So, you need to implement percent glass calculations in LEED? This has proved a bit confusing since the additions of doors to the "openings" and I think it requires explanation.

What's the relevance? Well, if you are near 40% glass, or say you're half glassed - this could make or break your model:

Here's the reason why: The TRACE 700 reports calculate the glass based on the Wall area only (and not the gross wall area, which includes Opaques doors). So if you have doors, your TRACE reports may over-estimate the percent glass. Let's take an example of a building that is "Half-glassed":

Let's take an example:

Alternative 1:

Wall 10 x 100 feet (1000 sq feet)

Window 5 x 100 feet (500 sq feet)

Opaque Door 40 x 10 feet (400 sq feet)

Building Area Report: 83.3% window.

Which is 500/(1000 - 400). In other words. It isn't accounting for the door area or the "gross wall aread". The window to wall ratio is actually 50%

In Alternative 2:

Lets say you tried to enter the same percentage and thus entered 83.3% glass on all walls (claiming the value from the report)

The report will say 100%

When you ENTER percent glass, TRACE uses the Gross wall area to calculate the total square footage of glass (in this case .83*1000).

But, in the Building area report, it calculates the Percent glass differently.

(.83*1000)/(1000-400) which is >100% so it comes out to 100% glass.

Kind of strange, you have a WWR of 50%, and you can somehow end up with 100% glass! This comes from an inconsistency in the definition of glass percentage (in your entered values, it is based on gross wall area, in the reports it is based on True wall area).

View the attached file to illustrate the example.

How do you calculate the Window wall ratio or WWR for LEED?

LEED requires that you use the gross wall area, defined by 90.1 users manual as:

Gross wall area = (opaque wall area + opaque door area + window area).

In this case that means it is 10*100 or 1000 square feet.

So, the WWR for this is 500/1000 or 50% (which of course is too much for LEED and you would need to reset to 40%, which is why you really need to understand this!

What's the solution:

Don't use openings for doors (maybe add another wall instead)

Show a separate calculation, when reporting glass area to LEED

Use the component Tree view and a spreadsheet to show the WWR as defined by LEED.

Another glass percentage tip:

If you are very close to the limit of the percentage of glass, do not forget to include the "slab thickness" in your calculations. You can either add this to your wall height, or implement it in a side calcultion. (If you consider a 6" slab and a 10 foot wall, it can make a difference of 5%)

About the Author

tracewindu

I'm a Jedi. That's all the credentials you need.

I'm the only Jedi focused 100% on Energy Modelling.

I heard a rumor the other day about military clones being produced on an outer rim plant. I'm sure it's nothing to worry about. Having to wait 3 hours for my TRACE 700 LEED file to calculate, now that's a concern!