Insulation Projects - Basement Insulation
Most basements are cold, damp places because they are surrounded by cold, wet soil. If the ground that surrounds your basement is frequently saturated with water from heavy rain and melting snow. This water can pass through the porous concrete block or concrete floor and into your basement.
Preventing the water from reaching the perimeter of your foundation is the first step in properly insulating your basement.
Direct the water from your gutters away from your foundation by adding gutter extensions or installing 4" drainage pipes underground. The goal is to get the water from the gutters as far away from your foundation as possible.
Examine the foundation of your home after a heavy rain and look for pools of water. If the water is puddling around the foundation it will seep into your basement. Fill in the puddles with enough dirt or stone to direct the water away from the foundation.
Now that you've done all you can to control water from the outside, it's time to prevent it from getting in through the walls. You can brush a masonry waterproofer like UGL DryLok to the inside of your basement walls. As DryLok dries, it expands to fill all of the pores in the concrete creating a waterproof surface that blocks moisture.
Choosing the Right Type of Insulation for your Basement
Besides death and taxes, another thing you can always depend on is water's amazing ability to go wherever it wants to go. Planning on some amount of moisture entering into your basement is only prudent. Choosing the right insulation materials in your basement is the most important decision you can make. Basement insulation must be able to perform in a damp environment.
Foam board insulation is a perfect match for basements which are under constant attack from moisture. Expanded Polystyrene - EPS and Extruded Polystyrene - XPS foam boards are typically used because they are semi-permeable, which means the allow moisture to pass through and allow the wall or floor to dry instead of rot. 2" thick, XPS is typically used in basements because of its strength and higher r-value per inch. You can buy the 2" thick R10 foam board at Lowe's or The Home Depot in 2'X8' or 4'X8' sheets.
The foam board insulation is glued and screwed directly to the foundation walls and sometimes the floor. It's very important to seal all of the seams between the foam insulation boards with a durable tape, like housewrap tape. A common brand known a Tyvek tape can be found in the siding isle next to rolls of Tyvek. Gaps around plumbing and electrical penetrations should be air sealed with an expanding spray foam like Great Stuff. You'll also need to seal around the top and bottom of the wall with Great Stuff. This creates an air-tight, continuous even layer of insulation we need to keep the moisture out and the basement comfortable.
Insulating Rim Joists and Sill Plates
Another place where moisture seeps into the basement is through the sill plate and rim joist. As you can see in the photo, the sill plate and rim joist sit on the foundation wall. The rim joist is the area with the silver foam board. Air leaks through the gaps and cracks all the way along your foundation wall carrying moisture into your home.
The rim joist may already be insulated with fiberglass or it may not be insulated at all. Either way, air is leaking in because fiberglass does a better job at filtering air than stopping it. So pull it out and take a shop vac to the sill plate and rim joist. Use a snap blade knife with a long blade to cut pieces of rigid foam board insulation to fit into the rim joist area. Grab a can of Great Stuff with the long clear tube on it and seal off the perimeter of the foam board. Then run a bead along the foundation wall and sill plate.
Heating ducts, plumbing and wires will inevitably get in your way. When they do, keep in mind that Great Stuff expands considerably and has about the same r-value per inch as foam board. Cut the foam board into pieces or a U shape to get around the obstacles and finish off the space with Great Stuff. Remember that plumbing pipes can freeze. Try to get as much Great Stuff or foam board behind them as you can. Never cover them from the inside.
Finishing the Basement
Foam board insulation is flammable, so it must be covered with a fire barrier like drywall.
The best way to cover the insulation with drywall is to frame a wall against the foam board. This will also give you the space you'll need to install any electrical wires, outlets and light switches. If you live in a very cold climate, you may want to fill the wall cavities with additional unfaced fiberglass insulation to beef up the r-value. Then cover the wall with drywall and you're ready to finish the basement.