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FenestraPro is a façade design tool that identifies energy-saving strategies, reduces project cost, and improves building resiliency. Used in Revit workflows, FenestraPro automatically selects optimal glazing types per facade from our database of over 1000+ IGUs. Users can also compare and contrast glazing types to select the best option for thermal performance and project specifications. Our in-house BIM modelers have established a step by step workflow below to calculate glass to wall ratio.

Designers can calculate glass to wall ratio (or maximum allowable glazing) for any model based on the thermal performances for elements of the building envelope. As you set the thermal performances for element types (walls, floors, roofs and glazing), FenestraPro will automatically indicate the optimal window to wall ratio for this configuration.

Current Glazing vs Maximum Allowable

FenestraPro will indicate both the current glazing percentage on the model and the maximum allowed according to the Building Code that you have input. The current glazing percentage may be set in two ways:

  1. Setting a value in Revit’s Energy Settings
  2. Inputting a value for Overall Percentage Glazing in Target
FenestraPro Calculating Glass To Wall Ratio 1

Image 1: Setting the Glazing Percentage in energy settings

FenestraPro Calculate GTW Ratio 2

Image B: Setting the Overall Percentage of Glazing

As performance values for glazing and walls improve, the maximum allowable glazing percentage will increase.

Calculate Glass To Wall Ratio 3

FenestraPro displays both the current glass-to-wall ratio and the maximum allowed under the building code. If the maximum allowable glazing percentage is greater than the current glazing percentage on the model, you may adjust the glazing area on the model up to the allowable value or simple use the button to set to maximum percentage glazing. You may also increase the overall percentage value which will apply to the entire model or by adjusting glazing areas on specific Surfaces.

FenestraPro Calculate Glass To Wall Ratio 3

Image C: Setting Maximum Percentage Glazing for mass models

By selecting specific facades or surfaces in the Façade Navigator, user controls will display for adjustment of those areas. To adjust the glazing percentage for a selected surface or multiple surfaces, choose the Glazing Dimensions icon and input a value. This will be applied to the selected surfaces only. If other facades or surfaces are unlocked (available for adjustment), they will be adjusted in order to maintain the overall glazing value for the model.

FenestraPro Glass To Wall Ratio 4

Image D: Setting Glazing Percentage for specific surface(s)

If other facades/surfaces are unlocked (available for adjustment), they will be adjusted in order to maintain the Overall Glazing value for the model.

FenestraPro will maintain the Overall Percentage Glazing value that is set in FenestraPro Target. For example, if 40% is set for Overall Glazing on the model, separate adjustments may be made for specific surfaces but the total percentage will be maintained.  If some Surfaces are raised to 60%, other Surfaces may then reduce to maintain the total model percentage.

Surfaces may be locked to maintain their unique settings. If this is the case, these surfaces will not be affected by adjustments to other areas. surfaces are unlocked by default and will therefore be affected by any alteration to other surfaces. The amount of adjustment will depend on the area of each surface since the changes applied are spread out among the remaining surfaces.

FenestraPro GTW Ratio 5

Image E: The remaining unlocked surfaces will also be adjusted to maintain the Overall Percentage

Selecting Surfaces

Selected Surfaces are modified to 60% while remaining Surfaces reduce slightly from 40% in order to maintain the total setting for the model (40%). If you wish to have multiple ‘windows’ on a surface rather than just one glazed area applied, you may create Edges on the mass using the Mass Editor in Revit. This will create more surfaces which can then be controlled separately. You may also set the default sill height and head height for glazing once a surface or multiple surfaces are selected. To lock any surface or multiple surfaces, the checkbox may be unticked. The label will then indicate that these surfaces are now locked and will not be affected by any changes to other surfaces.

selecting surfaces

Image F: Selecting locked surfaces

In the Facade Navigator, a padlock symbol will display beside the locked Surfaces to indicate this status. If Select All is chosen in the Façade Navigator, locked Surfaces may also be included but any changes to settings will not affect these surfaces. Further adjustment of multiple Surfaces may reach a point where the Overall Percentage for the model can no longer be maintained and this value will then be adjusted in FenestraPro Target.

glazing window to wall

Image G: Adjustment of multiple surfaces may eventually affect the overall percentage

About FenestraPro

FenestraPro is the leading façade design platform that supports the design and construction of beautiful, high-performing facades. Our integrated platform identifies and applies the optimal geometry, material selection, and fabrication information. The platform seamlessly integrates into BIM design workflows to:

  • eliminate the risk of late-stage redesign;
  • demonstrate local code compliance;
  • use data calculations in real-time;
  • calculate glass to wall ratios and thermal peformances.

Mike Flood

BIM Applications Manager @FenestraPro. Passionate about Revit and finding more efficient BIM workflows.