House construction on floating slab system that sits on concrete piles or posts is called pier and beam foundation. It is alternative to crawlspace foundation, but does not have enclosure and perimeter foundation wall with footings. Multiple concrete piers (like legs) hold main subfloor and weight of entire house.
For as long as we know houses were built on raised structures to avoid water floods and keep safe from animals. Eventually pier and beam foundation became a construction method on uneven or unstable grounds.
For example if house is being constructed on high slope land or on rocky surface. The cheapest and easiest foundation to hold home is drilling holes and pouring concrete for creating piers. It gives options for building on many surfaces that slab on grade or basement foundation would never work.
How Much does Pier and Beam Foundation Costs?
The average cost for pier and beam foundation is $10.5 per square foot of main floor space. In complicated areas where excavation for piers is deeper or much harder than regular soil the costs can get as high as $16-18 per square foot.
Our calculation tells us that regular size concrete piers are poured 6-8 feet apart from each other to support beams and main subfloor level. In this example 1000 square foot house would require 30-32 concrete piers and 7-8 beams on top.
Expect to pay $300 for each pier to be excavated and poured with concrete. Rebar or is recommended for additional strength, but it does not cost a lot and should be included in the price. Regular beams cost $200 with installation and additional hangers.
Contractors use sonotubes for easy installation of pier and beam foundation as well as any other concrete posts. It is a cardboard that servers a as form for concrete pouring. They are sold by regular dimensions used in construction.
Construction Method for Piers and Beams
The process of building a pier and beam foundation is relatively easy when soil is not without large rocks or too much water. It works great on Type 1,2,3 Soil, and slightly more complicated on type 4.
For home owners or contractors that are interested in step by step process we listed these 5 easy procedures:
Step 1 – Planning Piers
Hopefully you are working with licensed engineer that plans out entire load of house with exact amount and sizes of concrete piers. Planning on site consists of marking spots where new piers will be built. We suggest using strings to make sure markings are set on straight line.
Step 2 – Excavating Holes
Next we start excavating for required depth and size of piers that are confirmed with engineer. The old method of using shovel is long gone and nowadays special machines used for specific size and depth excavation. Bobcat attachments are also available for such work.
Step 3 – Pouring Concrete
Fours for each pier stick out of the ground to avoid direct contact between beam and soil. The most popular forming method is sonotubes as we mentioned before. Cardboard round shaped tubes are installed in dug out holes and concrete is poured inside. For extra strength metal rebar is used.
Step 4 – Attaching Beams
Hopefully concrete piers that were poured all line up and have the same height. Its better to get them slightly higher and chip off than redoing a pier completely because it sits lower than the rest. Beams are attached to piers and form a strong floating foundation for the house. Bolts and heavy duty hangers are used to attach beams together. Welding may also be required.
Step 5 – Installation of Floor System
The last thing is to attach floor joist to beams and start construction of the house. The sizes of all joists with connection should be specified by qualified engineer. Often enough we see entire prebuilt houses set up on pier and beam foundation systems.
Pier and Beam Foundation Pros and Cons
Every method of construction has advantages and disadvantages. To understand what works for your home build we decided to provide entire list of pros and cons for building a pier and beam foundation with key factors.
Pros
Less Chance of Flooding – Elevated main floor supported on long concrete piers has almost no chance of water coming in. Distance from ground is usually 2-3 feet to subfloor joists.
Ability to Build on All Sorts of Terrains – Other foundation methods can be used on flat grounds with stable soil. Few single piers allow homes to be built on almost any type of spoil and elevation.
Cheap Construction on Average Soil – Building piers and beams foundation on soil without complication is one of the easiest. It is also not complicated, comparing to basement or even crawl space.
Flexible Maintenance of Mechanicals from Underneath – There is a lot of space to maintain or fix plumbing pipes and electrical from underneath. Spaced out piers allow crawling under the house for repairs.
Cons
Need Maintenance of Piers Every Few Years – All structural supports are exposed to nature and need regular fixes. Water and wind deteriorates everything within time and exposed posts have to be looked at constantly.
Broken Pier can Damage House – Heavy load is spread between each post and if one gets broken the load goes onto nearest pier. This can potentially damage or tilt the house.
Animals and Insects Get Inside from Below – Because the house does not go all the way to the ground it is exposed from underneath. Without proper insulation in all spots with tight protection tiny animals or ants can start a nest.
Lose Heat from Every Side – Every house needs tight enclosure for keeping temperature inside. Unfortunately pier and beam foundation creates extra side (below) that affects it. Even with proper insulation the floor may feel cold in north regions.
Construction Materials and Tools Used
Some of you may think of doing this work on your own and wondering what type of materials does pier and beam foundation construction require. The second question we try to answer is what are the tools needed for work.
Before anything starts we always encourage contractors to plan out future house position and stability. Therefore working with soil is sort of mandatory. Even if ground is flat with perfect type of soil you don’t want to build it and later have plants starting to grow underneath.
Small excavator or bobcat does the trick. Scrape up to 10 inches of soil if possible and level it as much as possible or necessary.
Same machinery can be used to drill the holes for piers. Bobcat extension is available for rent in major hardware stores. Of course you can always shovel it by hand.
Forming for concrete pouring is necessary. Otherwise it will just flow everywhere and you will not get adequate structural strength. We suggest sonotubes for that purpose.
Materials that are used in concrete piers is obviously concrete itself and rebar. Regular finishing towel is handy for making smooth tops. Remodel On Point team suggest using concrete vibrator before it sets to make sure it falls all the way to the bottom of the form.
Levels, lasers, measure tapes, strings and other similar tools needed for accurate height and spacing of piers.
Next come the beams that sit on top and connect to each other. Set up requires drills, bolts, hangers and welding in rare cases. These beams may be extremely heavy when lifting by hand is not possible. For that reasons contractors use heavy machinery and boom trucks.
