A while back we talked about all of the different issues that a professional manufactured home installer needs to know regarding the marriage walls. I thought we should revisit that issue and focus only on the fastening together of the two halves to make the home a single, solid, integrated structure. Since this is a big topic, I think I will split things up and only discuss the fastening of the floors and walls. Let’s save the roof for a future date.
Your goal should be to make the joint between the home sections as tight as possible. There should be no gaps, and the fasteners must be installed per the manufacturers installation instructions. These fasteners should not split the lumber and must have adequate penetration to secure the home.
Remember that assembly of the home is critical to the home’s ability to survive high winds. A two (or three) section manufactured home must be able to transfer wind loads across the marriage line to the specific walls designed to accept these loads (shear walls), and ultimately into the ground through the anchoring system. Spaces, gaps, voids, etc., between the two sections, can prevent the home from safely handling these loads.
It goes without saying that you need to remove all shipping materials (plastic, straps, nails, staples) while you can still access them. Next, look over the marriage line gasket for damaged areas and add new gasketing material where needed. Ask the manufacturer to supply a decent length of extra gasket material to do this.
If you have attended any of my training classes, you know that I think the marriage line gasket is the weakest point in the entire design of a manufactured home. Take a few minutes to make sure the gasket can do its intended job. Consider offering better options, if possible. We can talk about this idea in a future post.
Be sure to protect yourself and others at the job site. Use cribbing or other support devices in the event that a home section should fall. Never allow a situation where a worker could be crushed or worse.
For new manufactured homes, the manufacturer will be providing all the fasteners necessary to secure the home sections. If you are not receiving these fasteners, you need to have a serious talk with someone at the factory.
Bring the home sections together as tight as possible. Any gaps between the sections must be shimmed! The manufacturers all say that if the gap is wider then 1”, you need to reposition the home to reduce/eliminate the gap. Any shims used at the marriage line are generally ¾” thick lumber, wide enough to accept the fastener without splitting. I favor a ¾” x 2 ½” pine firring strip. Be careful not to pull the rim joist away from the floor joists. The same is true at the roof ridge. Don’t pull the top rail or ridge beams away from the roof truss. Ultimately, the fasteners you install should just hold the home tightly together, not be pulling the sections tighter.
In general, most manufacturers (for homes in wind zone 1) require lagging the floor sections together using a lag screw and washer at each floor joist bay, and staggered from side to side. The lags may be installed at an angle (toe screwed), but not so much of an angle to reduce how far the lag goes into the other joist. You can also drive them straight into the floor joist, but that leaves a bigger hole in the bottom board to repair. At least 1 ½” penetration into the receiving joist is required.
Seal the bottom board with bottom board tape after the lagging is completed. Some manufacturers require additional fasteners at the ends of the home and at any through-the-rim heat duct connection. Be sure to check the manual, specific for the home you are installing.
Fastening of the walls is getting a bit more complicated with several manufacturers providing different options. Most installations I see still use wood screws (#10 x 4 ½”) 24” apart from the bottom plate to the top plate of the wall. Be careful using lag screws as they can split the wall studs.
Likewise, you need to fasten the marriage line along any openings or door ways with the same fasteners and spacing. I have been seeing some manufacturers sending brackets or plates for fastening the marriage line. Be sure to use the right number of nails per bracket and that you use appropriate length common nails. Not finishing nails, aluminum nails, roofing nails, etc.
Hopefully, this will encourage you to reexamine how you assemble multi-section manufactured homes. Make sure everyone on your crew understands how important this is! We will talk about roof fastening at a future date.
As always, refer to the specific manufacturers installation instructions for every home you install!