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Thread: Lot coverage ratio comparisons

  1. #1
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    Lot coverage ratio comparisons

    My community just enacted a LCR ordinance which, in my opinion, is completely insane. I'm a novice, granted....so I want to get some input from real planners who know what they are doing.

    It is my understanding that LCR's are, in and of themselves, somewhat controversial, but even putting that larger issue aside for now....I am curious to get your opinion as to how our ordinance compares to similar ordinances you have seen around the country.

    Our new standard is a max of 18% lot coverage for 1 acre lot....which includes home, garages, driveway, sidewalks, decks, pools.....any and all impervious surfaces. The scale slides depending on lot size. Link to copy of ordinance is provided below.

    Basic background: We are a rural community on well and septic. Lot sizes vary dramatically...from 5 acre estate lots with horses to 1/2 acre subdivision lots.

    My opinion is that this is insanely strict. I've tried to compile all the examples of LCRs I can on-line, and ours seems out of whack. Plus, it seems of questionable necessity in general, given the fact that home owners in our community already have to reserve a great deal of open space for a septic field + a 100% expansion area in case of field failure. Plus required setbacks, etc.

    Not sure what our PC is smoking...but I've requested and read through all their paperwork on this, and I *think* that what might have happened is this....they looked at percentages from another community's FAR ordinance and ran with them....not taking into account that FAR is not equivalent to LCR. (The first draft was a FAR chart....but it looks like it got changed into a LCR standard without changing the ratio.) BTW, the Plan Commission Chair told the community and Board that FARs are MORE restrictive than LCRs, so we are actually much more lenient. Am I missing something??.....doesn't the average additional floor of a home amount to a lot less square footage than all other imperious surfaces combined...driveway, sidewalks, etc., etc???

    Looking forward to your input. Thanks, glp


    Ordinance can be viewed at:
    http://northbarrington.org/content/H..._Ordinance.pdf

    Moderator note:
    (Dan) Fixed the URL. Sorry about not being able to use a URL until your fifth post; it's a spam prevention feature.
    Last edited by glp642; 17 Jul 2006 at 10:24 PM.

  2. #2
    Cyburbian mike gurnee's avatar
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    I have never been a community where driveways/sidewalks have been considered with the lot coverage ratio. If there are storm water runoff problems, then impervious surface area is important--and should be addressed through detention or retention plans. Do you have a homebuilders group that you can go to with such questions? Are these types of amendments well advertised (and explained), or just the legal minimum?

  3. #3
    Super Moderator luckless pedestrian's avatar
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    we count all impervious surface in our ratio (you need a building permit to install a walk) - it's a back handed way to control lot development - but it's a joke because we don't even require a survey with our building permits so how would you know - I'd like to get rid of it actually, at least where we require an FAR

    so yeah, you're right, imho!

  4. #4
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    Quote Originally posted by mike gurnee
    If there are storm water runoff problems, then impervious surface area is important--and should be addressed through detention or retention plans.
    Yes, there are water runoff problems. The Village has a chapter of code specifying the requirements for storm water management systems for all public and private developments....retention basins, etc. PC says that the intent of the ordinance is not water control, however, but teardown control (with water as a secondary benefit).


    Quote Originally posted by mike gurnee
    Are these types of amendments well advertised (and explained), or just the legal minimum?
    Well, yes in some communities (from what I have read). But in our case....unfortunately not at all. Only the legal minimum.

    Public awareness only began a week before the Board was to consider the proposed ordinance, as the result of a community member posting flyers. Sixty people showed up at the Board Meeting (...that is a huge turnout for our little Village). Board passed it anyway. THen over 100 people showed up at the next board meeting...asking for a motion to reconsider to table it for additional research. Nope.

    The most concerning aspect of this for many residents is that the PC did not collect measurements on a single property to backtest this. No data collection or mapping efforts at all. They assigned someone on the commission to measure 10 homes as a test...but it wasn't done before the ordinance was drafted and passed.

    When I first heard that there wasn't any data being used to make the decision, I gathered stats from county assessor myself to see what the current situation looks like.....sampled 80 properties (lot size & footprint area) & added on an average 3,000 sqft nonperm estimate. 22% of homes in one neighborhood are out of compliance currently using that nonperm estimate.

  5. #5
    Cyburbian abrowne's avatar
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    I've never heard of ANY impervious surface being considered into lot coverage ratio. Usually it's just structures - principal dwelling, and detached/attached accessory structures.

    Also, that 18% is the lowest I've heard of.

  6. #6
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    What is the Pre>Post SWM (stormwater management) req? 100>2?

    Whoever wrote the ordinance likely did a quick calc, backing into the the max impervious for the size of the district (including roads, walks, etc) that would allow them the highest Cn (Curve number (a multiplier, based on ground cover, used to determine runoff flows)) and still reduce the 100 year Post to the 2 year pre.

    Thats what I would've done anyway.

    The more impervious, the bigger the basin....not always what a town wants. Plus if you have alot of basins upstream, which were designed in earlier days, the peaks likely arent offset, causing flooding downstream. There may only be a certain volume of H2O they are looking to discharge (without holding it for a week).

    You gotta take into account the fluff too (all the stuf that get builts that nobody ever gets permits for).

    Better? Basically, what I'm saying, even if this isnt the reason for your 18%, there is likely a method to the madness. Ask!
    Last edited by ZoneThis!; 17 Jul 2006 at 10:18 PM.

  7. #7
    Cyburbian Plus Whose Yur Planner's avatar
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    Our Ordinance uses both structures and lot coverage. The percentage depends on the zoning district. I work for a county, so we have the range of lot sizes and uses.
    When did I go from Luke Skywalker to Obi-Wan Kenobi?

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    Quote Originally posted by Whose Yur Planner
    Our Ordinance uses both structures and lot coverage. The percentage depends on the zoning district. I work for a county, so we have the range of lot sizes and uses.
    For point of reference, do you happen to know the % LCR you use for 1-acre single-family residential? (....this is 18% for us, all impermeable surfaces including driveway).

    (Our ordinance uses the following equation to determine the max LCR: MAX = 0.18 * (lot size in acres ^(-.29))....resulting in 22% for half acre, 18% for 1 acre, 14.7% for 2 acres)
    Last edited by glp642; 18 Jul 2006 at 4:44 PM.

  9. #9
    Cyburbian
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    Lets do some math

    18% of 1 acre is 7840 sf.
    A one acre lot with a 3:1 width to depth ratio is about 360'x120'
    A 12' wide driveway the entire length of the lot is 4320 sf
    This leaves room for a 3500 sf house
    Less if there is a patio, more if the drive is shorter (which it probably will be)

    Oh yeah, that 3-car garage will take up 500-800 sf as well

  10. #10
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    Ok, good idea...let's do it...more math!

    Hey, Chris. I actually checked out your website just a few days ago. It's very interesting & you have clearly put a LOT of work into researching for your community. I hope they appreciate it.

    As for this LCR issue.... just want to clarify a couple things about adding up the lot coverage...

    I'm afraid you absolutely can't discount a garage here....residents aren't even allowed by the Village to park on streets after 2 a.m.! We are a rural suburb....no businesses in our village. People have no choice but to drive for everything, unfortunately. Plus, it is an affluent community generally speaking....believe you me, these people aren't going to park their benz on the curb even if they could. And the Village makes people store oversized vehicles, etc....doesn't allow them to be "eyesores" in driveways.

    Anyway, besides the garage....you have to count the front stoops and porches, all sidewalks and garden paths, back porch, etc. Plus, like I said...we are rural, so porches and decks are standard, and it isn't that uncommon for people to have small sheds in the backyard as well. We do tend have long driveways also....b/c many lots are long and narrow, with homes set far back from the road.

    SO....you often do end up having to add all of these items for a given house, which gets you up there:
    Home footprint + garage + driveway + sidewalks + front and back porches (+ accessory buildings, if any). Then anyone with a deck/pool adds waaaay more, of course.

    Average house footprint in neighbordhood studied was 1350 sq ft....range is pretty wide (Sdev 563), but using the ave:

    Ftprt (1350)+Driveway (3000) + Garage (700) + Porches (650) + Walks & Paths (700) + Accessory (200) = 6600

    For one acre lot, that would be 15% and would pass, but it wouldn't pass if the home were on the median size lot in the neighbordhood. Median lot = 32,250 sqft, allowable LCR = 19.6%, above example: 20.5%

    (an aside: just on a personal note...I do support preventive protective measures, & I think a lot of the residents do....just afraid the standard is off. I figure....if the median lot is out of compliance, imagine how many more are out once the variance is accounted for. Hoping research can lead to compromise b/w the different sides of the issue.)
    Last edited by glp642; 18 Jul 2006 at 11:25 PM.

  11. #11
    Cyburbian Emeritus Chet's avatar
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    I work in some communities that only deal with floor area ratio (FAR), and others that work in Open Space Ratio (OSR) and some that do BOTH. All are legitimate immplementations of police powers depending on your local conditions. I'd need to know more about your local conditions to opine on your specifics.

  12. #12
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    Quote Originally posted by Chet
    I'd need to know more about your local conditions to opine on your specifics.
    Hey Chet, thanks. I just added some info in a post below, but please let me know what else you need to know. I'd like to get your input on how this compares to what you've seen.

    hey all, i really shouldn't fall into debating the larger issue... sorry to do that. get carried away sometimes.

    back to the facts....

    i'm really just hoping to get concrete comparison standards of LCRs used around the country with which to compare ours. so i'll keep my mouth shut from here on out and just see if anyone has input!!!

    (if others feel like sounding off for or against lcrs, that's fine too...but i'll butt out and wait for some numbers!)
    THANKS!
    Last edited by NHPlanner; 19 Jul 2006 at 1:39 PM. Reason: double reply

  13. #13

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    I have written several ordinances for communities with sensitive watersheds and spent a lot of time in research to defend these ordinances. There is defensible science from places as different as Maryland and Washington State showing that stream health and channel stability inevitably deteriorate when impervious cover exceeds 10-12%. For a rural area where water quality is a concern 18% is a generous standard that will most likely result in visible, long terim damage to the watershed.

    As this thread has already demonstrated, people can inhabit rural landscapes within a strict cover limitation. What no one has pointed out is that this also demonstrates that large minimum lot sizes are not (for this and many other reasons) the appropriate way to protect rural landscapes. It is far easier to maintain low total impervious cover, as well as effective stream buffers (which are equally, if not more important), by requiring open space development patterns that cluster homes while protecting large blocks of open space.


    You have to remember that the tradeoff you make to allow a higher coverages while attempting to protect watershed's functions is stormwater management infrastructure, which is quite expensive. I am working in a community that sounds somewhat like yours (affluent suburb) with an impaired watershed where higher coverages were allowed. Thje result is that the town will be spending several hundred thousand dollars and developers and homeowner's associations will be spending millions to attempt to correct the problems.

  14. #14
    Cyburbian
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    Lee

    It seems to me the point of this thread is that the subject community has not appeared to articulate or justify the restrictions. Why 18%?.

    You have to do the math, so to speak.

    You lay out many of the reasons that an impervious surface cap may be appropriate in some cases, for reasons of surface and sub surface water quality, stream health, stormwater runoff etc...But the upfront justification and defense must be vetted by the community in order to reach the concensus sommunity standard.

  15. #15
    Cyburbian
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    I ran a quick calculation, a grass lawn with 18% impervious area has about the same stormwater runoff coeffient as cropland. Therefore stormwater detetention requirements would be minimal.

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    Reference communities?

    Lee, Thanks for this helpful input. Would you mind posting the names of the communities so that I can look up these standards?....and try to compare their watershed situation to ours, if possible? (even though the primary intent of our ordinance is not to address runoff or ground water, perhaps it should be? no data on this was examined when drafting the ordinance, but a consultant's guidance would no doubt be helpful to the planners here).

    Quote Originally posted by Lee Nellis
    It is far easier to maintain low total impervious cover, ....by requiring open space development patterns that cluster homes while protecting large blocks of open space.
    We have a large forest preserve and 7 other public wetland open spaces, but I am not aware of the extent of the water concerns here. Will need to look into it more.

    So far I have found two communities with comparable standards, Milford PA and Hopewell township, NJ. If anyone has knowledge of these areas, would love input.

  17. #17

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    The classic, and first as far as I know, example of limiting impervious cover was around Lake Tahoe, all the way back to the '70's. You can try the Tahoe Regional Planning Agency website for more on that. One of the most straightforward codes I have done is for the small village of Hauser Lake, ID, back in the early '90's. I don't know if their code is on-line, or how miuch they have changed it over the years. I would also check the Center for Watershed Protection's websiite. It offers all sorts of information on both the science behind this approach and ordinances. Finally, look for papers written by Derek Booth,a professor at the U of Washington.

    To find out if your community is in an impaired watershed you need to find your state's 303(d) list. It should be available on your state water quality agency's website.

    It is true that the community must articulate its reasons. And in this case, they do not appear to be based in water quality. All I am saying is that 18% is not unreasonable (except possibly because it is too much) in rural environs where there is no storm water infrastructure.

    FInally, savemattoon: if a construction site or urban development generated the same sediment/nutrient loads as most cropland, they would be shut down and fined. Ag uses have a special, exempt to semi-exempt status in water quality law throughout the US, but they are the single largest source of nonpoint pollution. An ordinary turf lawn with `18% cover generates a lot more runoff than a comparable area of native forest or prairie. And remember that rthe 18% limit we are talking about here applies to the private landowners - when you take the roads that serve the homes into account, the watershed is probably pretty stressed.

  18. #18
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    Pancakes and watersheds

    Quote Originally posted by Lee Nellis
    The classic, and first as far as I know, example of limiting impervious cover was around Lake Tahoe, all the way back to the '70's.
    I just did some reading on the limitations in Lake Tahoe region. Wow. The land coverage rules there are *extremely* complex -- crafted to fit the unique topography of the region. I was taken off guard by the huge body of research surrounding these regulations. Lake Tahoe's restrictions must take into account landslide risk, slopes, etc. Very complex indeed. The scene is much more boring out here in the pancake-flat midwest, to say the least! I get the feeling that the sensitive watershed areas in which you work on the coasts are probably not comparable to our Chicago surburb.

    Quote Originally posted by Lee Nellis
    To find out if your community is in an impaired watershed you need to find your state's 303(d) list.
    Just did some investigating with regard to our watershed. The main waterway (creek) that runs through our area is listed as medium priority for two items: algal growth and flow alteration.

    Our Comprehensive Plan calls for the development of a Watershed Development Plan and water table monitoring program. Looks like we don't have much in place right now to give direction.

  19. #19
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    Quote Originally posted by savemattoon
    I ran a quick calculation, a grass lawn with 18% impervious area has about the same stormwater runoff coeffient as cropland. Therefore stormwater detetention requirements would be minimal.
    Yeah, but nobody ever lets you use Rops as a cover type in the pre anymore. Most plaes dont even let you include existing impervious either.

    What am I getting at? I dont even know...carry on.

  20. #20
    Cyburbian
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    Quote Originally posted by ZoneThis!
    Yeah, but nobody ever lets you use Rops as a cover type in the pre anymore. Most plaes dont even let you include existing impervious either.

    What am I getting at? I dont even know...carry on.
    I think this is what Lee Nellis was eluding too. We must be way behind the times here, we're allowed to use conditions imediately prior to new development for our pre-condition calculations.

  21. #21
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    Impervious cover for Individual Lot --vs- Whole Community's Coverage

    Lee,
    I've been doing some more reading from the references you provided. Can you help me clarify something?

    Quote Originally posted by Lee Nellis
    stream health and channel stability inevitably deteriorate when impervious cover exceeds 10-12%. For a rural area where water quality is a concern 18% is a generous standard
    The research you were referring to here was addressing the percentages for the entire watershed / community, wasn't it...not 10-12% per individual lot? (I.e., the research I've read so far seemed to refer to the impervious cover of the whole areas...including not just individual residential or commercial lots, but all ag land, open urban land, parks, etc.). So our planners would need to study the overall impervious coverage of the whole area in order to thoroughly assess the impact on the watershed, right?

    Thanks, G

  22. #22
         
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    Our semi rural town here in central MA is rewriting our zoning bylaw, and we decided to add impervious coverage max to the code - they used to have only max building coverage (for all districts). During the review we changed it (for political reasons) so the impervious coverage only applies to non-residential and multi-family residential uses and not to one or two family residential (and those are much higher than 18%). While many of our lots are large enough for the lack of control to not be a problem, we have a LOT of lots that are small - half acre and less. Many of those are on the lakes, and I can only imagine the water quality problems this development pattern has created over the years. And of course there are no stormwater systems. You couldn't get me into one of those lakes to save your life - all are on septic (well, some are old cesspools), the majority of the homes must have well over 50% impervious cover... yuck. These areas were all subdivided decades before zoning and used to be summer cottage areas. Now the seasonal use houses are few and far between. Most are limited to 2 bedrooms, but people just cram the kids in anywhere - I've even heard of one family who converted a closet into a "bedroom"! All to live on a lake. People really are nuts!

    Do I think the lack of limitation on residential lots is the right thing to do? No, not at all... just because the town used to do stupid things doesn't mean we have to keep doing them. But tell that to the politicians - not to mention the voters at town meeting, where I need a 2/3 vote on the floor to get the new zoning adopted!

  23. #23
    Unfrozen Caveman Planner mendelman's avatar
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    Well, I'm in a Chicago NW burb just down the Metra from you.

    We have Building Lot Coverage (just building footprints), Impervious Surface Coverage (all impervious surface including buildings, patios, driveways, etc.), and Floor-Area-Ratio.

    We are a relatively dense community with average single-family lot sizes of about 10,000sqft. And here is what we what we allow in our various SF districts for Building Lot Coverage and Impervious Surface Coverage:

    BLC
    RE & R1: all lots sizes - 30%
    R2 & R3: Lots less than 6,000sqft - 40%, Lots 6,000sqft or greater - 35%

    ISC
    RE thru R3: Lots less than 6,600sqft - 55%, Lots greater than 6,600sqft - 50%
    I'm sorry. Is my bias showing?

    Let's not be didactic in this profession, because that is a path to disillusion and irrelevancy.

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  24. #24

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    Yes, you have to look at the whiole watershed. That's why I noted that lot-by-lot limits won't be as effective as an open space development approach that clusters homes and leaves large undeveloped tracts in strategic locations.

    Having a flat landscape doesn't exempt you from stream channel degradation as a result of development. It does change how the degradation will proceed. Among other things it can begin to interact with your ground water supply.

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