1: Very complex window layout and no overhangs.
As you can see above, the window openings in this house are many and complex. There are tall windows, arched windows, bay windows. And this would be fine, providing they were installed with all the bells and whistles (flashings, sealants) that prevent water from leaking in. But the sections of wall that have no overhangs may present a problem. Typically we homeowners think the main functions of overhangs are to create shade and drain water off the roof. But they also keep wind-driven rainwater from pushing into the walls through the windows. If you’re ever in the position to design a house or an addition to your house, it’s wise to include overhangs.
2: Angled fascia.
With the fascia (the horizontal board above the window) angled inward, it doesn’t take too much building knowledge to see that water from the roof will be directed right toward this window. The sloppy flashing (extra-strong insulating material between the window and house framing) gives water even more of an opportunity to seep in. Which leads us to…
3: Poorly installed flashing.
To keep water from getting inside your walls and causing all kinds of trouble, there must be a good integration between the window, the building paper (bottom right and left) and the flashing (the stronger material around the arch). In the picture above, the flashing is cobbled together and each break in its surface creates an opportunity for water to enter. In a correct installation, a stretchable flashing is used in one continuous piece, as opposed to patches.
4: Misuse of materials.
In this case, house wrap (building paper) is being used as the window flashing. For superior water protection, the carpenter should have used specially made flashing material. It’s stronger and does a better job around windows than the house wrap, which goes behind the home’s siding or brick.
5: No flashing at all.
We have to hope this window was just set into place temporarily and will be removed later so that flashing tape can be installed properly. If flashing tape isn’t installed the right way, water will get behind whatever kind of siding is put up (and water always gets behind siding) and then drip behind the mounting flange (the outermost edge of this window frame) and into the walls. It’s a good idea to use caulking to seal your windows, in addition to flashing tape.
6: Missing sealant, wrong type of nails.
You can see some sealant (caulk) behind the mounting flange on this window, but not enough. There should be a continuous bead of sealant behind the flange, and it should ooze out of any unfilled nail holes. And about those nails: They are obviously not corrosion-resistant (which is required), as you can already see the rust coming on. Plus, they were shot out of a nail gun (as evidenced by the little orange tab on the left nail). According to many experts, this is not a good practice, as window flanges require a precise fastener pressure and that is hard to control with a tool powered by compressed air.
7: Not shingle style.
If you want to know the secret to moisture management it is this: shingle style. That means that the top layers of a surface overlap the bottom layers. That allows gravity to move water down and away from the structure. If you violate this basic principle and put a top layer behind a bottom layer, you’re inviting water to come right in. In the photo above, the white building paper above the window should be lapping over the black flashing. It’s possible that with super-wide overhangs, and not much rain and not much wind, this penetration may not leak. But bring on some wind-driven rain and you’ve got trouble.
8: Cracked glazing putty.
This is easily corrected. Just pry it out and redo it. If not, moisture will continue to deteriorate this wood frame.
9: Lack of a paint seal.
Here’s something you may not know: When painting the exterior molding that holds a window into place, the paint should slightly overlap onto the glass. This may seem shocking as we typically do everything possible not to get paint on our windows. But the continuous membrane of the paint from the molding onto the glass creates a seal that is actually part of a moisture protection strategy. Professional painters and savvy DIYers already know this.
For more information on proper window installation, consult the industry bible on this topic, known as ASTM E 2112. ASTM stands for American Society for Testing and Materials, but now it is an international standards organization.