First used in the 1800s to support U.K. lighthouses built on sandy soils, adapted versions made use of this technology for commercial applications in the U.S. in the 1950s. Now helical screw piles are popular for new builds or supporting weak foundations; ideal for wet areas (sandy, silty, and clay soils) but cannot penetrate rock.
How they work: Hollow steel shafts with an auger-style blade screw into the ground until meeting sufficient weight-bearing pressure as determined by an engineer. Installers add extension shafts until attaining required resistance and then bracket them to exterior walls or I-beams installed below the cottage. Two pros: Winter installation may be possible and small hydraulic equipment means access to tight spaces and little disruption to terrain.
What they cost: Helical screws can cost about $600 each but, depending on whether you find stability at 10’ or 150’, you may need more extensions, which run approximately $300 apiece. For an 800 square foot cottage needing helical screws, the job could easily top out at $25,000 to $30,000, including lifting costs, engineering fees, and installation. The screws are warrantied (usually on a per pier replacement basis; check the fine print) plus backed by the engineer’s stamp and building permit. As with any contractor, ensure the installer is certified and not using recycled materials.
Read more: Cottage foundation problems 101