The company I work for builds seven to ten spec and custom
homes per year on the Kitsap Peninsula, just west of Seattle.
Our crew frames and does most of the siding and exterior finish
work. Wood siding is popular in this area, but it's too
expensive for spec houses. We used to side with L-P's
Inner-Seal, an engineered wood product with an OSB-like
substrate. We switched to fiber cement in 1996, when Inner-Seal
became the subject of a class-action lawsuit. Although improved
versions of engineered-wood sidings are available, we now side
almost exclusively with fiber cement. Our customers like it
because it looks like wood, and they are reassured by the fact
that it comes with a 50-year warranty. We happen to use James
Hardie's lap siding (Hardiplank), but I've talked to carpenters
who use other brands and hear they have similar results.
It wasn't easy switching to fiber cement. We had gotten used
to engineered siding, which is light, cuts like wood, and comes
in 16-foot lengths. Fiber cement, on the other hand, is heavy
and creates a lot of obnoxious dust when you cut it with a saw.
It also takes more pieces to cover a building because it only
comes in 12-foot lengths.
There are a number of ways to cut fiber-cement siding, but the
most common ones are with electric shears or circular saws
equipped with fiber-cement blades. Regular carbide blades will
cut fiber cement, but they dull quickly and overheat and warp
when you gang-cut. We also tried diamond abrasive blades; they
lasted longer than carbide but put a real strain on our saw.
Lately, we've been using Hitachi's Hardiblade. It's a
four-tooth polycrystalline diamond-tipped blade that's designed
specifically for fiber cement. These blades are expensive
— about $65 apiece. But they'll last for five or six
2,500-square-foot houses. They make smooth cuts, don't strain
the saw, and can gang-cut seven pieces of siding at a time (see
Figure 1.The author's crew gang-cuts as many as
seven pieces at a time using a wormdrive saw (left). In
contrast with a regular carbide blade, which would be dull
after a single day of cutting, this dedicated fiber-cement
blade from James Hardie has cut the siding for five
2,500-square-foot houses (right).
We also use a set of Snapper shears, basically an electric
drill motor with a special cutter head attached. The shears cut
fiber cement the same way double-action metal shears cut sheet
metal. A narrow strip of waste curls up between the knives as
the shears make their way through the material. We cut most of
our siding with shears. It's slower than using a saw, but it's
worth the time because the shears don't produce dust (Figure
Figure 2.Electric shears, like this Snapper model,
will cut fiber cement without producing dust. The downside is
that they're slower than a circular saw and can cut only one
piece at a time.
I've heard of crews using miter saws to cut fiber cement, but
I can't see doing that to an expensive saw. The dust is very
abrasive, which is why we set aside our oldest wormdrive for
cutting the material. Also, circular saws work better for
gang-cutting because you can cut the siding right on the pile
rather than having to position the heavy material on the miter
Dust. Dust is a big problem
when you cut fiber cement with a saw. The dust contains silica,
which can cause silicosis or lung cancer if you breathe too
much of it. The manufacturers tell you to wear a dust mask or
respirator and to cut outdoors or use some kind of mechanical
We've tried wearing dust masks, but they're uncomfortable to
wear all day, especially when it's hot. We've also tried
setting up fans to blow the dust away and have even held our
breath while cutting, but neither method works that well. The
best solution we've found is to avoid making dust in the first
place by using electric shears.
Makita makes a saw (5057KB) that's specifically designed to
cut fiber cement. It has a built-in dust collection container
and can also be connected to a shop vac. We've used this saw,
and it does a pretty good job capturing dust. We didn't stick
with it because we're diehard left-blade users, and it's
awkward for us to switch to a saw with the blade on the right.
We'd probably use this saw if there was a model with the blade
on the left.
When fiber cement first hit the market, Hardie recommended
fastening it with roofing nails. You're also permitted to use
certain types of common nails, siding nails, and screws.
According to Hardie, hot-dipped galvanized and stainless-steel
fasteners are preferred, but electro-plated fasteners are
permitted. Be sure to read the installation instructions
because each manufacturer has its own list of approved
fasteners. You'll void the warranty if you use the wrong
We still prefer roofing nails. It sounds kind of strange until
you realize that most people blind-nail this kind of siding.
When blind-nailing, you nail only the top edge, so the heads
are hidden by the course above. Check with your local inspector
before you do this, because blind-nailing is not permitted for
every siding pattern or in every wind or exposure zone. In some
cases, you may be required to fasten the bottom edge. Wherever
you nail, you have to hit the studs (Figure 3).
Figure 3.Blind-nailing is common with fiber-cement
siding; the standard lap is 1 1/4 inches.
Another reason we like roofing nails is that the nailers are
shorter and more compact than stick nailers, so it's easier to
fit them under the eaves. We have two Bostitch roofing guns.
Anywhere they don't fit we drive nails with a hammer or palm
nailer (Figure 4). We use 2-inch galvanized roofing nails for
any hand nailing. On a few occasions, we've fastened siding
with 8d galvanized nails. The siding came out fine, but we
prefer to use roofing nails because they seem to hold the
siding flatter and are less likely to be overdriven. You don't
want to overdrive fasteners because it will void the
Figure 4.The author typically uses a roofing
nailer because it fits easily under the eaves and in tight
spots. Also, the large nail heads are hard to over-drive and
hold siding flatter than nails with smaller heads.
A problem with blind-nailing is that it doesn't always pull
the siding snug to the house at the bottom edge. If there's a
bow in the framing, that can leave a gap between the bottom
edge of one piece of siding and the face of the piece below. We
have two ways to deal with this. If the gap is less than 1/8
inch wide, we'll caulk it. For larger gaps, we bottom-nail at
that location. If the gap is well above eye level, we might use
a roofing nail to fasten the bottom edge; if it's lower, we'll
use a smaller-head nail (Figure 5).
Figure 5.Wherever a butt joint doesn't lie flush
because of irregular framing, the head of a single nail will
close the gap and pull the pieces snug. This is less obtrusive
than putting a nail in the corner of each piece.
Fiber-cement siding is a lot more difficult to handle than
other siding materials. For one thing, it's very heavy. A
12-foot piece of Hardie's 8 1/4-inch lap siding weighs 19
pounds. Wider material weighs more. Fiber cement is also so
floppy that you need to carry lap siding on edge. It's liable
to break if you carry it on the flat or throw it over your
shoulder, like you're used to doing with other materials. It's
important to tarp the pile, because fiber cement is more prone
to break when it's wet.
I'm a pretty strong guy, and I won't carry more than three
12-foot lengths of fiber cement at one time. I used to carry
three or four pieces in the crook of my arm but ended up with
bruises where the siding rested.
When you take delivery, make sure they drop it close to where
you'll be working but out of the way (Figure 6). Depending on
the product, a unit of lap siding can contain 13 to 18 squares
of material and weigh somewhere around 5,000 pounds. You don't
want to move it any farther or handle it any more than
Figure 6.Have fiber-cement siding delivered to a
spot where it's out of the way and won't have to be moved. This
load weighed more than 4,000 pounds.
Our company recently bought a used all-terrain forklift, which
has been invaluable on siding jobs. It allows us to drive a
pallet of material around the job and lift material to
carpenters who are siding the second story.
Layout and installation are about the same as for any kind of
manufactured lap siding. It's great when the siding runs full
length, but you're going to have joints if the wall is more
than 12 feet long. Because the siding is all the same length,
we have the cut-man start by cutting random lengths of siding
in 32- and 48-inch increments to avoid creating a pattern. The
installers combine the shorts with full-length pieces to
produce a random joint pattern.
Hardiplank isn't beveled and is designed for a standard 1
1/4-inch overlap. Layout is easy because you can't really cheat
the coursing. We typically use 8 1/4-inch-wide material, so we
end up with a 7-inch reveal. We start at the mudsill and use
the same coursing all the way up the building. We hook the tape
on the mudsill and mark 7 inches, 14 inches, 21 inches, and so
on all the way to the frieze. We're usually framing 8-foot
walls, so the top piece of siding is a 4- or 5-inch rip. Since
the siding isn't beveled, you have to shim behind narrow rips.
If you don't, the top tips in too far, leaving a big gap under
the lap. We avoid this by nailing short scraps to the wall
above the last full course of siding.
Given its weight, you'll need some kind of installation jig if
you want to install fiber cement by yourself. One of our
carpenters made a sheet-metal jig to support the far end of the
material. His jig hooks over one course of siding and has a lip
to support the next course up. The problem is, the jig attaches
to the existing siding, so you have to walk down the wall to
put it on and then back to lift up the siding.
We recently tried out an inexpensive (about $30) ready-made
jig called the Labor Saver from Indian Valley Innovation. It
consists of a pair of metal clips that attach to the bottom
edge of the piece you're about to install. The clips catch the
top edge of the course below and support the siding while you
nail it off. There's no need to do layout for every course of
siding because the jig automatically gives you a 1 1/4-inch
lap. Malco makes a similar device called a fiber-cement siding
panel gauge (Figure 7). When there's no one there to support
the other end of the piece, either of these jigs would make it
much easier to install siding.
Figure 7.Because of its weight, fiber-cement
siding is trickier to install when working alone than wood
clapboards. Site-made or manufactured jigs, like the panel
gauges shown here, are helpful. The gauges catch the upper edge
of the previous course and hold the next piece in place while
the carpenter nails it off.
Raw, Primed, or Prefinished
Fiber-cement siding is available raw, primed, or prefinished.
We used to side with raw material but switched to primed when
our lumberyard started stocking it. This was definitely a
change for the better: I've compared houses we built in the
past, and the paint jobs on the ones sided with primed material
look better. We've chosen not to use prefinished siding,
because it limits color selection, and I can't imagine being
able to install it without scratching the finish.
Now that we're used to siding with fiber cement, we can
install it faster than OSB siding. This is partly because we
don't have to prime the cut ends of fiber cement, which you're
required to do with OSB material. This makes the work go much
faster, and you don't have to worry about getting paint all
Joints and Caulking
According to Hardie, end joints can be lightly butted or left
1/8 inch open and caulked. We leave a gap at every butt and
wherever the siding hits window trim, door trim, or corner
boards. We apply caulk as we go, because it rains a lot around
here and mud gets splattered on the lower courses. It's a lot
easier to apply sealant while the siding is still clean (Figure
Figure 8.The author's crew always caulk as they
go, so they won't have to clean the siding if it gets
splattered with mud. Here, a carpenter uses a foam shipping
block from a window to smooth the caulking at a
We save the 1x1 foam squares that manufacturers stick on the
corners of windows to protect them during transport. We use
them to smear caulking over face nails and butt joints. They do
a good job smoothing out the caulk, and it makes the paint job
The installation instructions say you should use paintable
caulk that complies with ASTM C 834 or ASTM C 920 —
basically, a paintable caulk that remains permanently flexible.
If you're not sure about a particular caulk, check the label;
the ASTM rating should be on it. It's so rainy here in the
Pacific Northwest that we can't use acrylics like Dynaflex or
Big Stretch because they'll wash off before they have time to
set. We've had good success with OSI Quad, which is one of the
recommended brands on Hardie's website.
Tim Uhleris a framer and exterior trim carpenter
for Pioneer Builders Inc. in Port Orchard, Wash.