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Many Materials
Before delving into the specifics of how to detail an insulated basement system for moisture control, what follows is a brief overview of the different insulating materials and approaches to various basement types.


While there are literally hundreds of products on the market, the five basic categories are foam board, spray polyurethane foam (SPF) insulation, fiberglass, cellulose and rock wool. In some cases, a hybrid of systems can also be effective, such Owens Corning’s Energy Complete.


In terms of the different basement types, John B. Smith, P.E., global platform leader, environmental construction, Johns Manville Technical Center, Denver recommends the following:


Monolithic concrete. If polyiso or extruded polystyrene (XPS) foam board is selected, then SPF should be used to air seal and insulate the rim joists, although a less costly option could be taped foam board. Another alternative is a combination of taped foam board and batt insulation.


Finished basement. Ideally, exterior insulation should be installed. However, if permanent features such as walks, driveways or patios make excavating the basement wall too costly, then foam board should run down several feet along the foundation’s outside wall and then continue horizontally for 3’ to 5’. Incidentally, this is the same approach for frost-protected shallow foundations.


Unfinished basement. Similar to monolithic concrete, a combination of foam board and spray foam is recommended, or taped foam board to air seal and insulate the basement walls.


Double brick wall with rubble fill or concrete block. Closed-cell SPF is the easiest way to provide interior insulation and air sealing. However, Dennis Socolean, CEO, Rinnovo Group, Danville, Calif., suggests that as long as insulation is installed at least 1” off the wall, and a drainage system is utilized at the bottom of the “dead” space, then any type of wall insulation will work.


Laid-up stone foundation. Smith recommends the same approach as the double brick, rubble-filled wall, while Socolean suggests waterproofing and insulating from the exterior with a vapor-retarding membrane placed throughout the floor.


Bringing out an important point about SPF, Colwell explains that the product can serve as the air, water, moisture and thermal control surface for the wall, and when applied in bulk quantities, should be a covered with a 15-minute thermal/fire barrier.


“Depending on the detailing, the spray foam can act as a drainage plane as well as an air barrier,” adds Todd. “This is an approach that is done in crawl spaces.”


Offering another insulation strategy, the California builder explains that foil-faced polyicocyanurate applied to the top half of a poured or block concrete can be a fast and effective approach, depending on how it is attached. “It has a high R-value per inch and is tolerant of moisture, but is not a very finished look and may or may not fulfill local fire codes.”


Because this insulation type is manufactured with a vapor barrier surface, should not be used for the entire wall to avoid trapping in moisture.


Moisture Management
As mentioned, moisture control–to prevent the unhealthy growth of mold and mildew– is a huge issue when it comes to proper basement insulation.


For starters, builders must address water management by ensuring that all gutters are intact, consider the use of a sump pump if the water table is high and make sure that the foundation drainage system is working properly.


In fact, foundations create a complex moisture flow which must be well understood in order to detail the building envelope properly. For example, says Smith, “the foundation wall needs to be warm enough to keep moisture from condensing, or the humidity of the basement air needs to be lowered. Air containing moisture can also move through the foundation, so the insulation system needs to control air flow, reduce the potential for condensation and tolerate water.”


 


Fiberglass insulating batts with wood studs can be used in basements, if the wall system is held away from the concrete wall by about an inch, with a drainage system at the bottom.

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