Don't neglect insulating the basement
Over the last 30 years, I’ve probably done well over 500 energy audits for our members. Sometimes I wish I’d kept an exact count, but I realize it’s not how many that’s important but rather what has been learned from these opportunities. As each home is a system on to itself, it is impossible to neatly classify the issues that have been found into nice little categories. There are is one however that seems to standout very frequently -- improperly insulated or uninsulated basements and crawlspaces.
There seems to be a common belief that “unheated” basements don’t need to be insulated. Even with no heat registers in them, uninsulated basements are a wasted heat loss on the home. The issue is the second law of thermodynamics which says that heat moves from high temperature regions to low temperature regions and never the reverse.
Many homeowners and builders believe that heat rises therefore basements and crawlspaces don’t need insulated. The truth is, warm air rises, not heat. Because warm air is lighter and less dense than cooler air, it does rise. Going back to the second law of thermodynamics, all heat knows is temperature differential. It moves from the warmer area to a cooler area, regardless of direction. Not a believer? Don’t try this, but what would happen if you grabbed hold of a metal pipe and someone put a torch to it 12 inches above your hand? Think it might get a little too warm to hold on to? It definitely will as heat moves from the warm to the cool! The same thing happens to your basement.
How much heat (btu’s) flows out the basement walls (or any other part of the house for that matter) depends on two things, the temperature differential and the resistance (R value) to heat flow of the material involved. We know in the dead of winter what the temperature differential is on a cold winter’s night, so let’s focus on the R-value involved.
An eight inch concrete wall has an R-value of .88, the same as a single pane piece of glass! Ever felt a concrete wall in the middle of winter? Going back to the second law of thermodynamics we learned heat moves from the warm to the cold so you realize a cold concrete wall is not cold coming in, it’s heat moving out so fast the air inside can’t overcome the heat loss to warm it. In essence, cold is the absence of heat.
Above the foundation, there is wood framing referred to as the sill, the 2 x that is perpendicular to the end of the floor joists and is actually one and a half inches thick. Soft wood has an R-value of 1.25 per inch, so the 2 x has an R-value of 1.88, somewhat better than the concrete, but not much better.
Above that is the floor. Plywood and OSB sheathing has an R-value of .94 for ¾ inch material. Add the carpet to it with R-1.23 with a rubber pad or R-2.08 with a fibrous pad. With the air between the floor and the basement/crawlspace providing an R-value of 1.0, there is a total R-value between the living space and the outside of 4.90 (with the fibrous pad).
The International Energy Conservation Code of 2009 (IECC 2009) which was recently adopted by the State of Illinois for communities and counties with a building permit process calls for basements and crawlspaces in our region to have an R-10 insulation value. This is actually the R-value of the insulation material applied to the foundation, not the whole wall R-value. In other words, if we include the concrete, floor and carpet, we would have nearly an R-15 level of insulation.
That’s how much insulation is needed, but how do we insulate to achieve that R 10? Before you start throwing insulation on the wall, be aware there is a dark side to insulation -- moisture related problems. A cold surface is created when you insulate as you have the flow of heat. If there is a high enough level of water vapor present or that can get to the cold surface, you get condensation. If the surface is wood or carbon based, mold, mildew and/or decay can set in. The key to insulating basements and crawlspaces is to recognize this, use the right products and do a quality job. First of all, no vapor barrier should be used in any wall below grade. This way if moisture should happen to get into the wall it can dry to the inside of the home.
There are a couple of ways to insulate that are recognized by building science as methods that will not create problems. One is to use 2 inch extruded polystyrene (commonly called blue or pink board). If the wall area is straight and smooth, it can be glued directly to the concrete. In the sill area, it should be cut tight and then edges sealed with caulk to prevent moisture migration. If you wish to finish the walls later on, you will have to build a frame wall in front of the insulation board.
The blue/pink board can also be held in place with metal “Z” channels that are fastened to the wall. As a sheet of foam board is put up, a Z channel is fastened to the wall, locking the foam board in place. Sheet rock can be fastened to the Z channel with drywall screws for a finished wall surface.
Fiberglass or cellulose insulation may also be used in a wood frame wall as long as no vapor barrier is installed and the wall is finished. I recommend not putting fiberglass batts in the sill area as fiberglass does allow air to move through it. If the air contains water vapor, it could cause condensation to occur wood sill.
Another insulating material that works is sprayed foam called Icynene. Icynene is an open cell foam that is excellent for sill areas and crawlspace walls where it can be applied quickly with little regard for its expanded, irregular shape.
According to the IECC 2009, code, “as an alternative to insulating floors over crawl spaces, crawl space walls shall be permitted to be insulated when the crawl space is not vented to the outside. Crawl space wall insulation shall be permanently fastened to the wall and extend downward from the floor to the finished grade level and then vertically and/or horizontally for at least an additional 24 inches. Exposed earth in unvented crawl space foundations shall be covered with a continuous Class I vapor retarder. All joints of the vapor retarder shall overlap by 6 inches and be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches up the stem wall and shall be attached to the stem wall.”
The key to insulation of crawlspaces is the Class I vapor retarder (6 mil polyethylene – commonly called visqueen). Without a vapor retarder, water vapor from the soil can condense on cold air conditioning ducts and water lines. Additionally, water vapor will permeate into the living area above, potentially causing air quality concerns.
Unfortunately, most basements and crawlspaces tend to be the “out of sight, out mind” places we don’t want to face up to. Keeping them out of mind though, does not reduce the amount of energy they cause our homes to consume in the winter. Only by putting them in the forefront and insulating and air-sealing them properly can we really put them in the back of our mind and rest comfortably knowing we have reduced our energy needs and done it in a manner that will not harm the occupants or the home.
