I have a master bathroom area (5×11) that I am looking to remodel — new floor tile, shower tile, rebuild the shower, new toilet, etc. I will likely be replacing all of the drywall in order to eliminate 5 layers of existing wallpaper, etc. The bathroom currently gets quite cold (three of the four walls are outside walls) and I am wondering if I should consider applying spray foam insulation to better seal up the room, insulate, etc? If so, is that something that I can do myself using a spray foam kit, since the amount of square footage is rather small?
Spray foam is the best way to fix this issue. However the DIY approach may not be as in-expensive as you may think. The cost of this DIY product is around $1.25 per board foot. This is a 12" x 12" x 1" space. It adds up rather quickly. Add to that your delivery charges and the fact that you really do not get the amount of yield out of the two cans if conditions are not perfect It comes up to closer around $1.50 per board foot to install.
With prices such as this you can get this done professionally using closed cell foam for the price you purchase just the material for. So this if your willing to pay that price would be a much better way to go without having to deal with the mess and time to do the job.
Tiger Foam is one of the leading companies that sell foam kits for the DIY and professional alike if your still interested in doing it yourself.
If you decide because of cost not to go the foam route there are several things you can do to make the batt insulation better. That is to air seal.
The biggest robber of heat energy is air flow. Air moves through fiberglass insulation quite well. Improperly installed this can cause thermal drafts within the wall making the insulation perform less then desired. Also this can cause mold development as well as higher energy bills.
To properly install and air seal a wall you must seal all openings in the wall cavity before any insulation is applied. Using a spray foam from a can. Ideally the stuff that does not expand to much. Seal the spaces between the plywood siding and the wall joists. The seams between the plywood itself. Seal the top plate as well as the bottom plate. Yes those little gaps make a big difference on the ability of the insulation to do its job properly.
Once sealed using a Un-faced insulation. Install it so its flush with the surface of the wall. Cut slits in it where wires are so it surrounds them. Do not allow for any gaps. The insulation should fit snugly between the studs and top and bottom plates. Once all of this is complete you then need to install a six mill plastic vapor barrier. Be sure to tape all seams so no air or moisture can get around them. Using a caulking gun apply caulk along the bottom plate and top plate to seal the plastic to the frame. Once done you will be ready for the wall material.
The choice of batt insulation you choose also makes a big difference. There are many Eco friendly insulation available on the market these days. many offer higher R values and are dense enough to make a difference on air movement through the batt. So shop around in your area were insulation is sold. And choose the highest R value that you can afford.