Boulder’s Solar Shadow Ordinance

Many decades ago, in an effort to ensure that the City of Boulder’s citizen’s houses always have the access to the sun, the City passed a Solar Shadow Access ordinance. If you have done any building work in town you have certainly run into this rascal as it applies to all residential districts and can be particularly tricky.

NOT ALL PROPERTIES ARE THE SAME This solar protection rule projects the potential shadow from new construction as calculated between 10am and 2pm as it would be on December 21st. This means that the shadow is a wedge casting north and 30 degrees east and west of north. So, if you live on the south side of an east-west street, your shadow casts mostly into the street. If you live on the north side of an east-west street you are a bit disadvantaged as your shadow most likely begins to violate the regulation by casting into your neighbor’s property. On north-south streets, this regulation pushes new work to the south side of the property to avoid solar trespass at the north edge.

available building area, north-south vs. east-west street

THE SIMPLE ANALYSIS In its simplest form, different areas of the city are divided into Solar Access Areas, one having a 12′ high solar fence, one a 25′ high solar fence. A solar fence is basically a theoretical plane of described height on the property lines. Based on a formula of pitch, you can build new construction as long as the pitch of the shadow of the new work does not cross your property line. The formulas are based on the assumption of the height of your Solar Access Area’s fence. That’s the simple part.

actual and solar fence site plan analysis

THE PAIN-IN-THE-BUTT ANALYSIS If your proposed work’s shadow as defined by the formulas described above, does NOT fall within your property lines or your lot is not “level”, you have to execute a solar shadow analysis based on Actual Shadow Lengths. A “level” lot is a point of contention as you can imagine and the process for creating this analysis is essentially to plot the shadow lengths twice, once for a level lot, then adjust the length of the shadow based on the change of grade between the end of the shadow and the projecting element. What is particularly tricky about this is the impact of the location of your neighbor’s house relative to their setbacks. Your new construction can only cast as far into their property as they are NOT allowed to build, in other words, it can fall into their setback but no further. Many zoning districts in Boulder have a rule that the combined sideyard setbacks of a property need to be 15′, but either side can be as small as 5′ as long as the total is 15′. If your neighbor’s house, on the north side your property conjoins, is 5′ away from the property line, then the Actual Shadow Length restriction can be a project killer. If your property is also on a north-south street and fairly narrow, you’re done in.

blue: actual shadow plane; green: solar fence plane

So, how do you figure out what you can build? We create 3D computer models, and reverse engineering the shadow, to determine the available building envelope. This can be very tricky or very simple based on the orientation of the lot and house, the neighbor’s property, etc. Can you or anyone else simply come out to your property, take a look-around and give you an answer – NO. Believe me, this is not a pitch for trying to get more work as architects. I am pretty sure that no architect likes doing this stuff, it certainly isn’t why I spent 7 years getting Bachelors and Masters degrees.

Now that you have done all that work, you simply have to overlay the Bulk Plane restrictions, wall articulation requirements, the maximum building coverage restrictions, the Floor Area Ratio restrictions, any easements, flood zone restrictions and of course all setbacks and building height restrictions and you have a clear picture of what is your potential building. Easy. Do all these restrictions help protect our neighborhoods – yes. Are they restrictive and simple to figure out – no.

For the past number of years now the costs for installing photovoltaic panels have dropped significantly and the rebates have made this work an almost standard part of most of our projects. It appears that the City’s forethought all those many years ago was indeed brilliant prognostication. As you do not currently take into account the shadows of surrounding trees (although your solar panel provider certainly does), let’s hope that the pending Tree Protection ordinance does not make this all more complicated.

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Boulder's Solar Shadow Ordinance

Many decades ago, in an effort to ensure that the City of Boulder’s citizen’s houses always have the access to the sun, the City passed a Solar Shadow Access ordinance. If you have done any building work in town you have certainly run into this rascal as it applies to all residential districts and can be particularly tricky.

NOT ALL PROPERTIES ARE THE SAME This solar protection rule projects the potential shadow from new construction as calculated between 10am and 2pm as it would be on December 21st. This means that the shadow is a wedge casting north and 30 degrees east and west of north. So, if you live on the south side of an east-west street, your shadow casts mostly into the street. If you live on the north side of an east-west street you are a bit disadvantaged as your shadow most likely begins to violate the regulation by casting into your neighbor’s property. On north-south streets, this regulation pushes new work to the south side of the property to avoid solar trespass at the north edge.

available building area, north-south vs. east-west street

THE SIMPLE ANALYSIS In its simplest form, different areas of the city are divided into Solar Access Areas, one having a 12′ high solar fence, one a 25′ high solar fence. A solar fence is basically a theoretical plane of described height on the property lines. Based on a formula of pitch, you can build new construction as long as the pitch of the shadow of the new work does not cross your property line. The formulas are based on the assumption of the height of your Solar Access Area’s fence. That’s the simple part.

actual and solar fence site plan analysis

THE PAIN-IN-THE-BUTT ANALYSIS If your proposed work’s shadow as defined by the formulas described above, does NOT fall within your property lines or your lot is not “level”, you have to execute a solar shadow analysis based on Actual Shadow Lengths. A “level” lot is a point of contention as you can imagine and the process for creating this analysis is essentially to plot the shadow lengths twice, once for a level lot, then adjust the length of the shadow based on the change of grade between the end of the shadow and the projecting element. What is particularly tricky about this is the impact of the location of your neighbor’s house relative to their setbacks. Your new construction can only cast as far into their property as they are NOT allowed to build, in other words, it can fall into their setback but no further. Many zoning districts in Boulder have a rule that the combined sideyard setbacks of a property need to be 15′, but either side can be as small as 5′ as long as the total is 15′. If your neighbor’s house, on the north side your property conjoins, is 5′ away from the property line, then the Actual Shadow Length restriction can be a project killer. If your property is also on a north-south street and fairly narrow, you’re done in.

blue: actual shadow plane; green: solar fence plane

So, how do you figure out what you can build? We create 3D computer models, and reverse engineering the shadow, to determine the available building envelope. This can be very tricky or very simple based on the orientation of the lot and house, the neighbor’s property, etc. Can you or anyone else simply come out to your property, take a look-around and give you an answer – NO. Believe me, this is not a pitch for trying to get more work as architects. I am pretty sure that no architect likes doing this stuff, it certainly isn’t why I spent 7 years getting Bachelors and Masters degrees.

Now that you have done all that work, you simply have to overlay the Bulk Plane restrictions, wall articulation requirements, the maximum building coverage restrictions, the Floor Area Ratio restrictions, any easements, flood zone restrictions and of course all setbacks and building height restrictions and you have a clear picture of what is your potential building. Easy. Do all these restrictions help protect our neighborhoods – yes. Are they restrictive and simple to figure out – no.

For the past number of years now the costs for installing photovoltaic panels have dropped significantly and the rebates have made this work an almost standard part of most of our projects. It appears that the City’s forethought all those many years ago was indeed brilliant prognostication. As you do not currently take into account the shadows of surrounding trees (although your solar panel provider certainly does), let’s hope that the pending Tree Protection ordinance does not make this all more complicated.

Boulder lot sizes and regulations

In conjunction with last Fall’s debates over the new City of Boulder Compatible Development regulations, the Planning Department posted a lot of information regarding the studies that were done in support of this legislation.  One of the most interesting maps made available was a color-coded map of the city based on lot size.  The largest lots were red to orange and the smallest blue to purple.

What struck me about this map was how the distribution of lot sizes across the city corresponded with the topography of the city.  Below is my version of the map, with the predominant high ground or mesas circled.  With some exceptions, the largest lots tend to be on the high ground.  Anyone who has lived in Boulder for any time would certainly recognize the map as also a fair approximation of house cost as well – larger lots, nicer views = more expensive.

What I found most interesting are the consequences of topography for the development of single-family houses.  The mesas and high ground areas were often the most coveted and were the first to have large private homes built, for the most part individually designed houses.  The larger sections of relatively flat land between mesas and sloping down from steeper slopes were more easily subdivided into smaller parcels.  Most importantly, these often developer-driven sections of the city were laid out with predominantly north-south running streets as opposed to the east-west streets of the mesas (which are more dictated by the topography).  In central and north Boulder these north-south streets were arranged in normative north-south blocks with few houses on the east-west connector streets.  In south Boulder, the north-south streets were subdivided into very long blocks.

I think that this development pattern was arrived at fairly innocently, without many of the current regulations as to building coverage, bulk planes, solar shadow regulations and house size in place.  However with the increasing overlay of each new regulation, even with a sliding scale of application with regard to lot size, the implications of the initial development pattern, north/south vs. east/west, has lead to a disproportional impact of regulatory restrictions.  Of greatest importance is the implications of the overlay of the new Compatible Development bulk plane ordinance with the Solar Shadow regulations on the smaller lots in the areas of the city with the north/south street orientation.

A combination of small lot size and shadow casting prohibitions on quite close neighboring properties makes additions to these properties significantly more challenging than other locations throughout the city.  That the overlay of multiple city regulations have a greater impact on lower cost properties may be of no surprise to conspiracy theorists, but I do not think that these impacts have been recognized by Planning staff, City Council or the public.  I don’t want to throw the baby out with the bath water, but some reconsideration of not just the Compatible Development regulations but also the existing Solar Shadow ordinance ought to be undertaken with regard to street orientation.  I wouldn’t advocate an even more complicated set of rules parsing these properties but some consideration ought to be given to the implications this map reveals.

Pops and Scrapes, new Boulder regulations, Part II

Side Yard Bulk Planes

As part of the recently passed Compatible Development regulations, the City of Boulder has included a bulk plane restriction.  This regulation limits any new construction or addition from building beyond a projected line starting 12′ above the property lines and sloping inward at 45 degrees.

Bulk Planes

As a real-world application, the impacts to possible second-story additions are significantly more restrictive than those imposed by the previous set of regulations.  As mentioned in the first post about these regulations, the devil is in the details, or more specifically in the combination of the new regulations with the existing solar shadow ordinance.

For so many homes in the affected areas, one side of the house is within 5′ of the property line in accord with the setback regulations.  This means any possible second story addition would be limited similar to the above diagram.  The available interior space of this addition is significantly lower than previously allowed as the head height at the edge of the room is now under 6′.

3oth street 2

Under the older regulations, Boulder pop-tops tended to be partial extensions of the floor below, weighted to the south side of the property to avoid the solar shadow restrictions.  As in the photo above, the addition to the original ranch created a distinctly either right-sided or left-sided house depending on what side of the street the property was located (again, driven by shifting this mass to the south side of the property).

The new bulk plane regulations will either shift this kind of the addition down, making it more like a series of dormers sticking out of a new roof, or shift the south side of the addition closer to the center creating a kind of bubble addition sitting on a ranch house.  There are some exceptions allowed for penetrating the bulk plane, however, most of the existing houses are not of a size to take advantage of some of the them.

So, the regulations may encourage more wedding-cake style houses with reducing layers as the building moves upward.

wedding cakes

The former regulations lent to additions that created a kind of asymmetrical balance – playing the long, low horizontal lines of the ranch house against the vertical lift of the addition.  Weighted to one side, this composition often closely paralleled the plan of the house, with public rooms of living room, dining room, kitchen, etc. on one side of the house and bedrooms on the other.

The wedding-cake style of house creates an entirely more complex composition, being neither predominantly horizontal or vertical.  The local architects, and especially builder/designers, will need to work harder to make each house or addition sympathetic to its neighbors and architecturally worthy.