You know there is a lot of pressure out there to replace windows. The home owner complains of old drafty windows, curtains blowing etc. So of course the first thought is to replace the units. This can cost $10,000 or more. Don't get me wrong, windows are a tool for increases performance, comfort and efficiency. But lets take a look at what you are actually paying for. There are 2 things I have as an issue with the capital improvement;
1 what is the increased performance you get for the cost comparison
2 Installation issues
First and for most we are all aware of the “R” value of insulation. Often we think of is as R-19 for walls in Mid Atlantic area, or R-38 for ceilings. But what is the R value of that window? First they are valued in different unit of measure, the “U factor” Most windows in the Mid Atlantic are some ware around U 0.30. to convert this to an R value, you divide 1 by the u value. So 1 divided 0.3 equalsis an “R”value of 3.33. Not to great of a” R” value is it? When considering a standard wooden single pane window which has a default value of U 0.55, this in turn is an R of 1.18. So if for $250 for that Home Depot windows you are increasing the effective R value by 2-3 points, that is a steep investment not worth making. The return on that investment, if you can get a manufacturer to admit it, is often 15 years or more! Close to the 20-25 year life of the unit. Often homeowners f
ind themselves in a situation of pending $10,000 on windows and not seeing an increase in performance.
Second, is the installation. usually when a new window is installed they remove the existing sash and leave the existing side jamb of the unit. Then instal the new unit inside of the old window jamb. That connection is usually OK, make sure they caulk and seal it though. The problem is the space between the old existing window jamb and rough framing. In most cases that has NO insulation or at best under-performing insulation. This is were the real leaks are and are hardly ever dealt with. A tube of caulk can go the distance in sealing this area. Better yet if you are painting after this is to pull the trim and seal the space with Window spray foam in a can.
So unless there is a direct functional problem with the windows I would not direct a homeowner to replace all the windows. Instead, if draftiness is the issue, a much greater percent of their complaints can be dealt with by guided air sealing with a blower door and thermal camera. The cost of air sealing and added insulation is often $2000-$4000, with a much greater reduction on drafts than windows alone. When comparing the costs of windows vs. air sealing and insulation it is not a fair comparison, windows do not score well. After air sealing is performed, yes the new windows would be a great addition but definitely NOT the first course of action in reducing draftiness!