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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Let’s Talk About Spacers and Shims

A few weeks ago, we looked at pier cap blocks, so now it makes sense to talk about spacers and shims.

Just so we are on the same page, a spacer can be used to fill in the space between the cap block and the frame (chassis) if that space is more than can be shimmed (1″). Sounds simple enough, right??? Well think again.

Double block pier, concrete footing under the ground vapor barrier, double 4″ solid masonry cap blocks, 2″ hardwood spacers and hardwood shims. Nice job!

The Model Manufactured Home Installation Standards describe a spacer as “Hardwood plates no thicker than 2” nominal in thickness or 2” of 4” nominal concrete block…”. (3285.304(c)(3)). But the individual manufacturers’ installation instructions often provide more options, and sometimes confusing details.

Most manufacturers allow 2” x 6” hardwood spacers. One spacer for single stack block pier, two spacers for a double stack block pier (one per cap block). If you stick with this, you will be in good shape.

 A recently revised instruction manual now defines a spacer as “hardwood, southern pine, or Douglas fir larch dimensional lumber 1x or 2x (2 layers maximum)”.  This is the first time I have seen pine in the same category as hardwood, not to mention allowing the spacer to be 1” thick. So, for those of you that like to use 5/4 pressure treated decking boards as spacers this appears to be one of the first DAPIA approvals for this method.

2″ hardwood spacer on a 4″ solid masonry cap block. Too bad the strap is loose.

When checking your installation manual, look at both the table and the text. Many instructions will specify “Nominal 2” thick boards” in the Pier Minimum Specification Table. BUT, if you turn to the text at “Install Shims” generally on the next page, they allow hardwood or concrete, not just 2” thick boards.

spacer text

Pressure treated hardwood dimension lumber is mentioned in a few manuals, but I have yet to see pressure treated hardwood. Maybe it’s a regional thing, but where I come from, hardwood is not pressure treated.

I even saw a few manufacturers’ installation instructions that don’t mention spacers. Just be sure to double check with your manufacturer to be certain that you are following their instructions.

When it comes to the overall size of the spacer, most pier illustrations show a 2” x 6” spacer board. While the installation instructions don’t specify the length of the spacer, the illustrations appear to show them the full length of the pier cap (16”). 

While there appears to be variation in the materials prescribed by different manufacturers, make sure to stay away from plywood or OSB! These materials will delaminate rather quickly and will certainly cause problems.

When it comes to shims, the installation instructions are more straight forward.

Use proper size spacers and hardwood shims! Not cedar shims like this!

Hardwood shims, 4” x 6” x 1” thick, must be used in pairs, and cannot occupy more than 1” total between the cap block (or spacer) and frame (I-beam). And like the spacers and cap blocks, a double block pier would require two sets of shims, one set atop each cap block.

Plastic Shims

Most manufacturers allow for plastic shims of sufficient capacity. I believe that plastic shims are a great choice for piers in porch areas, where water can pass between the decking boards and lead to premature decay of wooden shims. Also, the plastic shims are grooved so that they cannot slip apart. Again, I did see one manufacturer allows southern pine or Douglas fir shims in addition to hardwood. But generally plastic is the only exception to hardwood shims.

Hopefully, this post will encourage you to examine your current practices regarding spacers and shims, and to be certain you are following the manufacturers’ installation instructions. If you have questions, call the manufactuer’s Quality Assurance Manager and ask him to clarify their requirements.

A Week Worth of Inspections!

Through my career, I have inspected hundreds of manufactured home installations, but not too many as of late. That is why I jumped at the chance to travel west and look over 10 recently installed manufactured homes. I wanted to share what I learned with all of you.

Over the course of the week, I had the opportunity to meet with several installers, retailers and other industry representatives. Their knowledge and professionalism was impressive! They were proud of their installations, quick to answer questions, and eager to see if there was any information that I could share with them. These folks represent the industry well as evidenced by their work.  

Next were the homeowners. While only about half were home during my visits, when given the chance to talk about their homes, they had nothing but good things to say. They love their homes and they were sure willing to talk about it!

Also impressive were many of the installation techniques I observed.

 Most homes used some type of anchor and strap tie down system. I was pleasantly surprised to see that almost every home had strap protection where the straps wrapped around the main beams.  

The concrete work was very well done. The concrete footings were smooth and level, providing a great surface for piers.

Multi-section homes were well finished, joints were tight, trim and drywall were first rate, in fact it was difficult to find the mate line once you were inside the homes.

Ok, but what about areas needing a little improvement?

Site grading. It was easy to see where the term “flatlander” comes from. Most sites were completely flat. And since the sites are so flat, little or no excavation is needed. I suggest that a couple loads of fill dirt be included with every job to achieve that “turtle back” effect that is needed to get the water to flow away from all four sides of the home.

Pier construction. Overall the piers were great, with a few small concerns.  Several homes used ¾” thick 8” x 16” wood or 1″ concrete cap blocks or spacers on-top of the cap blocks. Most Manufacturers Installation Manuals require nominal 2” x 8” x 16” lumber or 2” or 4” concrete for cap blocks and 2” lumber or concrete spacers. Check your installation manual to make sure you are using the proper cap and spacer material.  

On that same note, I noticed some undersized hardwood shims. Again, don’t trust me, check your manual, but 4” wide x 6” long is what most require.

Dryer venting. I saw a few crushed ducts, and one duct that was blocked by the first course of siding.  I also ran across a few folks using the foil duct material. See my post  Clothes Dryers- What Every Installer Must Know! for more information on this topic.

It was a very wet and busy week, topped off by a cancelled flight and an all-night drive to get home.  But I am extremely fortunate to have had the chance to meet and work with such professional manufactured home installers, retailers and representatives. I hope to get the chance to work with all of them again soon.