Renovation & Design

Test windows with garden hose to find leaks

Question: I have a newer window that leaks when there is rain and an east wind blowing onto the front of the house. The company that installed the windows has looked at it and said it is not the window. I cannot identify any source for the leak. How do I find someone who can fix this? —Alan B.

Answer: Determining the cause of a window leak can be one of the trickier problem-solving inspections that I perform, which may only be possible with several trial and error tests. Remediation will often require removal and reinstallation by an experienced, independent window installer, or carpenter, to fully diagnose and remedy the problem, especially with newly installed windows.

One of the most common complaints with new homes, and with a very popular retro-fit, is leaking of newly installed windows. With new construction there may be several possibilities, most of which lead to an error or defect in installation. This may include the absence or improper installation of window flashing, which is critical over top of new windows. The flashing has to be properly installed with the housewrap to prevent water leaking behind the flashing. This may also be a function of the type of siding installed around the window. Common stucco may shrink away from the window frame or brick mould, over time, leaving a gap that could allow wind-blown rain to penetrate the area around the window.

Another common issue with new windows is lack of familiarity with newer siding types that may be installed afterwards. Every year there are new types of rigid siding coming on the market, with cement-board siding very popular. Each manufacturer has different specifications for installation, especially at joints, ends, and around doors and windows. Some versions require flexible caulking to seal the gaps, while others do not want these areas to be sealed. Some types of newer sidings have joiners and mouldings that should be used in these areas, which may not have been included. If these are an integral part of the siding installation, and are left out, potential leakage may occur. Personal investigation may be your first step, as many manufacturers have these details well documented on their websites. So, checking to see if any new siding materials were properly installed around your new window may yield an answer.

Since your home was already existing it can be assumed that it is older and the new window replaced one that was deteriorated or rotten. If the older wood frame was still in good condition, then a box unit may have been custom made to fit in the older frame. Removal of the original window sash and trim would have been necessary, but not the frame and brick moulding. In that situation, it is less likely to have a leak, as the original frame, siding, and flashing should remain untouched. If the entire window assembly was removed, then the exterior sheathing and wall framing would have been exposed and improper installation is the likely culprit. This could include missing or minimal foam insulation between the studs and the window frame, gaps between the older flashing and the new window brick mould, or several other errors. Most of those types of defects will lead to leakage around the window, especially on windy days.

The way to initially attempt to diagnose the problem is to locate the point of entry of the rainwater. This may be possible by simulating the east wind-blown rain with a garden hose. Spraying water on and around the window from the same direction may duplicate the intrusion. If that works, the next step is to do the hose test in individual areas to narrow down the spot where the water first enters the wall assembly. Further investigation of that specific area, if located, should yield the answer to your leakage issue. This may require removal of the window casing on the interior of the wall, to look for gaps that are allowing the rain to penetrate. Once located, the problem should be solvable with additional flashing, caulking, or blown-in foam insulation in the appropriate area or areas.

If the water test is inconclusive, or the leakage location cannot be found, removal of the window may be the only alternative. If there is newer siding around the window, this may be quite difficult without damaging the new material. If the original siding has not been disturbed, the temporary removal should be much simpler and the defect likely identifiable once the window is taken out. The final piece of the puzzle may be that the window itself is indeed the source of the leakage. That could be due to a damaged weatherstrip, misaligned hardware, shipping blocks not removed, or other manufacturing defect. In that case, the hose test sprayed directly on the window surface, from several angles, should show up the defective window. If that can be reasonably proven, the manufacturer should be on the hook to fix the defect, or supply you with a new non-leaking unit.

Figuring out why a newer window is leaking can often only be identified with several water tests and partial removal of the trim, and/or window, to locate the defect. An experienced red seal carpenter, or independent window installer, should be able to determine whether there is a defect in the installation or the window, itself.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)( Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at


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