How To Install A Leak Proof Window

leak proof window

Why Do Windows Leak In The First Place?

Everything that we will discuss in this post is in the context of a replacement window when the original window is removed and a block-frame window is reinstalled. When the original window is installed it will have a nail-flange that sits flush against the sheathing of your home. Done correctly, it will have a sealant behind it and flashing tape over the top of it. After which the window gets sealed against the brick, stucco, or siding.

Nail fin before flashing tape and siding

If and when that window gets replaced there is no longer a nail-flange and sealing it properly takes experience and more time. In truth, the vast majority of replacement window leaks do not originate at the window, instead, they typically reveal a leak from somewhere above in the siding or at the roof. The reason it’s now exposed is that, in the past, the water would get behind the siding, run to the top of the window, and hit the nail flange which would direct it around the frame and down the sheathing where it continues its way down.

When a window is replaced a nail-flange can no longer be used. Instead, a block-frame window is required to replace the window since brick, siding, or stucco is now in place. Since the nail fin can’t be used to secure the window in place screws have to be run through the window frame into the wall studs.

A block-frame window, the nail fin has been removed

A replacement window can be sealed in the opening but water leaking from above presents a whole new set of circumstances. Water that makes its way to the top of the window can get trapped by the caulking on either side and end up wicking its way through the sheetrock and making its way down the wall into your home. Call the window company that did the work and they are very likely to tell you that you have a leak somewhere above the window, the window itself is fine and it’s not their problem.

How We Install A Leak Proof Window

At Houston Window Experts we understand that issues like this do happen and that’s why we take the extra time and effort to not just seal our window to the opening, but we take additional steps to combat water intrusion from leaks above the window that find their way behind the siding or brick and keep it from making its way inside. While most other window companies out there do what we call the “caulk and walk” and don’t take the time to flash the opening. The technique we’re about to describe is pretty rare and it’s crucial that you find out what method an installer uses before you hire them.

It is important to note that the materials used here matter a great deal. If cheap flashing tape and caulking are used, they’ll deteriorate and provide no protection against the elements. That’s why we use the best products that are available, OSI Quad Max.

Once the old window has been removed and the opening prepped for installation the first thing that we’ll do is use flashing tape on the sill underneath the window. It’s very important that the tape also runs up the vertical leg of the opening from 4 to 6 inches. Doing this ensures that there is a good overlap with the next flashing. This creates the “shingle effect” and prevents water from getting behind any of the flashings. Also, the tape needs to form a lip against the window stool and overlap down the face of the opening. If any water does manage to find its way there, it has no way to soak the trim and is forced out of the opening.

leak proof window sill flashing
Flashing the sill
leak proof window leg flashing
Flashing the leg of the frame

Next, flashing tape is installed on the vertical legs overlapping the sill flashing and wrapping around to the sheathing. The last piece will be the head flashing. For this, we use metal flashing. If a flashing tape were used and water did start to drip down from above it would sit on the adhesive and eventually cause it to come loose.

Before the metal flashing is screwed in place a large bead of caulk is applied to create a watertight seal and then after it’s screwed in place another bead of caulk is applied for good measure. Once the window is set it’s foamed with high-quality low expansion foam, caulked inside and out, and ready for years of reliable protection.

leak proof window head flashing
Flashing the header

OSI Quad Max Technical Data

We are the Houston Window Experts! Contact us today for a Free Consultation on how we can help with your window needs. You may also call us directly by dialing 832-900-7024.

Our Services include: Replacement Windows Houston, TX metro area. Houston Window Experts is a privately owned and operated company in Houston TX. For more information about us, please write to info [at] or call our Houston office at (832)900-7024. All material is copyright of Houston Window Experts. Houston, TX.