Basement crawl space waterproofing means two jobs that people often mix up. Waterproofing keeps liquid water out of the space with grading, drains and sump pumps. Encapsulation seals the floor and walls with a liner to control moisture vapour. If water enters the crawl space, fix the water first. If the space is only damp and humid, a sealed liner may be enough.
Waterproofing and encapsulation are different jobs
A crawl space is a low, enclosed area under a floor. The Ontario Building Code treats a crawl space as an area with less than 1,800 mm of clearance. Many older Ontario houses have one under an addition. Many cottages have one under the whole building.
Waterproofing deals with liquid water. The water can come from surface runoff, a high water table or spring melt. The usual tools are:
- Grading that slopes away from the foundation.
- Eavestroughs and downspouts that discharge away from the walls.
- Perimeter drains inside or outside the footing.
- A sump pit and pump.
- Exterior membranes on the foundation wall.
Encapsulation deals with vapour and air. The contractor lays a heavy polyethylene liner over the floor and up the walls. The seams are taped and the liner is sealed to the foundation. The aim is to stop ground moisture from rising into the floor framing.
The two jobs work together. A liner over a floor that floods will trap water under plastic. Natural Resources Canada notes that a polyethylene moisture barrier is the minimum for a heated crawl space. It also says to renovate a heated crawl space like a short basement. You can read the guidance in Keeping the Heat In, Section 6.
An older National Research Council study makes the same point. A ground cover loses most of its value if the crawl space floods from time to time. The study is available in the NRC publications archive.
How to tell which problem you have
Look at the space after a heavy rain and again in late summer. The two problems leave different signs.
Signs of liquid water
- Standing water or wet soil after rain or snowmelt.
- Tide lines or mineral deposits on the foundation wall.
- Mud on the liner or on the pier bases.
- A sump pit that fills often.
Signs of vapour and humidity
- A musty smell that gets worse in July and August.
- Condensation on cold water pipes and ducts.
- Damp or cupped floor boards above the space.
- Surface mould on joists, with dry soil underneath.
Many Ontario houses show both. Clay soils around Toronto drain slowly, so water sits against the wall after rain. Ottawa sits on the Champlain Sea clay plain in many areas, and that clay also holds water. In the Ottawa Valley and on Georgian Bay, cottage lots often sit on rock or shallow soil, and water moves along the rock surface. A site visit is the only way to know which case you have.
Decision matrix
| What you see | Likely first fix | Add encapsulation? |
|---|---|---|
| Standing water after rain | Grading, eavestroughs, drain and sump | Yes, after the water is controlled |
| Damp walls, no standing water | Downspout and grading work, wall sealing | Often |
| Musty air, dry soil | Ground cover and sealed seams | Yes, this is the main fix |
| Mould on joists | Moisture source first, then mould removal | After the source is fixed |
| Winter-closed cottage on piers | Drainage and animal-proof skirting | Usually not as a full seal |
| Heated year-round space | Treat as a short basement | Yes, with insulation and air sealing |
The table is a guide, not a diagnosis. A contractor who inspects the space may reach a different result.
What encapsulation involves
Natural Resources Canada gives a minimum ground cover of 0.10 mm (4 mil) polyethylene, overlapped, caulked and taped at the seams. Contractors often use a thicker, reinforced liner because people walk on it and move gear across it. NRCan also warns against sand or gravel on top of the barrier. The same source says to hold the barrier down so that it does not billow.
A full job usually has these parts:
- Clear debris and level the floor.
- Fix any liquid water source.
- Lay the liner, lap the seams and tape them.
- Run the liner up the walls and seal it to the foundation.
- Insulate the walls if the space will be heated.
- Condition the air with a dehumidifier or a supply of house air.
Step 6 matters in Ontario because summer air is humid. NRCan advises against vents to the outside in a heated crawl space because of summer condensation. It suggests a whole-house ventilation approach or a dehumidifier instead.
Unheated crawl spaces follow a different rule. The Ontario Building Code asks for natural or mechanical ventilation in an unheated crawl space. It also asks for a ground cover. A homeowner who seals the vents on an unheated space can create a new moisture problem. Check the current code text and ask your local building department before you seal vents.
Houses and cottages need different plans
Houses
Most Ontario houses with a crawl space have a heated or semi-heated space. Ducts may run through it. A bathroom may sit above it. For these houses, the short basement approach makes sense: control water, seal the floor, insulate the walls and keep the air dry.
Cottages
A cottage faces frost heave, long closed periods and rodents. A cottage that closes in October and opens in May may do well with good drainage, a ground cover and a skirting that keeps animals out. Sealing and heating such a space adds cost and may not give a return. A year-round cottage is different. Treat it like a house.
Spring access also matters. Georgian Bay and Muskoka lots can have a high water table in April and May. A pump with no power at a closed cottage will not run. Ask about a battery backup or a plan for power loss.
What it costs
We could not find a reliable Ontario price source for crawl space work, so this guide gives no dollar figures. Costs in the United States are not a safe basis for Ontario quotes. Several things drive the price:
- The area and height of the crawl space.
- Access. A 500 mm by 700 mm hatch makes work slow.
- Whether drains and a sump are needed.
- Liner thickness and wall coverage.
- Insulation and a dehumidifier.
- Mould removal, if needed.
Ask each contractor for a written scope with a line for each item. Compare scopes before you compare totals. Costs vary by site, by season and by contractor.
Mould in a crawl space
Mould needs moisture. The Canada Mortgage and Housing Corporation lists crawl spaces and basements as places where most mould growth is found. It also lists fixing damp foundations and crawl spaces as a key step. See the CMHC mould resource guide.
If you see mould, do not seal it under a liner. Remove it first, or have a mould contractor assess it. Then fix the moisture source. You can compare mold removal companies in Toronto and mold removal companies in Ottawa on our boards.
What our boards show for Toronto and Ottawa
This section uses our own board data for October 2026. It describes the listings. It is not an endorsement of any company. Most boards rank companies by Google rating and review count. Crawl space work is a small part of what these firms do, so check each firm’s own services before you call.
| Board | Companies ranked | Median rating | Median reviews | Total reviews | Under 20 reviews |
|---|---|---|---|---|---|
| Toronto waterproofing contractors | 20 | 5.0 | 102.0 | 3,969 | 1 |
| Toronto basement waterproofing companies | 20 | 5.0 | 81.5 | 3,934 | 1 |
| Ottawa basement waterproofing companies | 20 | 5.0 | 61.0 | 1,482 | 5 |
| Toronto mold removal companies | 19 | 4.9 | 76 | 2,044 | 4 |
| Ottawa mold removal companies | 20 | 4.75 | 43.0 | 1,295 | 4 |
What this means for choosing:
- Toronto has a deep field. The median Toronto waterproofing contractor has 102.0 reviews, and only 1 of 20 has fewer than 20.
- Ottawa has a thinner field. On the Ottawa basement waterproofing board, 5 of 20 companies have fewer than 20 reviews. The median is 61.0.
- Median ratings of 5.0 on three boards show that rating alone does not separate companies. Review count and review content matter more.
- A rating below the board median is not a verdict. The Ottawa board lists The Foundation Guys Inc. at 4.2 with 223 reviews. That is a large sample, and a lower score from many reviews is a different signal than a lower score from a few.
- A company with a high rating from a handful of reviews has less evidence behind it than a company with a slightly lower rating and hundreds of reviews.
Review counts do not tell you who has crawl space experience. Read recent reviews for words such as “crawl space”, “drain” or “sump”. Ask for photos of earlier crawl space jobs. Ask for the scope in writing.
If you live outside these two cities, the waterproofing contractor trade hub links to every market. There are also boards for Mississauga, Hamilton and Barrie, among others.
Questions to ask before you sign
- Where does the water come from, and how will you stop it?
- Is the crawl space heated, and how will the plan handle summer humidity?
- What liner thickness and what seam method will you use?
- Will the liner go up the walls and seal to the foundation?
- Is a sump pump or drain part of the scope? What happens in a power cut?
- Who removes mould, if any is present?
- Does the job need a permit from my municipality?
- What does the warranty cover, in writing?
A contractor who cannot answer questions 1 and 2 has not understood the problem yet.
Frequently asked questions
Is crawl space encapsulation the same as waterproofing?
No. Waterproofing stops liquid water with grading, drainage, sump pumps or exterior membranes. Encapsulation seals the floor and walls with a liner to control vapour and air. Encapsulation does not fix a space that floods.
Do I need a dehumidifier in an encapsulated crawl space?
Often yes, in a humid Ontario summer. Natural Resources Canada advises a whole-house ventilation approach or a dehumidifier in heated crawl spaces instead of vents to the outside. Ask the contractor how the space will be conditioned.
Should a cottage crawl space be sealed and heated?
It depends on how you use the cottage. A winter-closed cottage on piers or a block foundation has different needs than a heated year-round home. Ask a contractor for a written plan that covers frost, drainage and ventilation.
How do I compare crawl space contractors in Toronto or Ottawa?
Check the Google rating and the number of reviews together, then read recent reviews for crawl space or drainage work. Ask for a written scope that names drainage, liner material and any pump. Get at least two quotes.