Recently I have been asked questions about anchoring manufactured homes using “J” Hooks (or “J” concrete anchors) that are wet set in the concrete footings. While I am not an engineer, let me share with you a few practical things that I learned over the years about anchoring and what you should consider if you want to use “J” type concrete anchors.
A quick look at an installation manual shows that in Wind Zone 1, we need to anchor the home with diagonal straps attached from the chassis beam to ground anchors placed just inside the skirting line of the home. In Wind Zone 2 and 3 we need both diagonal and vertical straps. In every case, diagonal straps are needed. Diagonal straps secure the home from sliding and up-lift in the event of windstorm. If the home is anchored only with vertical straps from the footing to the main beam, they might prevent up-lift, but not sliding of the home.
Most installation manuals require a maximum strap angle of 60° from horizontal. Installing “J” anchors in the footing generally result in a strap angle of around 90° . An inexpensive ($5 to $10) angle finder is a valuable tool to make sure you have the proper strap angle. Snap a picture for your installer file.
When I look over the actual instructions for proper use of the “J” anchor, it is obvious that these anchors are designed for concrete slab design, not to be placed in individual footings. This is based on the fact that each “J” anchor must withstand 4725 lbs. of tension without lifting. Assuming one cubic yard of concrete weighs about 4,000 lbs., you can see that you would need close to 1 ¼ yards of concrete per footing to properly hold the “J” anchor. A typical 24” diameter x 36” deep footing takes roughly 1/3 of a yard of concrete. Not even close to the amount needed to reach the required holding capacity of 4725.
So, where does this leave us? If we are placing a manufactured home on a frost protected concrete slab, the “J” concrete anchor might be the answer. Place them a minimum of 4” to a maximum of 10” from the edge of the slab, and keep an eye on the strap angle! The thickness of slab should be 2” greater than the “J” length where it is embedded in the concrete. So, a 6” “J” anchor should be embedded in 8” of concrete. But as always, you need to do your homework and make certain you are anchoring every home consistent with the home manufacturers installation manual and using the anchor components as they were designed!
My advice is to look at the newer anchoring systems that are available on the market today. Most of the home manufacturers have reviewed and approved them to properly anchor their homes. While they may be a little more expensive, they are certainly less labor intensive than other anchoring techniques, especially when you factor in end wall anchors. As always, talk to the home manufacturer. The anchor producers all have a lot of good information on their web sites and they all have some great technical folks on staff who are always available to answer any questions. So, give them a call before you start your next job!