Many older houses in Metro Vancouver have a crawl space, a low room between the ground and the floor, usually less than a metre tall. It is dark, it is not used for anything, and nobody looks at it until something goes wrong. It is also where much of the water in a house ends up. Wet crawl spaces are among the most common findings in our reports, and also among the most fixable.
Where the water comes from
Four sources account for most of it. A crawl space often has more than one.
- Surface water. Rain running off the roof and the lot toward the foundation. A downspout that ends at the wall, soil that slopes toward the house, or a blocked drain.
- Groundwater. In wet months the water table rises. In low-lying areas such as parts of Richmond and Delta, the ground is wet for much of the year. Water enters through the footing, floor or walls.
- Plumbing. A leaking supply or drain pipe, a dripping fitting, a condensate line from a furnace that discharges in the wrong place.
- Vapour from the soil and the air. Bare soil gives off moisture all the time, even if it looks dry. Warm, damp air from outside can also condense on cool surfaces in summer.
- 1 Floor framing and subfloor above
- 2 Downspout or grading that sends roof water to the foundation
- 3 Foundation vent (some crawl spaces are vented, some are conditioned)
- 4 Bare soil that is not covered: moisture rises into the space
- 5 Polyethylene ground cover, with overlapped and taped seams
- 6 Standing water or a damp patch after rain
- 7 Sump pit, where one exists
- 8 Cold water pipes that sweat in warm weather and drip on insulation
Signs you can see
You do not need to go in to spot some of these.
- A musty smell in the house, mostly in the lower floor
- Floors that are cold, springy or have a cupped look
- Condensation or rust on ducts and pipes in the space
- Stains on the foundation wall and a white powder on the concrete (efflorescence), which tells you moisture has been moving through
- Insulation between the joists that is sagging, stained or has fallen
- Dark growth on wood, which may or may not be mould, and which needs testing to say
- Standing water, damp or soft soil, a tide line on the wall
- Wood-boring pests or rodents
In the crawl space itself, an inspector adds a moisture meter to this. High readings on joists and subfloor are a concern, and what matters is whether the numbers are high everywhere or only at one spot near a leak. Meter readings give a snapshot. They do not tell you the cause.
Why it matters
Moisture in a crawl space does not stay there. It reaches the floor framing and, over years, can lead to rot and loss of strength. It feeds mould, and the stack effect carries some of that air upstairs. It attracts insects and rodents. It can corrode ducts and fasteners. And it wets insulation, which stops insulating.
None of this is quick. A problem found early is usually a drainage fix and a ground cover. A problem left for twenty years becomes a repair of joists and subfloor.
What to do about it, in order
- Stop the water at the source. Extend downspouts away from the wall, fix the grading, clear the drains. If a pipe leaks, repair it. This is the cheapest step and the one that matters most.
- Cover the ground. Modern practice is a continuous polyethylene ground cover over the soil, with overlapped and sealed seams and turned up the walls. Many old crawl spaces have none, or a ragged sheet that has been torn.
- Deal with standing water. Where groundwater is a recurring problem, a drainage contractor may recommend perimeter drainage and a sump pit with a pump. A pump is a mechanical part with a life of its own, and should be tested.
- Replace wet insulation. Wet insulation holds water against the floor and needs replacing once the source is fixed.
- Decide on ventilation. Older practice was to vent crawl spaces to the outside, and many still have vents. Some owners now seal and condition the space instead. There are views on both, and the right answer depends on the house. A contractor who has seen your crawl space is better placed than a general rule.
- Monitor. After a repair, look again through a wet winter. A hygrometer or a simple moisture meter, checked monthly, shows whether things are improving.
What an inspector can and cannot do
We go in if there is safe access. We look at the soil, the walls, the joists, the pipes and ducts, the insulation and the vents, and we use a moisture meter. If the space is too small, flooded or has hazards such as exposed wiring, a wasp nest, or animal nesting, we say so and note what we could not see.
We do not test for mould. If we see growth, we describe it and recommend testing and remediation by a qualified specialist. We cannot say whether a dark patch is a serious problem or a stain.
If you are buying
A wet crawl space is a common finding and is not a reason to walk away, but it needs a plan. Ask the seller about past water and any repairs. Look at the lot slope and the downspouts on your visit. Get a written quote from a drainage or crawl space contractor before subjects come off. And read the sections of the report on grading and on the foundation together with the crawl space section, because the cause is often outside.
If you are selling
Fix the downspouts and the grading, clear the access hatch, and if you have already done work, leave the invoice out. A buyer who can see that a crawl space has been dealt with is more relaxed than one who finds it damp.
A focused crawl space and attic inspection is available for owners who want a look at these two spaces without a full house inspection.