When looking at homes for sale, do you ever notice light coming into the garage from the corners by the floor? That is garage floor crowning, and it’s not ideal!
What is garage floor crowning?
Crowning refers to the shape of the floor with the high point in the middle, and sloping down toward the side. We sometimes also see crowning in hardwood floors, or the opposite shape, cupping, where the edges are raised and the center is depressed.
With the middle of the slab floor being higher, the garage door gets stopped at the high point, leaving the edges open. Sometimes, if it’s slight, the weatherstripping at the bottom of the door will stop light from coming through. So it’s helpful to not just look for light seeping through, but also note if the weather stripping is thicker at the sides than in the middle.
What causes the crowning?
Improper drainage appears to be the main culprit. With our clay soils, water not draining away from the structure can expand the soil and cause it to move depending on the moisture content. When dry, the soil contracts, and when wet, it expands. The back and forth is hard on foundations, including the slab foundation in the garage.
One common culprit for excess water at the garage are downspouts. Our home inspectors tell us that downspouts should be directed several feet away from the house to keep the soil near the home from getting overly saturated and going through the soaked-parched cycle. Most of the time, though, the downspouts simply dump water right next to the house, often near the large garage door.
Below is a collage with an example of a typical downspout termination (at the edge of a garage) and an upgraded one that ties into an underground drainage system.
What is the problem with garage floor crowning? Why is it potentially bad?
The risks of garage floor crowning appear to be shades of gray and dependant on how bad the heaving is.
With gaps at the corners, wildlife can get into your garage, such as insects or rodents. If the slope isn’t too bad, it may be possible to upgrade the weatherstripping to discourage them moving in to your cozy garage. And if crowning is caught early, perhaps taking care of the drainage issue can keep it from worsening.
If it’s really bad, the concrete slab may rise over the soil and rock bed and leave it vulnerable to signifant cracks and displacement (where one side is higher than the other). With a larger hump, there’s a risk of it being a trip hazard.
In extreme cases, the crowning can lead to damage at the walls and other structural elements of the home.
Grading, drainage, water damage to homes
We commonly see in home inspections references to “reverse grading”, which simply means that the soil near the structure is sloping toward the house instead of away from it. If it’s just a slight grade, perhaps someone could simply rake and shovel away some soil to cause the 5% slope away from the house over a few feet. The improper slope may bring water up to the foundation, and if the foundation vents are set low, water could even spill into the crawlspace, too.
When there’s hardscape involved, such as concrete or pavers, of course it is much more expensive to remedy the reverse grading problem. Some contractors may suggest installing drains to provide a place for water to percolate down before it’s too close to the house or to carry the water to a drainage spot further away.
Water is an underappreciated enemy to homes, frequently much worse than termites!
When viewing homes to sell, or looking at your own home to maintain it, look for the red flags that suggest that improper draining may be hurting your home, and if you find that it is, reach out to a reputable contractor to get it corrected before it worsens.
Related reading:
Do you have a high water table? (from our Live in Los Gatos blog)
Draining a pool or spa? The water should not go to the gutter! (from our Live in Los Gatos blog)
