The ICF wall system is a continuous
shell made up of 2 inches of polystyrene + 5 inches (7 inches in the
basement) of concrete and rebar + 2 inches of polystyrene from basement to
roof trusses. Since there are no wall studs tying the inner and outer walls
of the home together, there is no thermal bridging, or direct heat transfer,
between the inner and outer wall. In a frame wall the studs are lower R
value than the cavity insulation that is added later. A low R value means
that there is a low resistance path through which heat can be transferred.
In a frame wall this occurs at every stud - every 18 to 24 inches. In an
ICF wall this does not occur at all. The floors are suspended inside the
shell so that edge losses at the rim do not occur.
FIGURE 1: The
basement has been poured and joists for the first floor are being set in
this picture. A laminated beam has been mounted on the east and west walls
and supported every 4 feet by brackets that extend into the concrete core.
Conventional joist hangers are used to attach floor joists to the
laminated beams. Note that the wall system can continue to be built at
higher levels with no interruption in form.
ICF construction is more
expensive than frame wall construction, HOWEVER it was possible for us to
work with R-Value Concrete (our contractor) to select an option whereby
volunteers could be trained and supervised to do the assembly work. This
was a lower cost option and allowed us to incorporate volunteer work. Also
there is no need for additional cavity insulation or house-wrap.
Waterproofing for the basement is done with a thick polyethylene sheet as
shown below. Drywall and siding can be attached directly to the
polypropylene ties that are vertically placed on 8 inch centers in the ICF
blocks.
FIGURE 2: Students assemble the basement as part of a Heat Transfer lab assignment.
FIGURE 3: Students unrolling and attaching waterproofing to the basement.
|
