by Deborah Mesher, Architectural Designer and Alex Lukachko, Building Science Consultant and Climate Strategist
Deborah: I get a lot of homeowner questions about renovating damp basements in older homes. How to retrofit?
Alex: First action would be to find out how much and where it is coming from. Excess water must be prevented from entering before renovating or finishing a basement. The usual suspects for water into old foundations are high water table (ravine), storm water management (rain water coming in through cracks or saturating the foundation below grade) the grade sloping towards the house, eavestrough routing and downspout improperly directed, soft landscaping areas insufficient for storing storm water, and old clogged weeping tiles at the footing.
Deborah: How to know which type of water infiltration it is?
Alex: On the interior of the basement, you’ll look for particular corners or joints, finishes that are wet or spongy, or areas that have staining or efflorescence and take note of those first. Moving then to the exterior you’d assess the conditions of the eavestroughs and gutters, making sure they being routed down and away from the foundation walls, seeing which way grade generally slopes around the home, including how neighbouring yards drain as well. Doing this while it’s actually raining is even better. You might get lucky and find the main culprit by cross checking the conditions inside and out. Toronto properties are planned tightly together, so a neighbor with a self-watering back lawn could have an impact on your basement water problem. As well, on small lots there just isn’t enough soft landscaping around to absorb the excess volume from a storm, and the ground is really too saturated and comes in with gravity no matter what you do to prevent it.
Deborah: Any other causes of dampness?
Alex: Most downtown Toronto basements are made of brick, block or stone/rubble, and were designed to be cold cellars rather than the habitable warm spaces we need them to be now. In our hot and humid summer, basements stay cooler than the rest of the house and condensation may occur on basement surfaces (including uninsulated cold water pipes) if air from the outside circulates through the house. In winter conditions, basement surfaces may be colder where they are at or above ground level and that might mean that warm, moist interior air can cause condensation in these areas too.
Deborah: What are the best practices for waterproofing older basements?
Alex: Exterior waterproofing, which entails digging up all around the exterior of the house to install new waterproofing continuous drainage mat against the foundation with a new weeping tile at the footing that is diverted away from the house is the top choice. It can be disruptive in some tight urban lots, expensive, impact tree protected tree roots or sometimes be physically impractical due to equipment access. The same technique can be applied in an interior-only way, which involves the same continuous drainage mat on the interior of the bare foundation wall, the chipping up the slab to install an interior weeping tile directed to a new sump pump.
Deborah: If larger scope waterproofing isn’t possible, are there alternatives?
Alex: In older finished basements you will often see wood studs with fiberglass batt insulation between them pushed right up to the foundation wall. This is not a good long term approach for durability because the materials are sensitive to moisture. If the foundation wall is wet or damp, the wood rots, the mold grows, but both take time to notice. Using moisture tolerant materials like steel studs, plastic based insulation such as closed cell spray foam or eps/xps boards, mineral wool insulation can all get wet but take longer to degrade. Using non-paper faced gypsum board is also more durable than regular drywall. Last tip would be to keep the framing and finishes up off the floor by about 3/4” using thin blocks so that they are less likely to be damaged by small basement floods, and it goes without saying that using flooring like tile rather than carpet, vinyl or hardwood. All this said, invest in waterproofing the basement if you are going to be renovating the basement anyhow!
Learn more about Alex Lukachko here.