I would like to add more insulation to an attic. What measurements and points do I need to look at to decide what materials to buy?
How do I determine if I need airflow baffles?
How do I determine how much insulation to purchase? Measure the area of the attic and then figure out the necessary thickness to get the desired R value?
What ancillary items should I plan for? Insulated attic access, critter-proofing, etc?
What tools or extras will make the job easier?
There is lots of information about why to insulate and how to install insulation, but not much on how to buy the right materials and only make one trip to the store and do the job right the first time.
Best Answer
Actually it is quite simple.
Take your dimensions of the area to be covered. Example: 25 feet X 20 feet = 500 square feet.
Determine what kind of insulation you are going to use. Fiberglass blanket, blow in cellulose, etc. Blanket is easy, select the R-value type you need, look on the package for how much area it covers. Example; a package covers 88 sq ft. (typical). Divide the area to be covered by the amount in a package 500 / 88 = 5.68 or 6 packs.
You may have to double the amount if you want to double the r-value of the product. Example: two layers of R-22 give you R-44. (R-40 and above recommended for attics)
If you are considering blown-in cellulose, consult the chart on the bag to determine the amount needed for the R-value you want to achieve. The chart will have amount per square foot factors you need to determine how many bales it will take for your area.
Use "Propervent" panels, the air flow baffles you asked about, only if you have vented soffits and either a ridge vent or gable end vents. These must be installed before you add the insulation. They simply rest down on the soffit vents and staple between the rafters.
There are no special tools required to install blanket insulation. A good utility knife, blades, straight edge, dust mask, eye protection and maybe a cheap tyvec bunny suit. If you are considering blow in, you can rent the machine at many places including Lowes or HD for around $25 or less if you buy enough insulation from them.
If you give me the exact specs and dimensions you want, I can calculate the material list for you.