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.

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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.