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How did the attic get cold enough to burst a water pipe?

travisbuildsit | Posted in General Questions on

Need help for a friend with a multi-faceted problem here.

1. Home is located in Frisco, Texas (suburb of Dallas)

2. Large home with an unconditioned attic. Continuous soffit vent + ridge vent. 

3. A mix of insulation — walls and ceilings have open cell spray foam (~2″). But at least some of the ceiling penetrations aren’t sealed. A return register near the spot where the pipe burst is not sealed. There’s a mix of fiberglass batts and blown-in cellulose (~ 6″).

4. This house was built in 2005, not long after the city of Frisco mandated fire suppression systems be installed for homes over 5,000 square feet.

5. In the section of the attic where the pipe burst, there’s a 1′ x 2′ void where one of the flue pipes for one of the fireplaces is visible — which could be a path for the cold air. This section of the house is on the northeast corner of the property.

6. In a nearby attic space (though it’s 10′ up and 10′ over), there’s another large void 6′ x 3′ between two brick chimneys. That area is exposed to an uninsulated outside wall that faces west. 

7. During a recent hard freeze, with temps below 20 degrees for multiple days, a pipe in the fire suppression system burst when the outside temp was around 10 degrees. The homeowner was monitoring temperature with a Wyze device and said the temperature in the attic got to 10 degrees as well.

1. How did the attic get that cold? And is that preventable? (As a reference, I monitor the temperatures in my attics, and I never got to freezing during that weather).

2. Is insulating the pipes in the fire suppression system the answer? I don’t know much about these systems, but I read that anti-freeze can be added to them to prevent this.

3. This would be a costly project, but it seems the best best would be to suck out all the old insulation, insulate all water pipes going through the attic, air seal all penetrations into living spaces, blow in cellulose insulation to R-49.

Help! 🙂

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  1. Expert Member
    PETER G ENGLE PE | | #1

    This is the sort of thing that is hard to make specific recommendations without an in-person visit. It is somewhat common for "insulated" attics to not really be insulated because of holes and voids. It sounds like you have identified several. I've even seen attic where the rafters were spray foamed to make the attic "conditioned," but the gable and roof vents were left open because the attic "needed to breathe." Attics don't breathe; people do. If the attic is approaching the outdoor temperature, then it is not a conditioned attic. Whatever insulation is on the roof is doing nothing, most likely because of air leakage. This is a common cause of freezing of water pipes in the attic. Yes, the attic pipes can use antifreeze but it is messy and rally hard to clean up if/when there is a fire or problem with the plumbing. A local fire equipment company could provide information and estimates. If the attic is supposed to be sealed and conditioned, then seal and condition it for real. No more freezing issues. Be aware that if there is combustion equipment in the attic, it may require makeup air. If so, a dedicated air supply can work. Insulating the pipes will probably not work. Insulation will slow down the freezing process but not eliminate it. If the low temperatures are only for a few hours, this may be enough, but when the cold lasts for days the pipes can/will still freeze. I hope some of this helps, but I think you will need to find a local building consultant who can look at the house as a system and recommend the best course of action.

    1. travisbuildsit | | #2

      Thanks for the reply Peter. To clarify -- there is no foam on the rafters or roof deck. This is an unconditioned attic.

      My approach would be to suck out all the old insulation, air seal all sealing penetrations, seal problematic areas like voids by the chimneys, insulate attic access points, and blow in adequate insulation.

      My only pause is this fire suppression system. Once all the current insulation is gone, we could insulate the water pipes for the fire suppression system, and then they would end up getting buried in the new cellulose as well.

      I talked to local fire department and they suggested staying away from the antifreeze. They said that another option to protect the pipes is to install a "dry system" -- where there's no water in the pipes but there's some kind of compressor connected to the system that quickly fills the pipes with water when it's time.

      Two main issues are
      1. Protecting the pipes from freezing
      2. Air sealing and insulating the attic

      The thing that surprised me is how cold the attic got. As I said, I have a vented, unconditioned attic as well and my attic got to maybe 34 degrees at the lowest.

  2. walta100 | | #3

    I have to say are you really surprised the idea of a vented attic is that the attic is more or less the same temp as the outdoors.

    The more you air seal and insulate the cooler the attic will get.

    Solution 1 Is to move the sprinkler system into the conditioned space.
    Solution 2 is to enlarge the conditioned space and move the conditioned space around the sprinkler system. By removing the old insulation, sealing the soffit/ ridge vents and spray foaming the roof.
    Solution 3 Is common in commercial sprinklers. An air compressor keeps the pipes full of dry air 24-7 -365 so they do not freeze. Only when the system is activated do the pipes fill with water and put out the fire.

    As silly as sprinklers in a vented attic is 2 inches of open cell spray foam as the only attic insulation is even dumber! If true that is R7 where the code min is R30 23% of the requirement. what were they thinking?


  3. Expert Member
    BILL WICHERS | | #4

    You said this is an "unconditioned attic", which means it should be open to the outside air by way of vents, usually a combination of soffit vents at the eaves, and a ridge vent up at the ridge on the roof. Natural convection will draw air in through the soffit vents, and exhaust warm (relatively) air out the ridge vent. All the insulation would be on the attic floor in this case. This is what we commonly refer to as a "vented attic", and it SHOULD be very near outdoor ambient temperatures.

    Since an unconditioned attic is, by definition, unconditioned space, sensitive things like water pipes should NOT be run there. You could run the pipe down near the drywall, with the insulation "burying" the pipe, but in that case you need to ensure there are no gaps in the insulation that would expose the pipe.

    Remember that a fire suppression system typically has no water flow, it's just stagnant, waiting for a fire to break out to pop off one of the sprinkler head valves (which activate mechanically when high temperature is sensed). Since the water in those pipes isn't ever moving, those pipes are MORE susceptible to freezing. I would make sure to fill in any gaps in the insulation as a first step.

    In the commercial world where I normally work, we have what is called a "dry pipe preaction" fire suppression system we can use. These systems normally have all the pipes pressurized with air by a small air compressor that runs as needed. When a fire breaks out, a sprinkler head will pop off normally, bleeding out the air quickly, which triggers a central diaphram valve to open and flood the system. These type systems are pretty commonly used in large datacenter and telecom facilities, since they avoid the potential issue of water leaks. In your case, these systems would prevent issues from freezing too. You might look into such a system here if you can't reroute those pipes.


  4. canada_deck | | #5

    Pipe insulation is effective when you want to maintain the temperature of running water in a pipe. E.g. If you don't want the hot water from your hot water tank to lose too much temperature by the time it reaches your tap. It doesn't make as much sense in the context of a pipe with stagnant water. In this case, you want as little insulation as possible between the bottom of the pipe and the ceiling (so that heat from the house is reaching the pipe) but as much insulation as possible between the top of the pipe and the outside.

    Think of it like this:
    If the air inside the house at the ceiling is 70 F and the air in the unconditioned attic is 10F then you need to be sure that there is more insulation above the pipe than below the pipe to keep it above freezing. Of course, it's probably a little worse than that since you may have air movement through the insulation whereas you should have very little air movement below (through the drywall.)

    I'm in Canada and unfortunately had to run two short sections of pipe in my attic. I built a little wooden box (five sides, open on the bottom) that I was able to put over the pipes. So the pipes are running on top of the drywall - with no insulation between the pipe and the inside of the house - and are enclosed in this box. Then I buried the box in a ton of insulation on top.

    The basic principle is to just have as little insulation as possible between the pipe and the heated space and as much insulation as possible between the pipe and the cold air.

  5. Expert Member
    PETER G ENGLE PE | | #6

    The OP also asks why his unconditioned attic only got down to about 34F when the subject house was much closer to the outdoor freezing temperatures. Generally, this means that he's losing a lot of house heat to his attic - more than the vent system can remove. He would probably benefit from the same air sealing and reinsulation project that he suggests for the subject house. A well insulated and vented attic should run within about 5-10 degrees of the outdoor temperature, at least at night or other times when there is no solar loading.

  6. Expert Member
    DCcontrarian | | #7

    Where are the pipes located relative to the insulation? They need to be on the warm side of the insulation. Depending on the size of the joists and the size of the pipes sometimes you can run them through the joists with the insulation above. Sometimes you have to run them below the joists in a soffit or dropped ceiling. The easiest thing is to run them over the joists, but if you do that you have to put all of the insulation above them.

    Insulating the pipes themselves doesn't really help.

    1. Expert Member
      MALCOLM TAYLOR | | #8


      "Insulating the pipes themselves doesn't really help."

      You should get that printed as a sign and post it on all the rural noticeboards out our way. It's very common to see waterlines run along the ground, wrapped in batts and a layer of poly.

      1. Expert Member
        DCcontrarian | | #9

        If there's flow in the water it might help a little, slow the loss of heat enough to keep it from freezing overnight. And insulation and a heat tape is a pretty common stopgap solution for places where it doesn't get too cold too often. But a sprinkler pipe, where you hope there's never flow, isn't going to be helped by insulation.

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