If you read through our previous post (option #1) and have realized that rigid insulation is not the answer for your basement/crawlspace, then option #2 most likely will be. Rigid board insulation works very well for flat foundation walls (i.e. poured concrete, cinder block, etc), but is not a viable solution for older stone, granite, or even some brick foundation walls. For any non-flat foundation surface, closed cell spray foam is the optimum solution.
Where should Spray Foam Insulation be installed and at what depth?
closed cell spray foam being applied to 2' below grade at 2-3" average depth
In the same location(s) as the Rigid Insulation Board in Option #1 – starting at the top of the foundation wall (or even at the bottom of the basement/crawlspace ceiling as seen in the photo provided) and continued down to 2′ below grade (frost line). Since spray foam is difficult to install at a consistent depth, we like to say at least an average depth of 2-3″.
With this depth you will get high R Value (roughly R6-7 per inch) and an improved moisture barrier. Concrete, stone, brick and masonry all wick moisture, so the application of spray foam will certainly help slow the migration of moisture into your home from the foundation wall. (If your basement/crawlspace has high moisture content you ABSOLUTELY SHOULD manager the moisture level prior to air sealing/insulating your basement, crawlspace, or home)
Why Closed Cell Spray Foam? (vs. open cell)
Open cell spray foam has its place and can be a very cost effective solution, but never within a basement or crawlspace. Unless you live near/on the water, most of the moisture within a home enters from the lowest levels (basement/crawlspace) and travels upwards via stack effect. Ask yourself, do you ever have standing water in your basement/crawlspace? Do you have mold on the base of your foundation wall? Does your basement (or even your home) have a musty smell? Most people will answer yes to at least one of these questions…and this is why you need to use Closed Cell Spray Foam, as it helps block moisture intrusion occurring through the foundation wall. The difference between the two types of foam are as simple as their names. Closed Cell blocks/slows moisture intrusion and Open Cell reacts more like a spunge. Since the last thing you want to do is retain moisture within your home, open cell spray foam should never be used within the basement/crawlspace.
How do I know if my basement/crawlspace moisture level is too high to air seal/insulate properly without first managing the moisture level?
Best to leave this up to the professionals – have an energy audit or at least a consult with a specialist to rule out a bad scenario. Some good rules of thumb:
- if your basement/crawlspace has standing water intermittently throughout the year then you should contact a professional
- if you have exposed dirt floors, moisture management should be done first
- if you are constantly cleaning mold off your foundation walls, moisture management should be done first
- if the ceiling joist nails are rusted, moisture management should be done first
Some moisture management solutions could be…
- Vapor barriers to cover dirt floor
- Mechanical ventilation (i.e Humidex)
- French Drains within your basement/crawlspace
- Exterior drainage or improved grading
- Installation of gutters
