Question: I have a cold storage area under the concrete stairs in front of my house. The room is concrete on all four walls, the ceiling and the floor. We live in Victoria — where it rains most of the fall and winter season. The stairs and landing on the exterior are partially covered by the eaves of the house, but the outer edge does get rained on. There definitely were some ventilation issues before, but we have since installed an insulated door and drilled a four-inch vent into one of the walls. But now, we have changed our minds and want to finish this room and make it part of the conditioned space in our basement.
We brought in a contractor to look at it, and he said while it’s normally a good idea to seal and insulate cold storage rooms, it was not advisable in our situation because of the horizontal permeable concrete surfaces of the stairs and landing. He said that even if we sealed it from the inside, we would get water and mould issues on the ceiling under the stair treads and landing.
Can you confirm if this is the case? Do you have any suggestions?
— Jason Tang
Answer: Converting a cold storage area to usable, conditioned space definitely has its challenges, but may still be possible depending on what is outside. The configuration of the roof and stairs will determine whether this is a good idea, or if you are just asking for trouble with your plans.
I have written several times about this issue, which is one of the most popular inquiries I receive. While there are a limited number of cold rooms in our area, these rooms appear to be quite popular in other provinces. My standard opinion of these unheated, uninsulated spaces is that they should never be present in residential homes. That is because they are highly prone to condensation, which can lead to mould growth. Since the walls — and in cases like yours, the ceiling — are not insulated, they can remain considerably colder than the rest of the home. Any time you have a significant temperature differential like that, condensation is a given. Since these rooms often have poor air circulation as well, the condensation will not dry quickly and will provide an ideal environment for mould to grow on any dust, dirt or other materials in the cold area.
Many cold rooms have a fresh air intake duct to bring in winter air, which makes the rooms even colder and more prone to condensation and frost issues. In a damp but moderate climate like yours in Victoria, there may not be one of these ducts installed. Since the room is uninsulated, unheated and only has the concrete front steps or landing above, it may be even more prone to moisture issues than normal. Since untreated concrete is not waterproof, there is definitely a concern with this, even after insulation of the room. Your contractor is correct in his prognostication of potential mould growth under the insulation, due to the wet concrete of the stairs and landing. Having said that, there are ways this could be minimized.
You have stated that the eaves of your home partially overhang the stairs and landing. This may help prevent wetting of this critical area, but may do little if it is not completely sheltered from most precipitation. Since snow and ice buildup against the steps is not a significant concern in your area, rain may be the only issue. If you have a roof that extends beyond the entire area of exposed concrete, there may be much less concern with moisture intrusion. If this is not present, you may be able to construct a small roof over the stairs that will serve this purpose, enabling you to complete your plans. If neither of these are present or practical, there may only be one other questionable option.
It may be possible to install a waterproof membrane on the exterior of the stair landing, which will prevent it from becoming wet. There are numerous options for this, but many may not be suitable for continued foot traffic or may make the area too slippery. One option may be to install the type of membrane often now used on solid balconies, which may have a lifespan in the 15- to 20-year range. These are designed for this purpose, but would likely have to be installed down the entire sides of the landing and stairs to be completely effective. If you could completely cut out the possibility of wet concrete, it may be possible to use this space as you are planning.
The other two considerations for successfully using this space are to ensure warm-air circulation and proper insulation. Any insulation used should be waterproof and resistant to air penetration, so any type of loose fill or batt insulation is out of the questions. Rigid extruded polystyrene sheathing would be acceptable, if well sealed at any seams and edges. Blown-in high-density polyurethane would be the best, but most costly, choice. If you are able to protect the outside concrete from becoming wet, and completely seal the inside with foam insulation, then providing a warm-air source is the only thing remaining. You may be able to extend a heating duct to the room from the furnace, if you have a forced-air heating system. Alternatively, a small electric heater with fan could be installed, after the door to the room is removed, which would prevent stagnant air and condensation issues.
Warming up and insulating a former cold room will depend on how easy or difficult it is to prevent the exterior stairs and landing, which form the ceiling and walls of the room, from becoming wet. If you can do this by covering the area with a roof or waterproof membrane, then it may be possible. If preventing wet steps is not practical, alternative plans will be warranted.
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.