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Insulation of Building Against Highway Noise

Appendix B Use of the Manual

This manual contains various procedures for identifying residential highway noise problems and selecting building modifications as solutions. The flowchart of Figure 25 shows a step-by-step procedure which applies this information directly to the problem of determining building modifications necessary to adequately insulate a building against the noise from an existing or proposed highway. The procedures of this manual can most effectively be applied by following the steps shown in the flowchart. A short explanation of each step is given below.

Step 1Calculate Building Noise Reduction (NRc) using the methods of Chapter 2. Use normally open or closed conditions for the windows.
Step 2Calculate Interior Noise Level using the relation Lic = Lo - NRc.
Step 3Check to see if the Calculated Interior Noise Level, Lic, plus 5 dB, is greater than the Interior Design Noise Level, Lc. The calculated level is increased by 5 dB to allow for uncertainty in the calculated interior level. If the calculated interior level plus 5 dB is greater than the Design Noise Level, measurements must be made.
Step 4Measure the Exterior Noise Level, Lom, using the procedures of Chapter 3. If the subject highway is not in use, an artificial source must be employed.
Step 5Measure the Interior Noise Level, Lim, using the procedures of Chapter 3. Use normally open or closed condition for the windows.
Step 6Determine the Measured Noise Reduction using the relationship NRm = Lom - Lim - 5.
Step 7If the Given Highway Noise Level, Lo, minus the quantity (NRm) is less than the Design Noise Level, then the building attenuation is sufficient. If not, building wall modifications must be planned.
Step 8Plan Building Wall modifications using the procedures of Chapter 2.
Step 9Calculate New Noise Reduction using the procedures of Chapter 2 for the additional building modifications selected.
Step 10If the Given Noise Level, Lo, minus the Calculated Noise Reduction, NRc, is less than the Design Noise Level, then the building attenuation is sufficient. If not, additional modifications must be planned and Steps 8, 9, and 10 repeated until the condition of Step 10 is satisfied.
Step 11Select Compatible Ventilation System: If ventilation has been restricted by the sealing of cracks and forced closing of windows in order to reduce interior noise levels, mechanical ventilation must be provided. This is discussed in Chapter 4.
Step 12Determine Modification Costs: The costs of necessary modifications can be determined for comparative planning purposes using the methods of Chapter 5.
Figure 25. Flow Diagram for the Design of Noise Insulation of Buildings
Figure 25. Flow Diagram for the Design of Noise Insulation of Buildings

Example 11: It is desired to determine whether design modifications will be necessary for a 2100 ft²(195 m²) house located adjacent to a heavily traveled highway. Because of local terrain, the only exterior building walls directly exposed to the highway are two living room walls, and the rest of the structure appears to be well shielded. The exterior unshielded noise level in the vicinity of the house is 67 dB. The living room walls and roof have the following characteristics:

The house is located in Los Angeles and has a central heating/air conditioning unit which operates on gas. Assuming the living room to be the most critical room, determine whether modifications will be necessary to achieve an interior design noise level of 32 dB.

Solution: Following the steps of tie Flow Diagram in Figure 25:

Step 1: Calculate Building Noise Reduction

Figure 17. Worksheet No. 1 - Calculation of Building Noise Reduction
Figure 17. Worksheet No. 1 - Calculation of Building Noise Reduction
Figure 17. Worksheet No. 1 - Calculation of Building Noise Reduction

Figure 18. Worksheet No. 2 - Composite EWNR Calculation for Two Elements
Figure 18. Worksheet No. 2 - Composite EWNR Calculation for Two Elements

Figure 18. Worksheet No. 2 - Composite EWNR Calculation for Two Elements
Figure 18. Worksheet No. 2 - Composite EWNR Calculation for Two Elements

Therefore: NRc = 29 dB, Calculated Noise Reduction (From end of Step 1, Figure 17)

Step 2 - Calculate Interior Noise Level Lic

  1. Lo = Predicted outdoor noise level = 67 dB

  2. Lic = Lo - NRc = 67 - 29 = 38 dB

Step 3 - Is Lic +5 < Lc?

  1. Design Interior Noise Level = Lc = 32 dB

  2. Is 38 +5 < 32? No.

  3. Thus proceed to Step 4.

Step 4 - Measure Exterior Noise Level

  1. Subject Highway is existing:

  2. Exterior Leq is determined from measurements to be 71 dB = Lom

Step 5 - Measure Interior Noise Level

  1. Interior Leq is determined from measurements to be 39 dB = Lim

Step 6 - Determine Measured Noise Reduction

  1. Lom - Lim - 5 = 71 - 39 - 5 = 27 dB = NRm

Step 7 - ls Lo - NRm < L?

  1. Is 67 - 27 < 32? (L is given in Step 2)

  2. No. Thus proceed to Step 8.

Step 8 - Plan Modifications

  1. Begin with a simple modification. Treatment of leakage paths in windows,

  2. door, etc. will result in a structure EWNR increase of 4 dB.

Step 9 - Calculate New Noise Reduction

  1. New Calculated Noise Reduction will be:

  2. NRc (from Step 1) + 4 = 29 + 4 = 33 dB.

Step 10 - Is Lo - NRc < Lc?

  1. Is 67 - 33 < 32? No.

  2. Thus return to Step 8 and select additional modifications to give the needed Noise Reduction.

Step 8 - Plan Additional Modifications

  1. In surveying all existing wall elements, the large window appears to be the weakest. Thus, it is specified that this window be double-glazed with

  2. panes of 3/16 inch and ¼ inch separated by a 2-inch airspace.

Step 9 - Calculate New Noise Reduction

  1. Worksheets No. 1 and No. 2 are again used.

  2. The new window, from Table 7, will have an EWNR of 39 dB.

Figure 17. Worksheet No. 1 - Calculation of Building Noise Reduction
Figure 17. Worksheet No. 1 - Calculation of Building Noise Reduction

Figure 18. Worksheet No. 2 - Composite EWNR Calculation for Two Elements
Figure 18. Worksheet No. 2 - Composite EWNR Calculation for Two Elements

Thus the new NRc = 34 dB + 4 dB from sealing = 38 dB

Step 10 - Is Lo - NRc < Lc?

Is 67 -38 < 32? Yes.

Thus, the interior noise level criterion will be satisfied if the building sides facing the highway are well sealed and the specified double pane window is installed.

Step 11 - Select Compatible Ventilation System

Due to the high exterior noise levels, it is expected that the door and window would be kept shut at all times, relying on infiltration and mechanical ventilation throughout the year. Infiltration for the house will be greatly reduced by sealing the living room, however, placing a heavier ventilation demand on the HVAC system. This extra ventilation energy requirement is therefore a consequence of Noise Reduction modification.

The sealing and improved window will also result in heat energy savings. Proceed to Step 12 to calculate these energy changes.

Step 12 -

Figure 19. Worksheet No.3 - Fuel Savings Due to Acoustical Modifications
Figure 19. Worksheet No.3 - Fuel Savings Due to Acoustical Modifications
Updated: 8/24/2017
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