Square footage.
A lot of my customers believe "square footage" can be used for
calculating any kind of building material need. Not so.
An example: You're building a countertop for a cabinet you made
yourself, and it's going to have a ceramic tile surface. You did some
measurements and found out you need 32 square feet of material to build
the top.
Off to a home store, where your first stop is the tile department. You
get 288 four-inch tiles, some thinset, some grout, a notched trowel and
a grout float. So far so good.
The helpful tile associate tells you that your project would be much
nicer if you used backerboard under the tile, so you get three sheets
of it. Backerboard comes in 3-by-5 sheets--that's 45 square feet, not
32, so you'll have a little waste. But so far, not a big problem.
Now to lumber to get some plywood. A sheet of plywood contains 32
square feet--perfect! Get one and go home.
What you didn't tell anyone is that your 32-square-foot countertop is
12 feet long by 32 inches wide. If you try to do this with one sheet of
plywood, you'll be piecing together a third of the surface. That takes
a while and it's not very strong.
The very best construction is done with as few seams as possible. In
this case, I would take two sheets of plywood, rip them to 32 inches,
and miter one end of each. Lay the miters together with construction
adhesive in between, and you'll have a very strong countertop. Then
just cut it down to 12 feet long and you're done.
There are two other products you can't do by square footage--insulation
and fencing. Insulation first. Say you're doing a 160-square-foot wall.
If that wall is 8 feet high, you need 15 batts, or strips, of
insulation that are 93 inches long. These days, a lot of insulation is
sold in 93-inch batts. A bag of R-13 batt insulation has 11 batts in
it, an Owens-Corning miniroll has enough to make four batts, so you're
golden--one bag of each. If that wall is only six feet high (part of a
bonus room) you will need 20 batts to deal with the problem. If you
want to be cheap about it, you could save all the little hunks and
staple three of them into one space. If you want to be smart about it,
get two bags of batt insulation, insulate the wall then peel the little
hunks off their vapor barrier and stuff them around your windows. This
will save you money in the long run--I don't think there is such a
thing as "too much" insulation.
Fencing is the best one. A couple came in this summer and asked for
fencing sufficient for a "2000 square foot area." 40 by 50? Okay, so
you need 180 linear feet of fencing. Right? Well...no one told me that
they needed to go around six big oaks, around a pump house, around a
barn...turned out they needed something like 350 feet of fencing. (And
a 2000-sf area doesn't always have a 180-foot perimeter; a 100 by 20
area also contains 2000 square feet, but it has a 240-foot perimeter. A
200-by-10 area needs 420 square feet, and so on and so forth. And yes,
I have seen 200-by-10 fenced areas--I built one for a motorcycle dealer
who uses it to park repaired bikes.)
Roofing you can kinda do so long as you're working with three-tab
shingles. If you're using architectural shingles (they have two
shingles glued together; the top shingle has cutouts in it that give
the shingle a nice look) you really can't because you need three kinds
of shingles: the architectural shingles for the roof deck, three-tab
shingles to use as a starter strip, and ridge cap shingles to go across
the peak of the roof. You especially need the length of the ridge
because the ridge cap shingles are too expensive to overbuy and the
last thing you want to do on a roofing project is crawl off the roof
and go back to the dealer because you ran out of materials.
Concrete can definitely be purchased by the square foot, because it's
fluid when you pour it.
Moral of this story: When you go to buy things, take the length and
width of what you need, not just the square footage. We will thank you.
--
--jmowreader