Garden Shed Foundations

Published: 02nd February 2011
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The Pier and Beam Foundation

The foundation of your new garden shed is more important than you may think. Your new garden sheds may be stable to begin with but the overall stability of the structure will depend entirely on the type of surface you are building on, the mass of your building and the type of foundation you use.
For storage sheds and garden sheds, there are three common types of foundation and the type you use will be determined mainly by the size of your shed.

The types are:

1. Concrete Slab - The best method - provided it's done well. A job for a competent Do-it-Yourselfer, or a professional builder.

2. Pier and Beam - Straightforward, yet valuable. A good solution if the building may need to be moved in future years.

3. Treated Wood Runners - An easy temporary answer. You simply clear the site, level off the area and begin. Using treated wood is a must for this option.

Whichever method you use, it is important that the end result is above all, firm, level and square. If you are constructing the base for a building over 12' x 8', a garage, a sectional building, a corner unit, a gazebo, or a building with no floor, then the more permanent poured concrete slab might be best.
Your sheds plans or shed plan may give information on the type of foundation required.

The Pier and Beam Foundation- 8x8 Shed

I will outline the most common type of shed foundation, the pier and beam type.
We will use 4x4s lumber as skids or beams, with three concrete pads, spaced along the length of each cross member. This means that the concrete pads will be four feet apart side to side and front to back. The first procedure involves laying and leveling nine 1 x 1 concrete paving stones as support for the 4x4 beams. You don't need the most expensive blocks available. What is important is the compression strength, not beauty as these blocks will be hidden by the rest of the construction.

1. Carefully level the ground (keeping a slight grade so any water getting under the shed will drain away). Remove any grass or ground cover.

2. Next lay down and tamp in a layer of crushed stone or rock to aid in drainage. This will be a solid base for your project.

3. Lay out your foundation outline by using string and stakes, allowing about 6" excess from each of your measurements for the some overhang of the foundation blocks. The batter boards, H-shaped stakes made from scrap lumber, are outside the actual corner lines and allow for adjustments that define the square corners.

How to square a rectangular foundation.

Remember the Pythagoras Theory from High School? Well, now is the time to use it. Some building texts call it the 3-4-5 rule. In any case it serves well here. As used here, it will help in laying your foundation out squarely. Start by using your tape measure to mark some guide points to work with. Mark the string corner at a 3 mark on one side, 4' on another side and "checking" the right angle by adjusting the diagonal distance to the 3' and 4' marks by adjusting the angle.
The goal is to bring the angle between the two marked sides to a perfect 90 degrees such that it measures exactly 5' when measured across the diagonal.

Alternative method for squaring a foundation.

Another squaring method when laying out a square foundation is to simply layout your string lines or blocks and adjust by measuring the diagonal, corner to corner. When squared the diagonal corner measurements will be equal.

1. To level the blocks, lay them down inside the string perimeter. By using either of the methods outlined above you can square their position properly.

2. Now let's determine that each pad is sitting level. Place the four-foot level on each block, first east-west, then north-south and adjusting the fill under each block to ensure it is level.

3. Next, use the level to find out which of the nine pads was the lowest. Designate this one the "king pad." Now level the two adjacent perimeter pads in reference to the "king" pad. Remove a little crushed stone or dirt from under each pad until it is level with the king pad. This can take some time as you have to lift up the pad, remove some crushed stone, put the pad back and tap it solid, then re-measure the level and, if necessary, do it all again.

4. From here level each successive pad around the perimeter. Go both directions around the perimeter until you get to the pad diagonally across from the king pad. Level this last block from one side and check its level from the other side.

5. Finally, level the middle pad from one side and, as a final check of the entire process, check the level of the middle pad from the other three sides.

This procedure if carefully done should give you a very level base.Here are some tips that will help you with the slab or concrete foundation. The principals remain the same for layout and squaring the forms that will be required to pour the concrete into.

1. Inside the batter board and string outline the soil will have to be removed so that the concrete can be poured to a prescribed depth for your local codes and conditions.

2. Your local building supply store can provide information concerning materials required for a given slab dimensions. Many of the larger warehouse operations offer clinics and free handout materials that can help you get started on pouring your own concrete foundation.

3. Now you have a solid foundation on which to lie out your floor joists and flooring. Let's take a look at the Plans.


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