Our master bathroom is located over our unheated garage, which means that all of the water supply lines and drains are over the garage also. We live in Rochester, NY, which is known to get chilly now and then. It’s a half-assed design, but it’s surprising the things you don’t notice when you buy a house. The floor joists are 2X10 and the joist cavities are filled with fiberglass batts. The supply pipes are also wrapped with black foam insulation, perhaps an inch thick. It’s all enclosed by 1-inch rigid foam 4X8 sheets and covered with drywall. The pipes have only frozen once when I left the garage door open for several hours on a sub-zero degree day. Nevertheless, I’ve never been happy with the design (not only are the pipes at risk, but the bathroom above is notably colder than the rest of the house).
I’m re-insulating the garage ceiling / bathroom floor with closed-cell polyurethane spray foam, but the supply pipes are an issue. They are located about 3 1/2 inches from the bottom of the joist. Currently the only insulation between them and the garage is the pipe wrap, 3” of fiberglass and 1” of rigid foam. Theoretically they benefit from residual heat loss radiating down from the room above – whatever makes it through the 6” or so of fiberglass above the pipes. If we foam the bottom of the subfloor (3-4” thick) we isolate the pipes from any residual heat from above. Even if we re-wrap the pipes , surround them with fiberglass, and reinstall the foam-board under the drywall I think we’re still a little worse off than before, at least as far as the pipes are concerned. Would we be better to box in the supply pipes with plywood – essentially creating an un-insulated void space between the pipe and the bathroom floor – and spray-foam the space between the bottom of the pipe and the ceiling? Or is the residual heat theory bunk? Are their other options we should consider? Or, since I have full access to the pipes from below should I cut them and shift them up closer to the floor? I’m not a fan of creating new penetrations in my joists, but perhaps I can sister them to compensate. Bottom line is I don’t want frozen pipes but I do want a better insulated bathroom floor (and a stable floor also).
Thanks!
Rob
Replies
No matter what type of isulation you use make sure the pipe is 100% sealed, even a pin hole can cause freezing.
If these are supply pipes, you ought to be able to move them higher up.
When insulating, DON'T wrap the pipes, and DON'T insulate above them -- put all the insulation below them. Build boxes around them (open to the top) if need be, to keep the foam below them.
Hi,
I agree with the comment above that you want as little insulation above the pipe as possible and as much insulation below the pipe as possible.
In rough terms, if the room above is 70F, the garage is 0F (because the door got left open), and you have (say) R3 above the pipes (subfloor + carpet), and R20 below the pipe, then the temperature where the pipe is located in the insulation stackup would be about:
70F - (R3 / (R3 +R20) (70F - 0F) = 70F - 9.1F = 61F.
You can plug in the values that are right for your situation.
So, lots of insulation below, none above the pipe keeps it warm.
Insulating and sealing the garage walls, door, ... will alos help by making the garage run warmer -- as long as you don't leave the garage door open.
I would not rely on the mass of the water in the pipe keeping it warm -- there is just not enough water mass in the pipe to make much difference.
We have the same situation, and the problem for us comes when we leave home for an extended period and want to turn the furnace down as much as possible without freezing the pipes in the garage ceiling. This can be a touchy calc and we guessed wrong on one occasion and had a freeze and leak. I'm trying to work out a way to drain the pipes enough that freezing is not an issue.
Gary
Heat trace and a line voltage thermostat.
Set the stat at 40 F and forget it.
Cost a few cents a month on your electric bill.
Interesting, Dave - say more. Where would I start if I wanted to implement your approach?
Hi,
We turn the main supply faucet off, and open lots of valves, but I don't trust this scheme enough to really turn the furnace down a lot. Just not sure how much water gets left in the pipes even with the faucets open?
It really bugs me to leave the furnace set up at 50F when we go on vacation -- just a big waste of energy and carbon -- would love to hear from anyone who has a good solution.
Gary
It's really not good for the house to let the temp dip much below 50 anyway. Hard on the furniture and woodwork, and in a MT climate you run the risk of having the footing freeze.
But the heat trace tape is a fair option for your situation. Plumbing suppliers should have the stuff.
I'd run PEX fairly close to the floor, but leave space so that if anyone ever nails down underlayment it won't poke a hole in the pipe. Worst case, if PEX freezes it probably will not be damaged.