The process of underpinning or lowering a basement is done for a number of reasons: A homeowner may want to convert a crawl space or unfinished basement into a useable area, the original foundation might be unstable, the foundation walls could be heavily cracked and require additional support, or an extra storey may dictate underpinning to increase load capacity.
Basement underpinning is the process of removing soil below a crawlspace or concrete slab, excavating the area to create a lower support level and then adding new concrete footers, walls and floor to extend the depth or reinforce an unstable foundation.
WHAT IS BASEMENT UNDERPINNING?
This worthwhile home improvement requires professional expertise in foundation walls, excavation, footings and concrete floor replacement. We will do a careful evaluation of the foundation and surrounding area to determine job and building code requirements related to excavation depth, plumbing and electrical re-routing, and concrete work.
DESIGN STAGEWith the initial evaluation complete and your goals established, an engineer and architect will be brought in to design the new space. These experts will draw plans that detail moving and extending load-bearing walls required with this project. They will submit stamped drawings to the local municipality to obtain the necessary permits before work begins.
SITE PREPARATIONAfter plans are complete and permits issued, the site must be prepared for construction. Furnace connections must be re-routed to move all ductwork and equipment out of the way. The next phase requires technicians to install temporary supports or vertical jacks to hold the building in place while the underpinning is being done. Wooden boards or steel beams are used to disperse the weight of the structure and are removed once the project is complete.
LOWERING THE BASEMENTThere are several methods for completing the underpinning process, depending on the purpose for the project. The Traditional Mass method is used for shallow underpinning. In this instance, the soil underneath the foundation isn't strong enough to support the home. The weak soil is excavated and replaced with mass concrete. This provides both strength and a more efficient distribution of weight. The Beam and Base method utilizes the traditional mass base but also incorporates concrete beams. These are constructed underneath the concrete base to spread the load evenly for better support. A third method called Mini-piled underpinning allows the structure to rest on stable ground of 5 to 15 meters below the current footers. Piles are constructed and cased in steel. The 15 cm to 30 cm piles are driven into pre-drilled holes to rest on more stable ground.
The fourth and more aesthetic purpose for basement underpinning requires the existing concrete floor to be removed. The soil is excavated in sections, filled with concrete and small gaps are left between the old and new concrete. Non-shrink grout is used to fill the area in each section.