Pad and drainage

Drainage is structural, not cosmetic

Water that collects under a manufactured home does not stay a water problem. It becomes a frame problem, a ductwork problem, an insulation problem, and eventually a floor problem. Skirting traps humidity against the underside. Piers settle unevenly in saturated soil, and a home that settles unevenly needs re-leveling — repeatedly, if the cause is never fixed.

Re-leveling a home every year or two is the visible symptom. The cause is almost always underneath, and it is almost always grade.

What a correct pad does

It sits high enough relative to surrounding grade that water moves away from the home on every side, and it keeps doing that after the fill settles. That means the pad is built above the surrounding ground, the fall continues far enough out to actually carry water off, and nothing downhill — a driveway, a neighbor’s fill, a berm — sends it back.

Fill matters. Material that holds water or that cannot be compacted properly will settle unevenly, and uneven settlement under a pier line is exactly the failure you were trying to avoid. Fill goes in in lifts and gets compacted as it goes, not dumped and shaped.

When you need a retaining wall

Most bad grade can be solved with fill and shaping. A retaining wall becomes necessary when the fall across the site is steep enough that you would need an unreasonable volume of fill, or when the buildable area sits against a cut that will not hold at a stable slope.

It is worth avoiding when it can be avoided. Walls above a certain height generally require engineering, and a wall is a permanent structure that has to be drained behind and maintained. If the site can be shaped instead, shape it.

Floodplain and elevation

If any part of the parcel is in a mapped flood zone, the finished floor has to sit at or above the base flood elevation, and some counties require additional height above that minimum. One county in our area requires three feet above base flood elevation — two feet more than the federal floor — and that requirement appears on no fee schedule.

Elevation requirements cascade. More height means more fill, taller piers, longer steps, a steeper driveway approach, and different skirting. It is not a line item you can add at the end.

Where the floodplain is involved, expect to need an elevation certificate from a surveyor before a permit issues. And note that at least one county in our area treats any floodplain on a property as putting the whole property in the floodplain.

What fails inspection

The recurring causes are inadequate fall away from the structure, uncompacted or improperly placed fill, footings sized without regard for the soil’s bearing capacity, and finished floor elevation short of what the floodplain requires. All four are pad and site problems, and all four are cheaper to prevent than to correct with a home already sitting on them.