Windows experience heat loss by heat transfer through the window structure
itself and also by infiltration (air movement) through moving parts.
The windows installed in this house were argon-filled, low-e glass from
Rivertown Windows, which
greatly reduces heat transfer by conduction and radiation through the glass.
As an additional benefit the sound transmission is also lower.
The windows are set in a vinyl extrusion sash which is a complex extrusion
with many chambers. This design provides rigidity and it decreases conduction
heat loss through the sash by providing small reservoirs of trapped air in
the sash - air is an excellent insulating layer as long as it cannot move.
Single-hung windows were selected, providing for the possibility of a
window air-conditioner or fan if needed. With fewer moving parts than a
double-hung window there is less possibility of infiltration. The moving
part tilts in for easy cleaning.
The overall U-value (U=1/R) for our windows is 0.21 - which is 1/3 better
than the Energy Star guideline of U=0.35.
With 9 inch thick walls we were able to order windows with a drywall
receiver on the top and sides and a receiver for a 1x10 board as a sill.
The openings in the ICF wall were made with a plastic frame (V-Buck) that
overlapped the inner and outer polystyrene wall. Before drywall we used a
flexible foam to seal the opening between the window frame and wall opening.
FIGURE 1: Setting a window opening in the wall. Note diagonal steel bracing
in the corners - 8 braces total on the inside and outside - to withstand
hydrostatic pressure of wet concrete.
FIGURE 2: Finished windows in the dining area. Nine inch thick walls allow for deep
window sills which are 1 x 10 poplar boards. The windows came with a receiver for
the sill board at the bottom and drywall receivers on the other three sides so that
we could drywall back to the window. This gives a clean look and eliminates the
need for window trim - saving material and eliminating a source of construction waste.
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