How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
Why is the floor of a home required to be above the crown of the road?
Monday, November 13, 2023
Most communities have a requirement that a home be constructed so that the lowest floor of the living area is anywhere from 12-inches to 24-inches above the crown of the adjacent road. This is to prevent flooding problems in severe weather. They sometimes allow an exception when a floor built above the crown of the road would create drainage problems for adjacent homesites (like in the photo above). In that case, a site drainage plan must be approved by the local building jurisdiction; but, even with a drainage plan, it is a less than ideal homesite.
How the ground slopes around the house is equally important. One requirement of the International Residential Code, for example, is that the ground on all sides around the home slope downward a minimum of 6-inches in the first 10-feet—so that water drains safetly around and away from the house. This is usually accomplished by adding a shallow mound of fill soil under the footprint of a new home before starting construction, called a “building pad."
But too much added soil to raise the grade even higher than necessary may create a drainage problem for adjacent properties, since it is illegal to drain water from your property onto an adjacent one. Some Florida communities have recently revised their building regulations to limit the maximum height of the fill elevation of a new house.
Newer communities have master drainage plans for the entire neighborhood; but, even then, the carefully planned sloped grade and drainage swales can sometimes be obliterated over the years by fill soil used for a homeowner's creative landscaping mounds or concrete patios and walkways.
The worst homesite drainage problems we see are what we call “a house in a hole,” where a homesite is lower than the surrounding homesites, so the neighboring properties drain rainwater onto it. This occurs rarely and only at older homes, but the problem is impossible to fix without tearing down the house and regrading the site.
ONE FINAL NOTE: Although home inspectors are required to note “vegetation, grading, surface drainage, and retaining walls that are likely to affect the building adversely,” they are not required to determine the elevation of the finish floor above the grade of the road. That is done by a licensed surveyor.
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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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