✓Wet groundCity staff say ground water rises in filled wetlands in Madison, especially on the isthmus, after many wet seasons. A shallow crawl space sits right in that wet zone, so water and damp air come up through the dirt floor.cityofmadison.com
✓Deep frostWisconsin's home code asks for footings at least 48 inches below grade to get below the frost. Older porch and addition footings were often set shallower. When the ground freezes and thaws, shallow supports can heave up or sink down.dsps.wi.gov
✓Humid summers, cold wintersMadison gets about 37 inches of precipitation a year and about 52 inches of snow, based on 1991 to 2020 normals. Vents that let in humid summer air and freezing winter air put a crawl space through both extremes.climatology.nelson.wisc.edu
What it costs
Typical published ranges for Madison. The contractor's written estimate is the price, and the inspection is free.
Soft floors, musty smells or water under the house?
Crawl spaces are out of sight, so their problems tend to grow quietly. In Madison, they show up most under older home additions, enclosed porches, sunrooms and some smaller homes. You notice the floor dips in the back room. The kitchen smells musty. A pipe froze last winter.
These problems can be fixed. The first step is a look underneath. That is what the free inspection is for.
Does this sound like your house?
"The floor in the back addition sags or feels bouncy."
"There is a dip in the kitchen floor over the crawl space."
"It smells damp or musty in that part of the house."
"There is standing water under the porch or addition."
"The wood down there looks dark, soft or moldy."
"Pipes in the crawl space froze last winter."
"The addition is pulling away from the main house."
Why crawl spaces struggle in Madison
Water from below. Madison has a high water table, and ground water rises after wet years, especially near the lakes. A crawl space with a dirt floor sits close to that water. Damp soil fills the space with moist air that soaks into the wood.
Frost. The soil here freezes deep each winter. Wisconsin's code asks for footings at least 4 feet down today, but older porches and additions were not always built that way. Shallow footings and posts move with the frost, and the floor above moves with them.
Old wood. About 1 in 4 Madison homes was built before 1960. Many additions are just as old. Decades of damp air rot sill plates, joists and beams.
Vents that let in the weather. Open vents bring humid air in summer and cold air in winter. The humid air sweats on cool surfaces. The cold air freezes pipes.
How a local crew fixes it
New supports
The crew sets new steel posts or concrete piers under sagging beams and lifts the floor back toward level. Where old posts sank into soft ground, the new ones sit on a solid footing.
Wood repair
Rotted sill plates, joists and beams are replaced or doubled up with new wood. This is often paired with moisture control so the new wood lasts.
Vapor barrier and encapsulation
A thick plastic liner covers the dirt floor and runs up the walls. For a full encapsulation, the vents are sealed, the walls are insulated and a dehumidifier keeps the air dry. This also keeps the floors above warmer.
Drainage
If water stands in the crawl space, a drain and a small sump pump move it out before it can soak back into the soil. See basement waterproofing for how drains and sumps work.
Fixing an addition that pulls away
When an addition is settling away from the house, steel piers can support its footing. See foundation repair.
What it costs
Typical ranges are in the table on this page. A small crawl space under one addition costs far less than a full house. The crew should list the square feet, the liner, any supports and any wood repair on your written estimate. See the Madison cost guide for more.
Frequently asked questions
Do many Madison homes have crawl spaces?
Most Madison homes have full basements. Crawl spaces show up under porches, sunrooms, kitchen and back-room additions on older houses, and under some smaller homes. They are easy to forget, which is why problems there go unnoticed.
Why is my floor soft over the crawl space?
Damp air and standing water rot wood over time. The floor joists or the beam under them may be weak, or the supports may have sunk into soft ground. The inspector will check the wood and the supports.
What is crawl space encapsulation?
The crew lines the floor and walls of the crawl space with a thick plastic liner, seals the vents and often adds a dehumidifier. It keeps ground moisture out of the space and out of your house.
Should I close my crawl space vents in winter?
Many Madison homeowners do to keep pipes from freezing. Open vents let in cold air in winter and humid air in summer. A sealed and insulated crawl space solves both, but it needs to be done right so moisture has somewhere to go.
Will fixing the crawl space help with radon?
It can. Radon comes up from the ground, and about half of homes tested in Dane County had high levels. A sealed liner is often the first step of a crawl space radon system. Ask about testing before and after.
How long does crawl space work take?
A vapor barrier or new supports often take a day or two. A full encapsulation with drainage and a dehumidifier can take longer. Your written estimate should list the schedule.
Do I need to fix the addition or the whole house?
Only what is moving. If the main house is on a solid basement and only the crawl space addition sags, the fix is usually limited to the addition.
Get your crawl space checked for free
The floor will not get stronger on its own, and damp wood keeps rotting. Call (608) 719-3321 or send the short form, and a local crew will call you back, usually the same day. The inspection is free, and you get the price in writing.