Question: I hope you can help me. I have a four-by-five front porch with a same size fruit cellar underneath that is attached to my basement. It’s mouldy, wet, etc. I was going to remove the door, then add concrete block to seal it off. I will backfill the inside if I ever have to replace the porch slab. Do you see any issue with this?
— Jim Shina, Lordstown, Ohio
Answer: I receive many questions about problems with cold rooms, but yours may be unique in that you have decided to close it off, completely. While I cannot argue with that decision, your proposed method may only be exchanging a current moisture issue for a future, slightly different one.
Unheated rooms in basements used for storage, often referred to as cold rooms, are a bad idea as they can lead to moisture and mould issues. It is particularly concerning that your "fruit cellar" is underneath your concrete front porch. The fact that the porch has a concrete surface, which is likely not waterproofed, makes the chances of mould growth even higher. Rain, snow or ice saturating the surface of the concrete slab may prevent evaporation of moisture from the cool, underground room and further allow mould growth on the concrete ceiling. You are absolutely correct to explore options for preventing this from happening in your home.
Your suggestion of removing the door to the cold room is the logical place to start. The door, while preventing some warm air intrusion and heat loss from the basement, also will stop air flow from the drier basement circulating through the enclosed space. If enough warm air is allowed to circulate through the room, it could prevent excessive condensation of the concrete surfaces. That would minimize the amount of moisture available for mould growth, but it still might not be enough. Ensuring that the room would be warm enough to prevent easy condensation may require installation of a heat source, ideally one with a forced-air element to improve circulation.
Unfortunately, installing a heat register from your furnace, or a small electric heater, may be a waste of money and energy, as much of the heat will surely be lost through the front porch to the exterior. To minimize this issue, the entire interior of the room, including the ceiling will have to be insulated. This insulation will have to be moisture-resistant to prevent wicking moisture from the concrete, so blown-in high-density foam or extruded polystyrene sheathing may be your best options. If either of these moisture-resistant foams are used to line the entire inside of the room, then heating it may be effective enough to make it a usable storage space. The problem still remains with the porch surface absorbing moisture from precipitation.
It is possible that the porch’s concrete slab could be waterproofed successfully enough to prevent water leaking into the room below. This would require sealing the entire surface with a single-ply roofing membrane, or other suitable waterproofing covering. It would also have to be well sealed and flashed at the junctions with the house walls to prevent leakage in those areas. Finally, the portions of the concrete sides that protrude above grade would also have to be covered with similar materials to prevent water absorption at those locations.
While this waterproofing may seem like a labour-intensive and somewhat costly endeavour, it may not be much more difficult than hiring a mason to properly fill in the old doorway to isolate the room from the rest of the basement. It will also have the benefit of maintaining the additional storage space, instead of losing it with your plan. It may require some extra maintenance, due to the exterior exposure, but will not fundamentally change much with your home. It can also have the added benefit of extending the life of the porch by protecting it from harmful moisture over time.
The final reason that blocking off the door with masonry may not be a wise move, leaving an empty void behind, is the difficulty in preventing moisture intrusion into this space. If nothing is done to prevent seepage through the concrete porch, the old fruit cellar may become an impromptu cistern. Water may collect in this large concrete enclosure, which would have nowhere to go but to the new concrete block wall and surrounding foundation wall. The backside of this new wall section would be difficult to damp-proof due to lack of access to the space, until the time you removed the worn-out porch slab. By that time, the excess moisture may have caused enough deterioration to the concrete block, and possibly the foundation surrounding it, to make a larger repair necessary.
The only way I can think that your method would work is if you were to remove a portion of the porch slab at the same time as enclosing the door. That would allow someone to enter the void and apply waterproofing to the exterior side of the new masonry. After damp-proofing is complete, the opening would also be available for backfilling the space to prevent further moisture collection in the underground area. Leaving these steps until sometime in the distant future would surely be asking for a different, but equally problematic, moisture problem than the one you currently face.
Filling in your existing cold room door, without attention to damp-proofing or other moisture-control measures, is a recipe for a new water issue, rather than solving the original one. Stopping the water and cold temperatures from permeating the space may be the most effective solution, or filling in the entire room at the same time as decommissioning the room.
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.