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jpsmith 02-02-2009 01:57 PM

Will water lines freeze if placed behind insulated stud wall in basement?

Perhaps someone knows the answer to this. I'm currently finishing my basement. The foundation along the front of the house is completely below grade, except for the last 12". In the back, the top 4' of the foundation is above grade. The water main comes in through the front wall and travels between joists to a tee along the back wall where it branches to feed the bathroom and kitchen above, along with the laundry room and hot water tank in the basement. The hot water line exiting the hot water tank parallels the cold water line to the bathroom and kitchen. Basically, the bulk of my water lines run along that back wall, just below the joists at or slightly below sill height.

With my basement fully open, no interior walls, and no heat, it maintains about 58-60 degrees throughout the winter, even through this very cold January we just had where the temperature was in the single digits nearly every night. There's no risk of my water lines freezing. However, I am worried that I am introducing a risk of them freezing if I finish the basement.

For insulation, I am gluing 1" extruded polystyrene boards the concrete block foundation. Then I am building my 2x4 stud walls about 1" from the blue board, then putting kraft-faced R-13 fiberglass batting between the studs. I have sealed all cracks and gaps along the sill to ensure that no air is penetrating. I am also insulating the band joist with R-13 fiberglass.

Along the wall with the water lines, I will frame the exterior walls about 3" from the block to allow room for the water lines and drains from above to run between the stud walls and the polystyrene board. Once these walls are up, the water lines will be isolated from the main basement area. Might they freeze if they're behind the stud walls, along this above-grade block wall with only 1" of blue board between them and the concrete blocks?


Ron6519 02-02-2009 03:28 PM

I would add pipe insulation to all the pipes and you should be fine. Sealing the rim joist and filling all the open areas you did was very important in keeping the cold temps from the pipes. The pipe insulation is added insurance.

Reilley 02-02-2009 04:35 PM

Using Kraft Faced Batts will create an infamous "double vapour barrier"; the foam being the other. I suggest using unfaced batt insulation and spray foaming any voids in the foam insulation (where it meets the rim joist, floor, etc). So long as your plumbing is inside of the foam it won't freeze as the foam is acting as the vapour/moisture/thermal barrier. Check out this article for more information of basement insulation systems.

Wildie 02-02-2009 04:44 PM

If you live where I live (Ontario, Canada) the answer is yes! They will freeze! No insulation should ever be between the heated area and water lines. Even if the walls have foam insulation!
In south, you'll likely be OK!

jpsmith 02-02-2009 06:34 PM

Thanks for all the replies! I'd read that kraft-faced was OK to use and would not create a double barrier since the kraft-paper allows air/moisture to pass through. If that's not true, I have no problem using unfaced to avoid this. I'm trying to go out of my way to do this right, a large part of which is doing what I can to avoid mold.

Wildie - where in Ontario do you live? If it's Toronto or London, then your weather is somewhat similar to mine in Pittsburgh. If you live in, say, Thunder Bay, then no way. You're way colder.

Before starting the framing, I did make sure to seal up all air gaps in my blue board. I sprayed Great Stuff foam in any large gaps between the panels, taped all the joints with tyvek tape, and I sealed the perimeter - top, sides, and bottom with Great Stuff. I've tried to make sure that no air can get between the blue board and the concrete block.

If I Were to put the top plates of my walls a few inches below the water lines so that the lines sit in the area above the walls & ceiling and below the floor above, will this reduce the chance of the pipes freezing versus having them completely behind the insulated stud walls? I am going to use a low-profile drop ceiling and don't plan to use insulating panels because I don't care if heat escapes from the basement into the floor above.

Scuba_Dave 02-02-2009 06:45 PM

My basement is unheated & stays at 55 or better
There isn't any insulation except around the rim joist
My basement is also underground except the top 12"
The ground below the frost/freeze point stays at 50-55
I would have no problem installing water pipes about 1/2 way up the wall behind the insulation - provided they have pipe insulation on them

What water lines are you running?
Drop ceiling or wallboard?

jpsmith 02-02-2009 08:42 PM

1 Attachment(s)
The attached waterlines.jpg shows my 1/2" water lines along the wall I'm talking about. As you can see, the hot line is already insulated. I did that recently just to conserve energy and have hotter water faster at the taps & shower. It helps. I had to lower the thermostat setting on my hot water tank.

The top three and a half blocks in this wall are above grade. The frost line here is 36" below grade. If I were to place these water lines lower than that, they'd be right down around floor level. I could do that, I guess, but I really don't want to move the water lines... again. You can see in the picture that the copper is new. I just replaced the original 60 year old lines a few weeks ago. They were corroded at the connections and the previous owner had done some bending of the lines instead of using ells, and they weren't soft copper - they had kinks in them!

Having the walls not go all the way to the joists but rather stop a few inches below the water lines wouldn't be a problem for me, because you can sort of see that I'll need to put the ceiling below the valves, the large copper drain line (top center) and the duct work (top right). It will be a drop ceiling. For most of the finished area it will be right up against the joists, using something like a ceiling link system ( In the area of concern here, the ceiling will be dropped about 7" to account for the obstacles - duct work, drain pipes, and the water valves you can see in the picture.

Wildie 02-02-2009 10:32 PM


Originally Posted by jpsmith (Post 223932)
Wildie - where in Ontario do you live? If it's Toronto or London, then your weather is somewhat similar to mine in Pittsburgh. If you live in, say, Thunder Bay, then no way. You're way colder.


I'm about a 1/2 drive from Pt.Huron MI.
The thing to remember is that insulation retards the flow of heat, but it does not stop it! For instance, our homes require a continuous supply of heat to replace what is lost through the insulation! If heat is prevented from reaching your plumbing, its latent heat will eventually bleed away and when it reaches 32F it freezes.
Warmth from your home must be allowed contact the plumbing, and to replace heat lost through the insulation.
Pipe wrap only works for awhile, and if water flow doesn't replace the cold water, the pipes will eventually freeze.
Pipe wrap will delay freezing, but not prevent it!

Scuba_Dave 02-02-2009 10:37 PM

My last house had a crawlspace that was unheated
In addition the floor to the house was insulated
So no heat going to the crawlspace (or very little)
The pipes never froze in the 7 years I lived there

Reilley 02-02-2009 11:24 PM

Being that your basement is nearly completely below grade I doubt you would have freezing issues if the water lines were lower. The part of my basement (cellar, cold zone) which completely-submerged has not dropped below 2C, even during a week or two stretch of -20 to -30 degree Celcius weather. I record the temperature at the outside corner of the walls.

What worries me is that the pipes are very close to the rim joist, which is going to be the coldest spot on that wall.

Keeping it within the foam vapour barrier will prevent them from freezing so long as you insulate your basement header well (cut / seal pieces of foam in each joist bed). Otherwise, you could move your plumbing a bit.

Oh, and as far as I am aware, Kraft Paper is a vapour barrier.

Ron6519 02-03-2009 07:28 AM

I'd replace those shutoffs with ball valves before starting the framing.

jpsmith 02-03-2009 07:30 AM


Originally Posted by Ron6519 (Post 224202)
I'd replace those shutoffs with ball valves before starting the framing.

Why? Is there any benefit apart from being able to open/close the valve more easily?

AllanJ 02-03-2009 06:09 PM

I would omit or cut away insulation "in front of" the pipe while putting insulation as good as possible "behind" the pipe and lining the exterior wall. A suggested insulation free zone might be a triangular section of empty space following the pipe and about as wide at the wall surface as it is deep..

In the picture, you could put 10 inches of insulation up in the joists out to the band joist (rim joist)except less where a pipe sticks up through the edge of the subfloor into an exterior stud wall above. This batt insulation would stick in past the sill plate a few inches in most areas. No wall insulation would cover the pipe where it is attached to the sill plate.

joed 02-03-2009 07:30 PM

No insulation between the pipe and heated area. You need to let heat get to the pipes not insulate them from the heat.

jpsmith 02-04-2009 07:46 AM

1 Attachment(s)
Thanks again to everyone that's helping and offering suggestions. I've made a rudimentary mock-up, seen below. Would the system I've drawn up here allow enough warm air from inside to reach the pipes while keeping enough cold from outside from getting to the pipes to ensure they won't freeze? What I've drawn gives an R23 value to the rim joist area and R10 between the pipes and the concrete block. This should slow heat loss through the foundation wall and rim joist considerably, but will this setup allow enough heat to reach that space so that the temperature there never drops below freezing?

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