetrock) covering? I've read as much, but would like to know brands and availability. We need a 20 minute fire barrier on those walls I believe, per local code (in Anchorage, AK). I don't believe such a product is offered locally, so if anyone has ordering info., that'd be great.
- What's the best way to affix the polyiso to the (age 1969) concrete block, and the furring strips to the polyiso? I'm thinking some combo of Liquid Nails and screws/nails, but my husband is nervous about nailing/screwing into the older block, since it's the foundation and could be brittle (and we wouldn't be able to line up with mortar, realistically). Any suggestions? We're new to this, obviously.... :)
- Admitting that I'm still learning about the properties of heat loss, air sealing, insulating, etc., I am looking for guidance in how to place the foam board. In one resource, I read that floor to ceiling continuous foam board as a first layer is ideal to prevent thermal bridging. ( Elsewhere, I read that due to the wall needing to adjust to moisture exposure, leaving a 6 inch gap in the foam board at the bottom of the wall can help prevent moisture problems. ( We currently have baseboard units attached to what looks like a 2x4 along parts of two of the walls we need to insulate (with 3/4" copper piping running vertically up those walls in three places - see questions/concerns in next section of post). We'd like to minimize disruption/relocation of that plumbing, so the idea of leaving a 6" gap in the board would benefit us that way... but it seems that doing so would be allowing the cold to just exit the wall in that location (apologies if I'm totally off here - but I thought the idea was to close any/all gaps - maybe I'm getting mixed up with air sealing). In my mind, I could see the logic in leaving the 6" gap on the below grade wall (as it doesn't have chance to release moisture to the outside except for front corner), but that on the two above grade walls covering with polyiso from floor to ceiling would be best (it's painted concrete on the exterior - so may be able to release moisture that way?). Any suggestions/feedback?

Regarding plumbing:
- As I wrote above, the garage hot water baseboard units are on the two side walls (one above and one below grade), currently attached to the concrete by a 2x4. There are 3 vertical 3/4" copper pipes that run up along those walls that we are trying to work around, along with a horizontal pipe along one corner as it exits the living space and connects to the baseboard unit on that side. We'd like to not have to relocate those pipes, but rather, are trying to figure out if we can get some polyiso behind them, and then also wrap the pipes to provide additional insulation. However, due to lack of space behind the pipes, we wouldn't be able to put the full amount of polyiso behind (we're going to be shooting for R14 on the above grade and R10 on the below grade walls). We'd be sheetrocking over this then (assuming we don't find a fire-rated polyiso that doesn't need covering).
- In a cold winter climate like Anchorage (with temps often around or even below zero), how much insulation should we aim for behind the pipes (between the pipes and these exterior concrete walls), to avoid freeze-ups? I figure we *may* be able to get an inch (~R5) of polyiso behind the pipes in their current placement, then maybe foam wrap insulation around the pipes (trying to get the thicker stuff). I talked to one plumber up here recently who didn't think that plan would be a problem (re: freezing), but I'm hesitant to put the pipes behind the sheetrock (cut off from warmer garage air) without a whole lot of insulation behind it. So far we haven't had problems with freezing out there (except for when the circ. pump went bad during a really cold snap - so understandable), but that's with the pipes exposed to the warmer inside air (between 40-50 degrees in there normally). Any ideas/suggestions?

Thanks much for your assistance (and sorry for the long post),

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