MANUFACTURED HOME Glossary of Terms Part 7-C

MANUFACTURED HOME Glossary of Terms

Part 7-C

PIT SET, SUBTERRANEAN SET, CRAWL SPACE FOUNDATION 

The pit set/crawl space foundation system described here has two main distinguishing characteristics it incorporates full perimeter wall support together with internal, independent support points; and the space itself is not habitable.

Within that very broad definition, there are many styles, designs, and ways to build crawl space foundation systems. This is popular because the low profile appearance resembles a "site" built home on slab foundation. In the best case scenario, the perimeter wall rests on an excavated footer.

The wall itself maybe constructed of one or more conventional building materials (such as poured concrete, concrete block, or treated wood) and the entire perimeter of the manufactured home floor bears directly upon this wall. The chassis also is fully supported, but with relatively economical piers.

The manufacturer-designated ridge beam support points are carried by economical piers or posts. The home's resistance to horizontal or uplift forces is achieved through attachment of the floor joists to the exterior foundation wall. Ideally, the structural walls form a barrier to the entry of water underneath the home and act as a short retaining wall.

However, in developments where there is terracing or hydrostatic pressure, it is common for water to percolate under the home and these types of foundations because they are historically poorly ventilated actually trap water underneath. In some of the older developments, the low profile appearance was achieved by digging a whole for all the pier and pad components but there is no supporting perimeter wall.

In those cases, only the interior piers support the home. If water is a factor, ongoing review of these understructures is necessary to maintain proper support. The perimeter load-bearing enclosure wall support system provides excellent gravity load resistance.

The perimeter wall carries much of the roof load directly to the earth. The chassis main beams and piers carry only the interior floor loads. The perimeter enclosure wall supports the full perimeter of the home. Further, homes set in "low profile" offer less wall exposure to high winds, thus reducing the loads required to be resisted by the connections.

The perimeter load-bearing enclosure wall support system combined with a deep stemwall provides adequate seismic load resistance. The structural connection of the home to the perimeter foundation wall can be designed to effectively transfer the forces to the earth around the foundation.

PSF

Pounds per square foot.

PSI

Pounds per square inch.

REAL PROPERTY FOUNDATION

The manufactured home is the only type of residential dwelling intended to be used as either personal or "real property." Manufacturers often establish a special set of conditions for foundation systems intended for use with homes financed as real property with a mortgage or deed of trust.

The techniques for supporting homes financed as either real or personal property are intended to result in properly engineered and reliable foundation systems.

In all cases, real or personal property status is determined by state or local laws that may or may not reference foundation type. Similarly, eligibility for conventional long-term financing is determined by underwriting standards that may or may not reference the foundation type or real versus personal property status.

Registration

In the context of a MHD unit, registration pertains to a home that is NOT affixed to the underlying real estate. Registration is similar to the Department of Motor Vehicles program for vehicle registration.

Registration Card

Similar to the registration card issued by teh Department of Mortor Vehicles for automobiles, a Registration Card identifies the name of owner and any secured creditors. This document is issued by HCD each time a MH unit is reported sold. This is NOT issued for MH units that have been converted to a fixture.

RETROFIT

To upgrade an existing home's understructure by installing a state or federally certified tie-down, earthquake resistant bracing or foundation system to either satisfy jurisdictional codes or insurance and lending requirements.

REVERSE MORTGAGE LOAN

In a reverse mortgage loan, the borrower does not need to provide verification of income to procure a loan. The only determining factor for loan qualification is the assessed value of the home and the age of the borrower. In a reverse mortgage transaction, every foundation of the manufactured home must be inspected and certified by an engineer to specify that it meets the guidelines of the Permanent Foundation Guide For Manufactured Homes dated 1996.

RIM JOIST

The outermost joist around the perimeter of the floor framing.

SHEAR WALL

A general term for walls that are designed and constructed to resist racking (bending, twisting, torquing, etc.) from seismic and wind forces by use of masonry, concrete, cold-formed steel or wood framing.

SEISMIC BASE SHEAR

Codes: HUD “Permanent Foundations Guide for Manufactured Housing” 

ASCE “Minimum Design Loads for Buildings and Other Structures” 
ASCE Standard 7-05 

Per “Appendix A: Foundation Design Concept Selection” of the referenced HUD Foundations Handbook, the limiting seismic factor for most foundation types is the “Effective Peak Velocity Related Acceleration, Av,” = 0.3 and 0.4.

However, Av is a reference to a previous Uniform Building Code (UBC) method of seismic base shear determination. The current industry wide seismic base shear is derived from the referenced ASCE 7-05 code document. The following calculation will be a conversion of the previous code methodology into the new code methodology. 

Per previous UBC methodology, 
V=ZIKCSW 
Where 2.5Av = “Z” 
UBC Seismic Zones “4” for residential structures: V=0.186W (Av = 0.4). 
UBC Seismic Zones “3” for residential structures: V= 0.14W (Av = 0.3). 
This UBC base shear value, V, is expressed in an Allowable Stress Deign (ASD) force level. 

Per current ASCE 7-05 methodology, 
V=(Cs)(W) 
Where Cs = Sds /(R/I) and Sds is the “5 percent damped, design spectral response acceleration parameter at short periods” as determined in the USGS “Seismic Hazard Curves and Uniform Hazard Response Spectra” software. (http://earthquake.usgs.gov/) 

Per Chapter 12 of ASCE 7-05, take I=1.0 and R=4.0 for a manufactured home (if exterior plywood construction is used, R =6.5. However, for the “generic” case take R=4.0 which will yield more conservative results). For a manufactured home, V= Sds /(4/1)= (0.25)(Sds). 

Determine the “equivalent” Sds for Av =0.3. ASCE 7-05 is a “strength” based force level code. Converting ASCE 7-05 base shear to ASD force levels, Vasd =(0.7)(0.25)Sds W = (0.175)(Sds)W 

By setting the two base shear equations equal to each other, 
(0.175)(Sds)(W) = (0.14)(W) 

Sds = 0.8g. 

Therefore, Sds of 0.8g can be taken as the equivalent of Av = 0.3 (or 0.4) in Appendix “A” of the “HUD Permanent Foundations Guide for Manufactured Housing” handbook. In Table “A-1”, “Some” Seismic Zones is defined as a location with a site specific Sds equal to or less than 0.8g and “All” Seismic Zones is defined as a location with a site specific Sds greater than 0.8g. 

Example 

It is determined that “Site A” has a USGS site specific Sds equal to 0.9g. The manufactured home located at “Site A” has a HUD Foundation Type “E1”. Per HUD handbook Table A-1, foundation type “E1” is allowed in “Some” seismic zones and is ”Not recommended in seismic areas Av = 0.3 or 0.4 unless use reinforced piers”.

Therefore, unless the home’s foundation has reinforced piers, this foundation cannot be certified as being in compliance with the HUD handbook. However, had the USGS site specific Sds been 0.79g or less the foundation would had been “certifiable” without the reinforced piers.

SEISMIC LOAD RESISTANCE

Since the HUD standards have no provisions for seismic resistance design, almost all manufactured housing, (and, therefore, most pier and pad installations) is not designed specifically to withstand seismic loads.

Calculations show, however, that a manufactured home capable of resisting the HUD code wind forces will slightly exceed the requirements meeting for the highest seismic forces in the model building codes. Some manufacturers of proprietary systems have Standard Plan Approvals for Earthquake Resistant Bracing Systems or ERBS.

SKIRTING

Weather-resistant framing and sheeting used to enclose the crawl space of a manufactured home.

SLOPE

The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe.

SPA

Standard Plan Approval—Qualifying proprietary retrofit foundation systems have an SPA number that can be presented to the governing licensing authority, reducing the difficulty of pulling a permit.

UBC

Uniform Building Code

UNDERWRITER

In banking the term is used for the process of analyzing the credit worthiness of the property or borrower or both, based on credit history, appraisal of home, or other. The underwriter is often a different entity than the mortgage banker.

VA

Veteran's Administration

VAPOR BARRIER

The underbelly material that covers, holds up and protects the insulation under the subfloor. An intact vapor barrier prevents nesting of rodents in the insulation as well as minimizes the impact of moisture build-up in the sublfoor and wall systems.

VENT

Openings in the skirting to provide underfloor ventilation.

VENTILATION

The primary purpose of crawl space ventilation is to minimize the accumulation of moisture under the home. Excessive moisture accumulation under any home can create an ideal environment for moisture seepage, mold & mildew issues into the home itself. The general standard is one foot of ventilation for every 150 square feet of underfloor area.

WET STAMP

A wet stamp indicates an original signature. On plot plans, building jurisdictions often request wet stamp signatures of homeowner or homeowner's agent certifying authorization or lot lines. On engineering certification letters. underwriters generally want an original copy of the engineer's actual "stamp."

WMA

Western Manufactured Housing Association, a professional organization that works for the advancement and dissemination of information about the manufactured housing and factory-built housing industry.

18551(a)

California Heath and Safety Code section that permits a MH unit to be installed on a Foundation System as a fixture and improvement to real property.

18551 (b)

California Heath and Safety Code section that permits a mh unit to be installed on a foundation system as Chattel.

18555

California Heath and Safety Code section that enables a Registered Owner, under specified condition, to convert their MH unit to a fixture and improvement to the underlying real property without the benefit of a Foundation System.

Please consider us your GO-TO-GUY for any of your MANUCACTURED HOME needs. For immediate service please call Janis at 760 415-1982 or John at 760 815-6977. Or you can email us at janis@mh-processing.com