about to order the floor joist system for my house, and have been
hearing different things about
open-truss-systems: they sound like having a drum under/over you, or:
they will make your
plumber/electrician (me.) weep with joy. any direct experiences? any
downside to wood-I (TJI)?
We build 4 houses per week, and we used to use OJ 2000's . You are
correct in that the plumbers and electricians love them. They are
lighter, Great for PEX pipe and ductwork, with glued and properly
fastened flooring, we didn't have any 'drum' experiences. We did stop
using them about 5 years ago, mainly because modifcation of them is
impossible to do properly. If you need to cut one for a basement
stairwell modification, or adding a fireplace area, the structural
integrity of the joist is destroyed. Wood is easily modifiable down
the road, OJ's are not.
Yes, they can be ordered to length and actually must be, one of the
problems for us, instead of a lift of 2x10's we can cut ourselves,
each house must be kept seperate from the next, since all the lengths
will be different.
So it creates more inventory. As I pointed out, modification down the
road is not possible. If the homeowner, (or builder in our case),
decides to put in a basement staircase, you cannot cut the OJ's
without destroying their structural integrity. (There ARE ways of
course, but well above the average persons experience).
WE currently use 2x10's which we cut to length as needed. .
I'm an electrician and I LOVE open trusses. Not only are they great during
new construction, but they also make alterations easier later on. The
second best thing are the I-Trusses with the pre-punch knockouts. As far as
how sturdy the floor is depends on your truss spacing and the thickness of
your subfloor. If you space your trusses 24" apart and use a 5/8" subfloor,
you will have a little flex in the floor.
Regardless of what you use be sure the perimeter is air sealed and
properly insulated. This is an area of infiltration and heat loss/
gain that once it is covered will be there for the life of the
Proper installation on insulation is more critical than what type. NO
voids or gaps (one would not buy a winter jacket with holes), crushing
in as few places as possible and no more than 50% of the depth of the
Unless spay foam is used infiltration will not be stopped or reduced.
Be sure your contractor subscribes to Whole House Performance
(Building Science). A few dollars now will save many later.
A properly insulated house with a properly sized HVAC system can have
utility bills 60-80% less than a conventional built house. And if one
checks the national building code this is house houses are to be
built. I can assure you they are normally not.
Whole House Performance
Although the open trusses have been in existence for many years,
I would never use them in anything that I owned. For many years,
I was a general contractor doing a lot of insurance claim work.
One of the most common repairs that we did was repairing open
truss systems. They are only as good as the connectors, and they
tend to sag over time.
We would have to go in and either tear off the ceiling or floor.
Jack the trusses back into place and install plywood on both
sides, glued and screwed. The repair was designed by an
engineer. I have done literally hundreds of these repairs.
Perhaps as many as a thousand of them.
I have repaired a few joists (due to cracking, breaking, or
having been cut by a plumber or HVAC person), but not even 2% of
the amount of open truss repairs. I have never had to repair an
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