DECORATE YOUR OFFICE WITH
We've received lots of requests for posters of our January '06
cover. If you'd like one, go to
www.jlconline.com, where they're available for $14.95
postage-paid, or call 800/859-3669 and request item #JAN06.
Posters measure 18 inches by 24 inches.
The Case of the Missing Beam
Regarding the letter "Who Pays?" (11/05), Mr. Matteson may
be a fine engineer, but he's a rotten attorney. If he designs a
"simple carport and [his] plans don't show a beam that is
needed," he should not pay for that beam; the homeowner
If the beam was always needed, if the carport couldn't be built
without it, then the beam itself was always necessary, whether
drawn or not. Thus the owner was always going to have to buy a
beam in that location. We call this sort of thing "betterment"
and the owner does not get a "better" building than that which
was bargained for. (The owner wanted a carport that would stand
up, I presume.)
However, Mr. Matteson is very likely on the hook for the added
costs to install the beam and redraw and resubmit the plans,
and for any changes or delays caused by his mistake.
Attorney at Law
Dealing With Complexity
I realize we live in an age when stepping forward and taking
responsibility is increasingly rare, but Thor Matteson's letter
really pushes the envelope.
After stating that the meaning of "standard of care" can be the
source of a huge argument, he casually asserts that it is "easy
to overlook a beam" in "complicated designs." If there's an
argument in order, I'd say it's over exactly what Matteson
means by "complicated." I thought engineers went to school
precisely to be able to deal with complexity. That's their
Thinner Sheathing Could Cause Nail
There is another possible answer to the question about nail
pops in shingles in the South (Q&A, 10/05). As a former
Midwesterner, I know that the thickness of roof sheathing there
is dictated by snow loads. Here in the South, however, the
effects of weather are neglected, I believe, and the thinnest
possible sheathing is used, which reduces the holding power of
For example, I have 3/8-inch sheathing on my own house. I am
leery of being on the roof; the plywood begins to "crackle" at
the smallest amount of weight, and if I step between the
trusses I feel like I am going through.
The situation is made worse because the Southern heat can dry
out the plywood and cause premature delamination.
Raymond Bruntmyer, RLA (Retired)
Strength of OSB vs. Plywood
In the response regarding OSB vs. plywood I-joists (Q&A,
10/05), Paul Fisette states that "OSB has interlocking fibers
that transfer shear loads better than plywood does." This is
not quite true, because OSB is not made by actually weaving the
fibers of the wood flakes together such that they interlock.
Rather, the "mat" of flakes is made by laying the flakes out,
both laterally and on top of one another, and pressing the
entire mass into place in the presence of the resin that holds
everything together. The fibers throughout the OSB sheet are in
different orientations, but they are not interlocking, which
can easily be seen by looking at any piece of OSB.
While it may be true that the shear strength of OSB is greater
than plywood's, this isn't due to fibers interlocking, because
neither OSB nor plywood have interlocking wood fibers.
Paul Fisette responds: It's correct that the strands in OSB
are aligned. However, as the mat is pressed, the strands do not
form nicely arranged separate layers. OSB is made of many
— often about 50 — layers of strands. Even with the
best attempts at strand alignment, there are many
discontinuities of wood grain throughout.
Plywood typically has three, four, or five veneer layers and
has definite planes of failure along the glue lines. Shear
failure occurs along these "continuous" planes of weakness. OSB
does not have such continuous planes, because the strands are
not perfectly aligned; thus they exhibit greater "crack arrest"
behavior. One weak strand may have small localized failure, or
"micro-failure," but the group of strands around the weak one
tends to stop the progress of cracks.
Need Adequate Air for Spraying
Having spent a number of years in the automobile body repair
and refinishing industry before entering the rental property
rehab/remodeling field, I was especially interested in Randal
Weber's article "Spraying Clear Waterborne Lacquer" (10/05).
The article makes some good points, but I disagree with the
caption that says "any compressor capable of delivering 80 psi
is adequate for painting."
The actual volume of air supplied, or flow rate, must also be
considered. The compressor must be capable of delivering the
required pressure, measured at the gun inlet, while air is
flowing, with the gun in use. Although the compressor shown in
the illustration appears to be of adequate size, many smaller
portable compressors are not. They might deliver 100 psi, but
can't maintain that pressure if there is any significant amount
of air actually flowing.
The inside diameter and length of the air hose also affect
available air pressure and volume at the gun inlet. Generally,
a 3/8-inch ID hose is adequate, while a 5/16-inch hose may be
marginal for higher flow rates or longer runs. Air-hose length
should be kept as short as practical to reduce pressure losses.
The pressure and air-flow requirements of the particular spray
equipment in use must be considered when choosing both the
compressor and the air hose.
George Van Arsdall
Livingston Manor, N.Y.