In the last 6 weeks, much has happened on the construction of our house. Concrete footings were poured and stripped, stem walls completed and the "rat slab" in the crawl space poured. We decided early on that a crawl space would save money in excavation costs, given our subsurface bedrock. We also made the decision to encapsulate our crawl space by eliminating vents to the outside and insulating the exterior of the concrete stem walls. All of this provides a crawl space that is clean, dry and conditioned. I have been promoting encapsulated crawl spaces since 1995, when building science proved it was a better way to build, but before the UBC (our code back then) allowed it. Since then, the International Residential Code has accepted encapsulated crawl spaces and they have become popular with both homeowners and builders. The benefits of an unvented, insulated crawl space include:
1) better air quality in the crawl space and thus, the house;
2) 20% reduction in energy use;
3) increased efficiency and lifespan of HVAC equipment;
4) elimination of problems with finish floors (particularly wood floors) due to humidity in the crawl space.
5) happy plumbers and HVAC subcontractors.
As an architect I've been in too many vented crawl spaces with serious moisture problems, rotting joists, failing insulation and critters that enjoyed the easy access and humid climate. This was an easy decision to make.