Roofing contractor, Caldwell’s Roofing, recently ran into an unusual window leak from a window installed by someone else. Everything looked like it had been installed correctly, but the owner kept getting water pooling on the sill of the window when it rained.
A local glass specialist had been called out and had determined that there was nothing wrong with the window itself. As a roofing contractor, Caldwell’s Roofing could see that there was no possibility of a roof leak causing the problem. So, with the customer intent on getting to the bottom of the matter, Caldwell’s Roofing did a bit of research and proceeded to remove the vinyl siding from around the window.
Clear Window Tape – Not the Best Option
One thing that Caldwell’s Roofing noticed immediately, after removing the siding, was the use of clear window tape to “seal” the window. The problem with this is, as the siding is nailed on, the nails create leak-spots through the tape. When water runs behind the siding (as it always does for vinyl), a small amount of water can wick through the nail holes (as opposed to when an asphaltic-backed, silver-foil style window tape is used, in which case the asphalt “seals” around any nails).
But what’s more (and perhaps more applicable in this case) was that the clear window tape tears easily. Near the top left corner, we found two large tears in the tape that may have been the source of the leak. Underneath the tape, many of the nails securing the window to the wall had rust stains on their heads, indicative of leaking water. The fact that other of the window nails were still perfectly shiny proved that the rusty nails had not rusted during the exposed period of construction of the home (in fact, workers often tape windows the same day they install them).
A Cracked Window Flange – Another Problem Area
Caldwell’s Roofing also discovered, after removing the siding, that the bottom right corner of the window had a hole/crack in it, probably due to a missed hammer-swing or brittleness due to cold weather during installation. This is where we found the most evidence of water – the OSB substrate was badly stained here. Often in residential construction, things like this are “rushed” through, and it comes back to bite the homeowner later on. If homeowners insisted on quality (even at a slightly higher cost), they could save themselves some pain down the line.
Troubleshooting a Difficult Window Leak – Messy Taping/Housewrap at Top of Window
Caldwell’s Roofing further found that at the top of the window, the housewrap was going over the window flange in most spots (good), but under it near the center (bad). A joint in the siding near this area may have allowed water to get in behind the window’s top flange, travel through the window, and come out atop the bottom window sill. Also, the tape had tears, staples, nail holes, and wiggles that may have allowed water through. Caldwell’s Roofing cut the housewrap and clear window tape back two inches from the outer edge of the window flange, all the way around the window, and replaced it with 6″-wide, asphaltic-based, silver-foil style window tape. This tape should do a better job of sealing the few siding nails that are close to the vicinity of the window. Also, it did a great job of not tearing.
Because this window was a “triple window” on a large dormer, and there wasn’t much siding area around the window, we went ahead and taped the entire wall, lapping the tape always in a water-shedding fashion. Normally you don’t tape your whole wall, but here, as soon as you’ve taped your window sides, and your dormer corners (dark brown in photo, and not yet taped), you’ve taped the whole thing! We also taped the side laps such that they would lap over the top of the bottom piece of siding. This enables the water (that wicks over from the edge of the window and gets behind the siding) to be diverted back out to the front of the siding. Here’s a closer picture of that:
The jury’s still out on whether solving these three leak spots will remedy the strange water-pooling-on-window-sill occurrence, but Caldwell’s Roofing thinks it will. The job was done today, and we’ll update you as soon as a good heavy rain comes.