CRAWL SPACES
Understanding Crawlspaces in Pacific Northwest Homes
What Homeowners Usually Think
“As long as the crawlspace has vents, it stays dry.”
What Actually Happens
In the Pacific Northwest, a vented crawlspace almost never stays dry.
Cold, damp outside air enters through the vents, cools the warmer crawlspace, and drives the relative humidity up—often high enough to create mold, rot, and structural damage.
Instead of ventilating moisture out, the vents often bring moisture in.
Why Crawlspaces Fail in Our Climate
High Exterior Humidity
Here, the outside air is already wet. When that air enters a cooler crawlspace, humidity spikes and condensation forms on framing.
Inadequate Vapor Barriers
Most older homes have thin, loose polyethylene on the ground—torn, poorly sealed, or missing entirely—allowing moisture and soil gases to rise into the home.
Air Leaks Between Crawlspace and Living Areas
Gaps around plumbing, HVAC, and subfloor seams allow moist or contaminated air to enter the home.
Rodent and Pest Activity
Vented crawlspaces pull in rodents, droppings, and dander—often into the home through pressure changes or duct leakage.
Duct Leakage + Pressure Imbalance
Leaky ducts depressurize the home, pulling crawlspace air upward.
This is a major cause of indoor air quality issues.
Standing Water + Poor Drainage
Hydrostatic pressure, high groundwater, or improper grading often lead to pooling water and saturated soils under the home.
Signs Your Crawlspace Is Failing
Musty odors inside the house
Cold floors in winter
High energy bills
Visible mold on joists or subfloor
Rodent activity or droppings
Damp or sagging insulation
Standing water
Chronic allergies or respiratory symptoms
Floor cupping or wood movement indoors
The Modern Standard: Conditioned Crawlspaces
A conditioned crawlspace brings the crawlspace inside the home’s controlled environment—similar to a short basement.
When built or retrofitted correctly, it becomes:
Dry
Clean
Sealed
Pest-resistant
Thermally efficient
This method dramatically improves indoor air quality and the durability of the home.
How Emerald State Contracting Fixes Crawlspaces
1. Seal the Exterior Vents
We close and seal all vents and gaps to prevent outside air, moisture, and pests from entering.
2. Install a High-Quality Vapor Barrier
We use heavy-duty, reinforced vapor membranes that are fully taped and sealed around all seams and penetrations.
This stops moisture and soil gases at the source.
3. Address Standing Water
Depending on the site, we may install:
Perimeter drains
Dimple mat systems
Sump pumps with backup protection
This handles groundwater and hydrostatic pressure.
4. Insulate Correctly
Depending on the home and moisture conditions, we use:
Closed-cell spray foam on rim joists or underside of subfloor
Rigid insulation on walls
Hybrid systems for difficult or low-clearance spaces
This controls vapor movement and improves thermal performance.
5. Air-Seal Critical Areas
We seal all plumbing penetrations, wiring holes, joints, and rim interfaces to prevent moisture and crawlspace air from migrating into the living space.
6. Provide Controlled Air Exchange
A conditioned crawlspace needs intentional ventilation from the home’s HVAC system or a dedicated dehumidifier.
This keeps humidity stable year-round.
Why This Matters for Northwest Homes
Crawlspaces have major impacts on:
Indoor air quality
Energy efficiency
Floor comfort
Mold risk
Structural lifespan
More than 50% of the air you breathe inside your home originates from the crawlspace.
A dry crawlspace means a healthy home.
When to Call a Professional
You should have your crawlspace evaluated if:
You smell mustiness
You see mold on framing or insulation
You have cold floors or high heating bills
Water pools under the home
You notice pest activity
Anyone in the home experiences unexplained allergies
You’re planning a remodel or adding insulation