To limit dampness coming through exterior walls, cover the wall from the ground level down with plastic sheeting. Using a caulking gun , adhere the plastic sheeting to the wall with asphalt roofing cement. Take the time to seal the joint between the foundation and the mudsill — the framing member that rests on the foundation — with an expanding foam sealant to stop air infiltration.
Understand "R values" — the measurement of insulation's effectiveness or thermal resistance. The Model Energy Code recommends R insulating values for basement walls in most of the country and R for the northernmost states. Because building codes require insulation be covered, you'll have to build wall "frames" before installing any kind of insulation.
Install 2x2 wood boards every 16" along the basement walls and pressure-treated 2x4 boards for the bottom plates on the floor. Most basements are an average height of 8', but you may have to trim a couple of inches from the bottom of the vertical boards in order for them to fit on top of the bottom plate. These boards should sit just below the sill plate on top of the foundation wall. If you have windows in your basement, frame around them using 2x2 boards. Attach the bottom plate to the floor using "liquid nails" adhesive , then drill holes with a masonry bit every 16" into the floor.
Drive concrete screws into the holes using a power screwdriver. Next, attach the vertical 2x2 boards to the wall following the same steps. Start from the top and drive in screws every 2". Using a level , be sure the boards are level and perfectly vertical before attaching them to the wall with the concrete screws.
Measure the height of the wall and use a utility knife to cut insulation batts to fit snugly between the top and bottom plates - the horizontal members to which studs are attached. Make sure it fits well between the studs, too.
If you are using high-density R unfaced batts or special unfaced insulation for masonry walls, press the insulation into place. If you are using a faced batt, press it into place and staple the flanges to the edges or sides of the studs every 8 to 12".
Work from the top down, pulling the flange down as you staple to remove any puckering. To cut fiberglass insulation, you'll need a sharp utility knife and two scrap pieces of plywood.
Place the insulation kraft paper side down on a scrap of plywood. Lay a board across the roll and press down to compress the insulation while you cut through the insulation with a sharp utility knife in one or two passes. Airborne fiberglass is irritating to your skin, eyes and lungs. Always wear a dust mask or respirator and gloves when working with insulation. Be sure to wear safety glasses and clothing that covers your skin.
Wash work clothes separately and run an extra rinse cycle. Using a utility knife, cut the foam board insulation to fit in between the studs on your wall frame. It helps to bend the board a bit where you're going to cut and then slicing through with the knife.
Using construction adhesive , attach the boards to the basement wall. Don't use nails, as the holes will make the insulation less effective. In walls perpendicular to the first-floor joists, cut short lengths of unfaced batt insulation and press them between the joists and against the band joist. On walls parallel to joists, press faced insulation with the kraft side facing toward the floor above, holding it in place with wire insulation hangers pressed between the joists.
Faced insulation may be used only if it will be covered with drywall. The contractor must make sure that the foundation drainage system is working properly. Foundations create a complex moisture flow, which must be well understood in order to detail the building envelope properly.
Air containing moisture can also move through the foundation, so the insulation system needs to control airflow, reduce the potential for condensation and tolerate water. Whereas builders have traditionally used batt insulation directly against the concrete foundation, and covered it with wallboard, this is risky, if the foundation walls have not been installed and waterproofed carefully. Similarly, Smith recommends foam insulation or a hybrid system with foam against the foundation.
Meanwhile, Colwell points out that the most important aspect of this installation is to ensure continuity with the above-grade wall system air and insulation barrier. Consequently, when using SPF, he explains that the band joist and box ends must be insulated and connected to the subfloor of the first story. A kit system polyurethane foam air sealant should also be used to air seal the rigid insulation board to the first story subfloor in order to create the necessary air barrier and thermal barrier continuity.
Every project must be evaluated based upon its own specific variables such as climate, temperature, moisture loads, wall materials and whether the foundation can be excavated and insulated from the outside. Ultimately, the goal is to reduce energy consumption and heat loss, at same time improving indoor comfort. Barbara Horwitz-Bennett is a seasoned business reporter, writer, and editor specializing in the building and construction industry.
As a regularly contributing editor to Green Builder magazine, she has deep knowledge of building materials and systems. Foam board, whether polyisocyanurate or polystyrene, requires a lot of fossil fuel to manufacture. As Colwell points out, foam board can make a stronger argument for sustainability from the perspective of how much energy it will save over its lifespan.
But more hard data on life cycle is needed. Probably not. A typical home humidifier might remove 30 pints of water in a day. If your basement walls are dripping from condensation or the floor tends to get wet after rainfall, you could be looking at 50 or gallons of wicking water at regular intervals.
The most commonly used insulation materials in the basement include spray foam, fiberglass, and foam board. RetroFoam of Michigan has more than 17 years of experience insulating thousands of homes from top to bottom. In our continued efforts to educate homeowners so they can make the best-informed decisions for their homes, we have compiled the pros and cons to help them choose the best insulation for their basement. Foam board insulation is a rigid panel of insulation that can be used to insulate any part of your home from top to bottom.
Fiberglass insulation is made from plastic that is reinforced with extremely fine glass fibers. As a traditional insulation, fiberglass can be found in most older homes in the walls, attic, crawl space, and rim joist.
Spray foam insulation is designed to fill all of the nooks and crannies wherever it is applied, including your basement.
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