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Icy basement walls common in new homes

Posted by Curt K. on Sat, Mar 2, 2019

QUESTION -- We moved into our brand new house in October 2006. The basement is not finished, just insulated and has a vapour barrier. Last year, around this time, I noticed small water leaks, in three locations, on my basement floor coming from under the vapour barrier.

You cannot believe my surprise and shock when I opened the vapour barrier and removed the insulation on those leaking locations in my basement. My basement walls were covered in a fairly thick layer of ice and the walls were really wet.

I called the builder, New Home Warranty people and one home inspector in Winnipeg. All three gave me the same answer -- that it is normal in new homes and common in Winnipeg during extremely cold days. I just cannot accept such an explanation. I am very disappointed knowing that we paid over $300,000 for the house and that ice is going to be part of the interior of the house.

I am considering bringing in a contractor and spray-foaming the basement with three-inch-thick foam insulation at a cost of approximately three dollars per square foot. I am not sure if that will help at all. I am also thinking about digging out all the dirt outside my basement, putting a Delta Wrap and then insulating with Styrofoam. That will be very expensive work and the second concern is that my new home warranty might be void if anything goes wrong with my basement in the future. I am also not sure how effective that might be.

I hope you can understand my frustration, especially after the New Home Warranty person told me that he has received hundreds of similar questions in the last month from Winnipeggers. He also told me the building code should be changed to include insulating basements with the Styrofoam from the outside so this problem is remedied. Why do builders still build houses without that type of insulation if this ice problem happens to homeowners all the time?

Your professional advice will be greatly appreciated.

-- Jasmin Ismailovic, e-mail

ANSWER -- It seems to me that this winter I have answered more inquiries than normal regarding newer homes and basement issues. While attempting to maintain a balanced approach to the topics reviewed, there appears to be increasing concerns with these issues. This is particularly true with indoor air quality problems and your question also is in this general area. I have inspected several homes this winter with problems very similar to yours so I thought it timely to review this issue as we prepare for the annual spring thaw.

While it may be very difficult for you to accept, I strongly agree with those individuals you have approached who told you that frost buildup behind insulated basement walls is a very common situation in new homes. I also agree with the New Home Warranty representative that it is a problem with basement insulation methods in new homes in Winnipeg. While I concur with these assessments, it doesn't mean that I agree the problem is necessary or unavoidable. With the risk of offending my friends in the building officials department at city hall, the problem is primarily caused by foundation insulation requirements on new homes in this area.

Because of the current desire to make our homes as energy-efficient as possible, especially with newly built homes, we have created a dilemma with moisture control in the homes. With new houses, these problems are unique due to the nature of the building materials used to construct the dwelling. Most of the components of our wood-frame homes have fairly high moisture contents when installed. This includes not only the wood framing & sheathing materials, but also the concrete in the foundation and basement floor slab as well as the drywall, taping compounds and paint used to finish the inside of the home. Some of this moisture is easily released into the air in the home as materials like paint and drywall compounds dry, but other sources may be more slowly released as the material ages. Concrete is in the latter category and it will typically release moisture gradually, as it cures, for the first couple of years after installation.

Some of the moisture from the foundation curing process will be released to the exterior of the home, above grade, in the warmer months. Unfortunately, this expiration is limited during the cold winter months, when the ground is hard as a rock and the concrete above grade is well below the freezing point. The only area left for the moisture to escape to, at this time of year, is the heated indoor environment -- the basement. If the interior of the foundation is left uncovered, there may be some minor moisture issues, but these are not normally problematic. When we cover this new concrete with highly air-permeable fibreglass insulation and then a plastic air-vapour barrier, we are trapping this water vapour in the insulated wall cavity. Also, there may be some additional moisture inside this wall cavity from the drying of wood framing around the insulation. When the temperature drops low enough outside, this moisture will freeze and change to the ice and frost that you are seeing.

While I have not provided the complete explanation for your problem, the solution to your frost buildup is to remove the polyethylene sheathing and insulation from the entire interior foundation. The foundation concrete should be left uncovered for a minimum of one full year following installation, with frequent window ventilation of the basement in the moderate seasons, before re-insulating. Use of extruded polystyrene or blown-in foam will significantly reduce the chances of the problem reoccurring but will be more costly. Excavation and insulation on the exterior is not a practical solution, but I agree that it may be a superior option for new homes and a practice that will become more common in the future.

Article by Ari Marantz - Ask the Inspector - published in The Winnipeg Free Press March 2, 2008

Topics: home maintenance, pacesetter homes Regina, icy basement walls