Crawlspace Encapsulation in Landmark

Landmark, east of the Red River in the RM of Taché, is a farming community that has grown into a commuter town while keeping much of its original rural housing stock. Those older homes are where we do most of our crawlspace work. They sit on heavy clay, typically on shallow footings, and many have crawlspaces that were excavated just deep enough to run services. Soil floors, open vents and batt insulation between the joists are the standard configuration, and it is an assembly that fails slowly and invisibly in our climate.

The clay around Landmark drains poorly, so snowmelt and heavy rain stay at the surface and move laterally. Foundation backfill is the easiest route down, which is why so many crawlspaces here take water in the first warm week of spring, while the subsoil is still frozen and nothing can percolate. Through summer, the same spaces swing the other way: humid outside air enters through vents, condenses on cool soil and framing, and keeps wood moisture content in the range where mould thrives. By the time there is a smell in the house, the framing has usually been damp for years.

For rural properties like these, we build systems that run unattended. Drainage is installed where the water actually arrives, with a sump and freeze-resistant discharge routed well clear of the foundation and septic field. The barrier is reinforced, mechanically fastened, and sealed at every well, septic and plumbing penetration. Insulation moves from between the joists to the perimeter wall so the floor assembly stays warm and dry, and the space is brought into the conditioned envelope. Where we find tipped piers or soft sill plates, structural repair comes first so the rest of the system has something stable to seal against.

Calls from Landmark are mostly from owners of the older rural housing stock, and they tend to arrive after someone has finally gone into a crawlspace that had been left alone for years. The findings are consistent: soil floor, open vents, batts sagging out of the joists, elevated framing moisture, mould on the subfloor sheathing, and sometimes a pier that is no longer bearing properly. The second category of call is seasonal — water in the first warm week of spring, gone by June.

Rural systems have to run without supervision, which drives our specifications. Mechanically fastened barriers rather than loose poly. Sumps with freeze-resistant discharge routed clear of the septic field. Dehumidifiers with permanent drains. A high-water alarm where a failure would cause real damage. And insulation at the perimeter rather than the ceiling, so well lines and plumbing in the space are protected by ambient temperature rather than by pipe sleeves alone.

Our first recommendation on a Landmark property is almost always exterior water management plus a structural assessment, in parallel. The exterior work is cheap and removes much of the load on dense clay. The structural assessment tells you whether the piers and sill plates can support a sealed system or need correction first. Together they define the project, and we would rather establish both before quoting anything.

Crawlspace encapsulation means building a continuous, sealed envelope between your home and the ground beneath it. A reinforced polyethylene membrane — we specify 12-mil as a minimum and 20-mil where there will be foot traffic or sharp aggregate — is laid across the soil floor, carried up the foundation walls, mechanically fastened and sealed at every seam and penetration. Vents are closed and sealed from the inside. Insulation moves from between the floor joists to the perimeter wall, so the crawlspace joins the heated envelope of the house instead of sitting outside it. Humidity is then held at a stable target, usually in the 50 to 55 percent range.

The reason this matters so much in Winnipeg is that our climate attacks a crawlspace from two directions in the same year. In January, an unconditioned, vented crawlspace runs close to outdoor temperature. Warm, moist air from the living space moves down through the floor and condenses or frosts on the cold underside of the subfloor and on cold rim joists. In July, the direction reverses: humid outdoor air enters through the vents, hits soil and framing that are still cool, and condenses there instead. Either way the wood stays wet, and wood that holds above roughly 19 percent moisture content supports rot and mould.

Encapsulation also addresses something many homeowners here have never considered: soil gas. Manitoba records some of the highest indoor radon concentrations in Canada, and a crawlspace with bare or poorly covered soil is the most direct entry route into a house. A properly sealed and fastened membrane is the foundation of any radon strategy, and in homes with elevated readings it becomes the sealed layer that an active sub-membrane depressurization system draws from. Sealing the floor does double duty — it stops both water vapour and soil gas.

A real encapsulation is not a sheet of poly thrown on the dirt. The membrane must be continuous, with seams overlapped and taped on both faces where the material allows. It has to be carried up the walls and terminated with a mechanical fastener and sealant, not just tucked behind a rock. Piers and columns are wrapped individually. Plumbing, electrical, well and septic penetrations are sealed with foam and compatible tape. Any dehumidifier gets a permanent gravity drain or a condensate pump, because a unit draining into a bucket stops working the first month nobody empties it. Shortcuts at any of these points leave a bypass that undoes much of the benefit.

Before we encapsulate anything, we establish that the space is not taking liquid water. Sealing a crawlspace that still receives groundwater during spring melt just traps the water inside the membrane, where it is harder to find and does more damage. If the inspection shows an active water path, drainage and a properly discharged sump go in first. Once the space is dry and sealed, the results are measurable within weeks: framing moisture content drops, the musty smell in the house above disappears, the floor over the crawlspace stops feeling cold in winter, and the furnace stops working to heat a space that was open to the outdoors.

The mistakes we find in previously encapsulated crawlspaces are consistent enough to list. The membrane stops at the base of the wall instead of being carried up and terminated, so soil moisture simply travels around the edge. Seams are overlapped but taped on one face only, which fails the first time anything moves. Vents are covered on the outside with foam board rather than sealed from inside, so they still admit air. The dehumidifier drains into a bucket. Insulation was left in the floor joists, so the space stays cold and the barrier is holding back vapour from a surface that is still below the dew point in summer. Each of these is individually small, and together they are why a homeowner can pay for an encapsulation and still have a damp crawlspace two years later.

On a typical project we work in a defined order and tell you in advance what each day involves. Day one is clearance and assessment with the space fully exposed. If structural repair or drainage is in scope, that happens next, because both involve excavation and cutting that would destroy a finished barrier. Then the floor is graded where it is uneven enough to leave low spots under the membrane, the barrier is installed and sealed, piers are wrapped, and penetrations are detailed. Perimeter insulation and rim joist air sealing follow. Humidity control is commissioned last, with its drain run and tested. We photograph each stage, partly for your records and partly because once the barrier is down, most of what we are documenting is no longer visible.

Maintenance afterward is minimal but not zero. Once a year, ideally in early spring before melt, the space is worth opening: confirm the sump runs and the discharge line is clear, check the dehumidifier is cycling and draining, look along the barrier terminations for anything that has worked loose, and check the access hatch still seals. Twenty minutes. Keep stored items in sealed plastic bins rather than cardboard, and keep a clear path to the sump and any structural posts so the space can still be serviced. If you ever have plumbing or electrical work done in the crawlspace, ask the trade to tell you where they cut the barrier so it can be patched properly rather than discovered years later.