by Bill Van der Meer
This article also appeared in the July/August issue of "Modern Homes."

“Set day” dawned clear and full of promise that a new modular home would exist by late afternoon on an already-built, full-basement foundation. The set crew had already started prepping the boxes (modules) that would be set in place by a crane.

The builder, who we’ll call Joe, had an advantage in that he was already experienced in site management, scheduling and the technical requirements of constructing a stick-built home.

Like so many of his peers in the business, Joe was attracted to the modular approach as a means to reduce the move-in time for his customers. This timesaver would certainly result in interest savings on the construction loan as well.

Like so many of his peers in the business, Joe was attracted to the modular approach as a means to reduce the move-in time for his customers. This timesaver would certainly result in interest savings on the construction loan as well.

In his mind the other huge advantage of going modular was the fact that the majority of the framing, drywall, electrical, plumbing, cabinetry and finish flooring had already been installed in a factory-controlled environment. This meant fewer subcontractors and, correspondingly, less quality-control issues than those he faced during his stick-building days.

Having reached an agreement on the home design and features with the customer, Joe scheduled a delivery date. He then coordinated with the manufacturer and hired an experienced set crew and crane operator. All he had to do was provide a dimensionally correct and level foundation along with clear access to the site by the transporters and crane. While this was his first modular home, he felt he had done his homework.

Trouble at the Worksite

The first signs of trouble appeared early when a routine check of the dimensions by the set crew revealed that not only was the foundation off by more than one inch on a diagonal measurement but also that the long-wall dimension was too short by roughly 3/4-inch when compared to the dimensions of the first story boxes. Still, the set crew gave Joe a degree of confidence that these discrepancies, which are generally unacceptable in modular sets, could be overcome by splitting the difference with slight overhangs and by racking the boxes during the set.

As Joe started to feel comfortable, the crane maneuvered into position next to the foundation and became mired in an area that had not been adequately hard packed. It seemed hopeless. Fortunately, crushed stone on the site was placed underneath the wheels and the crane was dislodged. But it took time, valuable time at $300 per hour, for the crane to lift itself out.

Besides a few other minor delays, everything else went well on this four-box, two-story set. The customer moved into their newly completed modular home some five weeks later, after the finishing process and the garage and porch were completed on site.


Valuable Lessons

Although a bit flustered by some of the hiccups, our builder came away with a few valuable lessons learned about site and foundation preparation unique to modular construction. Little did he realize that there was another lesson to be learned.

Roughly six months later he received a call from the homeowner concerned about drywall cracks and a sticking window on the South East corner of the house due to a slight dip in the foundation. On set day this 3/4-inch gap between the sill plate and the box was noted, but not properly shimmed. Settling caused the problems to surface.

While most of the problems described may be somewhat manageable, much worse can befall the uninitiated – with disastrous consequences. The learning curve may be steep for those who have little experience in residential construction or for those who are transitioning from other housing-related fields such as real estate, land development or HUD-Code home retail sales. The devil is truly in the details of site and foundation preparation.

Access to the Site

To ensure a problem-free delivery to the building site, the access route must be properly researched and planned. The manufacturer usually plans the delivery route on highways and main roads, while the builder verifies adequate clearances on secondary roads and the site itself. Planning an appropriate route involves good cooperation and communication between the builder and manufacturer.

Basic rules of access:

- 20-feet wide by 15-feet high clearance along the entire route;

- No grade change over 1 foot in 20 feet;

- Account for sharp turns and “S” curves;

- Account for bridge clearances and weight restrictions, which may also be an issue at certain times of the year;

- Consult with state transportation departments and inform all parties including the manufacturer and the crane company;

- Get necessary permits.

Even though a box may only be 14-feet wide, a wider tolerance must be made to account for curves and intersections. Also, along the way transporters may need to be parked, such as at a truck stop or church parking lot. Access routes must be planned for transport between these holding areas and the building site.

At the development site, make sure to pay attention to obstructing overhead and underground utilities in the access path and be ready to protect curbs. Attention to details up-front will save a lot of anguish later. One mistake, such as a transporter getting stuck in a dip on a secondary roadway, will eat into a builder’s profit margin as the crane and set crew wait.

Site Preparation

The central consideration in preparing the site for a modular set is the crane. The crane operator is the one in control on set day. If he determines that the site is unsafe, he can call off the set. Provide easy access and a level crane pad as close to the foundation as possible. Specific requirements are:

- 30-foot wide area for crane and module(s) depending on the size of box;

- Appropriate and close location with reference to foundation;

-Level site with no greater slope than 1 foot in 30 feet;

- Additional cribbing may need to be provided by the builder;

- Site graded for run-off and hard-packed.

A word about cranes: Most cranes used in residential modular sets are rated from 75 to 90 tons. The weight of a typical box, with materials that have been “shipped-loose,” is about 45 lbs. per square foot. This means that a 14- by 40-foot box (560 square feet) would weigh about 13 tons. Another factor affecting crane capacity is the distance between the transporter trailers to the farthest point on the foundation. Provide this information to the crane company.

In addition to the crane, a bulldozer with the correct trailer hitch should always be available to move transporters into position for the crane pick. Don’t rely on the “toter” (tractor trailer cabs) to move boxes on the job site. Some new builders, attempting to shave costs, try to do without one, but they almost always end up in a jam.

Foundation

Modular veterans will tell you that the foundation is everything. Some manufacturers will even send out a field technician the day before a scheduled set to check out a foundation before they agree to place their house on it.

Modular home foundations are governed by prescriptive code requirements. Whether a crawl space or full basement, the builder is accountable for complying with local building codes. In addition to code compliance issues, the builder must comply with manufacturer specifications regarding dimensional tolerances, locations for central support columns, anchoring methods, etc. The builder also needs to be aware of anchoring or bracing methods associated with different types of foundation systems.

Regardless of how reputable the excavation or masonry contractors may be, the builder should verify dimensions and level at every step of the process and most certainly when the foundation is complete. The fixed dimensions of modular components dictate fairly tight tolerances. For instance, differences between the diagonal measurements should not exceed 1/2-inch. However, diagonal measurements alone are not enough to guarantee a “square” foundation. The bottom line is that diagonals and opposite sides must be equal. Cross reference the dimensions with the manufacturer-supplied “working blueprint” rather than the “sales print.”

Settling will cause all kinds of problems in an out-of-level foundation. Components may not mate correctly, with errors compounded at the roof-ridge line. Check for level at the top of a foundation with an optical or laser-transit level. Slight variations may be corrected by shimming, as per manufacturer recommendations. At worst, a grossly out-of-level foundation may have to be reconstructed.

Finally, there are some important things to keep in mind before the foundation is backfilled.

Don’t backfill until:
1. the home is set
2. the foundation is waterproofed
3. the basement floor is poured and bracing has been installed as per foundation type.

The ground rules for site and foundation preparation are intended to provide some basic guidelines to the would-be modular builder. They don’t cover all of the fine points. When in doubt, consult with the manufacturer, network with other builders or better yet, get training. All of these resources are available to help. Not only do manufacturers want your repeat business, they want to help foster an ever-increasing market share. Improved skills development and communication will ultimately advance the overall quality of the home for the customer.



Bill Van der Meer, director of the Pennsylvania Housing Resource Center at Pennsylvania College of Technology, directs the development of educational programs, including the Modular Housing Training Institute (MHTI) and the Manufactured Housing Resource Center (MHRC). He can be reached at 570-320-2400, Ext. 3304, or bvanderm@pct.edu.