No, this is not a post about wool socks (though goodness knows I love ‘em). This is about an odd bit of house anatomy that many times get forgotten in the insulating operation. People at this point are very familiar with insulating attics, walls, around windows and so on, but if you live in an older home (and Chez Siberia has two flavors of older: the original part of the house built in 1939 and the newer part of the house, added in 1987), one place that is often forgotten is the sill.
Yes, my little wombats, the sill. This is the big piece of wood that is put on top of, and is connected to, the foundation of the house and is the starting place for building the house (hopefully your home has a foundation of poured cement or cement block but if you live in a REALLY older home, it could be laid up stone, in which case, you have a whole different issue to deal with and you might want to check out “This Old House”, and the old house forums on the internet). The floor joists of the first floor are attached right to the sill and the subfloor and the finish flooring are attached to the floor joists.
But, Aunt Toby is getting a bit ahead of myself. To return to the sill. The sill is one of those places where the chances of cold air leaking in and the warm air escaping out are quite good; the top of the foundation is never, ever flat and smooth and the sill plate (or the timber) itself is not perfectly flat and smooth either. So there are all sorts of little cracks, crevices, etc. for there to be air exchange. In an older home, you cannot completely eradicate those little holes (unless you somehow find every single one of them and spray the living daylights out of them with that closed cell spray-in foam which has its own set of issues which we are not going to go into here), so you have to do your very best to seal them off.
Today, we are going to discuss and the DH will demonstrate how to insulate the sill in our back basement (the ‘new/old’ part of the house), using two-inch foam board. This part of the house has been cold since the day we finished the addition for the following reasons:
First: the furnace, although big enough theoretically to handle to extra space, is in the opposite corner of the ‘old/old’ part of the house in the basement and the duct runs have to go all the way across the house, through the basement wall and all the way across the ‘new/old’ basement to the floor registers before warm air from the furnace can go up into the dining room upstairs. Since there is a basement wall separating the new and old parts of the basement, there is this physical barrier to any of the heat in the old part of the basement coming into the new part of the basement.
Second: Since the duct run is going through this new basement, which is in effect, unheated, the duct is exposed to the relatively cooler (and in some cases, much colder) air of the new basement, so it is very easy for the warm air in the duct to be chilled inside the duct before it can even get to the floor register upstairs. We solved a good bit of that issue by insulating the duct work with big fiber glass bats and duct tape.
This project has actually been going on for a while. Last year, the DH and our son put two layers of foam board in between the floor joists (that is, if you were standing in the new basement and looked up, you would not see the wooden subfloor because it would be hidden by the insulating board) and started the process of insulating the sill in that part of the basement. The goal for this holiday season, when the DH has some time off, is to get the rest of the sill in that part of the basement insulated. He is also planning to do some insulating on the sills in the front, old, part of the basement, using a different technique, which will be the next post.
For the moment, however, we will be discussing and showing you how we did the blue foam board. For this operation, here’s a list of what the DH used:
2″ foam board insulation – this is something that you can find literally at your local hardware store or lumber yard.
small serated knife
Roll of household aluminum foil
Step One: Measuring
Step Two: Cutting
Step Three: Installing