Follow International Residential Code for crawl spaces


Regardless of where you are located in the USA, the foundations of the houses you build will generally be among three types: A concrete slab, a crawlspace or a full basement.

The concrete slab is a common type of foundation in the warmer areas of the USA and the crawlspace and full basement are more often found in northern climates, where there is seasonal ground frost. It is possible, however, to find examples of each type of foundation in all areas of the country.

Although better than a concrete slab because it keeps the living area above grade, a crawlspace requires particular attention to prevent your construction project from becoming a liability.

In climates where there can be a high degree of humidity, such as in the eastern United States, heavy humid air from the outside entering the crawlspace can generate condensation when the water vapor in the air comes in contact with the cooler surfaces inside the crawlspace. The result creates an environment that could easily develop mold and attack the structural integrity of the of the floor system constructed over it.

This is why the new IRC (International Residential Code) calls for the sealing off of any possible source of humidity, allowing no unconditioned ventilation from the outside and, if the crawlspace has a dirt floor, a polyethylene sealant to keep out humidity from the earth. The code also calls for the insulation of the walls to prevent condensation created by the temperature difference between the warm inside and cold outside air and frozen ground, during winter months. Finally, the IRC also requires a duct or transfer grill with a continually operating fan, or a forced air register to ensure consistent crawlspace ventilation and temperature, using the living area’s conditioned air.

Following the IRC during crawlspace construction will ensure ideal conditions for your Engineered wood floor system. Nevertheless, be careful: If the foundation was open during rainy weather before the house was closed in, it is strongly recommended to run a dehumidifier in the finished space for at least a few weeks to extract all excess humidity.

The amount of work that goes into creating a crawlspace that has adequate moisture protection makes It worthwhile consider building a full basement instead. The additional investment isn’t as big as you may think: a full basement uses all the same excavation and foundation laying equipment as a crawlspace, and the drainage system required is identical. In the case of a basement, the resulting additional space allows a lot more storage and even additional living area. Most experts agree that crawlspaces have no real advantage over full basements and most won’t recommend them.

That said, if you’ve chosen the crawlspace as a foundation, ensure the structural integrity of your building for many years to come by making sure to follow IRC requirements closely.

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