Dual Flush Flow Rate

Hi Leanne, USGBC's Water Use Reduction Additional Guidance states that, for dual flush toilets, "In cases where the manufacturer’s specifications provide a different weighted average, it is acceptable to use the recommendation. Please upload the specifications or provide a narrative and calculations to explain how the weighted average flush rate was derived." See www.usgbc.org/resources/water-use-reduction-additional-guidance

The guidance is from v2009, but I don't see why it shouldn't carry over to v4, so I say go for it! It might be a good idea to reference the document in your application too.

I asked GBCI specifically about v4 Additional Guidance and got the following response:

"Thank you for contacting GBCI regarding Additional water reduction guidance specific to v4 projects. We do not have a new document but most of the general issues covered in the previous version are applicable."

They also said to contact them if there were any specific questions. I second Trista's comment to attempt it and definitely include a narrative explaining the different rate and your source. If you're uncomfortable submitting without feedback since you're on the cusp between two thresholds, you could just contact GBCI, explain your approach, and ask for confirmation that it's appropriate. They won't pre-review what you plan on submitting, but they should be able to tell you if your approach is on- or off-track based on the 'Additional Guidance' document they provided everyone.

I don't think your proposed approach makes any sense for this one. The calculator is using a formula that takes into account how many men are going to use the low-flush option on the toilet based on what you enter for % that have access to urinals. If you put in 0% of men have access to urinals, then the calculator will show the weighted average for the dual flush as 4 liters (the same as what your manufacturer is claiming). This assumes that one man and one woman would use the toilet a combined 6 times in a day, 2 full flushes (12 liters) and 4 low flushes (12 liters) for an average of 4 liters (24 / 6). The reason it is showing 4.5 is because you have 100% access to urinals for men. Now if you have one man and one woman using the toilet in a day you get 2 full flushes (12 liters) and 2 low flushes (6 liters) for an average of 4.5 liters (18 / 4). Men using the urinals won't be using the low-flow option on the toilets. Your manufacturer is giving you a one size fits all, best case number that assumes no urinal usage. Every dual flush should have the same solid flush to liquid flush ratio based on the men / women usage after account for urinals. You're trying to claim people using a flush valve from this manufacturer pee more and / or poop less than those using other flush valves from other manufacturers.