When windows are replaced, there are usually two alternatives. The simplest way that is the least expensive and fastest is to leave the old window frames in place. Just remove the sashes and the glass, slip a new window inside the old frame, and clad the old frame with aluminum. Clear Creek Windows almost always uses the other method. Typically, we completely remove the old frame and go back to bare studs. Then we use self-adhesive membrane flashing on the rough stud opening and install a brand new window.
There are several reasons for this.
A.) Comfort and energy efficiency
Consider this comment from a customer....
When we bought our home, one of the original windows had already been replaced in one bedroom. The new window had been inserted within the old window frame. When we decided to replace the rest of the windows, Peter suggested that we remove the old frames entirely, and go back to the bare studs. Thank you! The new windows you supplied are very bright, tight and draught-free. The other window is draughty in comparison, has less glass area, and that room is now the coldest in the house. CK, Kingston
The old window frames were never sealed to modern workmanship standards. Leaving the old frames in place fails to fix this “source of draught and air infiltration”. As one experienced window practitioner expressed it.... “what farmer would only fence 80% of his field?”
B.) Size of window
If the old window frame is left in place, the new window is approximately 2” smaller around the entire perimeter. Removing 2” from the entire perimeter of a window can make the glass area, on a % basis, significantly smaller. Hence, the room is not as bright and cheerful as it could be.
C.) Exterior appearance
When a new window frame is inserted inside an old window frame, the cumulative effect is to make the “total frame” of the window appear much heavier than it should be in a house of that age. This noticeably detracts from the exterior appearance. Similarly, there is an extra line of caulking on the exterior (between the new window frame and the cladding covering the old window frame) – a source of a “dirty grey line” a few years hence as the caulking surface “picks up dirt” over the years.
D.) Weather-tightness and building durability
The principle enemy to long-term durability of a building is the weather-tightness of the exterior building envelope. Inserting a new window frame inside an old window frame doubles the amount of exterior “joints” that have to be kept in a weather-proof state of repair.