The previous two blog postings have concentrated on pier footings and caps. Now we should look at the pier itself to make sure we understand the backbone of the support pier.
Most piers are constructed with dry stacked concrete blocks. As we mentioned in the previous posts, a single stack concrete block pier can typically carry a pier load up to 8,000 lbs. (with an exception made for at least one major manufacturer). I have had installers ask me about the difference between 2 core and 3 core blocks. For our purposes, there is no difference. There is a defined top and bottom to the block, but that is for the laying of block and the application of mortar (the webs of the block are slightly wider at the top to give a bigger surface for the mortar). This doesn’t impact their ability to carry loads should you stack them up-side down.
Look over the typical “Load on Frame Supports for Homes Not Requiring Perimeter Blocking” chart below. There are very few configurations that exceed the 8,000 lbs. where you would need double block piers.
NOTE: this chart is for a typical manufactured home. If you are installing a manufactured home that has features like a steep pitched or hinged roof, high side walls, tray ceilings, terra cotta roof tiles, stone veneer finishes, etc., the pier loads can be significantly higher. Always consult the installation instructions for the home you are installing!
The bigger issue that should concern professional installers is the pier height. In general, if you are using single stack block piers, there are two height limits to keep in mind:
- The piers at the corners can be no more than 3 blocks high (approximately 24″ plus the cap block)
- Typical piers along the main beam are limited to 36″ high.
Should you exceed either of these limits, you need to use double stack (16″ x 16″) block piers. Unless your pier is 67″ or higher, dry stacking of the blocks is acceptable (mortar is not required between or filling the blocks). If you need to construct a pier higher than 67″ most installation manuals require you consult a professional engineer. I did notice that Clayton Homes provides a design in their installation manual for double stack block reinforced piers up to 108″ high, however the footing and pier require reinforcement and there are some big concerns with anchoring a home that high above grade.
Given that rarely are piers overloaded with our conventional installation methods, I am still surprised at the number of installers that continue install manufactured homes with double block piers. Bigger is not always better, and often it is more difficult to construct.
A double block pier that is not properly capped, or not properly centered on the footing, is more prone to failure than a single block pier that is well-constructed.
There are some other pier options available that I think we should take a quick look:
- The Steel Support Pier. I haven’t seen a lot of installations that use steel support piers, but maybe it is time to reconsider this option. First of all, these steel piers must be listed and labeled to show they are properly designed, manufactured and can carry the loads. If you are buying from one of the major suppliers, you will likely be fine.
In general, these steel support piers are limited to 6,000 lbs. This is sufficient for pier spacing of 8′ apart supporting a typical 14′ or 28′ wide manufactured home. Also be aware that the adjustable riser (screw) should not extend more than 2″ when finally positioned.
Steel support piers must be painted or otherwise protected from corrosion, and must be stamped with their capacity.
I understand that the material cost compared to concrete block may be slightly more, but I think you will easily save that much in labor.
- Pre-cast Concrete. As above, pre-cast concrete piers must be labeled and listed, and here is where I find the problems. Very few of the pre-cast concrete piers I have seen were fabricated in a facility where a quality control program is overseen by an independent inspection agency, with testing or calculations to determine the capacity. To be blunt, if some guy is making pre-cast concrete piers in his barn or garage, it is a good bet that these piers are not labeled or listed. Stay clear!
If you are using any pre-cast concrete piers, ask your supplier to provide evidence that their products are labeled and listed.
- Helical Pile Foundations. This could become a more common foundation in the future, especially in areas of deep frost penetration.
This foundation installs quickly, with no concrete, no excavation, and it is removable! BUT, you need to get approval from your manufacturer before you proceed.
Ok, I think we should talk just a little more about supporting manufactured homes with piers, so in a few weeks we will look at pier locations to properly support the manufactured home.
As always, refer to the installation manual before you proceed. If you have any thoughts or images, feel free to send them my way!