As explained in the previous Article “ Window Installation, Part 1, A Little History.” There are a number of techniques used for the proper installation and water proofing of new windows. Be it in old construction or in new construction.

There are several factors to consider for a window to be properly installed. Among them are framing of the window opening, position and size of the header, correct window type and quality for the region, sequence of installation, and most importantly, water or weather proofing.

These articles are geared specifically to the water or weather proofing. Primarily, because moisture related issues can be prevented if the windows are installed correctly and secondly, because water proofing or flashing installation is the most important item being neglected by the people installing windows.

We all know by now what nightmares can be created by moisture so we are not going into that subject. Rather, I’ll explain the proper way to install a window and you can also see several installation instructions provided by different manufacturers.

Installing a window.

After insuring the opening is as needs to be for new construction, or cleaning the opening of an old opening for a window replacement. The first step is to install flashing at the lower horizontal edge of the opening. Next, the vertical sides are installed overlapping the ends at the sides of the horizontal lower flashing. Last, the top horizontal flashing is installed overlapping the top of the vertical sides. The lower flashing will overlap downward towards the exterior approximately 4 to 5 inches. See the installation instructions provided by the AMSCO window manufacturer for details and illustrations of the installation process.

Properly Installed Flashing and weather Proofing

In new construction, where a moisture barrier has been previously installed, the flashing is installed at the opening overlapping the moisture barrier on all sides. The top flashing will be placed under the edge of the moisture barrier, so that the barrier will overlap the flashing.

When a weather exposure material such as felt paper is installed in new construction, the materials should be installed from the bottom up.

Improperly Installed Flashing and Weather Proofing

The edges of the material below the window should be placed so that the lower horizontal flashing at the window opening is overlapping the weather proofing barrier, and NOT with the barrier overlapping the flashing, as it is shown with the black material in the picture below.

For old construction, the installation of the flashing is as important as in new construction and the sequence of the flashing installation is the same. The only difference is how the top flashing is installed and how it overlaps the siding.

The flashing material for the windows is a rubberized self adhesive membrane that comes in a roll. This flashing can be purchased from stores like Lowe’s and Home Depot but is also available at lumber yards and other construction materials establishments.

It is important to mention as well, that the installation of a metal flashing, typically galvanized material readily available at the stores mentioned above or copper for higher quality construction, is recommended for either new or old construction window installations. This flashing is typically knows as “Z” flashing for its shape and it is installed under the siding at the top edge of the windows with its overlapping drip edge covering the top edge of the window below it.

The last part of proper water proofing of a window is caulking around the trims and siding. This simple task is nowadays ignored by most construction companies and sub contractors and in and of itself could prevent a large number of moisture issues if it was actually done. Home owners have a portion of blame when it comes to caulking as well, as most home owners will never perform annual or bi-annual weather proofing maintenance on the exterior of their homes. However, caulking will be addressed in an article of its own.

So what does the building code says about window installation and it’s water proofing? Well, here there are two accepted Codes used by most building departments throughout the US. One is the International Residential Code (IRC), and the other is the Uniform Building Code (UBC). The IRC is the code that is being adopted at a fast rate by most jurisdictions and so I’ll mention it first.

“IRC2003 R703.8 Approved corrosion resistant flashing shall be provided in the exterior wall envelope in such a manner as to prevent entry of water into the wall cavity or penetration of water to the building structural framing components. The flashing shall extend to the surface of the exterior wall finish and shall be installed to prevent water from reentering the exterior wall envelope.”

The UBC1997 reference number is UBC1402.2 and it basically says the same thing. It is important to mention also, that where specific manufacturer’s instructions exist that go above and beyond that which is mentioned in the code books, those manufacturer’s instructions take precedence. This is widely acknowledged by the industry as well as code references. Window manufacturers will quickly void any warranty offered for their windows if they discover that the installation was not done per their instructions.

How can you correct this? If you know for a fact that improper flashing exists around your windows, then the only way to correct this is to remove the trims, siding and some times the complete window depending of which flashings were missed or improperly installed. This includes stucco finishes.

Who can perform the work? This should absolutely be performed by a licensed contractor unless you are well versed with tools and can follow instructions. (Which whom ever installed your windows in the first place did not).

What can you do if you do not want to go through the trouble? The best thing is to annually check and redo the caulking around the windows and trims. Use caulking that is rated for at least 50 years because it will last longer. Not 50 years, but longer than 6 months in most cases. I personally have had good luck and longevity from products like “GE’s Max 5000” which is a siliconized acrylic product that can be painted. Next on my list of readily available off the shelf products would be DAP’s dynaflex 230 but this is a latex based sealant. For applications where top quality is needed, I use products from the Sika corporation or Sonoborn when possible but these products are not readily available at most regular stores and people using them need to be familiar with the different qualities and performance as well as application of these products as they are designed with professional users in mind.

Below are links to 4 different window manufacturer’s instructions provided as PDFs as published by the manufacturer’s websites. All instructions are the ownership of the respective companies mentioned within the instructions. AskHomepedia.com does not claim any copyright to these documents and are only provided through this site to allow access to the readers as it is made publicly through the respective websites of these window manufacturers: Amsco, Jeld-Wen and Pella. Installation instructions for Sillguard from Marvin Windows & Doors is also provided as this product is specifically designed for water proofing of windows as well.