Crawl Space Pests: What’s Living Under Your Maple Ridge Home
Out of sight, out of mind — that’s how most homeowners think about their crawl space. It’s dark, cramped, uncomfortable to access, and easy to ignore. Which is exactly why pests love it. Your crawl space offers everything unwanted guests are looking for: moisture, shelter, darkness, warmth in winter, and a direct pathway into the rest of your home.
If you own a home with a crawl space in Maple Ridge or anywhere in the Lower Mainland, understanding what lives down there — and how to keep it out — is essential for protecting both your home’s structure and your family’s health. Crawl space pests are one of the most common and most under-addressed issues in our region.
Why Crawl Spaces Are Pest Magnets in the Lower Mainland
Not all crawl spaces are equal, but the Fraser Valley’s climate and building history create conditions that make our crawl spaces particularly vulnerable.
Moisture: The Root of Everything
The Lower Mainland receives an average of 1,500mm of rainfall annually. That water has to go somewhere, and a significant portion of it ends up as ground moisture under your home. Even with a vapour barrier in place, crawl spaces in our region tend to run humid — 60%, 70%, sometimes higher. That moisture creates the conditions that virtually every crawl space pest depends on.
Homes in lower-lying areas of Maple Ridge (near the Pitt River floodplain), Pitt Meadows (where the water table is naturally high), and parts of Port Coquitlam near the Coquitlam River are especially prone to crawl space moisture issues. Many homes built in these areas between the 1960s and 1990s have crawl spaces that were constructed with minimal or no moisture management — and decades of ground moisture have created ideal pest habitat.
Easy Access From Grade Level
Unlike attics, which require pests to climb, crawl spaces sit at or below ground level. Any creature that can walk, crawl, or burrow has direct access to the perimeter of your crawl space foundation. Vents designed for air circulation also serve as entry points for rodents, insects, and wildlife — especially when screening deteriorates or was never installed to current standards.
Darkness and Minimal Disturbance
Most crawl spaces are entered once or twice a year at most — during a home inspection or when a plumber needs access. That level of disturbance means pest populations can establish, grow, and thrive for months or years before anyone notices.
Common Crawl Space Invaders in BC
The crawl space ecosystem under a typical Lower Mainland home can be surprisingly complex. Here are the pests we encounter most frequently.
Rats and Mice
Rodents are the most common and most destructive crawl space pest in the Fraser Valley. Norway rats burrow under foundations and access crawl spaces through gaps in foundation walls, damaged vent screens, and spaces around utility penetrations. Mice enter through openings as small as 6mm. Once inside, they:
- Nest in insulation, destroying its thermal value and creating unsanitary conditions
- Gnaw on wiring, creating a genuine fire hazard
- Chew through plumbing (especially PEX and PB piping), causing water damage
- Contaminate the crawl space with droppings and urine, which can affect indoor air quality through the floor system above
- Use the crawl space as a base to access the rest of the house through wall cavities, plumbing chases, and gaps around ductwork
In Maple Ridge, where agricultural land borders residential areas and wooded lots are common, rodent pressure on crawl spaces is consistently high. Properties near the Albion Flats, homes backing onto farmland, and lots adjacent to Kanaka Creek see particularly heavy rodent activity.
Carpenter Ants
Moisture-damaged wood in a crawl space is a carpenter ant buffet. Floor joists, rim joists, and mudsills that have been exposed to high humidity or direct moisture contact develop the softened wood conditions carpenter ants need to excavate their nesting galleries. A mature carpenter ant colony in your crawl space slowly compromises the structural integrity of your floor system — and because it’s all happening in a space you rarely inspect, damage can be extensive before it’s noticed.
Signs of carpenter ants in a crawl space include smooth, clean galleries in wood members, frass piles (fine sawdust mixed with insect body parts) on the vapour barrier below affected joists, and visible ant traffic along foundation walls and joists.
Termites
While BC doesn’t have the severe termite pressure of warmer climates, dampwood termites and subterranean termites are present in the Lower Mainland. Crawl spaces with wood-to-soil contact — where foundation posts, form boards, or debris sit directly on the ground — create the conditions termites exploit. Mud tubes running from the soil up foundation walls are a telltale sign of subterranean termite activity.
Spiders
Crawl spaces host healthy populations of various spider species, including giant house spiders and hobo spiders. While generally not dangerous (hobo spider bite concerns have been largely debunked), heavy spider populations indicate an abundant insect prey base in the crawl space — which means other pest problems are present.
Sowbugs and Pill Bugs
These moisture-dependent crustaceans (yes, they’re more closely related to lobsters than to insects) thrive in damp crawl spaces. They feed on decaying organic matter and are usually present in large numbers when ground moisture is high. They’re not destructive, but their abundance is a reliable moisture indicator.
Earwigs
Another moisture-loving pest that uses crawl spaces as harbourage. Earwigs enter the crawl space for shelter and moisture, then migrate upward through the floor system into basements and main-floor bathrooms — often alarming homeowners who don’t realize the source is below them.
Raccoons and Skunks
In Maple Ridge and Coquitlam, it’s not unusual to find raccoons or skunks using an unsealed crawl space as a den — especially during spring birthing season. A damaged vent screen or a gap in the foundation is all they need. Wildlife in a crawl space creates immediate problems: noise, odour, structural damage from denning activity, and parasites (fleas, ticks) that can migrate into the living space above.
Warning Signs of Crawl Space Infestation
You don’t need to crawl under your house weekly to monitor for pest activity. These indicators, observable from inside the living space, can alert you to problems developing below.
Musty or Unusual Odours
A persistent musty smell rising through the floor — especially noticeable in winter when the house is closed up — can indicate mould growth (driven by excess moisture), rodent urine accumulation, or wildlife denning. The air in your crawl space doesn’t stay in your crawl space. Studies show that up to 40% of the air you breathe on the main floor originated in the crawl space through a phenomenon called the stack effect.
Sagging or Damaged Insulation
If you can access your crawl space hatch (typically in a closet, utility room, or exterior access), look at the insulation between your floor joists. Insulation that’s falling down, compressed, stained, or has been pulled apart is almost certainly rodent-damaged. Rats and mice shred batt insulation for nesting material, and the damage is visible from the hatch opening without fully entering the space.
Droppings on the Vapour Barrier
Rodent droppings visible on the crawl space vapour barrier (the plastic sheet on the ground) are a clear indicator. Rat droppings are roughly the size of a raisin; mouse droppings are rice-grain sized. Fresh droppings are dark and moist; old droppings are grey and crumbly. The quantity and distribution of droppings indicate the severity and duration of the infestation.
Increased Pest Sightings on the Main Floor
Seeing more earwigs, spiders, sowbugs, or ants on your main floor — especially in bathrooms, kitchens, and laundry rooms — often indicates that populations in the crawl space below have grown large enough to push individuals upward through gaps in the floor system.
Gnaw Marks and Damage to Utilities
During any crawl space visit (or by asking your plumber or HVAC technician to check), look for gnaw marks on wiring, plumbing, and ductwork. Rodents gnaw continuously to wear down their constantly growing incisors. Damaged duct insulation, chewed flexible ductwork, and gnawed pipe insulation are common findings.
Moisture Control: The #1 Crawl Space Pest Prevention Strategy
Every pest on the list above is either directly dependent on moisture or attracted to conditions that moisture creates. Address the moisture, and you address the root cause of most crawl space pest issues.
Vapour Barrier Installation and Maintenance
A proper vapour barrier — 6-mil or thicker polyethylene sheeting covering the entire crawl space floor and sealed to the foundation walls — is the foundation of crawl space moisture management. Many older homes in the Lower Mainland either lack a vapour barrier entirely or have one that’s deteriorated, punctured by rodents, or only partially installed. Replacing or properly installing a vapour barrier is often the single most impactful improvement you can make.
Drainage and Grading
Water should drain away from your foundation on all sides. Downspouts should discharge at least 2 metres from the foundation. Grading should slope away from the house at a minimum 5% grade for the first 2 metres. In areas of Pitt Meadows and lower Maple Ridge where natural drainage is poor, a perimeter drain (weeping tile) system may be necessary to keep groundwater from accumulating around and under the foundation.
Ventilation
BC Building Code requires crawl space ventilation — typically 1 square foot of ventilation per 150 square feet of crawl space area. Ensure foundation vents are open and unobstructed. In some cases, particularly in very damp locations, mechanical ventilation (an exhaust fan on a humidistat) is more effective than passive vents, especially during BC’s wet winter months.
Dehumidification
For crawl spaces with persistent moisture issues despite proper vapour barriers and drainage, a dedicated crawl space dehumidifier is an effective solution. Modern units designed for crawl spaces are energy-efficient, drain automatically, and can maintain humidity below the 50% threshold that most pests require.
Professional Crawl Space Inspection and Treatment
Because crawl spaces are difficult to access and assess, professional inspection provides value that’s hard to replicate with a quick look through the access hatch.
What a Crawl Space Inspection Covers
A thorough inspection evaluates:
- Pest activity: Evidence of rodents, insects, and wildlife — droppings, damage, nesting, live sightings
- Moisture levels: Humidity readings, vapour barrier condition, signs of standing water or water intrusion
- Wood condition: Floor joists, rim joists, mudsills, and structural posts checked for moisture damage, rot, and pest damage
- Entry points: Foundation vent condition, gaps in the foundation wall, utility penetrations, access hatch integrity
- Insulation condition: Whether insulation is intact, damaged by rodents, or waterlogged
Exclusion Work
The most important outcome of a crawl space pest service is exclusion — sealing the crawl space against pest entry. This includes:
- Replacing damaged or missing vent screens with 1/4-inch galvanized hardware cloth
- Sealing gaps in the foundation wall with concrete patch or metal flashing
- Sealing around utility penetrations (plumbing, electrical, HVAC)
- Repairing or replacing the access hatch with a properly sealed and latched door
Insulation Replacement
When rodents have damaged crawl space insulation, replacement is typically necessary. Contaminated insulation can’t be effectively cleaned — it needs to come out, the area needs to be sanitized, and new insulation installed. This is often combined with vapour barrier work and exclusion for a comprehensive crawl space restoration.
Ongoing Monitoring
Crawl spaces should be inspected at least annually — ideally in spring before pest season peaks and again in fall before rodents seek winter shelter. Professional monitoring catches problems early when they’re small and inexpensive to address, rather than after months of unchecked pest activity have caused significant damage.
Don’t Ignore What’s Under Your Home
Your crawl space may be the part of your home you think about least — but for pests, it’s the most attractive entry point your house offers. Moisture, darkness, shelter, and a direct path into the living space above make it a pest superhighway. And in the Fraser Valley’s wet climate, the conditions down there are working against you year-round.
The fix isn’t complicated: control moisture, seal entry points, and monitor regularly. But it starts with knowing what’s actually happening down there.
When was the last time someone inspected your crawl space? Call Canadian Pest Control at (778) 598-7378 or visit cpestcontrol.ca to schedule a free crawl space inspection. We serve homeowners across Maple Ridge, Coquitlam, Port Coquitlam, Pitt Meadows, and the Lower Mainland — and we’ll give you an honest assessment of what’s living under your house and what it’ll take to keep it out.