Most windows that you buy today have a nailing flange that goes all the way around the window. This allows for easy installation with little to no need for extra caulking flashing or other such extra steps. In other words, installing windows properly is easy. However, you may notice that there is a great deal of trim on the inside of your windows and they always feel drafty and there always seems to be condensation in the winter time. Why is that?
The air movement you feel in front of your windows usually is not air moving through them if they are newer. That air movement is what is referred to as the “convective loop”. This loop is the product of the cold temperature outside convecting through the glass and meeting the warm air of the house. This is the same way wind is formed. Warm air from the ground rises up into the atmosphere meeting with the cooler air in the sky. Anytime you have the meeting two different temperatures, you will get air movement and the beginnings of condensation. The amount of wind and condensation depends on how drastically different the two temperatures are when they meet.
This is a product of the glass convecting the cold temperature through it to meet the warm temperature inside. Condensation, if severe enough can be the cause of mold, wood rot and ruin your windows and cause serious health problems in a very short amount of time.
There are very few manufacturers that make windows installable in the correct fashion, but actually Any window can be installed to minimize, if not eliminate, this issue.
First, remove the window and nail a 2×4 flush with the inside of the original framing. The new window you order will be the size of the opening between the 2×4’s. It will come standard with a nailing flange all the way around the window.
Now nail the window into place by centering it in the opening, making sure that there are shims under the sill, and the window is plumb and level.
You will notice that instead of an extension of the jamb being needed on the inside, there is some space on the outside to cover. You can use cedar or have a local gutter contractor bend you some cap made out of extruded aluminum coil stock. Make sure you caulk the outside and seal the window inside with fiberglass stuffed around the edges, or window/door can foam. Simply Move the window trim to cover the new jamb and paint the drywall where the trim used to be.
You will notice that the window does not condensate anymore and there is not air moving around the window. It must be the window right? Actually no.
By moving the window to the inside of the frame, it is directed closer to the warm side of the heating envelope. Because of this warm house temperatures are more prevalent and the warm air convects outside and forms the convective loop on the outside of the house. If there is condensation that forms, it will be on the exterior where the air can properly dry it and take it back into the atmosphere.
This method will not lower your energy bills and will not have any other effects other than removing the convective loop to the exterior of your home and eliminating moisture issues on your windows. There are many other methods of controlling window moisture. For most details on moisture control methods, see my article on HRV units and other Home Tips.