Trained Eye

 
 
 

Carpet in Basement

Question:

We are slowly renovating our basement to make a rec-room for the kids to play in. 

Currently we have no floor covering in the basement. We are planning to re-carpet the rest of the house in the next few weeks and would like to carpet the basement, as well. 

  The concern we have is that last summer our basement was quite damp.  No visible water on the floor, but a definite dampness feeling.  We already have a de-humidifier in the unfinished half on the basement that runs almost continuously in the summer. 

 Is there something we can do before we put in new carpet, or a recommendation of carpet type or installation method?  We also heard that there is a surface mountable exhaust type fan to exchange the air.  If there is such a thing, where could we get one? 

 I am just concerned about spending the money on carpet and find it mouldy and have to remove it in a few years.

Thank You.

Answer:

Installing carpeting on a concrete basement floor slab will make it much more comfortable to walk on, but may absorb moisture and odours from the basement. Minimizing the amount of moisture in the home and basement will be the best way to prevent this from happening.

The “surface mountable” air exchanger mentioned is likely a Heat Recovery Ventilation (HRV) or similar ventilation system. These are self-contained units that bring fresh outside air into the house and exhaust stale air, at the same time. They have an internal unit that passes the air leaving the house by the incoming air, to minimize heat loss. In the winter the heated house exhaust air will warm the freezing cold air coming in and vice versa in the summer. This allows the units to be relatively efficient compared to an open fresh air duct and a normal exhaust fan. These HRVs or ERVs are common in many areas in Canada and are becoming increasingly popular in our area.

Ventilation systems are available mainly through heating, ventilation, and cooling (HVAC) contractors who will sell and install the units. When done properly, the units are installed in conjunction with the home’s furnace and ducting system and often the bathroom and kitchen exhaust system, as well. The furnace fan is normally wired to the HRV to assist in moving the air in the home when the unit is on. In new home installations, the bathrooms and kitchens will have switches or controls to turn the HRV on when cooking or bathing. This will help with removal of excess moisture in the home caused by daily activities. It is very important that these units are installed and balanced by properly trained and knowledgeable contractors to avoid ineffective operation. I have seen several units installed incorrectly by poorly trained technicians that may be useless or detrimental to a home’s ventilation. There is some regular maintenance involved with these ventilators and homeowners should get guidance from the installers on specific cleaning, drainage and filter change requirements.

Installing an HRV will definitely help reduce excess humidity in the home, especially in the summer, and operating central air conditioning will also dehumidify the air in the home considerably, as well. Both of these systems are excellent for air quality and home comfort, but may not completely prevent a damp smelling carpet. Often carpets become damp and musty from moisture absorbed from the concrete floor slab below. Purchasing carpet with a moisture resistant underpad may help prevent odour and mildew build-up, but other solutions may help even more. In any event, gluing the carpet to the concrete floor is not recommended, so that it may be more easily removed and cleaned if it does become wet or smelly.

Installing a plywood subfloor suspended on moisture resistant strapping or sleepers will prevent the carpet from absorbing dampness from the concrete. This is not inexpensive, but will ensure a dry carpet. The difficulty with this system is that moisture and condensation may be trapped under the subfloor and actually allow mould and rot to develop in this space. Care should be taken to run the strapping in the direction of the floor drain to allow moisture to drain and not become trapped by the wooden supports. There are also several products marketed as subfloor support systems that provide a rot proof barrier, made out of corrugated plastic, that allow drainage. These may have similar problems to wooden strapping with trapping moisture beneath the subfloor.

If active seepage is found or white powder (efflourescence) is visible on the concrete or cracks in the floor, elimination of the source of the moisture should be done before anything. Exterior grading, eavestrough downspout extensions or repairs, upgrading weeping tile or installation of a sump pit and pump may be needed to stop the moisture intrusion. Spending considerable money and effort to create a comfortable basement rec-room area may have many benefits, but will not be worth attempting if water and moisture is allowed to enter this new living space.

 

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