Basements are increasingly becoming an integral part of the modern home. Initially used as storage for parishables with dirt floors, basements have evolved to become a significant part of the living space in the home. This trend started in the late 50's, when the post-Second World War baby boomers sought recreation rooms. This evolution has gone so far as to provide a large amount of residences in the form of rental, family and caretaker suites.
But as this evolution took place, the construction methods remained unchanged. Concrete or masonary walls formed the foundation, and if living space was desired, a wood framed wall was added to finish the inside. Many companies have produced innovative components for such a wall system, but little thought was given to the dynamics of such a wall assembly as a whole. As a result, moisture, mould and heat loss are serious problems for manyof these homes.
Separating the outdoor environment from the indoor environment is the goal. The keys to that goal are controlling water and water vapour, soil gases, heat and air flow, and concealed condensation. Of course, cost is always a factor, and some solutions may not be cost effective for existing buildings. The most obvious improvement that can made is limiting the amount of components in the wall system. The average finished basement wall has dampproofing on a concrete or block wall, wood framing, insulation, a vapour barrier, and gypsum board or paneling. Combining two or more of these components into one can reduce material and labour costs, construction time, waste, and a potentially inadequate structure. But in reducing the number of components, the goal must not be compromised.
It is best to keep the entire wall warm. This will prevent condensation. To do this, external insulation can be applied to the concrete wall. This requires excavation around the entire perimeter of the basement living space. Clean drain rock should be used as backfill for about a foot out from the wall. This acts as a thermal break, as well as diverting water from the concrete wall. This also gives you the opportunity to inspect your perimeter drain system for blockages.
This works fine for keeping the wall safe from water penetration, but where does the water go instead? It will travel down to the footing where the concrete floor is. Depending on the base your concrete slab was poured on, among other things, water can enter between the slab and the footing. More on the floor system, and the danger of soil gases will be discussed in the next newsletter.
If the exterior approach seems unrealistic for your application, there are improvements that can be made at the interior wall face. But keep in mind that the standard practice of framing a wood wall against the concrete wall is costly, uses valuable floor space, and is predisposed to water damage. If your home is less than two years old, moisture may still be present in the concrete. By finishing the inside, you will trap moisture in the wall. This moisture will eventually cause rot and mildew. Should you have a very old concrete foundation wall, it's likely absorbing water from the ground and maybe even leaking during heavy rains or flooding. There are products that can be applied to seal the wall from the inside, and this should be done before any other finishing is undertaken. But let us assume that the wall is dry, and relatively safe from water penetration from the outside. The first step is to frame the wall. Pressure treated lumber would be the best option to avoid moisture problems, although has potential adverse health risks attached. Secondly, insulation is needed. In this situation, a rigid type of insulation is superior to batt because moisture will not damage the rigid foam. If moisture eventually ocurrs in the wall, this will render the batt insulation less effective. A vapour barrier (plastic sheeting) is the primary defence against moisture. Make sure you seal any opening made for electrical outlets, fixtures, etc. with the proper tape. Next is drywall or some other wall board finish. Now you can enjoy your new warm, dry space...that is, as long as your concrete floor is in good shape....stay tuned for part 2!
*Going Green - Building materials and ideas
*Basements Part 2 - Is your basement sick?