Dear Mr. Marantz,
We had a new home built and have been living in it a year last January. We have a full basement and have had it finished. On the main floor our laundry room is located in the house directly behind the garage. The house narrows by approximately 5 ft. behind the laundry room. The configuration of our basement below the laundry room is identical. When we were strapping and insulating the basement walls and putting up dry wall, we did not do the area that jutted out under the laundry room but followed the outside wall line. We insulated and put a door in the wall to create, what we hoped, was an efficient 5×8 ft. cool storage area. We insulated the ceiling as well.
In this storage area, the common wall with the garage has an access opening for drywall etc. This opening is covered by pressed wood board, only. Last winter the humidity level was extremely high and we are concerned about mould forming and would like to remedy the situation before this winter comes. We hung a sack of desiccant, purchased at Home Depot, to remove the moisture but fear that will not be adequate for winter as we are often away for extended periods of time.
Could you advise us as to other measures that are needed to solve our humidity problem? Would painting the floor and exposed cement outside walls of the room help? Could you suggest anything else?
Thank you for your attention and assistance.
The solution to your problem is simple, but may not have the end result that you desire or expect. Removal of the cool storage area and completion of the insulation and air-vapour barrier, to match the rest of the basement, is the proper way to proceed.
Cold storage areas in basements have always been an area of concern with respect to mould and condensation issues. These unheated rooms have become much more of a problem with newer, highly insulated finished basements and rec-rooms. The better the insulation and air sealing is in the majority of the basement, the bigger the problems in the cold room.
Warm air in the home is circulated by the heating system and carries a fair amount of water vapour. When this warm air hits a much cooler surface, it will condense and the water will form on the cool surface. In a well-insulated basement, with a proper polyethylene air-vapour barrier, this condensation should be minimal. There will be some air that will penetrate the poly barrier and insulation and condense on the inside of the foundation wall, but this should not create a significant problem. Air normally moves from an area of high pressure to one with lower pressure. Simply put, warm air that is pushed through the heating ducts and registers by the furnace fan, under pressure, will move to areas where there is little air movement, or lower pressure.
What you have done with your cold storage room is provide an ideal location for the warm air in the basement to enter and cool past the dew point, causing condensation. Because this room has a door, and no heat or ventilation source, this condensation will be trapped and not allowed to dry. This will eventually promote the growth of mould. Having a poorly sealed opening into the cool garage may accelerate this problem and leads to another health concern.
Attached garages should be properly sealed from the living space in a home, to prevent intrusion of exhaust fumes from vehicles. That is the reason that entry doors from garages have weatherstripping and self-closers. The opening you mentioned that is covered by “pressed wood board”, probably OSB, will not be sufficient to prevent exhaust from entering the basement. This access area was likely left open to allow for easy transport of building materials or concrete to finish the basement. Once the basement was completed, this opening should have been sealed. This can be completed with proper installation of insulation, air-vapour barrier and proper sheathing on the garage side of the opening.
You will probably be disappointed with losing your cold storage area, but this type of room should not be included in a modern insulated basement, without proper ventilation and humidity controls. The current room could be renovated by substantially improving the insulation and air sealing and adding a humidity-controlled ventilation and cooling system, but this may not be financially practical. Purchasing a second refrigerator for the basement may be a better alternative.