Lately I have been running into situations where manufactured homes have been damaged as a result of excessive rust to the metal parts under the home. I am seeing reports of rust on the frames, gas lines and anchoring components. In my opinion there are two different sources of these problems; one is a problem with the installation, the other may be a potential problem with the design of the homes.

The installation problem that has been causing rust issues should be obvious; improper site grading. Compounding the issues of poor site grading, a home placed in a pit that collects water can accelerate corrosion of the metal parts under the home.

Pit set-area under the home is lower than the surrounding grade. Water fills the crawl space.


The rules for grading a manufactured home site are no different then site grading for any other home. The site must slope away from the home by ½” per foot for the first 10’. If needed, a swale can be cut into the ground but bottom line, you MUST grade the site to shed water. Flat sites are not acceptable. If the site cannot be properly graded, the home should not be placed there! I like to encourage installers to bring a few lifts of fill dirt to the site to allow proper grooming of the site.

Rusted frame in a pit set home.


However, there are still too many manufactured homes being installed in pits. What I mean is, the area under the home is excavated to be below the surrounding grade, and as a result it collects water. I can think of no better way to encourage rust than to place the home over a pool of water.

If you have no choice than to set the home in a pit, you should be constructing a masonry crawl space consistent with the state or local building code. This would mean a frost protected, damp proofed, perimeter wall that will prohibit water infiltration. Ultimately, keeping the crawlspace dry.

This crawl space is parged (damp proofed) to prevent water infiltration.

OK, but there is also another issue that seems to be contributing to the rust problem that is outside of the installation process. I am talking about recessed porches. It appears that in some cases, as water comes through the porch decking boards, it is leading to rusting of the frame in these areas. Keeping in mind that the frame must be able to transport the home for its intended life, these rusted frames can represent a failure to meet the HUD Code. We all know that the frame is painted to protect from rust and corrosion, but is it good enough in the porch area?

Decked porch lets rain drain onto the frame!

Frame under porch area with significant rust.


I know a lot of installers have begun using plastic shims (wedges) on the piers in the porch areas, as the typical hardwood shims have been rotting away as a result of water coming through the decking boards. I think this is smart!

Typical plastic shims


As a professional installer, be certain that the homes you install are placed on properly graded sites to allow water to drain away from the home.

If you happen to see, or if someone tells you about frames rusting under the porch area, be sure to report it to the manufacturer (regardless of warranty). Maybe in the near future, we will see a better way to protect these frames to improve the durability of the homes!

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