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Personal: Residential


Fenestration Products –
Importance of Installation

A knowledgeable professional should install windows, doors and skylights according to the manufacturer's instructions. A poorly installed product may not operate properly and could cause drafts even though the product itself is energy efficient. Poor installation may also allow water to leak into the home, leading to costly damage.

Here are some installation guidelines:

  • The installation should provide an airtight, insulated seal.
  • After installation, the window or door should retain its original shape and be level (plumb) from side to side and top to bottom. Windows may be installed on an angle (for example, in an attic) only if they are designed to do so.
  • A window or door should not support any load other than its own weight.
  • Any exterior finishing, such as flashing, should prevent water penetration.
  • A skylight should be well sealed where it meets the roofing material, and any tunnel up to the skylight – such as a tubular daylighting device – should be well insulated.

There are two types of installation for replacement windows and doors:

Complete tear out:

This involves removal of the old window, door or skylight, including the frame. Because the installer can make a completely airtight insulated seal between the product and the rough opening, this type of installation is normally recommended. The original door opening or window glass area is usually retained or enlarged.


Retrofit involves the installation of a new window or door into the frame of the window or door that is being replaced. It is usually less expensive and minimizes the disturbance to the surrounding wall and trim. It also narrows a door opening and reduces the glass area of a window by about 10 percent. Skylights are typically not retrofitted. Such an installation is appropriate only if the existing frame has not deteriorated and is properly sealed and insulated.

Most suppliers offer installation, and some insist on using their own installers for warranty purposes. If your supplier does not, look for a list of window and door contractors in your local Yellow Pages. When getting estimates, ask if the contractor has training in energy-efficient installation and if the company offers a third-party warranty on products and services.

There are also installation certification programs (such as Window Wise) that train installers and warrant the quality of the installation.