insulating pipes

[RobRing]

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

[cacher_chick]

Residual heat loss is most effective based on the fact that heat RISES. Your bathroom might gain heat from the hot water piping in the floor below, but the piping is benefiting very little from the heat above, especially given the insulation.

4" of extruded polystyrene attached to the bottom of the joists would give you R-20 between the garage and the bath. It is also possible to cut the insulation to fit between the joists under the piping, but it is much harder to get an airtight seal even when taping all the joints. Depending on the direction of the joists in relation to the piping (and your needed ceiling height), you might chose this method only in the area of the pipes. Individual joist spaces insulated from below can also be kept warmer by ducting air from the existing heating system.

Do your homework on the building code regarding the firewall between the garage ceiling and living spaces. Most areas require one, and some TWO layers of 5/8" drywall.

[Lightwave]

There's a load of ways to tackle this:

1. Insulate the garage and heat it to just above freezing with a dedicated heating system.

2. Install heat tape on the pipes.

3. Install a thermostatically controlled circulator system with a heat exchanger to warm the cold line.

[jastori]

I would definitely not leave any insulation between the pipes and the floor above. Routing the pipes closer to the floor would help, but it obviously more work. Keep in mind that drilling small holes in joists for supply lines is not going to hurt, so long as it is done properly (as close as possible to the center of the joist). A 1" hole in the center of a 10" joist will have practically no impact on the joist strength. You do want to avoid notching the joists and drilling close to the top / bottom. Given how few problems you have had so far, I would personally not be worried about the pipes freezing if you are able to bring them up close to the floor, and insulate well underneath. The best way to make the bathroom really comfortable would be to install some in-floor radiant heat while you are at it.

The idea that "heat rises" is not really correct. It is true that warm air rises with respect to cooler air, but there are other forms of heat transfer that have nothing to do with "rising" (i.e. conduction and radiation).

[RobRing]

10-4 on the radiant heat - it's just been installed.

[Gary Swart]

You will appreciate the heated garage in the winter! I have an overhead Reznor NG heater in my garage/shop that is normally set at the lowest setting on the thermostat, about 50 degrees. While the car will not be actually "warm" on cold winter mornings, it is far better than 20 or ??. Also, if I want to work in the shop, it takes just minutes to bring the temperature up to 65 or 70. Stored paint and etc. don't freeze.

[export!]

I have the exact same setup in my detached garage. I couldn't find a thermostat to hold the temp as low as I wanted (I keep it around 40). My easy solution was to mount a simple mercury thermostat to the wall with one screw and tilt it to get my desired temp. Once I "calibrated" it with the garage thermometer I drew a line on the wall.

I love not worrying about paints, caulking, glues, pressure washer, pool filter, etc freezing.