It’s been nearly 7 months since my basement was ruined by flooding. I ripped out the wall paneling and furring strips that made up the walls, tore up the vinyl flooring tiles and took out the ceiling panels. I learned the basics of a Home Designer program relatively quickly in order to play around with layouts and embarked upon a journey that has proven to be much more complex and time consuming then I had ever thought…I wanted to know what the proper way was to construct a finished basement.
If one wants to know proper construction techniques you need to go beyond the knowledge of not only most “Do-It-Yourselfers”, but also many contractors as well. It’s a relatively easy field to get into it and not surprisingly many do not know or seem to care about the science and technology of construction. Many stick to the common and well-known techniques that have been around for decades and are accepted as common-place. These are the recommendations you will get from walking into a Home Depot and asking one of the workers. What many people do not appreciate however is that there is actually a on-going research and development to improve existing construction methods. This is called Building Science and is studied at many Colleges across the country. One of the most useful websites for information regarding the latest recommendations can be found at none other then buildingscience.com.
To Vapor Barrier or Not to Vapor Barrier
To illustrate some of the difficulties and confusion in construction here’s my story of what I thought was a simple question - “How should an interior basement wall be constructed?”. Ask 4 ‘experts’ and you may very well get 4 different answers. Such was my experience and I decided I really needed to get to the bottom of this. While science sometimes does not provide conclusive answers, there often is a ‘right’, or at least a ‘best’, answer - it’s just typically mis-understood, mis-applied, or purposely obfuscated.
Basements require careful consideration as they tend to trap moisture laden air. In the summer time the moisture condenses on the colder concrete surfaces. Vapor barriers trap this moisture and can promote mold growth. Even if the vapor barrier is completely air sealed, moisture can wick up though the concrete and get trapped behind the vapor barrier. Fiberglass batt insulation, especially those with the kraft paper facing, can suck up and trap moisture and provide paper-food for mold. The proper way to construct basement walls therefore is by covering the concrete with extruded rigid foam insulation (XPS) who’s purpose is several-fold.
- water comes up and through concrete via capillary action. The XPS insulation serves as a capillary break, limiting the amount of water transported into the basement through the walls and footing.
- It raises the temperature of colder concrete wall, thereby stopping water from condensing on the surface.
- It serves as an air barrier, preventing drafts from entering. All the insulation in the world won’t help if air, laden with moisture, has a way to enter. While less of a concern along the basement walls, this is an important consideration above the foundation walls in the rim joists. Therefore, XPS or a sprayed foam, is recommended all the way up the wall and in the rim joists.
By reducing the possibility of condensation, and allowing the walls to dry if they get wet (the XPS is permeable), unfaced fiberglass batts can often be used as cavity insulation (between the studs) without as much worry. The use of a dehumidifier in combination with ventilation is also a good idea. One can also use paper-free wallboard if mold-growth is still a consideration (if the dehumidifier properly controls humidity then regular wallboard can be used with worry). All these recommendations can be found at buildingscience.com, textbooks on Building Science, numerous technical articles.
The General Contractors
In the last 7 months I’ve had 5 general contractors come to my house to discuss the basement, not to mention water-proofers, concrete cutters, electricians, and plumbers. Here’s what each GC had to say about basement wall construction:
- GC #1: A carpenter by trade, he was a really nice guy and even offered to help me load up a truck with brush while he was there. His idea of a basement wall was to cover it with a vapor barrier, use a double layer of fiberglass batts followed by a second vapor barrier! I’d have 10″ walls, with wood, fiberglass, and paper trapped between two vapor barriers.
- GC #2: This was one of the big guys in town. He did lots of basements, with the standard old approach. Framing with fiberglass batts, followed by a vapor barrier. As an aside I never heard back from him with an estimate until a couple months ago when he send an email saying “wow I really dropped the ball on this and your file got pushed aside - sorry, does your basement still need work?”
- GC #3: The 3rd contractor struck me as very knowledgeable. His specialty was high efficiency homes but not much building going on these days. He was very conscious about proper building techniques and I learned a lot in the 2 hours he was here. Unfortunately, he was never able to make time to do an estimate for me, much less any work. We communicated via email and he seemed to want to work for me (”I like customers like you who understand quality”) but had too much other stuff going on. It was too bad.
I had pretty much decided to go with GC #3 at this point by as time went on it had become apparent it wasn’t going to happen. During this time, sparked by my conversations with GC#3, was when I really started researching building science and educated myself. Eventually, I started the process again, bringing in another two contractors.
- GC #4: This contractor worked in a pair, and they both came. They had done the nursery school in the neighborhood this summer after it was flooded, and worked at the teacher’s home as well. He was highly recommended. They recommended rigid foam insulation and had experience in all types of work. There were a few things that concerned me, such as they wouldn’t bother with foam sill gasket between the concrete and wood (recommended for same reasons as XPS on wall), but that was really a minor issue.
- GC #5: The last contractor I brought in came to my house a few times, was very interested in doing the work, but his methods left a lot to be desired. When I spoke to him about my concerns of moisture and thought rigid foam should be used his response was “this isn’t the right application for rigid foam”. He would use fiberglass insulation with the kraft paper facing. GC#3 had suggested azek board (it’s like a plastic) for baseboard or a wainscotting in case things flooded again and I asked this contractor about it…..he finally gave me a quote using the azek board but also the fiberglass batts. Sticking with the batts completely defeated the purpose of the azek board. Not to mention he was going to put in carpet and said if it ever flooded ALL I would have to do would be rip up the carpet, let it dry, and replace the carpet padding. Hmmm, ok - how about a solution that can tolerate water in the first place??? His estimate of $50K seemed quite high considering he didn’t listen to anything I wanted and it looked like it would be a hack job.
In the last month I’ve brought in GC#4 to do other, related work: new basement windows, some rotting wood and sill in the front of the house, and installation of a active radon mitigation system. I’ve been testing radon myself with an electronic radon sensor over the last several months and found this house had extremely high radon levels (16+ pCi/liter vs the max EPA recommended of 4 pCi/liter). With the radon system the levels have dropped to 1.7 pCi/liter…I just have to live with the pipe going up through closets in my house and a suction fan in the attic.
Someday, hopefully soon, we’ll actually get the basement project underway. I think I still have some more research and planning to do but overall the time spent has been worth it. Contractors are often viewed somewhere between used car salesman and lawyers and it’s definitely worth spending time to find one that you can trust. It’s important to do your homework and ask questions about the things that are important to you.
by matt
@ 3:31 pm. Filed under blog.
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