Question:
At the bottom of two closets in our 1954 bungalow there is frost and damage to the plaster walls. Can you please suggest an inexpensive way to solve this problem?
Thank you. Lawrie Marmel
Answer:
There are a couple of simple things you can do to prevent frost buildup inside the closets in your home. One of these should help address the problem of minimal insulation in older homes like yours and the other will help solve a couple of habitual problems caused by homeowners.
Before you tackle the issue of frost and damage occurring inside the closets in your home, you should know the causes. Having this knowledge will not only help solve the problem, but it should prevent a recurrence, should you forget this advice in the future. There may be several contributing factors to the appearance of frost in your closets.
Initially, I will assume the frost is only appearing in closets that have one or more walls which is an exterior wall of the home. The reason this is likely is these walls may have minimal or no insulation in some areas, which can allow them to be much colder than surrounding areas. Heat can be lost by thermal bridging of the material that makes up the construction of the wall to the cold air outside the home. With little insulation to prevent heat retention, this is almost a certainty. Even if the wall has some thermal insulation between the studs, there may be nothing in the corner in the exterior wall. Also, it is quite common for small gaps to appear under the bottom plate of these stud walls, due to normal shrinkage or warping of the wood over time. Both of these areas may allow a substantial amount of cold air to infiltrate this section of the building envelope, creating an excellent location for condensation.
The second requirement for frost buildup in this troublesome area is moisture. Where does this moisture come from in a closet that is nowhere near a water source? The answer is the warm heated air inside the home. This heated air will contain a certain amount of moisture, depending on the relative humidity (RH), at any given time. In the middle of winter, the air in the home may seem quite dry, but it actually contains much more moisture that the frigid air outside the home. When this warm air hits a very cold surface, or drafty cold air from outside, it will condense on the cold wall surface. If it is cool enough, this condensation will freeze, and then you have the conditions for your frosty wall. Keeping the RH lower in the home may help prevent excessive condensation, but keeping the closet walls from getting cold enough inside to freeze any condensation is the key to solving your issue.
The first thing to address is the lack of insulation or air sealing, typical in homes of your age. If the back or side walls of the closet are indeed exterior walls, it is almost certain that there is no insulation in between the studs that make up the inside corner of the closet. Because of the configuration of an inside corner of a wood framed wall, there is often a natural void in the exterior wall at this location. If both walls sharing the corner are outside walls, the problem may be exaggerated. To fill this void after the fact, small holes may be drilled right in the corner, angling toward the exterior wall. Care must be taken not to drill through any electrical wires, or other obstructions, so doing a little exploratory work ahead of time may be prudent. Once the holes are drilled, filling the void may be no harder than pumping in a few cans of expanding polyurethane foam insulation through these small openings. Once the foam is cured, the excess that oozed through the holes can be cut off with a utility knife and the walls repaired with a patching compound before painting.
This same method may also work if there is substantial air leakage under the bottom plate of the stud wall. This may only be identifiable by removing the baseboard or quarter round at the bottom of the wall. Once these are removed, a flashlight or thin metal blade may be used to determine if the gap in this location is large enough to cause an issue. If the gap is larger than three to five millimetres, blowing in more foam to air seal this location is warranted. Because of the location and size of this gap, low expansion foam, designed for door and window installations, may be a better choice in this tight spot. If the space is smaller than a few millimetres, filling the gap with a good quality exterior grade caulking may be all that is needed to stop the cold air infiltration.
The last issue that will cause excessive moisture, frost, or mould in closets is a lack of airflow along the walls. Because most closets have doors that prevent heated air from the warm air registers easily accessing the inside walls, they can be substantially colder than outside the closet. This may be compounded by the common practice of storing large amounts of boxes, shoes, or clothing on the floor of the closet. If this storage is touching the exterior walls, it will further prevent warm air from circulating over the cold wall surfaces. The stored clothing can trap moist air that does enter the closet, ensuring slow cooling and guaranteeing condensation. With limited warm air circulation to dry the condensation, it may freeze, as the exterior closet walls further cool, at night.
The frost forming on the inside walls of your closets is likely a combination of a normal defect in the construction methods used in your home, combined with some of your natural habits. Filling the gaps inside the corners and under the baseboards will minimize the effects of the construction flaws, while eliminating excessive storage and leaving the closet doors open will help prevent a small problem for escalating to the point of frost damage.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors -- Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.
trainedeye@iname.com
