Size of Concrete Footings for an Outdoor Screen Room

Foundation Choices

• The most common type of outdoor screen room, the attached screen porch, can be supported by any of the foundation types used in residential construction. These foundation types include slab-on-grade, pier-and-footing designs, and foundation walls used for crawl spaces and basements. All of these foundation types must comply with accepted building codes covering residential structural foundations. These building codes -- which include the International Residential Code as well as state and local codes -- consider such factors as soil load-bearing capacity, grade ratios and drainage, and regional environmental factors such as frost line depths and hurricane zones.

Footing Size Criteria

• The size of the concrete footings for an attached screen porch must meet the minimum requirements set forth by the IRC and any other relevant building codes. Footing size criteria is always determined by the load, or weight, of the structure resting on the footings, as well as the bearing capacity and content of the soil beneath the footings. One-story structures must have concrete footings at least 12 inches wide when light-frame construction -- with or without brick veneer -- or hollow concrete masonry construction is used in the structural design. Concrete footings for solid or grouted masonry construction must be at least 16 inches wide. These minimum dimensions are adhered to by all building codes regardless of jurisdiction in the United States, as outlined in Section R403 of the IRC relating to the size of concrete footings.

Tributary Load and Soil Bearing Capacity

• Concrete footings must be able to support all loads placed on them, as well as any objects -- including inhabitants -- that will rest on the structure's floor. This ability to withstand load pressure is calculated by understanding the soil bearing capacity for all foundation types, as well as the tributary load placed on pier-and-footing designs specifically. It is recommended that you read the IRC sections pertaining to foundation footings for the minimum requirements, and that you contact your local code authority. However, the 12-inch and 16-inch minimum widths applicable to all concrete footings is a good rule of thumb to use when designing your outdoor screen room.

Submitting A Plan

• Your local code authority requires you to submit a building plan for any residential construction projects, including any screen rooms. Detached outdoor structures don’t always carry the mandated minimums for concrete footing sizes, depending on your code jurisdiction, although the distinction between a screened-in structure and a sunroom will affect the building codes applicable to your project. However, a basic project submittal will include a floor plan that outlines the type of foundation supporting the screened-in structure you are proposing, along with the construction materials and dimensions of the foundation members. Local frost line factors, flood zone platting, and all environmental data pertaining to your region that affect the solidity of your building project are available through your local code authority.