Introduction
Are you planning to build a shed but unsure about the best foundation to use? Perhaps you have some ideas but need more detailed information to make an informed decision.
By choosing precast concrete piers for your shed foundation, you’re opting for a durable and reliable solution. Depending on your specific situation, precast piers can be an excellent choice.
A precast concrete pier foundation is one of the most stable foundations available, second only to a concrete slab. It offers superior stability compared to skids, ensuring your shed remains sturdy for years to come.
Additionally, there are methods to protect concrete pier foundations against frost heaving if that’s a concern. Piers extend deep into the soil, so if your soil is prone to frost heaving, we can modify it with a more suitable material.
Choosing the right foundation is crucial not only for the longevity of your shed but also for preventing future issues such as uneven flooring, structural instability, and moisture damage. This guide will walk you through the entire process of installing a precast concrete pier foundation, ensuring your shed stands strong and level for years to come.
Pier and Beam Foundation Summary
Concrete piers work in conjunction with other components; they need elements that transfer the weight of the floor, walls, and roof into the ground. Wooden beams are commonly used for this purpose as they are cost-effective and capable of supporting significant weight based on their dimensions.
The precast concrete piers are embedded in wet concrete footings and support 4×6 pressure-treated timbers once the concrete has cured. Piers should elevate the shed high enough to prevent moisture from seeping into the structure.
Air circulation can occur beneath the shed, and pressure-treated timbers resist moisture effectively.
The pressure-treated beams resting on the piers provide the necessary support for the shed.
That sounds promising. So, how do we install the concrete piers?
- First, determine the size and number of piers your shed requires based on your shed’s dimensions and the load it will bear. Consider the weight of items you plan to store to ensure adequate support.
- Once you have a clear plan, mark the outlines of your shed and excavate the area to a depth of 3 to 4 inches.
- Determine the depth of your frost line through prior ground studies or by consulting a professional. Key factors include soil texture and capillary water content. If dealing with fine-grain soil like clay, replace some of it with dry gravel to enhance stability.
- Dig holes 10 inches below the frost line for the footings. If the soil is fine, dig 20 inches deep and fill the bottom 10 inches with gravel, compacting it with a tamping rammer or similar tool to protect against frost heaving.
- Pour the concrete into the footings of the precast piers and set the piers into the wet concrete.
- Use a laser level or a leveling tool to ensure all precast concrete piers are aligned at the same height, facilitating the installation of the 4×6 beams.
- After the concrete cures, lay down landscape fabric and a gravel drainage bed, then install the beams. If the ground drains well and remains frost-free year-round, you might not need the gravel drainage bed. Otherwise, proper drainage installation is essential, which will be explained later in this guide.
Everything above is a simplified overview. For a shed adjacent to a small house, 4-6 concrete piers might suffice. However, for larger sheds, precise calculations are necessary to ensure safety and stability.
If you properly compact the soil around the shed and under the concrete piers, they can support substantial weight, as concrete provides solid resistance to straight pressure.
So, how many pier blocks do you need for the shed foundation?
Technically, one well-installed concrete pier on solid soil can support the weight of a standard tool shed adjacent to a house. However, to support the structure adequately, four concrete piers are typically sufficient for a small cube-shaped shed. For larger sheds, two rows of three piers each (totaling six piers) might be more appropriate.
When determining pier and beam foundation spacing, consider the shed’s shape and the size of your beams. Do the beams require more than two support points? In which directions should they run?
What should be the size of the concrete piers, and how much weight can they bear without sinking into the soil?
Local building regulations can provide guidance or specify requirements. Generally, a 6-10 feet distance between concrete piers is considered reasonable for standard applications.
More piers won’t hurt; fewer might compromise stability.
How to Build Concrete Pier and Beam Foundation in More Depth
The previous section provided a summary. For those who prefer detailed information, here is an in-depth guide to building a concrete pier and beam foundation.
Start by Laying Out the Concrete Pier Foundation Design on Paper or in Nature
Every project should begin with meticulous planning on paper. While some may manage without a plan, having a detailed layout helps in maintaining project scope and controlling costs.
Draw the shed dimensions on paper, determine the number of piers needed based on the distance between them, and calculate the number of beams required. This will help in estimating the materials needed for walls and roof construction.
Next, visit the hardware store to check prices. If costs are too high, consider scaling down or exploring alternative solutions to stay within budget. Proper planning helps prevent incomplete projects.
With everything planned on paper, proceed to gather the necessary materials and prepare for the project.
Begin by laying out your project area. Remove the sod and excavate 3 to 4 inches of soil from the site. This preparation is essential for installing drainage systems later.
Use batter boards and a string line, marking every 4-6 feet to outline where the piers will be placed. Accurate marking is crucial to avoid repositioning piers and footings after installation. Take your time to measure everything correctly to ensure precision.
Run string lines across the marked points and square them using the 3:4:5 triangle rule. This ensures that your shed will have right angles and a proper rectangular shape.
With a plumb bob and powdered chalk, mark the exact locations of the piers on the ground where the string lines intersect.
Dig Holes for Concrete Footings
The footings act like shoes for the concrete piers, distributing their weight over a broader area to prevent sinking.
Next, dig holes for the concrete footings. These should be 12 to 14 inches square and 10 inches below the frost line.
As mentioned earlier, if dealing with fine-grain soil, dig 10 inches deeper (20 inches total) and fill the bottom 10 inches with gravel. Compact the gravel with a tamping rammer to prevent the piers from sinking under load.
Why do we do this? Fine soil, like clay, has high capillary water properties, allowing water to rise higher. By replacing some of it with rougher material, we prevent moisture-related issues.
If the soil is suitable, shovel approximately 4 inches of gravel into the holes for drainage and tamp it down with a 2×4 or similar tool. Ensure the bottom is level to facilitate the installation of forms if used.
If you choose to make your own concrete forms, construct square forms using 1×6 materials for the top of the footings. Position the forms over the holes and level them on all sides. Use stakes to secure the forms in place if necessary.
Another professional tip is to measure the distance between the top of your form and the intended 4×6 beam height. This ensures that the precast concrete pier foundations are set at the correct height.
Add rebar to the footing to enhance its strength. If there are no specific instructions, place the rebar 1-2 inches deep from the sides to ensure adequate concrete coverage. Rebar should run in both the x and y directions.
Finally, mix the concrete and shovel it into the forms and holes. Move the shovel up and down to eliminate air pockets or use a vibrating tool for the same purpose. Use a straight edge to scrape the concrete level with the top of the form.
Attach Concrete Pier Foundations on the Footings
Next, it’s time to install the precast concrete pier foundations on the footings. This must be done before the concrete fully cures to ensure a solid bond. This method ensures that the cement in the concrete adheres to the precast piers and the aggregates within.
Align the piers by placing a straight board across them horizontally. Then, position another straight board at the edges and set it on top to level the anchors from end to end.
Use a laser level or another precise tool to ensure all piers are at the correct height. Avoid adjusting them after installation to maintain structural integrity.
Allow the concrete to set for at least 24 hours before removing the forms. Depending on the concrete mix, this may take 2-3 days.
After removing the forms, water the footings to allow them to harden further. This step also helps prevent potential cracks.
If necessary, place landscape fabric and gravel for drainage. If your drainage is already effective, this step may be skipped. However, when in doubt, it’s better to install proper drainage to avoid future issues.
Compact the gravel around the concrete piers thoroughly and under the shed. This compaction helps protect against frost-thaw cycles.
Finally, place 4×6 beams into the anchors on the piers. Beam sizes may vary based on the shed’s dimensions; for example, a 6-foot shed might use a specific beam size.
Level the beams from end to end, side to side, and with each other by adjusting with shims if necessary. Then, attach the anchors to the beams using nails or screws.
Now, the precast pier foundation is ready for the shed. This method provides a stable foundation suitable for most applications, including wet or uneven ground and areas prone to frost heaving.
For added stability, consider anchoring the beams securely to the piers using metal brackets or straps. This ensures that the shed remains firmly in place, even during extreme weather conditions.
Additionally, incorporating a moisture barrier between the ground and the beams can further protect against potential water damage and prolong the life of your shed.
Conclusion
Precast concrete pier foundations have their place in building both houses and sheds. They offer an excellent way to elevate structures off the ground, especially in areas with ground moisture issues.
This method is also ideal for building on uneven terrain. You’ve likely seen precast concrete piers on hillside homes and similar structures. For more detailed information, refer to additional resources on concrete foundations.
I prefer elevating most storage and other buildings off the ground on my property. Elevated floors allow the structure to breathe and can add a quality aspect to the design.
By raising the structure sufficiently, you eliminate concerns about sinking. I once had a kid’s playhouse built on piers, and when it began to sag, I simply raised it back up using leverage and concrete pads. In my defense, I didn’t build it myself.
If you’re interested in various methods to support concrete foundations, check out our article on precast concrete piles supporting underground foundations.
By following this comprehensive guide, you can confidently install a precast concrete pier foundation that ensures your shed is both stable and durable. Proper installation not only enhances the lifespan of your shed but also contributes to its safety and functionality. Whether you’re a seasoned DIY enthusiast or a novice builder, the steps outlined above provide a clear roadmap to achieving a robust foundation for your shed.
Remember, investing time and effort into a solid foundation now can save you from costly repairs and structural issues in the future. Take the necessary precautions, adhere to local building codes, and don’t hesitate to consult professionals if needed. With the right foundation, your shed will serve its purpose effectively, providing ample storage space and enhancing the overall value of your property.