What Is the Process for Shoring Up a Crawl Space Foundation?

Signs of Problems

• The foundation carries the total weight of a house. Improper placement of the foundation piers, damage from water or insects or different types of soil beneath different parts of the house can cause the building to settle unevenly. These stresses may reveal themselves first in areas far from the crawl space, in the form of doors and windows not opening smoothly, wood floors that squeak or dip, cracks running along brick mortar in stair-step form, floor tiles or sheetrock cracking or gaps developing between exterior walls and fascia boards at the roofline, especially at the house's corners.

Leveling Options

• Correct small or localized settlement problems by installing shims (thin pieces of wood) or cookies (large, thick concrete pads) between the top of the affected piers and the bottom of the foundation beams once they are jacked apart. Replacing or adding piers requires pushing or driving segmental concrete or steel pilings — or digging holes to install footing pads and cedar or bois d’arc posts or tube forms for concrete. Strengthen and stiffen a bowing or buckling wall surrounding the crawl space with concrete or masonry supports called pilasters (straight, column-like) or buttresses (triangle-shaped) installed against the wall.

Special Equipment

• In addition to accurate measurements and soil studies, Federal Emergency Management Agency encourages consultation with an engineer trained in calculating building loads when planning to replace or add piers in the crawl space beneath a house or business. Raising the building off the foundation requires hydraulic jacks with a lifting capacity of 20 to 50 tons. Drive new piles or piers to depth of refusal using a hydraulic ram. Clay soils may need water injected at the driving site to allow the pier to reach a more stable layer. Keep detailed records of the processes and supplies used, as well as before and after drawings or photos of all work done.

Preventing Problems

• Reduce potential damage in buildings on pier and beam foundations by ensuring the soil is adequately compacted and the frame rests on a girder or beam rather than a sill plate. Use hurricane straps or other fasteners to tie the house together from roof to foundation. In earthquake zones, FEMA encourages adding a cripple wall to the crawl space perimeter or bracing the stem wall with plywood or diagonal sheathing and using sill bolts to prevent damage from horizontal movement. In flood-prone areas, deeper or higher crawl spaces allow water to flow under houses rather than overturning or pushing them off their foundations.