Improving full-depth basements into conditioned living space has become an increasingly popular remodeling project as homeowners remain on the fence about buying a new home.
And builders of new homes with full basements (about 30% of all homes built in 2010, per U.S. Census data) are obliging buyers with basement upgrades to boost usable square footage without expanding the home's footprint.
Both scenarios offer an opportunity for LBM suppliers, as the bulk of the materials needed to improve a full basement are typically in inventory. But building it right takes far more than slapping carpet on the slab or gluing drywall to the concrete walls. If finished basements are to perform like above-grade living space, they require similar, if specific, protection from the elements and the ability to support rather than hinder a home's overall energy performance.
Waterproofing Improving a basement in new-home construction is a far easier task than a retrofit, specifically in terms of providing a watertight structure. Ideally, that's done from the outside in, starting with a drainage media along the base of the foundation walls that creates a path of least resistance for any groundwater that builds up against the walls. In addition, a polymer-enhanced, spray-applied waterproofing membrane covered by an insulated drainage plane (vertically grooved rigid foam insulation panels) on the foundation walls, taped along every joint, both blocks and sheds water away from the structure.
Without those methods and materials, groundwater can build up against the walls, a condition called hydrostatic pressure that eventually causes cracks in the walls that allow water to seep through.
The same methods and materials can apply to a retrofit job, but the task requires extensive excavation (down to the footings) and repairs to the outside face of the foundation walls for that approach to be successful.
When budgets are tight, remodelers often turn to waterproofing treatments that are applied to the inside face of the walls to at least seal and block moisture that might seep through.
For new and remodeled homes, a proper gutter and downspout system is a critical cog in keeping rain and snow runoff away from the base of the home's perimeter walls to help reduce hydrostatic pressure that can lead to leaks.
Insulating Like waterproofing, creating a comfortable finished basement is easier and less expensive in new construction, but the real sweet spot for LBM revenue is the retrofit market. Tens of millions of homes across the U.S. have basements (most of them unimproved), and the average job cost for a basement remodel is more than $64,500, according to Remodeling magazine.
For a so-called whole-house Deep Energy Retrofit of a 1950s-era house in Millbury, Mass., remodeler Gary Bergeron of Synergy Companies Construction in nearby Leominster insulated the inside of the concrete walls to R-20 with 3-inch-thick foam panels and applied expanding spray foam insulation to the mudsill cavities.
For the basement's slab floor, Synergy sealed the concrete surface before installing (in progressive layers) a drainage mat; a polyethylene vapor barrier; and R-10, 2-inch-thick foam insulation panels–all taped and sealed at each stage and joint to effectively block thermal transfer.
A new tongue-and-groove subfloor topped the assembly, creating what's called a "floating" floor that can accept almost any floor finish, including wood. "If you are going to superinsulate the above-grade spaces, you have to address the basement, too," says Bergeron. "Otherwise, you create a cold sink that will undo all of your other efforts to make the house energy efficient."