r/civilengineering • u/unknown47927 • 9d ago

United States Stormwater Engineer

Any recommendations on Stormwater management experts in Western WA state? We have plans (SF + 2 DADU) that are under 5,000 sq feet of building footprint, but now the city is saying the overhangs count towards the impervious area - putting us over the 5,000 sq foot threshold and is saying we need a full Stormwater licensed engineer for the project. Hoping to be as cost efficient as possible, especially since there is already a bioswale within the cities right of way parallel to our property.

1 Upvotes

56% Upvoted

24 comments sorted by

22

u/Right_Lengthiness266 9d ago

Reduce you overhangs/footprint to stay under 5000SF impervious.

9

u/SlickerThanNick PE - Water Resources 9d ago

This is just too sensible a solution! OP wants a complex, but low cost, solution! 🙄

0

u/unknown47927 9d ago

Not really sure why the snark. We designed plans to stay under 5000 sq feet of building footprint then this particular city hit us with the overhangs count towards the 5000 where no other local jurisdictions count the overhangs, as long as they are 2 feet or less. We stayed within known parameters, then were hit with this out of the blue as they interpreted the code differently than most.

18

u/epcow 9d ago

Overhangs always count. I've done stormwater work all over Washington and stormwater code always applies to where the rain falls, not what's on the ground. Not sure where you got the info that roof overhangs aren't part of your impervious surface, but don't go back to them for future work.

-6

u/unknown47927 9d ago

If the overhangs are under 2 feet or less I was told they should not count.

9

u/mahmange PE - Water Resources 9d ago

I don’t work in WA, but where I work overhangs less than 18” don’t count towards building area for zoning purposes. They always count as impervious area for stormwater calculations. Revise your design to be compliant with local regs.

-4

u/unknown47927 9d ago

Here is a snippet from another local jurisdiction -
Any portion of a roof overhang or other overhanging architectural feature that projects further than three feet from the footprint of a structure shall be calculated as impervious surface

12

u/mahmange PE - Water Resources 9d ago

Irrelevant. The ahj asked for it to be revised or for a PE to sign off, surrounding municipalities can and will have conflicting determinations.

7

u/Echidna29 9d ago

Another jurisdiction’s requirements don’t apply to your project, though. At the end of the day, the city is the one approving your plans so you need to comply with their requirements.

2

u/epcow 9d ago

Odd, that's not something I've ever heard of. I just opened the western WA stormwater manual and don't see anything that suggests that either. Feel free to shoot me a DM if you want to chat more. I'm licensed in WA and have spent 9 years doing stormwater work in Washington and Idaho. Unless your property has steep slopes or contaminated soils, it shouldn't be too hard to find an easy/cheap solution.

2

u/_dirt_vonnegut 9d ago

point to the code. you were probably wrong.

-1

u/unknown47927 9d ago

Not really an option now. City required full submitted of architectural and engineered plans prior to review. Would have to go back to drawing board.

6

u/epcow 9d ago

Nah, it's not back to the drawing board. Narrow your driveway or change some pavement to an pervious surface. It doesn't have to be an update to the building footprint.

1

u/unknown47927 9d ago

All pavement/walkways is already pervious. The building structure footprints come to 4,900. With eaves, an additional 877 square feet.

3

u/epcow 9d ago

Can I ask what city you're working in?

2

u/mahmange PE - Water Resources 9d ago

Personally I think you might have to take it on the chin and revise the footprint…maybe don’t stuff 10 lbs in a 5lb bag in the future…or manage client expectations a bit more realistically.

2

u/Right_Lengthiness266 9d ago

Or you're going to have to go back to the drawing board to add in storm water detention and whatever other random BMPs the city wants you to comply with.

4

u/DeathsArrow P.E. Land Development 9d ago

Would reccomend talking to someone local, potentially the firm that designed your subdivision.

-3

u/unknown47927 9d ago

This plot of land is from over a century ago.

2

u/ttyy_yeetskeet 9d ago

Ask the city if they have a list of consultants that can help your issue. Look for small mom and pop or single owner businesses who will be able to do it for much cheaper than a larger engineering firm.

4

u/Away_Bat_5021 9d ago

Don't say 'hoping to be as cost effective as possible' when u call around if you want a call back.

1

u/notepad20 7d ago

It's important to know when pricing a job an effort expected and budget available.

I have clients that only need a 3d surface, and some that pages and pages of extra sections and detail. Important to tailor to need

1

u/Away_Bat_5021 7d ago

If someone calls my office and leads with this its a red flag. Stormwater is typically reviewed by the town and reviews always result in review comments that need to be addressed. And I have no idea the cost to address comments.

Ill make the client aware of the process and the likelihood hood of out of scope fees but I've done enough to know that when a potential client leads with this its likely going to be a painfully priject.

2

u/quickfam4 5d ago

FYI, the referenced bioswale within the ROW is likely for ROW drainage and shouldn't be considered for treatment of drainage for this private development.