As solid
wood becomes more of a disappearing resource, products such as processed
wood (OSB), plastic composites (newer decking materials), and metal
is going to become more common place. With the introduction of these
materials, comes proper yet differing installation techniques. Unfortunately
some of these techniques are not sought after by their installers.
Also some installation criteria will be developed as problems present
themselves. Along with this will come an evolution of material,
knowledge and skill.
Metal framed buildings have been constructed
in the southern regions for years. The popularity of metal as a
framing material was desired in these climates due to high risk
of termite and rot damage. Metal studs were more prevalent in commercial
construction, but have since shifted to residential. It is estimated
that between 10,000 and 15,000 metal framed homes were built in
1993, and that number is expected to more than triple by 1996.
As the use of metal studs spread to the
northern regions, some problems have arisen. Many carpenters and
builders have not had the proper education or training with respect
to proper installation methods. These are a few areas to inspect
for structural inadequacy:
- Proper fastening techniques to areas
such as roof trusses, are necessary using techniques such as,
metal tie straps or spot welds. If the trusses are only merely
screwed to the top plate, high winds could lift the roof system
from the house.
- Exterior and load bearing walls should
have a heavier gauge steel channel, than nonload bearing walls.
Bridging in the wall cavities, can help to prevent stud movement.
Floor systems that use channel steel require
bridging to prevent racking and crushing to the web. Bridging should
be used in the center of the spans and also below load bearing points,
such as where a load bearing wall rests on a main girder. Another
area to reinforce would be a parallel wall bay. This could cause
sagging between the joist unless properly supported. This can be
supported by installing bridging 24" oc., or installing two
parallel joists offset from the wall, one on each side.
Another point of contention is thermal conductivity
in the northern regions. This is where outside air temperature is
transferred through the metal stud to the inside and warmer air.
This is referred to as thermal bridging, resulting in condensation
forming inside the wall. This can be evident by streaking showing
through the drywall. The streaks are lines reflecting location of
the metal framing in the wall, and may be vertical or horizontal.
Frost and mold can form inside the wall cavity as well.
Metal conducts heat and cold 300 times faster
than wood. This drops the R-value of the wall significantly. There
is research being conducted on proper remediation and installation
techniques to deal with this issue.
This situation can be aggravated by using
hardboard wall sheathing such as oriented strand board. One recommended
procedure is to install extruded polystyrene foam over the studs
on the cold side to reduce the chance of a condensation problem.
This is referred to as a thermal break. One problem with this method
is that the fasteners conduct the cold to the stud and the problem
can still exist.
Another method of prevention being studied
is the use of horizontal "hats." This is a channel ran
across the studs that break the thermal bridge. Some companies have
developed studs that have an opened webbing, as opposed to solid.
These studs are supposed to significantly reduce thermal bridging.
Any areas susceptible to air infiltration
should be caulked or spray foamed. There is other research going
on including the use of wooden washers and other methods.
If these conditions are not rectified, the
condensation could lead to rusting and possible failure of the metal
studs and the walls. Further evaluation and monitoring is recommended.
Eventually a system will be worked out so
metal studs and applications will have guidelines to prevent such
problems. A professional should be consulted, if you suspect a problem.
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