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Thread: Single-family vs two-family: a real difference?

  1. #1
    Unfrozen Caveman Planner mendelman's avatar
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    Single-family vs two-family: a real difference?

    A question to challenge assumptions.

    Is there substantive differences between single-family residential and two-family residential?

    The general points usually are traffic, scale, unit density, building bulk, rental/owner occupied, etc.

    I, personally, see little difference, on average, bewteen single-family residential and two-family residential. You could have a single-family house with 6 occupants all driving and have a "parking lot", whereas a two-family could also have 6 occupants each driving.

    What are your thoughts?
    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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  2. #2
    Cyburbian estromberg's avatar
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    The main difference I see is more of an ownership thing. Single family residential is usually owner occupied, leading to generally better upkeep; while 2 family residential is largely investment/rental property, however in my area this is an increasing amount of duplex ranch-style condominiums.

  3. #3
    Forums Administrator & Gallery Moderator NHPlanner's avatar
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    The biggest difference in my community, where 80% of homes have on site septic, is sewerage loading. A duplex structure requires a larger septic system to handle the bigger septic flow coming from a 2 family home vs. a single family home. We allow them in our residential districts, but increase the lot size requirement for them (we use a soils based lot size when public sewer is not available) on a per bedroom basis over what would be required for a single family lot.
    "Growth is inevitable and desirable, but destruction of community character is not. The question is not whether your part of the world is going to change. The question is how." -- Edward T. McMahon, The Conservation Fund

  4. #4
    Cyburbian wahday's avatar
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    I assume you are talking about some sort of duplex or townhome type place as opposed to two families living together in a single home??

    The differences I see are also infrastructural (if that is, indeed, a word). A two-family home will have two kitchens, two or more bathrooms, etc. with their own meters and systems for water, sewage (or septic, depending), and gas. They will also have additional requirements for ingress and egress.

    I hear what you are saying about the parking/car use situation, but if this is new construction or a modification of an existing home, there may be requirements to add additional parking through the zone code (forget for a moment the sensical nature of this...). Here, the number of parking spaces required is determined by the number of baths (I have no idea what the logic is, but..) and so these kind of changes, or a new home with additional baths, would require more parking.

    I might quibble a bit with estromberg's assumption that single family is usually owner-occupied. In my particular part of town, there are a very high number of renters, including families. Its really a socio-economic issue (these folks can't afford a home to own), but even after I moved into my block, I was surprised to learn how many folks rented. In the area north of me, a majority of the single family homes are rentals (they recently completed a plan and I noticed this demographic info). I definitely agree that the trend is that owner-occupied residences tend to be better cared for and the occupants are more engaged in up keep, maintenance, and generally invested in the neighborhood.
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  5. #5
    Unfrozen Caveman Planner mendelman's avatar
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    Quote Originally posted by wahday View post
    I assume you are talking about some sort of duplex or townhome type place as opposed to two families living together in a single home??
    Yes, I am talking about two units versus single unit residential.
    I'm sorry. Is my bias showing?

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

    Six seasons and a movie!

  6. #6
    Cyburbian btrage's avatar
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    The difference is that "renters" are evil people, or so I've heard.

    The bad part is that a lot of people actually think this.

  7. #7

    Renter response

    Renters aren't "bad" people. They just have much less incentive to put further investments into their property. They are not tied to it. I wouldn't even say they don't take pride in their property, but they just don't have that incentive to maintain their property as a home owner does.

  8. #8
    With our aging population, we're seeing a lot of two-family housing units being developed here. Indeed, such units make up perhaps 80% of our subdivision requests since 2000.

    Rather than call them duplexes, I call them single-family attached units. For many people, duplexes mean 'investment' properties, which every NIMBY knows is evil. Since I'm statutorily prohibited from regulating the type of occupancy, avoiding trigger words -- like 'duplex' --helps my boards get past the occupancy issue and on to issues that truly matter.

  9. #9
    Cyburbian KSharpe's avatar
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    Even when I was renting, I didn't waste money landscaping the yard, I wouldn't invest in the home- why would I? It just makes sense that renters don't maintain properties as well as owners would.
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  10. #10
    Unfrozen Caveman Planner mendelman's avatar
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    Ok...let's not get off-topic with a "renter vs owner" digression.

    Perhaps I need to refocus the discussion. When I am asking the question about the real difference between SF and 2F, I am really asking about the real substantive differences from a land use perspective.

    wahday mentions infrastructure (2 kitchens, etc.) but that really doesn't concern land use is a real way.

    Gedunker talks about the semantics of names for forms, but that is political.

    So...what are the real substantive land use differences between the two, if any?
    I'm sorry. Is my bias showing?

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

    Six seasons and a movie!

  11. #11
    Cyburbian Streck's avatar
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    I would think the real difference is density (a legitimate city planning concern and function).

    All things being equal, two families occupying the same lot size lot generate more vehicle trips, requires more parking space, water use, energy use, waste disposal, delivery vehicle traffic (ie mail and UPS), and guest parking on lot or in street.

    Unequal things might include number of occupants for principle residence vs secondary dwelling based on size, number of bedrooms, relationship to owner (mother-in-law or other relative), and reaction to neighbors of a perceived occupancy problem. The number of occupants may be addressed by sub-regulations such as building size, setback, frontage, parking limits, etc.

    Also, the extent of the area in which the two family provisions are allowed, and the context in which the area is located (ie, is it already a relatively high density or changing area?).

    I think all these aspects have an impact on planning (city services required and traffic and complaints).

    This thread is bringing up interesting points that I don't think we have sufficiently addressed in our own regulations, yet.

  12. #12
    Cyburbian Streck's avatar
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    I think another real danger to planning might be that once you start allowing a second residence on a lot, you may have inadvertently given up your rights to holding on to Single Family Zoning.

    What is to keep developers from applying for a second residence on any and all Single Family lots? If you try to deny some while allowing others, you are subject to the claim of being arbitrary and capricious - or worse - and subject to law suit if you don't grant it to any and all who apply. Ergo - you have lost Single Family zoning.

    Yes, there is something about a Single Family lot that is not enjoyed by having others share your lot. Privacy and the ability to use any part of your lot at any time for any legal purpose. This is important to the sense of "ownership," which translates to a desire to protect property value. This also indirectly and positively affects adjacent property values.

    Also consider that after granting a legitimate "granny residence" status on the property, when the property is sold, that Use may not continue, but will become a two family or Duplex Use.

    I think this is a significant impact on Planning and Zoning.

  13. #13
    NIMBY asshatterer Plus Richmond Jake's avatar
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    I don't see an issue here. The residential density remains the same because it's controlled by the maximum allowed in your Comp Plan. It's only a matter of appearance. Everything else is a constant, IMO.

  14. #14
    Cyburbian Masswich's avatar
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    Density is obviously the main issue - which reflects itself in urban areas mostly as privacy issues and traffic impacts.

    But if you're asking if, holding density equal, is there any difference between detached single familieis on separate lots and two-families on lots double that size, I'd say that any impacts are perceived rather than actual.

  15. #15
    Quote Originally posted by mendelman View post
    A question to challenge assumptions.

    Is there substantive differences between single-family residential and two-family residential?

    The general points usually are traffic, scale, unit density, building bulk, rental/owner occupied, etc.

    I, personally, see little difference, on average, bewteen single-family residential and two-family residential. You could have a single-family house with 6 occupants all driving and have a "parking lot", whereas a two-family could also have 6 occupants each driving.

    What are your thoughts?
    Your hypothetical about 6 persons driving who live in a single family dwelling requires a consistent assumption that a duplex could result in 12 persons driving. That in itself should represent a rather considerable and substantive difference between the two densities. Carry the same concept forward and you could have 6 people needing school facilities versus 12 people needing school facilities ( substitute if you want parks, police, drinking water, trash service, etc.). If single family and two-family are virtually the same, then wouldn't a three-familly use be nearly the same as the other two densities? In effect, you've allowed for a doubling of density - no trivial matter.

  16. #16
    Cyburbian transguy's avatar
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    In most areas I've seen, the minimum lot size is not dependant on the dwelling being attached / detached. While districts that allow attached districts generally allow smaller lot size than do districts only allow detached housing, this does not have to be the case. The minimum lot size has far greater control over density than if two, three, or ... units share a wall. So long as the density remains equal, the only difference is political.

  17. #17
    Member Oz_developer's avatar
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    I agree with transguy. Most councils here have a dwelling per square metre ratio to control for density. It's this that dictates wheter dwellings be attached, detached or in rows.

    I'm 99% sure it is no longer permissable to build two dwellings on the same title here (the Aussie planners may correct me on this). Lots with attached dwellings must be subdivided or strated (like an apartment block, not sure what the US terminology is)

    Indeed it is difficult to get approval to build a second kitchen in a house even if there is only one family in it, such is this regulation enforced.

    Hope I'm not confuing the issue.

  18. #18

    Duplex vs. two smaller SFR's

    The question I have is why do the two family codes almost always require one structure?

    Carriage house and granny flat laws fix the problem for "front and back" units, but generally a duplex in the "R-2" zone requires that the two units be attached.

    IMO, the added value of being detached more than compensates for the loss in floor area caused by not sharing a wall.

    Here's a photo of what the code doesn't allow: http://friends-of-granny-flats.googlegroups.com/web/SFR%27s%20on%2025%20feet.jpg?gda=JzgP9EcAAAAsDyWuUqZlQ4ByzpQFMZrkJmQykie1HWf6tB1GJNLzamG1qiJ7UbTIup-M2XPURDSfGEQpEA-6uAmBvXilkgFdYZZucXWaofuqzP4ltZnKIA&gsc=vcdwOQsAAABOARw5wuSU48Fs7fZnekdj

    Here's another case of zoning laws violating the common sense test, please help me understand?

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