Challenging the 'Insulation Protects Against Burst Pipes' Theory

[kyphysics]

This has been a debate we've been trying to solve. My dad's house has had a moisture problem in the crawl space and thus insulation (which was compromised by moisture) was removed from there. There is currently no crawl space insulation at all.

I have read online if temps get below freezing for a significant period of time, the lack of crawl space insulation could lead to frozen and burst pipes (from fluids in them expanding when frozen). Numerous articles say this.

Enter local crawl space company X. C-X told me that the crawl space (and thus pipes in there) would actually be warmer w/o the insulation. He said to think about this. That crawl insulation is supposed to keep cool air from moving up and into the home. Floors will be warmer indoors, b/c less heat will be escaping and less will be coming up into them. However, if you remove the insulation, then more heat will escape from inside your home and into the crawl space. That heat WARMS the crawl, he said. He said to walk outside on any given winter day. Feel the air temperature. He said any crawl space will be 20 degrees warmer than the outside air, because of heat from the home (including HVAC ducts) escaping into them. He said he's been doing homebuilding work since he was 11 years old, as his father was a housing contractor and he learned as a kid that crawl spaces are always about 20 degrees warmer than the outside air. Thus, he argued that:

a.) having no crawl insulation would actually make it warmer in there and make pipes LESS likely to freeze/burst;
b.) one should not worry about sub-32 degree F weather outside, because the crawl temp will likely be in the 50's. He said if the weather got into the teens (say, 15-degrees F) for an extended time, then, yes, worry at that point.

His argument actually sounds logical, but I wonder if it has scientific merit? Is there anything flawed in this thinking?

 

[Rive]

I think it'll depend on where the pipes are installed. Seen them either in- and outside of the (supposed) insulation.

 

[jrmichler]

My dad's house has had a moisture problem in the crawl space and thus insulation (which was compromised by moisture) was removed from there. There is currently no crawl space insulation at all.

I have read online if temps get below freezing for a significant period of time, the lack of crawl space insulation could lead to frozen and burst pipes (from fluids in them expanding when frozen). Numerous articles say this.

Clearly, you are in a moderate climate that rarely gets far below freezing. In such a climate, most people can get away with an uninsulated crawl space. Your post implies that the insulation was under the floor. If so, the purpose is to keep the floor warm when the crawl space is cold. Your reference to moisture implies that the crawl space has a dirt floor with no vapor barrier, and possibly is ventilated to the outside.

If all of that is true, then that is a classic recipe for mold, rot, and frozen pipes. There are two ways to eliminate these problems:

1) A fully ventilated crawl space. The house is on pilings, and open all around. Any pipes are insulated with heating tape. Outside air freely circulates through the crawl space, so no moisture buildup. And the pipes do not freeze as long as the heating tape is turned on and working.

2) An insulated crawl space with vapor barrier. The walls are air sealed and insulated. The floor has a vapor barrier. The crawl space is then inside the house thermal envelope, and has the same temperature and moisture as the house. No rot, no mold, and no frozen pipes.

I live in a Northern Wisconsin climate that is much colder than yours. Today is a typical January day, and my morning run was at a pleasant -12 deg F. My crawl space has four inches of foam insulation on the outside of the walls, four inches under the footings, and four inches under the floor. It has a vapor barrier under the floor foam. The crawl space is warm and dry, so no mold, no rot, and no danger of pipes freezing.

There is a lot of good published information on crawl space design for various climates at BuildingScience.com: https://buildingscience.com/documen...field_doc_document_type=All&items_per_page=50.

 

[kyphysics]

I think it'll depend on where the pipes are installed. Seen them either in- and outside of the (supposed) insulation.

Insulation (prior to removal) never touched the pipes, but was still very close to it. The pipes "sat" below the insulation mostly. So, they (I'm guessing) provided little to no pipe insulation value (if Company X guy was correct).

I could imagine pipes sitting very close to subfloor and be surrounded by crawl space insulation. In that case, yes, I could see the insulation protecting them a bit more.

 

[kyphysics]

Clearly, you are in a moderate climate that rarely gets far below freezing. In such a climate, most people can get away with an uninsulated crawl space. Your post implies that the insulation was under the floor. If so, the purpose is to keep the floor warm when the crawl space is cold. Your reference to moisture implies that the crawl space has a dirt floor with no vapor barrier, and possibly is ventilated to the outside.

If all of that is true, then that is a classic recipe for mold, rot, and frozen pipes.

He's got automatic vents (open and close automatically based on outside temperatures).

Yes, Virginia rarely gets sustained freezing temps, but this winter (2023-2024) has been unusually cold and we'll get into the teens this week.

Yes, I'm talking about crawl space insulation (under the house floor). Of course, there is indoor insulation in between wall cavities too.

No, there is not a dirty floor, as there is a vapor barrier. But, yes, the automatic vents do vent to the outside. The allows airflow in and prevents the build up of dangerous gasses (VOCs) and radon. The moisture issue has other causes, such as a sloped backyard where water intrudes into the back side of the home's crawl space and pools/puddles after heavy rains. He's got to get that fixed and we're working on it (finding a company to reslope the yard).

 

[BillTre]

Optimal approaches will vary with the details of your set-up.

Is the perimeter of your crawl space enclosed or open?
Ours is enclosed with a cement will with openings for ventilation. We put pieces of styrofoam sheet in the ventilation opening to retain house heat which leaks through the floors into the crawl space. This will tend to keep the pipe from freezing.

Insulation only prevents heat from transferring from hot to cold so quickly.
Insulation between the pipes and floors above will reduce the amount of heat the pipes will get from the house.
I have pipe insulation on hot water pipes to prevent heat losses from the hot water heater to the point of use.

It won't heat the pipes, just retain more heat that is already in there.

in a couple of places, I have some plug in heater tapes wrapped around exposed pipes with a thermostatic control that only turns on near freezing (its a product in hardware stores). This is like an electric blanket.

 

[jrmichler]

No, there is not a dirty floor, as there is a vapor barrier. But, yes, the automatic vents do vent to the outside. The allows airflow in and prevents the build up of dangerous gasses (VOCs) and radon.

A properly installed vapor barrier is also a radon barrier. Where are the VOC's coming from? Is the house built on a toxic waste dump?

Vents to the outside bring in warm humid air, and Virginia certainly gets its share of that. That warm air hits the cool crawl space, the moisture condenses out, and the result is mold and rot. PLEASE start reading those BuildingScience.com crawl space documents.

The moisture issue has other causes, such as a sloped backyard where water intrudes into the back side of the home's crawl space and pools/puddles after heavy rains. He's got to get that fixed and we're working on it (finding a company to reslope the yard).

+1000 to getting the yard sloping away from the house. Puddles in the crawl space are absolutely, completely not acceptable.

 

[MarkSch]

Living in Alaska for 32 years gives one a certain amount of practical experience with the issue surrounding building envelopes and frost points. Your contractor is correct in that pulling the insulation out of the floor will increase heat flow/loss into the crawlspace, but if the crawlspace is not insulated and actively venting, you are most likely "heating the outdoors" and driving up the heating bill. Temperature monitoring/alarming might be of use.

One solution I have used is to on nights where the temperature in the crawl space is below freezing, make sure that the hot and cold taps that are supplied through the crawl space are cracked so that there's a steady slow drip to keep a small flow of water moving through the pipes. I have kept plumbing intact on multiple occasions down to about 0 F.

Alternatively temperature monitoring and a heat source can keep things from freezing. The pipe insulation suggested above in my experience without a heat source such as heat tape is only for the higher end of the freezing temp range.

Years ago while on vacation my oil tank ran out of heating oil during a -20 spell. I came home to every single piece of pluming burst due to the amazing powers of expansion of water in it's solid phase. Even the toilet exploded.

 

[dlgoff]

A solution I used once was to put an electric space heater in the crawlspace. May not apply in your case though.

 

[jrmichler]

It was -12 deg F outside yesterday morning at about 9:00, and colder before that. My house was 71 deg, and the crawlspace 67 deg. The only heat source in the crawlspace is from uninsulated heating ducts. Insulated crawlspaces (Post #3) are nice, and so are the resulting warm floors.

 

[dlgoff]

It was -12 deg F outside yesterday morning at about 9:00

Sounds like what it's been around here. It's 12 deg F here in Kansas at 4:30 pm. It's forecast to be -7 deg F Friday.

edit: now they are forecasting -11 deg F Friday.