A crawl space is often the least visited part of a house and one of the most revealing. The main things to look for are moisture, the condition of the ground cover and insulation, damage to the framing that supports the floor, plumbing and wiring problems, and signs of pests. Problems here affect the floors above, indoor air quality and energy use.
Why crawl spaces matter
Air moves upward through a house, so air from the crawl space ends up in the living areas. A damp, mouldy or musty crawl space can affect indoor air quality throughout the home. Cold crawl spaces also lead to cold floors, frozen pipes and higher heating bills in a Canadian winter. And the floor structure sits directly on the crawl space walls and piers, so any rot or settlement shows up as sagging or bouncy floors.
What to check
Moisture and ground cover
- Standing water, wet soil or water stains on walls.
- A continuous polyethylene ground cover (vapour barrier) over exposed soil, with overlapped and sealed seams, and no large tears or gaps.
- Condensation on pipes, ductwork or the underside of the floor.
- Musty odour, visible mould or efflorescence on foundation walls.
- Working sump pump, if there is one.
Structure
- Floor joists, beams and the sill plate: look for rot, soft wood, cracking, sagging or past repairs.
- Posts and piers: plumb, sitting on proper footings, not on bare soil or loose blocks.
- Foundation walls: cracks, bowing, or gaps under the sill plate. See foundation warning signs.
- Notches or holes cut into joists for plumbing or ducts, which can weaken them.
- Wood in direct contact with soil, which invites rot and insects.
Insulation and air sealing
- Whether the crawl space is designed to be vented or unvented (conditioned), and whether it is built consistently with that.
- Insulation in place on the walls or between floor joists, not fallen down or wet.
- Rim joists insulated and air sealed.
- Gaps around pipes and wires through the floor sealed.
Services
- Leaking supply or drain lines, and drain lines with poor slope or sags.
- Pipes at risk of freezing, and heat tracing that is installed and working where used.
- Ductwork that is disconnected, crushed or leaking into the crawl space.
- Wiring that is loose, unsupported, damaged, or has open splices outside of junction boxes.
- Dryer vents and bathroom fans that discharge into the crawl space instead of outdoors.
Pests
- Rodent droppings, nests, chewed insulation or wiring.
- Evidence of insects that damage wood.
- Openings where animals can get in.
Vented or unvented?
Older homes often have vented crawl spaces, with openings meant to let moisture escape. In cold and humid conditions, venting can bring in moist air or freezing air instead, and many building scientists now favour sealed, insulated and conditioned crawl spaces in cold climates. What is right for a given house depends on the design, the local building code and the soil conditions. Mixing the two approaches, such as insulating the floor above but sealing the vents, can create problems. Get advice before changing how a crawl space is set up. Our guide to building envelope basics explains the principles behind these choices.
Working through a crawl space, step by step
A methodical walk-through finds more than a quick look from the hatch. A typical order, with what to note at each stage:
- From the hatch. Before going in, smell the air, look for standing water, and check for hazards such as exposed wiring, sharp debris or signs of animals. Note anything that means the space should not be entered.
- The perimeter. Follow the foundation walls around the space. Record cracks, water staining, efflorescence, gaps under the sill plate and the condition of wall or rim joist insulation, with a rough location for each.
- The floor framing. Probe suspect wood with a screwdriver or awl. Wood that is soft or crumbles is a sign of rot. Note sagging joists, cut or notched joists and any past repairs such as sistered joists or added posts.
- Posts and piers. Check that each sits on a proper footing, is plumb and is firmly in contact with the beam above. Shims stacked under a post or posts on bare soil are worth recording.
- Services. Look along supply and drain lines for leaks, drips and sags, follow ducts for disconnections, and check that fan and dryer vents carry on to the outside.
- The ground. Lift the edge of the ground cover in a few places to see if the soil beneath is wet. Record tears, gaps and areas with no cover.
- Photos and readings. Take photos with something for scale and, where a moisture meter is available, take readings on framing in several areas so changes can be compared later.
Common findings and usual fixes
| Finding | Likely cause | Usual fix |
|---|---|---|
| Wet soil, musty smell | Missing or torn ground cover, poor outside drainage | Install or repair the cover; correct grading and downspouts |
| Condensation on pipes and framing in summer | Humid outside air entering through vents | Get advice on air sealing and drying the space |
| Soft or rotted sill plate | Long-term moisture, wood in contact with concrete or soil | Structural repair by a qualified contractor |
| Fallen floor insulation | Poor support, moisture or pests | Fix the cause and reinstall or reconsider the approach |
| Frozen or burst pipes | Cold space, gaps in insulation or air sealing | Insulate and seal; check heat tracing |
Getting in safely
Crawl spaces are tight, dark and sometimes wet. If you go in yourself:
- Tell someone where you are and how long you will be.
- Wear coveralls, gloves, knee pads and a headlamp. Wear respiratory protection if there is visible mould, droppings or loose insulation.
- Watch for exposed wiring, nails and sharp debris. If there is standing water and electrical equipment nearby, stay out and call an electrician.
- Do not disturb old insulation, pipe wrap or other material that might contain asbestos. See asbestos in older buildings.
- If the space is very tight, has poor air, or you are not comfortable, leave it to a professional.
Musty smell upstairs? If the house smells musty and the basement looks fine, check the crawl space. Damp ground with no or damaged ground cover is a common source of moisture and odours.
How ehZee can help
Where it is accessible and safe to enter, an ehZee home inspection includes a look at the crawl space for moisture, structure, insulation and services. You can be there with the inspector and hear the findings on the day, then receive a written report within two days.
Common questions
Is some dampness in a crawl space normal?
Soil gives off moisture, which is why a sealed ground cover matters. Standing water, wet framing or condensation are not normal and need attention.
What if the crawl space cannot be entered?
An inspector will note that it was not accessible and may look from the access hatch. Limited access means some problems may not be found, so consider arranging access before buying.
Should I close the crawl space vents in winter?
It depends on how the crawl space was designed. Closing vents in a space that relies on them, or opening a sealed one, can cause moisture or freezing problems. Get advice specific to your house before changing it.