Older Homes in Old North, Wortley Village and Old East: Common Moisture Problems

Old house moisture problems in London, Ontario come from how these homes were built: foundations with no waterproofing or working drainage, solid brick walls, attics with little ventilation, and plumbing well past its service life. Homes in Old North, Wortley Village and Old East were designed to be drafty and to dry out on their own. Problems start when later renovations seal them up or finish spaces that were never meant to be dry.

Basements that were built as cellars

Many older foundations here are stone, brick or early concrete block. They were built without a waterproof coating on the outside, and any drain tile at the footing is clay pipe that has often collapsed or filled with silt and roots. The basement was a place for the furnace and the coal, and some dampness was expected.

These walls let moisture through as vapour all the time and as liquid water in wet seasons. You will see white powdery salts on the masonry, crumbling mortar and flaking paint. Left open to the air, the wall dries into the basement and a dehumidifier handles it.

The trouble comes when someone frames a wall against the masonry, fills it with batt insulation and covers it with drywall. Now the moisture is trapped in a dark cavity full of paper and wood. Mold grows on the back of the drywall for years before a smell or a stain gives it away.

Solid brick walls and plaster

Double-brick walls absorb rain and release it again. Heat leaking out of the house used to help dry them. Tuckpointing that has washed out, cracked sills and missing flashings let much more water in, and it shows up inside as bubbling plaster or stains below windows.

Adding insulation to the inside of solid brick changes how the wall behaves. The brick runs colder and stays wet longer, and warm indoor air can condense behind the new insulation. It can be done well, but it needs someone who understands old masonry. If a renovated room in an old brick house smells musty, the insulated exterior wall is the first place we check.

Attics, bath fans and ice dams

Older attics often have thin insulation, few vents and many air leaks from the house below, such as open plumbing chases, gaps around the chimney and old light fixtures. In a cold winter, that warm, moist air hits the underside of the roof boards and turns to frost. When it melts, the wood gets wet, and after a few seasons it turns dark with mold.

Bathrooms were added to many of these houses long after they were built, and the fan was sometimes ducted only as far as the attic. That puts shower steam straight onto the sheathing. Complex old roofs with dormers and valleys are also prone to ice dams, where meltwater backs up under the shingles and runs down inside the wall.

Aging plumbing and drains

An old house can have several generations of pipe in it: galvanized steel supply lines that rust from the inside, cast iron drain stacks that crack or rot through at the bottom, and newer copper or plastic patched in between. Slow leaks at old joints are common, and they often run inside plaster walls where nobody sees them.

The sewer lateral to the street is frequently the original clay pipe. The mature trees that make these neighbourhoods attractive send roots into its joints. A partial blockage gives little warning before it backs up through the floor drain.

What to check in an old house

• Musty smell in a finished basement, especially at exterior walls and in closets.
• White salts, damp patches or flaking on bare foundation walls.
• Dark staining or frost on the underside of the roof boards in winter.
• A bathroom fan duct that ends in the attic.
• Stains on ceilings below bathrooms and along exterior walls under the eaves.
• Rusty or corroded pipe joints, and a main shutoff that will not turn.
• Downspouts that empty beside the foundation or into old underground drains.

Fixing old house moisture problems in London, Ontario homes

Start outside. Clean eavestroughs, downspouts carried away from the wall, soil sloped away from the foundation and repaired mortar and flashings keep most water out and cost far less than interior work. Run a dehumidifier in the basement through the humid months. Seal the air leaks into the attic and vent every bath fan to the outdoors.

Do not finish a basement wall until you know how wet the masonry gets through a full year. Have the sewer lateral looked at with a camera, and replace old supply lines when you open a wall for any other reason.

One caution before any tear-out. Houses of this age can contain asbestos in plaster, pipe wrap, old flooring and vermiculite attic insulation. Suspect materials should be tested before they are disturbed. If you want to know where the moisture is before deciding anything, a thermal camera and moisture meter inspection will map it without opening walls. Those inspections run $249 to $549.

Common questions