A good foundation gives homeowners peace of mind. For manufactured homes, one option is a disaster-resistant pier system -- stout members rigidly connecting the home's chassis to a slab, grade beam, or array of pads. Some systems incorporate lateral or diagonal bracing for greater resistance. Although often referred to as "earthquake resistant bracing" (ERB) systems, many also resist high winds, frost heaves, and floods. Not only are these systems cost-effective in reducing structural movement (compared to conventional manufactured housing foundations), they can save lives and property.
In a complete disaster-resistant pier system, several rolled steel beams (the chassis) are supported by an array of stout, adjustable steel piers, which are connected to both the chassis and the concrete slab or base pad with high-strength bolts. Individual pier adjustment usually consists of threaded rods or a vertical series of holes for a cross bolt. Several manufacturers offer a secondary support system, or seismic isolator, to prevent the home from dropping too low should the piers fail. This can be installed separately as an economical retrofit. Optional brackets connecting pier heads to floor joists help prevent piers tilting from a vertical position.
Pier overturning from wind or earthquake loads is one of the most common types of failure, and there is a variety of remedies. Many systems use pyramidal piers secured to pads at the base and to locking devices at chassis beams. The pier is made of steel angles that meet at a collar holding an adjusting bolt. One system, embeds the pier base in a concrete "foot" poured into a geotextile form bag. Another system substitutes recycled plastic pier pads for permanent (pressure treated) wood or concrete pads.
Other systems, install piers on precast grade beams or broad pads. The pier base is secured to a wide horizontal steel plate or frame to distribute the pier's base load pier over a broader area. The pier has a square cross section. Some systems feature rigid steel angle struts and cross-bracing to stabilize adjacent pier, triangulating the loads.
Pier system retailers tend to specialize in retrofit, while wholesalers try to deal exclusively with new construction. Distributor locations vary by manufacturer. Many pier units are shipped at least partially assembled, so shipping costs may be high. Lead time varies from two days to about two weeks.
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The pier system is separated from the soil by a pad or concrete block or slab, not making rust and deterioration a major concern.
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By its very nature, the system helps to reduce severe damage due to strong winds, seismic activity and flooding.
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Pier systems are usually easy to install, but many manufacturers will void the guarantee if not installed by a certified installer. Pier systems without ground anchors may not provide adequate wind resistance. Some Earthquake-resistance systems allow for floatation that may allow lighter homes such as single-wides to move excessively during high winds. There are many factors that go into determining an appropriate foundation system for a manufactured home, including home configuration, anticipated loads, soil characteristics, first cost, and maintenance. A structural engineer should always be consulted.
One manufacturer estimates total cost for its steel buttress system under a typical double-wide home to be less than $2,500, including a six-hour installation. Another manufacturer offers a comparable system for less than $3,500, with a three-day installation, and one without cross-bracing for less than $2,500, that still qualifies as a permanent foundation.
It is necessary to ensure that the system does not deteriorate, but that is easily observable and done. Because repair costs for earthquake damage can approach $20,000, even a retrofit installation can pay for itself after one incident.
Many states do not require lateral load resistance for manufactured housing foundation systems. For those that do, wind load provisions to guide foundation design are established by MHCSS (Manufactured Home Construction and Safety Standards). The California Department of Housing and Community Development (HCD) has a list of earthquake-resistant bracing (ERB) systems. However, under California state law, HCD cannot require the installation of ERB systems, though some local jurisdictions do. Since HCD qualifies many of these systems as permanent foundations, HUD/FHA will approve the house for long-term, low-interest financing.
Not Applicable
Base supports are usually pressure-treated wood or concrete pads, grade beams, or a poured slab. In cold climates, most pier system designs require footings to be below code frost depth to prevent frost heave. With shallow piles there is no need for footings. Some manufacturers offer a perimeter enclosureto protect the steel against weather.
Installation times vary from a few hours to a few days. Most systems are designed for retrofit as well as new construction, and are relocatable. Depending on the adjustability of the piers, systems can be adapted for sloping sites with a few foot difference in elevation.
Typically guaranteed for the lifetime of the structure they support, provided they are installed according to manufacturer's specifications
In earthquake zones, most disaster-resistant pier systems are classified as permanent foundations, and are more cost-effective than reinforced concrete foundation walls and footings. They can be designed and constructed to resist lateral high wind and seismic forces.
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