The procedure to repair a pier and beam foundation properly requires a thorough inspection of the crawl space. The crawl space is the area beneath the floor that has pier supports, girders, sill plates and joists that need to be visually inspected for termite damage, dry rot, mold and proper engineering.
A structural engineer should be involved in the inspection and repair analysis to insure the proper repair is outlined correctly. Expansive clay soils can move the independent areas of the foundation and crawlspace causing distortion in the structure and leaving signs of foundation movement in different degrees. Plumbing leaks and poor drainage are contributing factors that can influence the clay soils causing them to swell and compromise the supporting elements of the structure.
The repair method is dictated by the findings in the inspection that the engineer outlines in his report. A repair must follow the engineers outline to insure longtime performance of the end result. Using sub grade materials can result in a failed longtime repair causing costly future expenses to maintain the foundation.
There are different types of pier and beam foundation construction depending on the interior and exterior loads the structure is carrying. The size of the girders or beams along with the size of the joists dictate the design layout of the pier and beam structure. The larger the joists the further the girder supports are allowed to be spaced. The larger and deeper the interior girder supports or piers the further the allowed space between piers.
Ventilation is critical underneath the floor to reduce the effects of moisture in the wood elements and mold. An engineer should include in his report if the ventilation needs to be increased and how many, type, size and locations of vents to promote proper ventilation. Improper ventilation can result in reduced longevity of the wood elements resulting in future avoidable expense.
Drainage correction in areas of ponding water within 10 feet of the structure should be addressed by the engineer. Poor drainage can cause the crawlspace area to accumulate standing water especially if the ground surface elevation underneath the floor is lower than the exterior ground surface elevation, A french drain is usually recommended to address drainage issues around the foundation where your trying to lower the water table.
Pier and Beam foundation are classified as deep foundations. They have builders piers beneath their exterior grade beam. The pre-construction piers are installed before the exterior footing of the grade beam is poured giving the exterior beam extra support and a deeper foundation. Diameter and depths of the piers vary depending on the loads and geographical locations. Most builders piers I have run into on pier foundations are attached to the grade beam footing with rebar even though Engineers recommend to not attach the footing to the piers.
When built in areas with expansive clay soils void boxes are implemented under the footing to help allow the clay soils to swell without lifting the structure. Soil tests are done to determine the amount of swell in the clay soils called PVR ( Potential for Vertical Rise). In Irving TX there are areas that have as much as 13 inches of swell in the soil.
The problems with repairing a pier and beam that foundation companies run into are usually with older structures with brittle concrete footings. If a repair is done with push piers using the weight of the structure the grade beam will not be able to take the stress required to install the piling without damaging the footing. Concrete pressed pilings are problematic when installing because pier and beams are light structures and proper depth is hard to achieve. I have run into the same problem installing steel piers either the structure is to light or the beam gets damaged from the flex of the beam during the driving process.
A drill pier or helical pier works for installing without compromising the integrity of the concrete in that they are not a push pier installation but are limited to the depth they can achieve but are still a better alternative. The main focus should be on proper maintenance regimens after the repair to help keep the moisture content more stable after the repair is done.
Re-shimming the crawlspace should be done with steel shims as they will not compress or rot. Solid concrete blocks should be used in lieu of cinder blocks. Engineers do not like to see concrete cylinders unless they are poured in place band are reinforced with rebar.
Another type of pier and beam structure is called a block and base foundation. A lot of homes that were built in the 1800’s and early 1900’s were of this type of construction with bois d’ arc piers. I still work on these type of foundations today. They are well ventilated most of the time because they have a skirting instead of a concrete perimeter beam. If installing new pads it is recommended they either be poured in place or the foundation of the pads need to be buried a minimum of 6″ beneath the soils surface to prevent the pads from tilting over time.