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Concrete footings 101
Bearing capacity of soil
Understanding soil type and bearing capacities
Footing size
How to determine the minimum size for soil conditions
Footing problems
Pouring in wet soil and more
Frost heave & foundation footings
Frost protected shallow footings
Related Information:
Concrete calculator for footing pours:
Figure out how many cubic yards you'll need
Foundation drains for concrete footings

The proper specification of insulation products is paramount to the success of an FPSF application. Few insulation products are able to maintain a dry R-value in a moist, below-ground environment over any great length of time.

Insulation products specified for an FPSF must be rated with an effective R-value that can be maintained in such an environment for the expected life of the structure. Because some insulation materials resist water absorption less effectively than others, which in turn degrades their thermal resistance (R-values), insulation material should be specified carefully.

The current HUD design procedure addresses the design of frost-protected shallow foundations which use insulation to prevent frost heave in cold climates. It is specific to slab-on-grade foundations on residential homes but may also be used on commercial and agricultural structures. The design procedure does not apply to buildings on permafrost, to areas with mean annual temperatures less than 32F, or to crawl-space construction.

Polystyrene insulation for below-ground, frost-protection applications in the U.S. must comply with the only available U.S. standard, ASTM C 578-92 for Rigid, Cellular Polystyrene Thermal Insulation. Although this standard does not provide for adjustment of thermal resistance in potentially moist, below-ground conditions, appropriate adjustment factors for EPS and XPS have been determined based on international knowledge and experience.

The HUD design procedure specifies insulation and foundation depths which ensure protection against frost heave damage for all types of soils. The procedure is conservative in that it assumes a 100-year return winter and no insulating ground vegetative or snow cover. The designer assumes responsibility for compliance with all local building and energy codes. The HUD document addresses heated, unheated, and semi-heated structures as based on the expected average indoor monthly temperature range of the building from Table 1.

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Click here for a larger view of table

The HUD design guide contains two approaches: a simplified design and a detailed design.

The simplified method streamlines the design process of FPSFs for heated buildings. The procedure is in a form suitable for adoption by the major model building codes and is intended to promote widespread acceptance and use of the technology. In consolidating the design steps for the simplified method, R-values for the vertical insulation were established so that the performance level of various conditions, including slab surface temperatures, were conservatively accommodated. Therefore, more economical construction costs may be obtained when the detailed design procedure is followed.

The detailed design procedure must be used when buildings include unheated areas such as attached garages.

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