Building a foundation on poles - construction pole or pier foundation considerations explained...

When considering a foundation on poles, cottages or log cabins from a distance can appear fragile when they are resting on wooden foundation poles. In reality, such a foundation can provide decades of strong support and withstand storms and floods.

Pole foundations do not meet every code requirement in all localities. Some building codes require you to build continuous-wall foundations. Walls are also recommended in earthquake-prone regions, cold climates and on building sites with insecure soil (sand and soft soil).

When to use a foundation on poles or construction pole or pier foundation?

A foundation on poles is designed primarily for level sites and stable soil. The best type of poles to be used for construction pole or pier foundation situations are pressure-treated ones.

Make sure they are straight and uniform in diameter and in most designs, they should be placed about 8 feet apart.

For a level site, they need to be long enough to extend 1 1/2 to 3 feet above ground level and at least 4 feet below it, or at least 6 inches below the frost if it is deeper than 4 feet.

Where the ground slopes gently, buy poles that are one foot longer. For the beams, obtain pressure-treated lumber long enough to span the rows of poles.

To anchor poles in the holes, you will need concrete or a wet mixture of 1 part cement to 5 parts clean soil, free of roots, leaves and other organic matter.

Here are recommendations for construction pole or pier foundation design and building. Instead of mixing the ingredients for the concrete (cement, sand and gravel) - get the cement and sand premixed.

During the early stages of foundation on poles construction, place the bags on wooden pallets and cover them with plastic sheets.

To clean up your tools after a day's work, keep buckets of water on hand and when you are finished with a tool, place it in the bucket. Replace the water as necessary.

Prepare this mixture by combining the dry ingredients, then adding slightly less water than you would for concrete - the amount of water will vary depending on the soil.

For this kind of foundation pole construction, you will need goggles to protect your eyes, especially when you are using power tools and the hammer. Wear gloves and a dust mask when cutting the wood.

A foundation on poles that is 16 feet square consists of three rows of pressured-treated poles sunk into the ground at 8 foot intervals. Each pole is firmly anchored in a jacket of concrete or soil-cement mixture.

The tops of the poles are sandwiched between 2x10 pressure-treated beams, fastened in place with 1/2-inch carriage bolts, washers and nuts.

The 2x6 pressure treated floor joists, which span from the outside beams to the middle beams, are fastened to the beams with framing anchors.

They are also nailed to the header joist at each end of the foundation.

The outer joists are placed to coincide with eventual location of the cabin's walls. Sheets of plywood nailed across the joists can serve as a sub-floor or as a finish floor - construction pole or pier foundation building.

Putting up a foundation on poles platform...

1- Digging the holes for foundation pole construction.

• Lay out the site as you would for a block wall, marking the location of the poles in relation to the walls.

• Rent a power auger to dig each post hole to a depth of 4 feet and 6 inches below the frost line, whichever is deeper. You can use a one-man power auger but a two-man version is more powerful and easier to handle.

• With a spade and a clam shell post hole digger, widen the holes to 16 to 18 inches in diameter.

• Set all the poles in their holes.

On a gently sloping site - one with a rise of 1 in 10 or less - you will need to dig the post holes deeper and larger than those on a level site.

Check with your building construction professional or check the building code that is required where you are building for requirements for a foundation on poles.

2- Setting the poles.

• Plumb the corner poles with a level and, while a helper holds them straight, brace them with 1x2's nailed to stakes.

• Measure down from the top of one corner pole the width of a beam plus 3 inches, and make a mark there. Drive a nail at the mark.

• Stretch a string fitted with a line level from the nail to the other corner post, and mark the second corner post at the height of the level string. Drive a nail there and tie the string to it.

• Align the middle pole with the string, then plumb and brace it. Mark the point where the string touches the pole.

• Prepare enough concrete or cement-soil mixture to fill in around the poles and shovel it into each hole.

Make sure you overfill it slightly. Tamp the mixture with a 2x4, and slope the top downward from the pole to the ground.

• Repeat the process on the other rows of poles, then remove the strings and nails and let the concrete cure for a day.

3- Starting the "daps".

To enable the beams to sit squarely against the poles, you'll need to cut a notch, called a dap, on both sides of each pole near the top.

With a bucksaw or pruning saw, first make a series of horizontal cuts 1 and 1/2 inches wide and 1/8 to 1/4 inch deep on one side of the pole. Work from the top to the mark you made.

4. Finishing the daps.

• Place the saw on the top of the pole and align the blade with the ends of the horizontal cuts from the top to the beam mark.
• Cut daps on the same side of the remaining ones.

5. Locating the outside beams for foundation on poles.

• You may need someone to help you doing this job. Set a beam against the outside of one row of poles so the bottom edge sits squarely in the daps in the posts.
• Holding the beam level, temporarily fasten it to each pole with a 3-inch common nail.
• Nail a beam to the outsides of each remaining row of poles in the same way.
• Cut the tops of the poles flush with the tops of the beams.

6. Positioning the inside beams.

• Run a string across a row of poles on the side opposite the beam.
• Line up the string with the edge of the pole that is smallest in diameter.
• Mark the tops of the larger poles at the string line, and cut a dap at each mark.
• Temporarily nail beams to the inside of the poles as described above.

7. Bolting the beams to the poles.

• Measure and mark a point 1/3 of the way from the top and bottom of each beam.
• Install a 1/2 inch auger bit in an electric drill and bore a hole through the beams and pole at each mark.
• Insert a 1/2 inch carriage bolt about 1 inch longer than the combined thickness of the beams and pole into each hole.
• Tighten washers and nuts onto the bolts.
As wood tends to shrink over time, check the nuts for tightness several weeks after the foundation on poles is completed and tighten them as necessary.

8. Attaching the floor joists.

• Set the joists across the beams at 16-inch intervals, letting them extend beyond the outside beams by a foot and overlap at the center beams by a foot.
• With 3-inch common nails, fasten together the joists that overlap at the center beams.
• Fasten the joists to the beams with multipurpose framing anchors and the nails recommended by the manufacturer of the anchors.
• Nail header joists across the outside ends of the floor joists, and fasten them to the end of each joist with 2 and 1/2-inch common nails.
• Lay a subfloor across the joists.

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