Design Checklist

(to be completed for each sash size)

When designing a system for multiple window sizes, choose the window with the highest width/height ratio to check for system feasibility.

a) Overall sash opening height ________inches
b) Single sash dimensions: sash width ________inches
c) sash height ________inches
d) sash thickness ________inches
e) Available vertical space in weight pocket calculated by measuring from the heel of the side jamb to the bottom of the sash pulley housing less 2" for attachment of the counterweight ________inches
f) Vertical travel requirement (a - c) ________inches
g) Maximum counterweight length (e - f) ________inches
h) Weight of unglazed sash ________lbs
i) Glass size (total area) ________sq. inches
j) Weight of glazing per square foot ________lbs
k) Total weight of glazed sash (i x j) + h ________lbs
f) Weight of single counterweight (k/2) ________lbs

Calculate the length of the sash counterweight needed*, and compare that dimension to the maximum counterweight length computed in step g above. This will determine the feasibility of the proposed design.

* Consult manufacturer's literature for sash counterweight dimensions.

Weight and Pulley Calculation Examples

Note: These two examples show calculations for a weight and pulley window system. The first example shows the window with single glazing, the second with double glazing.

Example #1

1 3/4" pine sash, single glazed

  • Double-hung overall sash opening: 3'-0" x 5'-10"
  • Individual sash height: 3'-0"
  • Vertical travel requirement of sash: 34"
  • Glass size: 2'-8" x 2'-8" (double strength glass - 1.55 lbs./sq. ft.)
  • Maximum counterweight length: 28"
  • Estimated weight of glazed sash: 22.22 lbs.
  • Counterweights required: 2 pieces - 11 lbs.
  • Length of counterweight (1 3/4" square stackable cast iron): 16 3/8"
  • Maximum travel of specified counterweight: 42"
  • Jamb thickness: 7/8"
  • Required distance to throw weight into pocket: 1 7/8"
    (jamb thickness + 1/2 weight diameter + 1/8" clearance)
  • Recommended pulley size: 2 1/4"

Example #2

1 3/4" pine sash, double glazed

  • Double-hung overall sash opening: 3'-0" x 5'-10"
  • Individual sash height: 3'-0"
  • Vertical travel requirement of sash: 34"
  • Glass size: 2'-8" x 2'-8" (two layers double strength glass; 2 X 1.55 lbs./sq. ft.)
  • Maximum counterweight length: 28"
  • Estimated weight of glazed sash: 31.18 lbs.
  • Counterweights required: 2 pieces - 16.75 lbs.
  • Length of counterweight (1 3/4" square stackable cast iron): 24 7/8"
  • Maximum travel of specified counterweight: 35 3/4"
  • Jamb thickness: 7/8"
  • Required distance to throw weight into pocket: 1 7/8"
    (jamb thickness + 1/2 weight diameter + 1/8" clearance)
  • Recommended pulley size: 2 1/4"

Additional Articles and Useful Information

Weight and Balance Systems for Wood Windows Design issues of the weight and pulley system are dicussed in detail ... read

Selecting Sash Chain and Cord Information regarding material, size, length and load rating ... read

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