My friend, Jason: What kind of insulation is this?
Me: Spray foam.
Jason: Like... Great Stuff?
Haha, yes. Can you imagine me spending days going through can after can of great stuff to insulate the entire basement? No, this is the kind of insulation that comes from a truck...
Down a hose and through a window...
and into the spray gun of a competent professional.
This stuff is really amazing, I could go on and on. It insulates at 6.5 R per inch, is air tight, and is water tight. The main reasons we went with this type of insulation were to keep water out of our house, and to keep heat in.
Mold needs three things to grow: water, air, and food (any organic compound). There are two common scenarios that create this condition in a basement.
Water seeping in through cracks in the foundation - Water enters the basement in a liquid form, comes in contact with wood, batt insulation, or drywall, and mold grows. To stop this, the foundation can be water-proofed from the inside or outside (so no water can't get in), you can make sure the ground is graded away from the foundation at 1" per foot for at least 3 feet (so water doesn't stay near the foundation), weeping tile and a sump pump can be installed (to remove water as soon as it's in), and you could make sure downspouts send the water at least 3 feed from the foundation (so water doesn't stay near the foundation).
Condensation on the interior walls - When warm, moist, air comes in contact with a cool surface the moisture in the air turns into liquid water, aka condensation. Think of a cold glass of water/lemonade/beer on a hot day, the glass gets covered in condensation pretty quickly. The same thing happens on the cool foundation walls when the basement air has a lot of moisture and is warmer than the walls. Without ANY insulation there's not really a problem because the walls are room temperature and if any water condenses it evaporates back into the room.
Now, if you put insulation in front of the walls there's a thermal break between the walls and the room. On a fall day the room is 70 degrees but the wall will be much cooler because it's insulated from the warm air in the room. If any air gets behind the insulation it will condense on the wall and turn into water. This is the reason you need to have a vapor barrier (sheet of plastic) on the warm side of the wall. In my example, the vapor barrier would be between the drywall and the batt insulation, the foundation wall would be cooler than the room but the vapor barrier would block any moist air from getting to the foundation. If the vapor barrier was on the cool side of the room - between the insulation and the foundation wall - moist air would get behind the insulation and condense on the "cold" vapor barrier and mold.
So, batt insulation and a vapor barrier work together to make a warm room that doesn't promote mold, but the vapor barrier is extremely important. If it's not air tight, the whole system starts to fail. If the seams of the vapor barrier aren't sealed, it doesn't work. If there's a hole in the vapor barrier, it doesn't work. Any drywall screws that miss the stud can pop a hole in the vapor barrier, any pictures hung on the wall can break the vapor barrier. If you use batt insulation and a vapor barrier, the vapor barrier has to be perfect.
Because the vapor barrier is never perfect in reality, batt insulation is not a great insulation for basement walls. The next best option is rigid foam insulation. Polystyrene (Styrofoam) and Polyisocyanurate (called poly-iso) insulate and don't allow water or air to pass through the 4x8 sheet. You need to carefully tape each of the seams and make sure there isn't a gap at the top or bottom or air can pass through and condense on the foundation. Rigid foam insulation makes a great basement insulation if you're careful to seal everything up. Spray foam insulation has the same properties as rigid insulation but is custom fit to any wall. It's sprayed on as a liquid and expands to fit every bump, hole, or crack. It becomes one continuous piece of insulation with no gaps or seams which guarantees no air can pass through to condense on the foundation. Neither rigid or spray foam is water proof but they're both so impermeable that essentially no water can pass through it.
We went with spray foam insulation because we wanted to make sure our home was safe of any mold and we didn't want to worry that the seams or gaps (which would be many with our uneven walls and floors) in rigid insulation would be letting water and air in/out. Now that we have our insulation in, our sea foam green walls are out and beige color insulation is in. Here's how everything is looking.
See the big sheet of drywall in the living room?? We'll update you more on that soon since there's progress being made as I type!
Once the insulation was up we could finish installing the shower that needs to be up before drywall. We don't really anticipate this shower getting used much so we saved some money and got a pre-fabricated shower. It looks ok for a pre-fab, right?
We may not have a toilet or a working sink, but we have a shower and we have beautiful spray-foamed walls! Now onto drywall...