The procedure to properly repair a post and beam foundation requires a thorough inspection of the crawlspace. The crawl space is the area below the floor that has pier supports, joists, sill plates, and joists that should be visually inspected for termite, dry rot, mold, and proper engineering damage.
A structural engineer must be involved in the inspection and repair analysis to ensure that the proper repair is correctly described. Expansive clay soils can move the freestanding areas of the foundation and driveway causing distortion in the structure and leaving signs of foundation movement to varying degrees. Plumbing leaks and poor drainage are contributing factors that can influence clay soils and cause them to swell and compromise the supporting elements of the structure.
The method of repair is dictated by the results of the inspection that the engineer describes in his report. A repair must follow the engineers’ outline to ensure long-lasting performance of the end result. The use of subgrade materials can result in a failed repair that is time consuming and will cause costly future expenses to maintain the foundation.
There are different types of column and beam foundation construction depending on the interior and exterior loads that the structure supports. The size of the joists or rafters along with the size of the joists dictate the design of the column and beam structure. The larger the rafters, the greater the distance between the rafter supports. The larger and deeper the interior beam or column supports, the greater the space allowed between columns.
Ventilation is critical under the floor to reduce the effects of moisture on woodwork and mold. An engineer should include in his report if and how many vents need to be increased, type, size, and location of vents to promote adequate ventilation. Inadequate ventilation can result in a reduced longevity of wooden elements, resulting in avoidable expense in the future.
Correction of drainage in areas of standing water within 10 feet of the structure must be addressed by the engineer. Poor drainage can cause the crawl space area to collect standing water, especially if the elevation of the ground surface below the floor is lower than the elevation of the exterior ground surface. A French drain is usually recommended to address drainage issues around foundations where you are trying to lower the water table. .
Pier and Beam foundations are classified as deep foundations. They have construction piers under their outer beam. Pre-construction piers are installed prior to pouring the exterior base of the grading beam, providing the exterior beam with additional support and a deeper foundation. The diameter and depth of the piers vary depending on loads and geographic locations. Most construction piers I have come across in pier foundations are attached to the grade beam foundation with rebar, although engineers recommend not attaching the foundation to the piers.
When building in areas with expansive clay soils, void boxes are implemented under the foundation to allow the clay soils to swell without lifting the structure. Soil tests are performed to determine the amount of surge in clay soils called PVR (potential vertical lift). In Irving TX there are areas that have up to 13 inches of surf on the ground.
Problems with a pillar and beam repair that foundation companies run into are often older structures with brittle concrete foundations. If a thrust pile repair is made using the weight of the structure, the grading beam will not be able to withstand the stress required to drive the piles without damaging the footing. Pressed concrete piles are problematic when installed because the piers and beams are lightweight structures and it is difficult to achieve the proper depth. I have encountered the same problem when installing steel pillars, either the structure is too light or the beam is damaged due to the bending of the beam during the driving process.
A drill pier or helical pier work for installation without compromising the integrity of the concrete, as they are not a push pier installation, they are limited in how deep they can go, but they are still a better alternative. The primary focus should be on proper post-repair maintenance regimens to help maintain more stable moisture content after the repair is done.
Shims should be re-shimmed in the access space with steel shims as they will not compress or rot. Solid concrete blocks should be used instead of cement blocks. Engineers don’t like to see concrete cylinders unless they are poured into place and reinforced with rebar.
Another type of column and beam structure is called a block and base foundation. Many houses that were built in the 1800s and early 1900s were of this type of bois d’arc spring construction. I still work on these kinds of foundations today. They are well ventilated most of the time because they have a plinth instead of a concrete perimeter beam. If installing new pads, it is recommended that they be poured into place or the bottom of the pads be buried a minimum of 6″ below the ground surface to prevent the pads from sagging over time.