Trained Eye


Replacing Rotten Window


I have a home built in the mid 1950's.  Several years ago, a Hi-efficiency furnace was installed by the previous owner but without adding additional ventilation. Having lived in the home during the last five years I have had problems controlling moisture and humidity. One problem that seems related to this is deterioration around some windows. I am seeing some rot on the wood frame and wood brick moulds.  In particular, a bathroom window which has an aluminum vertical slider, with single panes of glass spaced apart by the width of the exterior wall.  Tile is on the inside of this wall and stucco on the outside.  One day, when checking paint that had lifted on the sill between the two windows, I was able to pull out pieces of rotted wood which revealed a gap and dry rot that seemed to go into the sill plate and beyond the jamb, possibly into the adjoining wall stud.  I can’t tell because all I can do is look in with a flashlight which shows several inches of badly decomposed wood. 

What I am wondering is; if I replace the window with a full frame unit is it likely that the bathroom wall will have to be broken out to facilitate the installation and confirm the necessary repairs? Could the entire stud have to be replaced and thus most of the wall board removed?  I presume there is no way even an experienced renovator can tell without going into the wall.  The window replacement company I called sent a sales rep who seemed to suggest that when the old window is removed they can determine at that point what to do.  However, once the window is removed, there is no turning back and I may find myself having to authorize extensive repairs at the last minute.  Do you have any advice or precautions I could take.  I am quite unhappy because the bathroom wall was re tiled, not too long ago, and new cement board was placed all around the tub area, which is on the window side.

Who could I call beside a window replacement company to look at the problem and give me impartial advice?


Moisture on windows in the heating season, and what to do about it, is probably the most common question that I receive. It is refreshing to see someone asking about remediation of the damage that can be caused by this excess moisture, rather than simply how to avoid the problem.

I have replaced many, many older windows in homes and unfortunately you are correct that there is no way to determine the extent of the rot and moisture damage to the studs without opening up the wall cavity, somewhat. This is normally only possible once the old window has been removed, unless you want to cut large holes in the exterior or interior sheathing on the wall. If done carefully, you may be able to replace sections of the damaged wall studs without affecting the interior tile wall covering. If only the bottom sections of the studs surrounding the window are rotten, it may be possible to cut out and replace these sections by removing a portion of the exterior stucco and sheathing. This is largely dependent on the amount of moisture damage to the framing near the window.

Normal framing in homes will include at least a double stud at the sides, below and above an exterior window. This is done to strengthen the wall, where a larger than normal opening is cut, and allow for proper installation of the sill plate and header at the top and bottom of the rough opening. Quite often, moisture damage from leaky windows is confined to the shorter studs adjacent to and underneath the window, with little damage to the full height boards that these are nailed to. If this is the case in your home, it may be possible to cut out only the damaged studs below the window along with the exterior walls sheathing and stucco. Once the wall cavity is exposed and the rotten wood cut out, new framing may be installed at the bottom of the opening, along with replacement of insulation, air-vapour barriers, and exterior sheathing. This opening is now set for installation of the new window and the stucco may be patched after completion.

If the wall cavity is opened, after removal of the old window, and more extensive moisture damage is seen, then a major interior repair may be warranted. If the cement board behind the tiles is attached directly to the studs, there is a good chance that they may be in reasonable condition. Otherwise a responsible contractor would have replaced damaged sections of the wall framing before covering it up with sheathing and tiles. If the cement board is installed over top of older plaster or drywall, then more extensive rot is possible and a major renovation is more likely.

Often, window companies employ installers that have a wealth of experience in installation of custom made replacement full frame or simpler box units, but fall short in areas where further repairs are required. Removing a window or sash from an older home and replacing it with a properly measured replacement unit is often a very straight forward operation. Relatively complex renovations, such as the one you are about to embark upon, should be done by an experienced carpenter or general contractor with many years of experience in residential renovations. I would recommend hiring such an individual before ordering the new window, in case major changes are necessary. Once the wall is opened and evaluated, or repaired, the new window can be ordered to suit the situation and a temporary plywood cover can be installed until the new unit is ready. If you are concerned that the contractor may be trying to sell you a more extensive repair than is necessary, a member of the Canadian Association of Home Inspectors (CAHPI) is likely the answer. Hiring an independent CAHPI home inspector to evaluate the damage and offer advice, at the time the wall is opened, may eliminate your worries.




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