When building foundations for sheds and small houses there are lots of options to choose from when it comes to foundation construction materials and techniques. Durability, simplicity and cost are the factors that often determine the foundation type selected for a particular project.
It’s difficult to beat concrete foundations from the standpoint of durability which explains why concrete is so widely used in foundation construction. Three of the most common types of concrete foundations are the;
A fourth type of concrete foundations is that where hollow concrete blocks are used to build a stem wall similar to that obtained with poured cement.
Using this method involves laying hollow concrete blocks with mortared joints between them. This method isn’t widely used for do-it-yourself projects because it requires a fair amount of masonry skills to obtain a foundation that is level and plumb.
There is however an excellent technique involving the use of concrete blocks that can be effectively used by the average homeowner in building a strong, durable foundation for shed and small house construction projects. The method involves dry stacking the blocks on a level grade without the use of mortared joints.
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Advantages of Dry Stack Concrete Block Construction
Reduced concrete foundation cost is one of principal advantage of building foundations from concrete blocks. Using cement blocks eliminates the materials costs associated with forms and the work required for all types of poured concrete foundations. The savings with block construction are especially significant in comparison to forming and pouring slabs and continuous stem walls.
Dry stack cement block construction is both strong and durable. According to the article “How to Build a Mortarless Concrete Stem Wall” published at the Wonder How To website, when properly constructed a dry stack cement block stem wall foundation can be “seven times stronger” than a traditional mortared block stem wall.
Building foundations using this method is simple with no masonry skills required. Once proper attention has been devoted to leveling the first course of blocks on a prepared grade it is a simple matter of creating a level and plumb foundation stem wall by dry stacking the additional block courses.
Blocks are relatively inexpensive and widely available at most lumberyards and home improvement retailers. While hollow concrete blocks come in a variety of sizes the 8 inch x 8 inch x 16 inch block is a good choice for foundation construction.
Foundation Construction Site Preparation
Traditional methods of laying out a square foundation including the use of batter boards are used with the dry stack technique.
Once the perimeter of a square foundation has been identified, excavation is the next step. The grade needs to be excavated so that the first course of blocks will be set below the local frost line to minimize the chance of foundation settling.
Some pick and shovel work is generally sufficient for excavations that will accommodate small buildings up to about 12 feet x 16 feet but renting a small excavator from a local construction equipment rental retailer can make the job easier and faster.
Devoting some attention to getting the bottom of the excavated perimeter as level as possible will simply the leveling of the first course of blocks but once the process of laying the first course begins, each block will need to be leveled in both directions block by block. Once excavation is completed unless poured concrete footings will be used, the earth should be well tamped with a hand tamping tool.
Wooden stacks driven at each of the four corners and mason string should be used to define the outside perimeter of the foundation to ensure that the first course is laid in straight lines.
Dry Stack Cement Block Construction Technique
Starting at one corner, the first course of blocks is laid. Each block must be leveled in both directions when set and each subsequent block must be checked to make certain it is level with the previous block. The first course is the most time consuming but once it is finished it is a simple matter of stacking blocks in a running bond pattern to complete the additional courses.
After all courses have been completed the next step is inserting rebar. The 3/8 inch rebar is a good choice since it can be cut to length using a bolt cutter if a chop saw is not available.
Rebar should be cut to a length equal to the height of the stem wall plus 12 inches. A length of rebar should be driven into each of the holes in the hollow blocks until the top of the rebar is below the top of the last course of blocks.
With the rebar in place, using a trowel all of the voids in the blocks should be filled with mixed concrete level with the top course of blocks. J-bolts can then be installed at desired intervals for use in attaching the building sill plates.
Once the concrete has set in the voids of the wall an optional but recommended step for getting the strongest foundation is the application of structural stucco to the inside and outside of the stem wall. In addition to added lateral structural applying the stucco gives the foundation a smooth attractive appearance.
The dry stack cement block construction technique for foundations is nothing new. As noted at The Natural Home Building Source website, the technique has been effectively used for more than a century. It is a simple, strong and cost effective foundation method for any small building home construction project.