Summary of Ordinance
Boulder, Colorado, 1991
In response to the diminishing supply and increasing cost of conventional
energy resources, the City of Boulder has enacted an ordinance to protect
the potential for the use of solar energy. The ordinance guarantees access
to sunlight for homeowners and renters in the city. This is done by setting
limits on the amount of permitted shading by new construction and requiring
that new buildings be sited to provide good solar access.
The degree of solar access protection is defined by either a 12' or
25' hypothetical "solar fence" on the property lines of the protected buildings.
The ordinance is designed to protect access for a four hour period on December
21st. Under most circumstances, new structures will not be allowed to shade
adjacent lots to a greater extent than the applicable solar fence.
By definition, all lots in RR-E, ER-E and LR-E zoning districts are
in Solar Access Area I and are protected by a 12 foot "solar fence." All
lots in LR-D, MR-E, MR-D, MR-X, HR-E, HR-D, HR-X, I-E, and I-D zoning districts
are in Solar Access Area II and are protected by a 25 foot "solar fence."
All other zoning districts, including P-E, A-E, CB-E, CB-D, RB-E, RB-D,
RB-X, TB-E, and TB-D, are in Solar Access Area III and are protected only
through the solar permit process.
A solar access permit is available to those who have installed or who
plan to install a solar energy system and need more protection than is
provided automatically in Solar Access Areas I and II. The permit application
must include detailed information describing the solar energy system, existing
structures and vegetation on adjacent properties and the location and dimensions
of the solar easement requested. Solar access permits do not affect vegetation
which exists at the time of permit application submittal. Solar access
permit application forms are available from the City Department of Planning
and Community Development. The Board of Zoning Adjustment will review applications
and award permits.
Members of the City of Boulder planning staff are available to assist
architects and builders design for solar access and will be responsible
for assuring that all plans are in compliance with the ordinance.
Compliance with the Ordinance
When applying for a building permit, a simple shadow analysis must be
submitted to the Building Department. By knowing the height and orientation
of the proposed building and the slope of the land, the shadow that it
will cast on the 21st of December between 10 a.m. and 2 p.m. can be approximated.
The following steps should be completed and the results submitted with
the building permit application:
1. Draw the proposed site plan. The solar access site plan should
be drawn to scale and show existing improvements and the proposed building
or addition, the property lines, and a north arrow. A site plan with this
information is already required by the City Building Department.
2. Determine the height of the shadow casting portion of the roof.
Label on the site plan the height of corners and peaks of the proposed
3. Draw the approximate shadow cast by the proposed structure.
If your building is on a level lot and if adjacent property to the north,
east and west is part of the same solar access area the following chart
may be used to check that your building's shadow is in compliance with
the ordinance. Use the shadow pattern illustrated below as an example.
Noon shadow lengths are projected directly north on the site plan. The
10:00 a.m. and 2:00 p.m. shadows should be drawn at 30 degrees west of
north and 30 degrees east of north, respectively. After the representative
shadow lines for the four hour protected period have been drawn, simply
connect the outer band of points to determine the four hour shadow pattern.
4. If your proposed structure is not located on a level lot, please
contact the Planning Department for information on adjusting actual shadow
lengths for changes in grade.
5. If the shadow cast is entirely within your property lines, the
proposed building or addition is in compliance.
If the shadow cast by the proposed structure does not fall within
your property lines, you may choose to redesign your project. Alternatively,
you may choose to prepare a shadow analysis based on the actual shadows
cast by the proposed structure. An actual shadow analysis will illustrate
the true impact of all proposed shading on adjacent properties. An actual
shadow analysis will be required to demonstrate that the portion of the
shadow which exceeds the solar fence falls within an exempt area. It will
also be required as part of an application for either an administrative
or a board level solar exception. Please contact the Planning Department
for additional information.
Adjusted Solar Shadow Lengths for Level Grades
In a number of circumstances, even if the proposed structure shades
the adjacent lot more than the solar fence would, the structure may still
be in compliance. Compliance may be demonstrated through completion of
an actual shadow analysis.
1. If your neighbor's property is already shaded by existing buildings,
mountains or other permanent objects (not including vegetation such as
trees), you can build anything which does not add to those existing shadows.
2. If your proposed building or addition would shade part of your neighbor's
property which is outside the building envelope, you are exempt from the
provisions of the ordinance.
3. A minimal amount of shading, as outlined in the ordinance, may qualify
for an exemption and is not prohibited.
If your plans shade the building envelope of adjacent property greater
than the shadow cast by the solar fence, you may have to redesign your
project or apply for a solar exception.
An application for an administrative exception must include the following
a) The applicant's name and address, the owner's name and address, and
a legal description of the lot for which an exception is sought;
b) Accurate drawings showing lot lines, structures, solar systems, dimensions
and topography as necessary to establish how basic solar access protection
on nearby lots would be affected by the exception, together with the graphic
representation of the actual shadows that would be cast by the proposed
structure during the period from 10:00 a.m. to 2:00 p.m. on December 21;
c) A list of all lots that may be affected by the exception, including
the names and address of all owners of such lots;
d) A statement and supporting information describing the reasons that
less intrusive alternatives cannot or should not be implemented; and
e) A statement certifying that the attached property owner has seen
the actual shadow analysis and does not object to the additional shading.
A public hearing before the Board of Zoning Adjustment will be required
when either the affected property owner objects to the increased shading
or staff finds the proposal does not meet the criteria for a solar exception.
An application for an exception from the Board of Zoning Adjustment is
available from the Planning Department. Solar Siting in New Construction
The ordinance sets standards for the siting of new development. It requires
that, to the maximum extent feasible, all units in new developments which
are not planned to incorporate solar features have:
a) their long axis within 30 degrees of east-west;
b) roofs which are physically and structurally capable of supporting
at least 75 square feet of solar collectors per dwelling unit; and
c) unimpeded solar access through the provisions of this ordinance or
through private covenants.
Non-residential buildings have similar requirements for siting. The
following figure is an example of a small project where 100% of the units
are sited in accordance with the provisions of this ordinance.
Typical Subdivision Site Plan
The planning staff or the Planning Board may waive the solar siting
requirement for reasons of topography or lot configuration, substantial
planning and design expenditures incurred before ordinance passage, or
reduction in other aspects of energy efficient site planning (density,
transportation). The incorporation of solar energy systems or other renewable
energy sources may also be viable alternatives to the solar siting requirements.
If you have any questions or would like more information about requirements
of the solar access ordinance, please contact the City of Boulder Department
of Planning and Community Development at (303) 441-3270.
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