Building Truss Roofs The Safe Way, continued
Installing the Corner
At this point I check the position of the hip truss, bracing
it in place so it's equidistant from the girder and the nearest
jack. I also check that the location of the tail of the hip
matches the dimension on the truss plan (Figure 10).
Figure 10. Before
installing the corner jack trusses, it's important to
recheck the position of the end of the girder truss and
the hip truss.
Before I mark the locations of the corner jacks, I need to
know how they were fabricated. If I'm unsure, I call the truss
fabricator. Some corner jacks are fabricated to the correct
length and are designed to be installed as delivered. The top
and bottom chords have a square plumb cut, not a beveled plumb
cut, and those chords contact the hip only at the corners of
the cut. Because there is not much contact, I think this is a
cheesy way of doing it. If the trusses are delivered this way,
I first nail the square ends to the hip truss. At the top
chord, I then add a 2-by block with a bevel cut at the top end
of the top chord to make a stronger connection with the hip
If I have any say when the trusses are ordered, I ask the
fabricator to leave them long. That way the top and bottom
chords of the corner jacks have the same style plumb cut, but
since they're long, they can be beveled on site. It's easiest
if the length of the top and bottom chords corresponds to the
long points of the 45-degree bevel cuts. It's important not to
get the right-hand bevels and the left-hand bevels confused. To
keep things organized, I pile the corner jacks near each hip by
Corner jack layout.
Marking the positions where the corner jacks fasten to the hip
trusses takes two people. The first step is to consult the
"length hip or valley per foot run" line on a framing-square
table. I follow the line across the table until I reach the
roof pitch for the trusses I've got. The table is in inches and
tenths of an inch per foot of run. Since roof trusses are
generally set on 2-foot centers, I just double the number.
For example, if the trusses have a pitch of 10/12, the
framing-square table would give me 19.70 inches per foot of
run. For 2 feet of run (trusses on 2-foot centers), I would
double the number, yielding 39.4 — about 39 3/8 inches.
Starting from the point where the hip touches the corner jack,
I would mark down the top chord of the hip 393/8 inches. Then I
would place the end of my tape on that mark and measure the
position for the next corner jack — again 39 3/8 inches.
Since my starting point would be the outer face of the last
jack truss, my marks would indicate the locations of the short
sides of the corner jacks.
I use the same stepping method to locate the attachment
points for the corner jacks along the bottom chord of the hip
truss. But for the bottom chords, there's no need to look up
any numbers on the framing-square tables, since all
24-inch-on-center trusses with 45-degree hip trusses have the
same bottom-chord offset — about 33 15/16 inches.
I like to nail the corner jacks through from the hip truss as
well as toe-nail them (Figure 11). After the top chords are
tacked together, I check whether the bottom chords of the
corner jacks and the hip truss are flush. If they're off by
more than 1/8 inch, I probably made a mistake with the
Figure 11. It's handy
to have two people to help position the corner jacks on
the hip trusses. The corner jacks are nailed at the top
through the top chord of the hip truss.
Next I tack the tails of the corner jacks, spaced 24 inches
on-center, to the 1x3 brace (Figure 12). Once the corner jacks
are nailed in, I eyeball up the hip truss to see that it's
still straight. If necessary, I use 1x3s nailed back to either
the jack trusses or the girder trusses to straighten it out
until the sheathing goes on. If the truss plan requires hangers
for the corner jacks, I install them after I've nailed the
bottom chords of the corner jacks to the hip truss.
Figure 12. To hold
the tails of the corner jacks at 24 inches on-center,
they're nailed to the 1x3 that was used to position the
Subfascia and Sheathing
Although some builders don't install subfascias, I find them
especially useful when preassembling hip trusses on the ground,
because they lock the tails of the end jacks and corner jacks
in place (Figure 13). Before nailing a permanent subfascia to
the tails of the jack trusses, I check that the girder trusses
and hip trusses are straight and that the trusses all line up
fairly well along their tails. (I usually don't install the
subfascia on the girder-truss tail side until the assembly is
on the roof.)
Figure 13. A
subfascia ties the tails of the trusses together and
stabilizes the truss assembly for lifting.
On the ground, I sheathe only the end slope of the roof, not
the return facets of the hip trusses. The lowest row of
sheathing is either omitted entirely or tacked lightly in
place, so it can be lifted up for toe-nailing the trusses to
the wall plates. Sometimes I start with 24-inch rips of
sheathing along the eaves, because they're easier to handle two
stories up (Figure 14).
Figure 14. To
facilitate fastening the trusses to the wall plates,
the bottom course of sheathing can either be nailed
loosely or be omitted.
On one job, I rushed the assembly of one of the truss
assemblies; once the crane dropped the assembly in place, it
didn't sit evenly on the wall plates. We ended up having to pop
off several sheets of sheathing to make corrections. The
lesson: It's important to take the time during assembly to make
sure the trusses are square and straight.
Call in the Crane
Before the crane arrives, we mark the truss layout on the wall
plates, paying special attention to the girder-truss location.
We attach the fabric lifting straps to the hip-truss assembly
through the top corners of the girder trusses, where the hip
trusses are attached. We protect the lifting straps from the
sharp edges of the truss plates by first wrapping the area with
To balance the weight of the assembly so it flies level
during the lift, I run additional straps out from the crane
hook to the subfascia or tails of the jack trusses. To make it
easy to balance the assembly, I like to use adjustable straps
or cable come-alongs. (There isn't nearly as much force on
these straps or cables as there is on the primary straps;
they're only needed to balance the load.) I have the crane
operator lift the load until the girders are about a foot off
the ground, and then I adjust the come-alongs until the system
I always assign one crew member to use a tag line to control
the assembly until it comes within reach of the crew on the
staging (Figure 15). Once it settles onto the marks for the
girder trusses, we slide the girders back and forth until the
overhang is equal on both sides. The hip trusses should lie
flat on the plates and should extend out from the corners of
the walls. Once we're satisfied, we release the crane hook and
nail the girders to the plates.
Figure 15. The truss
assembly is easier to control if it flies level.
Secondary straps extending to the subfascia can be used
to help level the trusses during the lift.
An added benefit of assembling a hip system on the ground is
that it gives a stable point from which to brace back the rest
of the roof trusses, making installation of the remaining
trusses faster and safer.
Mike Guertinis a builder and remodeler in East