Reduction of Roof Live Loads (LR) |
  
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Reduction of Roof Live Loads (LR) |
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If the user does wish to take advantage of LR reduction, the appropriate reduction factor is calculated using the inputs provided in the window. These inputs correlate directly to the parameters and limitations outlined in ASCE 7 and IBC for reduction of roof live loads.
As the inputs in this window are modified, the LR reduction factor to be applied will update in real-time, as indicated on the “Apply…” button.
The tributary area is manually modified by typing a numerical value into the “Tributary Area:” textbox. Note that the window will not respond to tributary area modifications when the roof pitch has not been set. The roof pitch is selected from preset options.
When the cursor passes over the “Apply…” button, the button will show a notification reminding the user to hover over the button for detailed information about the LR reduction factor being presented.
In scenarios where the R1 and R2 factors for roof live load reduction both reach minimum values simultaneously, the resulting reduction factor is forcibly limited to a minimum of 0.6. The basis for this restriction is the code requirement that roof live loads may not be reduced below a magnitude of 12 psf. Based on the presumption that nearly all uniform roof live loads will have an unreduced magnitude of 20 psf, any reduction factor less than 0.6 would violate this requirement.
In special cases where the user deems it appropriate to reduce below this threshold or apply an arbitrary reduction factor for any reason, the “Factor Override” input may be used. This override functions identically to the corresponding field on the “LL Reduction” tab.
When a numerical value is entered in this field, all other inputs will be disabled. The form will not update in response to a non-numerical value. When the form is in this state, the reduction factor is not a calculated value. All roof live loads will be uniformly reduced using the exact factor entered by the user.
When the form is in this state, ENERCALC for Revit does not perform any checks to validate the provided reduction factor against code restrictions.
Removing the override by “backspacing” the numerical value in the textbox will return the form to a calculated state based on current inputs.
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