Let’s Talk About Marriage Line Fastening

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.

This gap must be shimmed!

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.

Look closely where the staple keeps the sections apart.

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.

Never work under a suspended load! Support the home with cribbing every time!

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.

These lags should be staggered and the bottom board patched!

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.

This manual requires additional fasteners at the floor of the home.

 

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.

Brackets at marriage line opening

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!

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Electrical Crossovers

While inspecting some multi-section manufactured home installations recently, I noticed some areas needing improvement regarding electrical crossover connections.  So I thought we should talk about this issue as we head into the summer season.

Should not be exposed!

One of first things to keep in mind is that you should never have any Non-Metallic Sheathed Cable (also called NM Cable, often referred as Romex®) used for branch circuit wiring visible under a manufactured home. Crossover wiring is always to be tucked inside the floor cavity or walls, and protected with an access panel or hatch.

Molex brand connector. Look closely for release tab.

Secondly, to make this connection most manufacturers generally use either electrical connectors or junction boxes. Connectors are pretty straight forward, just snap them together. Most manufacturers in the northeast use Molex® brand connectors, and the great thing about these connectors is that they have release tabs so you can separate the connectors without any damage and reuse them as needed. This is important for relocating a home, or if the home were on display before being moved to it’s installation site.

This brand has no release mechanism.

Some older manufactured homes used a connector made by Amp® that was a single use connector. If you looked closely, you would see: “One Time Use Only, Do Not Re-terminate. The issue was there was no release tab on these connectors, so if you pulled them apart the plastic housing would bend and distort the device. When reconnected, the housing wouldn’t be able to connect securely and safety became a concern. The good news is that I haven’t seen these used for at least eight to ten years. But be alert if you are installing older homes as you may see a connector that is not intended to be reused. If so, cut it off and either install a new connector or use a junction box inside an access panel in the floor cavity or marriage wall.

Look closely to see grounding screw.

Greeny grounding type wire nut.

Speaking of junction boxes, here are a few basic things to remember. Where the NM Cable enters the junction box, there should be a cable clamp or connector. Don’t overtighten the clamp onto the cable, just snug it down. The cable should be secured within 12” of the clamp or connector (check the actual installation manual as some require cable securement within 8” of the cable clamp). If the junction box is metal, it should be grounded. You can use a ground clip, ground screw or a “greeny” wire nut for this.  Twist the conductors together before installing the wire nut, and make sure to use a wire nut that is the proper size. Usually the capacity and number of connectors are identified on the top of the wire nut itself. After grounding the junction box and making good connections, place the cover on the junction box!

I am seeing a few of the push-in type connectors in place of the twist style wire nuts, and these seem to work fine. Just make sure you strip the conductor with the proper tool to the proper length per the installation instructions. I saw a few brands of these push-in connectors that limited their use to solid wire only (no stranded wire). On solid wire conductors, these push-in types are generally reusable. But it can be difficult to get the conductors to disengage. You may be better served replacing them.

If you notice that the outer sheathing (or jacket) of the NM Cable is nicked or damaged, make sure you address it properly. If there is a superficial nick in the outer sheathing, wrap electrical tape around the cable at the nicked area, to a thickness that equals the depth of the nick. If the damage exposes any of the conductors or the paper inside the cable, the affected area must be removed! There is no repair for damage that significant.

End wall crossover. Cables need better protection!

If the manufacturer notched out a wall stud or other structural member to run the NM cable, make sure to protect the cables with wire protective plates or “mash or smash” plates as they call them in the south. And make certain the cable is 100% protected!

Always replace the access panels or close the access area to protect the connection from moisture and possible damage. If any floor insulation is missing, replace it as well!

Revisit the manufacturers installation instructions for a little more detail. On a new home, use the connector type the manufacturer provided.  If there are problems making this connection on a new manufactured home, take a picture and report it back to the manufacturer. They can only make improvements if they get feedback from you!

Keep in mind that you should always refer to the Manufacturers Installation Instructions, but if you want to learn more, the Manufactured Home Construction & Safety Standards (MHCSS) at 3280.801 is where you will find the actual code requirements.  Click Here for the MHCSS  Also, it is worth knowing the MHCSS adopts Article 550 of the 2005 National Electric Code. So, check them all out to make sure you are doing things right!

The Importance of a Good Marriage (Line)!

A good marriage is critical to your emotional and financial security.  The same can be said about the marriage of two or three sections of a manufactured home. For all of the good work and craftsmanship that goes into the construction and installation of a manufactured home, I can’t help but think that the marriage line joint is the weakest link in the process. If the marriage line is not secure, level, and reasonably tight, problems are sure to creep in! Heat loss, wall and ceiling cracks, carpets and floors shadowing the seams, and doors binding can all be symptoms of a good marriage gone bad.

 So, let’s talk a little about the marriage line to make sure we are doing all we can to strengthen this weak link.

Everybody knows to remove all shipping plastic from the home. But it is especially important along the roof line as venting of the roof cavity depends on air flow from one home section to the other. Any plastic left around the roof line can restrict the air flow to properly vent the roof.

Look closely for the staple!

Inspect the marriage wall for leftover staples or nails once the shipping plastic is removed. I know they are a pain in the neck, but one staple left in the marriage line can cause big problems.

Damaged heat duct crossover gasket.

Inspect the heat duct gasket. If it is damaged, you need to replace it. Was it the shipping plastic or straps that caused the damage? If so, snap a picture and let the manufacturer know! Consider a shield made from coil stock that can be removed once the home is in place.

Look for any electric cables that might get pinched or otherwise damaged when the sections are pulled together.  Re-secure them to prevent damage.

Gasket needing inspection!

Is the marriage line gasket intact? Damaged? Properly placed?  If you read my previous posts, you should know I think this is a big problem area. Read my post from April 17, 2017 “Would You Like That Supersized?” for some other thoughts on this gasket.

Gaps between the A and B sections of a home can lead to structural problems over time. While professional installers generally don’t pay much attention to shear walls (the walls that transfer wind loads through the structure of the home to the anchoring system), it is very important to understand that in many two-section manufactured homes, all of the shear walls are found in only one of the sections. The manufacturer is depending on you to make a structurally sound joint to transfer these wind loads across the marriage line to the section of the home with the shear walls.

Wind loads are safely transferred only when you properly fasten the sections together. Basically, a structural, tight fitted joint is required in order for the home to withstand wind storm. No gaps in marriage line!

The manufacturer’s installation instructions states, “Shim any gaps up to one inch between structural elements with dimensional lumber. If any gaps exceed one inch, re-position the home to eliminate such gaps”Read that carefully. It means gaps are not permitted! You must either use shims up to 1″ or get the home sections closer.

mate line 1 gap

This needs a shim!

This is very important not just at the floor, but the walls and roof as well! Gaps between sections can cause the screws, nails, or lags to shear off, pull out, or fail at the exact time they are needed the most!

These lags should have been staggered!

Make sure to stagger your fasteners (A half/B half), and be sure they don’t split out the lumber. The lags or screws you use must properly penetrate into the receiving members by 1 ½”. You might need to use longer fasteners than the ones provided by the manufacturer.

Strapping at roof line.

If you are using straps at the roof, it is critical to remember that this joint also needs to be solid and tight. If the staple crowns or nail heads cut through the strap material, the strap won’t be able do the job that the manufacturer intended.  Make sure your fasteners go through the blocking, beams, or rails provided, and not into the truss!

Take a few minutes before your next set and double check the manufacturer’s instructions for fastening the marriage line. Take a lot of pictures, and give some feedback to the manufacturer (the Quality Assurance Manager in this case). They might be able to tweak things at the factory to make your job easier. In fact, if you aren’t on a first name basis with the QA Manager at the factories you deal with, you need to change that. These guys are a wealth of knowledge! Every QA Manager I have ever met wants to produce the best homes possible. What they are lacking is feedback from you!  

A good, strong, tight marriage line is not always easy and at times very difficult. But, with a little tender loving care, you will get that good marriage line, and we all know, a good marriage is well worth any price!