Indoor Air Quality Project Part 2 - Upgrading Basement Insulation

One of the indoor air quality complaints that we have is now that we've improved the envelope of the house, installed mechanical ventilation (ERV - energy recovery ventilator), and have improved the insulation around all the doors, windows, and attic, we have conditions in the summertime where there is a musty odour when entering the house. I knew we had excessive humidity in the house in the summertime with the air conditioning running - from tracking humidity using a simple digital hygrometer - getting levels up to 60% relative humidity.

Completed Polyurethane Foam Installation in the Basement

Research into this problem led to some findings, some of which have already been corrected:

The third and final issue was in the way our basement walls were constructed 25 years ago - typical for the time - all the perimeter walls of the house were framed with standard 2x4 stud walls, with an air gap between the poured concrete foundation wall and the stud wall. The stud walls were then insulated with fibreglass batts from the top down to 2 feet from the slab, with no insulation at all in the bottom 2 feet of the wall. Instead of a poly vapour barrier, a foil backed paper was installed, but only where there was fibreglass batt insulation. So - there was nothing to prevent humid air from inside the house permeating the drywall or finding its way to the cold concrete foundations through air leakage through the tops of the stud walls which were not sealed, the bottom, or the many apertures for plumbing access, outlets, etc. When I opened up a 2' x 2' section of the basement wall - I found the lack of insulation, and evidence of seasonal moisture accumulation - cobwebs and spiders, efflorescence on the concrete, water stains on the electrical wiring, and a humid, musty odour. 

Inspection Hole in Basement Wall - White dust is from cutting the hole in the drywall. Note the cobwebs, Efflorescence on the Concrete Wall, Construction Debris, and Gap between the Wall and the Slab
Another issue revealed with the inspection hole was that our basement concrete slab was poured with a formed gap of 1 1/2" between the concrete wall. I believe this is referred to as a "floating slab" installation - which is done in cases where there is a concern that the slab may either raise or settle. If the slab is poured directly against the wall - the perimeter of the slab can't rise or fall, and if the slab moves, it may cause cracks. The issue, however, is that this gap was never filled prior to the construction of the perimeter insulated inner wall. Once the gap was cleaned under the inspection port, wet sand was evident in the gap. The construction debris left in this gap seemed to trap the humidity in this area, and this seemed to be the source of our musty odour getting into the rest of the basement, and distributed in the whole house by the central HVAC system.

Top of photo - poured concrete wall. Bottom of photo - base plate for inner wall - pressure treated 2x4. Just above the 2x4 is the poured concrete slab, and the 1 1/2" gap with gravel and damp sand at the bottom. 

Photos of construction debris taken from the space behind the perimeter wall, sitting in the gap between the slab and wall. Note the water stains on the scrap of drywall at the top. Definitely an accumulation of moisture here.
So - we've found our source of moisture, the cause for the moisture, and the probably source of our musty odour. Before getting into the repairs from the inside of the house - it was almost wintertime at this point, and we wanted to rule out poor foundation drainage as a cause of the moisture at the interface between the slab and the footing. So - we called in a drain company to excavate and inspect the foundation footing perimeter french drain. I'll write about that inspection in another post, but the result was that our french drains were clean, dry, and working well. So it was on to the planning for the repair of the basement wall insulation problem, and the gap in the slab.

I researched the best ways to seal the gap in the slab and the wall. Some believe that this gap can serve as a drain - a way for condensation that forms on the cold walls of the basement to trickle down and escape without collecting on the slab and damaging the walls or finishing of the basement. Well - in our case - we don't want the condensation in the first place - we want a clean, dry basement that is properly air conditioned with good air quality. Multiple sources, including the Canada National Research Council (NRC) publications on building construction, advise to repair all sources of water entry into the basement prior to interior finishing or insulation. In my case - I didn't think that I had any cracks or leaks, and I had my foundation drains inspected and found them to be working. So - on to how to seal this crack between the wall and the slab. There are different products available to seal a gap in concrete - there are caulks designed for expansion / construction joints, there are epoxies designed for structural repairs, and there is expanding polyurethane foams designed for waterproofing and non-structural repairs. I sought out the advice of contractors and a civil engineer, and in the end decided that since this gap is not structural, and that the slab may continue to move slightly, a product that had some flexibility and was highly adhesive and would bond to the concrete would be the best fit. Closed cell polyurethane expanding foam was my choice. By the way - if you ever get into this type of situation - I advise you to not only do your own research, but to also consult professionals with appropriate experience. Your building envelope is critically important for the integrity of your dwelling - improper decisions can lead to further problems - moisture, rot, mould, etc. Seek professional assistance. 

Now - as a minimum, I was going to have to open up the bottom of all my basement walls and seal the gap between the slab and the wall with closed cell polyurethane spray foam. I also needed to insulate the bottom 2 feet of the walls where there was no insulation - so an obvious choice was to continue with the closed cell polyurethan spray foam. At this point, it was obvious the best solution was to open up all the basement perimeter walls - and insulate with the same foam. The basement is about 50% finished living space, and 50% storage / mechanical space - extending under the structural slab which is the garage floor. Total basement permimeter wall surface area - approximately 1400 square feet. At this point it's worth mentioning that when you consult the building construction literature - such as NRC "Keeping the Heat In" basement insulation chapter, or Bulding Science Corporation basement insulation - there are many different ways of constructing a basement wall insulation system - which includes insulating the exterior of the foundation wall, and various ways of insulating the inside of the foundation wall - 2x4 walls with mineral wool / fibreglass batt insulation, rigid polystyrene foam insulation, spray polyurethane foam insulation, etc. Again - I recommend highly that if your considering a repair or retrofit, that you consult reputable sources of information, and that you pick an appropriate system with professional advise as required, and implement the complete system carefully. If you or your contractor cut corners here - you may be exposing yourself to potentially significant problems in the future - water problems, condensation, wood rot, mould, etc. Take your time, think it through, get professional assistance. I really don't think this is a place to be cutting corners. 

I pulled together three different contractor / self perform scenarios, consisting of two contractor quotations and a self-perform option where I would hire some demolition and construction labour to help out with me assisting. I finally decided on the third option - and got started on the project about 2 weeks ago. 

We started by removing all the drywall and starting in the storage room, mechanical room under the garage slab. About half the drywall was fairly easy to remove - it wasn't even taped yet. The remainder was taped, and some of it could be saved, some of it couldn't. In a full day - we had exposed the concrete basement walls of about half the perimeter of the house. 

Perimeter wall with gyproc and fibreglass batts removed. 2' of rigid polyurethane foam at the top of the wall, gap between the interior wall and the foundation wall.
At this point - I decided I would try using the Touch-n-Foam closed cell kits to do the 3" minimum foam - so that I could proceed with the project sequentially and move into the living space later. I went out to my local home improvement store, and purchased two of the 600 board feet kits - each kit consists of 2 cylinders (A and B which mix together in the gun) of 45 pounds for each cylinder. So - 2 kits - 180 pounds of foam in the 4 cylinders.


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