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STEP 7: DETERMINE WINDOW AND PATIO DOOR AREA <br />Calculate the percentage of total exterior wall area (in square feet) <br />represented by windows and patio doors (glazed), or take this information from <br />the standard calculation needed to meet the state energy code. This and the <br />STC values of walls and the ceiling -roof assembly will be used in Step 8 to <br />determine the required window STC. If a particular room has a relatively large <br />window or patio door area, the percentage of window and wall area should be <br />computed separately for this room (see Step 8). Skylights should be included <br />in the window area. <br />STEP 8: DETERMINE REQUIRED WINDOW STC <br />Based upon the percent of window area and patio doors determined in Step 7, use <br />Figures 1 through 6 to determine the window STC required to meet the <br />Metropolitan Council Land Use guidelines for particular noise zones. <br />These figures assume a door STC of at least 26 (with no more than 1 percent of <br />exterior wall area) and a patio door with STC 28. Patio doors with STC less <br />than 28 are not recommended. These figures are applicable to Noise Zones IV <br />and B. For sites located in Noise Zone A or III, add 5 STC to the values <br />determined from these figures. The roof and wall STC closest to that <br />determined in Step 6 should be used to select the correct figure. If values <br />are well outside those used in the figures, then outside assistance may be <br />required. <br />A number of assumptions are used to generate these curves. Correction factors <br />to be applied to these curves are indicated in Step 9. <br />If a room is determined to have a window area of 30 percent or greater of its <br />exterior wall area, then an STC 35 window will be required. If less than half <br />of this window area is to be operable, this area (as a percentage of the <br />exterior wall) should be entered into Figure 1 and the STC rating for this <br />percentage read from the figure. The operable portion of the window should <br />have an STC of at least this value in conjunction with the 35 STC rating for <br />the fixed portion of the window. <br />Figures for Determining Required Window STC Ratings for Noise Zone IV <br />Figure 1: Roof -ceiling STC 40; wall STC 40 <br />Figure 2: Roof -ceiling STC 40; wall STC 45 <br />Figure 3: Roof -ceiling STC 40; wall STC 50 <br />Figure 4: Roof -ceiling STC 45; wall STC 40 <br />Figure 5: Roof -ceiling STC 45; wall STC 45 <br />Figure 6: Roof -ceiling STC 45; wall STC 50 <br />14 <br />