The saddest question I often hear in my engineering inspection practice is, "Buck, I need an engineering inspection of a manufactured home foundation for an FHA loan. The mortgage underwriter wants assurance that the foundation meets their "permanent foundation" guidelines. Can you do this and what is the cost?"
Why is this a sad question? Well, it's because I've never inspected a manufactured home that had a foundation meeting this guideline.
Why is this? Well, it's because the foundation beneath the home was never designed per the guidelines to begin with. And this is sad, because an FHA Permanent Foundation would likely ensure that the manufactured home would survive the worst of thunderstorms and straight-line high winds and perhaps even some lower category Hurricanes, nor would it ever likely settle or sink into ground unevenly.
What is so special about an FHA Permanent Foundation?
According to this publication, in Chapter 1, "Permanent foundations must be constructed of durable materials; i.e. concrete, mortared masonry, or treated wood - and be site-built. It shall have attachment points to anchor and stabilize the manufactured home to transfer all loads, herein defined, to the underlying soil or rock. The permanent foundations shall be structurally developed in accordance with this document or be structurally designed by a licensed professional engineer for the following:
1. Vertical stability:
a. Rated anchorage capacity to prevent uplift and overturning due to wind or seismic forces, whichever controls. Screw-in soil anchors are not considered a permanent anchorage.
b. Footing size to prevent overloading the soil-bearing capacity and avoids soil settlement. Footing shall be reinforced concrete to be considered permanent.
c. Base of footing below maximum frost-penetration depth.
d. Encloses a basement of crawl space with a continuous wall (whether bearing or non-bearing) that separates the basement of crawl space from the backfill, and keeps out vermin and water.
2. Lateral stability.
Rated anchorage capacity to prevent sliding due to wind or seismic forces, whichever controls, in the transverse and longitudinal directions."
So, an FHA Permanent Foundation is essentially identical to a wood frame dwelling constructed on a conventional crawl space, slab or basement foundation. The foundation components (perimeter walls and interior piers) are all supported by buried concrete footings or monolithic concrete slabs, and furthermore, unlike conventional houses, because of the FHA requirements, these above-footing components are connected or tied to the buried concrete footings with embedded rebar or some engineered tie-down components. This is needed, engineering-wise, to "hold down" the home and also prevent the home for sliding off and/or overturning on the foundation, whenever the home is exposed or subjected to very high winds.
Unlike a conventional wood-frame dwelling, manufactured homes are extremely lightweight. Whereas the dead weight of a conventional home often prevents the home from being uplifted or slid on the foundation, manufactured homes can be easily picked up or slid or overturned on substandard foundations. This is why we often hear TV weatherpersons warn manufactured home dwellers to leave their homes and head for safe cover whenever some on-coming windstorm is prevalent. In an FHA Permanent Foundation System, the combined weights of the buried concrete footings and above-footing components are "designed" to "hold the home down" for the design wind speeds established by local Building Codes.
I am not suggesting that these foundations will protect a manufactured home from a tornado. We all know that even conventional wood-frame dwellings cannot withstand the horrific tornadic wind speeds. However, most other forms of high wind can be withstood if the manufactured home is properly attached to and supported by an FHA Permanent Foundation.
So, whenever a Realtor calls on me to perform such an inspection, I always tell them about my experiences, and explain that there will be a minimum fee for my inspection. If I think the foundation might meet the FHA guidelines, then I'll make the necessary measurements and collect the necessary data during the inspection, then come back to the office and perform the necessary calculations to hopefully allow me to write a positive report. In this case the cost of my services will be substantially higher because of all this additional work. If, when I get to the site, I see that the foundation does not meet the FHA requirements, I will tell you this and expect to be paid the minimum fee I quoted. Or, if you want, I can perform the same measurements and collect the necessary data to design or develop a construction repair plan to transform the existing foundation into a "Permanent Foundation" that will meet the FHA guidelines. And this will likely be even more expensive (my-fee-wise) and unfortunately, probably cost-prohibitive construction-wise.
If you're reading this and think I'm full of baloney because you've had other engineers approve many existing foundations for you in the past, I'll bet dimes to dollars that the engineer was either ignorant of the FHA requirements or was simply selling his stamp! Otherwise, you've been extremely lucky.
So, is there a moral to the story here?
It would be: If you know of anyone buying a new manufactured home, have them contact me or some other knowledgeable engineer, to design an FHA Permanent Foundation for their home, not only to better help protect them and their home during high wind events, but to also ensure that they will be able to sell their home, at some future time, to a buyer seeking an FHA loan!