Construire des fondations par piliers et poutres pour faciliter la maintenance et la réparabilité

La conception de piliers et de poutres était l’une des techniques de fondation les plus populaires jusque dans les années 1960, lorsque la technologie du béton a amélioré son système de dalles flottantes. De nombreux constructeurs utilisent la construction sur dalle, en particulier dans les régions chaudes. We're going to find out why professionals Jordan Smith of @jordansmithbuilds and Kyle Stumpenhorst of @rrbuildings chose pier and beam over slab-on-grade for the All-in-LP Build in Bellville, Texas. But first, let's delve into pier and beam foundation.

What is a pier and beam framing concept? 

Pier and beam design features deep concrete footings to which piers are attached or, in some cases, piles drilled deep into the ground. Beams are connected to the top of the piers so they are above the ground. The floor joists then sit directly on the beams.

Pros and cons of pier and beam foundation

A number of different factors influence the type of foundation used in home construction—local building codes, frost lines, soil conditions, and whether the area has a tendency to flood.

Pier and beam foundations tend to be more expensive than traditional slab-on-grade foundations. Since slabs are dug just below the frost line, they are an affordable option for houses built in warmer regions and new residential construction. However, big repairs can be a headache as most plumbing pipes are buried in gravel or sand beneath the slab. Repair often means removing hardwood floors or carpet and jackhammering into the concrete to locate and replace pipes.

Pier and beam construction typically sits 20 inches from the ground and allows for a crawl space, which offers easy access to plumbing and HVAC. While slab foundations are often ranked better in areas that flood, pier and beam construction elevates the home for good protection.

Where is pier and beam construction used?

Pier and beam design can be a good option for areas of the country that have more clay soil, which expands and contracts and moves around a lot. A simple slab-on-grade foundation will move with the subsoil and can cause issues with the home, including cracked drywall; sticking doors and windows; and in extreme, but not uncommon cases, a cracked slab. A pier and beam foundation can be less affected by underlying soil conditions, and if the foundation does move over time repair is much less costly than with a concrete slab.

Based on soil conditions and the geotechnical report, Smith and Stumpenhorst felt a simple pier and beam foundation would be inadequate for the All-in-LP Build in Bellville, Texas. They decided to use helical piles to create a deep foundation that will be stable for decades to come.

"The Gulf Coast is renowned for foundational issues, and there are a myriad of foundation repair companies who stay busy repairing slab-on-grade foundations in this area. With this deep foundation, the future homeowners can rest easy knowing they won't have to worry about sticking doors or cracked drywall," explains Smith.

Advantages of helical pile and beam construction 

What is the difference between pier, piles and helical piles?

• A pier has everything excavated out and transfers all of its load to the bottom of the pier

• A pile is held in place by friction and the load is transferred to the soil around it

• Helical piers are different from simple piles because they screw into the ground for even more load capacity 

The main advantage of helical pile and beam construction is the known load-bearing capacity of each pile. "If I put enough torque on this helical pile, I get more support. I put 5 900 foot-pounds of torque down and will get 70 000 pounds of capacity out of this design," says Smith of the Bellville project.

While the soil surface appears consistent, a pier in the construction system can unknowingly stand in soft soil or water table. Depths of helical piles are determined individually, which is similar to a soil sample taken at each pier. "One of our piles only went in seven feet before we hit our required torque and depth. We moved over fifteen feet and it took eighteen feet to hit our same load-bearing soil conditions," explains Smith.

How do you frame a pier and beam foundation for best load capacity?

After the helical piles were put down, Smith and his team attached plates to the LP® SolidStart® LVL. LP SolidStart LVL is a strong, straight and durable framing product made for superior performance. Il peut remplacer le bois de charpente traditionnel pour accroître la consistance et la flexibilité du design. “This LVL gives us the most load capacity,” says Smith. “As this beam is loaded, the top side is coming into compression and the bottom side is being pulled into tension. The grain going in one direction gives us a stronger beam out of the laminated wood than what actual solid dimensional lumber can be.” 

Since there is no need for a concrete flooring system, LP Legacy® Premium Sub-Flooring was installed on top of the I-joists using high performance adhesive to ensure a squeak-free floor for years to come. LP Legacy sub-flooring is an oriented strand board featuring Gorilla Glue Technology®. “It's super-precise on how long the strands are as well as the orientation of the strand. Because the board is stiffer lengthwise, it's important how OSB is installed because the strength axis makes a difference on how it's put together,” explains Smith.

LP Legacy sub-flooring requires a 1/8-inch gap at every interface. “This gap is important,” says Smith. “It allows the board to expand and contract without giving us any type of lippage between the boards or trying to pull the nails out.”

The tongue and groove profile of LP Legacy sub-flooring allows Smith to quickly install the product because the gap is already calibrated to the right thickness.  

Learn more about helical piles from Smith in this video. Curious about the All-in-LP House? Check this article.