Go to the dealer who will be providing the windows (eitehr directly to you or to your contractor). Ask them for a factory installation instructions. (don't worry, it's not a book but a short pamphlet). Look it over and become familiar with the recommended installation.

Other than the support for the bow being structurally strong enough, the simgle most important factor is the use of window tape, (Vicor or some other brand). This must be installed per instructions, overlapping like roof shingles. In addition, the contractor may use silicone to make sure there are no gaps for water to seep in. A great percentage of window problems that leak water is not the window but how it was installed.

If it is new construction or you have all the siding off, absolutely use a house wrap like Tyvek, again following instructions.

Lastly, the window must be installed level and plumb then shimmed (top at both sides and at the check rail for DH. The shim should be snug but not forced in. This is critical on DH windows. You want the sashes to slide up and down without being too loose or too tight. Shimming is critidal here.

If you see the contractor putting the windows in and just nailing the nailing fins without first checking level and shimming, you will have trouble. This could be especially troublesom if he takes the sashes out to reduct weight and installs the window frames in the same manner by just nailing the fins without leveling, shimming.

Thanks a ton!