HomeMy WebLinkAbout08142008 ZPC Agenda Item 4
List of Concepts and Guidelines
Excavations and Underground Structures
August 14, 2008
At the meeting on July 10, 2008, the Zoning and Planning Commission comprised a
list of agreed upon concepts and guidelines to use in possible regulation
development regarding excavations and underground structures. Two basic concepts
that will apply to all of the possible regulations are:
1. Keep regulations Simple and straightforward
2. Look to pool construction rules for guidance
The basic purposes of the regulations seem to be centered on protection of
adjoining properties and safety of the structures and its occupants. The
following concepts and the areas of responsibility between ZPC and the BSC, as
well as affected code references are listed below:
Zoning and Planning Commission {ZPC} Zoning Regulationsl
A. Second form of egress (window) to the rear of property only. {ZPC}
[Article II Definitions; Table 7-2 Setbacks; or Table 7-6 Projections]
B. Basement may only be located beneath building footprint. {ZPC} [Table 7-2
or Table 7-6]
C. Basement may not be located in an easement. {ZPC} [Table 7-2 or Table 7-
6]
D. Basement may not be located closer than 5 feet to the side property line.
{ZPC} [Table 7-21
E. Does not count as pervious area (for underground structure located in a
front or rear yard). {ZPC} [Table 7-6]
F. Limit framed area and number of stories (based on increased density and
possible impact on infrastructure). {ZPC} [Article II Definitions of
Framed Area]
G. Limit basement area to 50% of area of floor above {ZPC} [Article II
Definitions-either definition of basement or half-story]
H. Restrict uses and occupancies (storage and non-sleeping area only){ZPC}
[Article II Definitions]
Building and Standards Commission {BSC} [Chapter 18 Development Regulations and
Appendix C - Technical Codes Schedule]
A. Special engineering and hydrostatic pressure questions {BSC} [Technical
Codes and Drainage Regulations - Chapter 18]
i i
B. Drainage provisions must be included {BSC} [Drainage Regulations-Chapter
18]
C. Sill heights for egress from basement areas {BSC} [Technical Codes]
D. Require a wider staircase (for safety/egress) {BSC} [Technical Codes]
E. Sprinkler requirements for the structure {BSC} [Technical Codes - Fire
and/or Building Code]
F. Assume it will flood and protect against consequences {BSC} [Chapter 18 -
Flood Prevention Regulations]
G. No sanitary facilities below grade {BSC} [Technical Codes - Building
and/or Plumbing Code; Flood Prevention Regulations]
H. Vertical (inside) access only (no ramps or exits to outside) {BSC} [Flood
Prevention Regulations]
i
EXCAVATIONS AND UNDERGROUND STRUCTURES
By Debbie Scarcella, city Planner-, June 9, 2008
The key issues regarding excavations and underground structures are as follows:
I . A. Should the underground structure project into the yards and if so, then how much?
Should the excavation area be allowed to project into the yards'? (ZPC)
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B. Should underground structures be allowed on narrow lots taking the 3/7 alternate side
yard exception'?
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2. If an underground structure is allowed in the yard areas, should there be special rules for
lot drainage regulations? (BSC)
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3. Underground strictures in the 100 year floodplain are strictly controlled. Should there be
additional regulatory language controlling the basements outside the 100 year
toodplain?(BSC)
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4. Should there be additional engineering criteria for the foundations of underground
structures? (BSC)
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5. Should the area included within the walls of an underground structure be counted toward
framed area'? (ZPC)
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6. Should the area included between the floor and ceiling of an underground stricture be
counted as a story? (ZPC)
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7. What types of uses of an underground structure will be allowed? (ZPC or BSC)
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Sallye Clark
From: Debbie Scarcella
Sent: Wednesday, June 11, 2008 11:04 AM
To: Sallye Clark
Subject: FW: ZPC Meeting of June 13, 2008
Attachments: Underground structures.doc
o; Jo cU lvs~;,.,~Y"i~ aePiher,3 --:nd then let's m_,i!o, hard,--'cc s '~1t"?t:~Y~a0Y104V 1151t) T"ank ou.
From: Richard Yehle [mailto:reyehle@comcast.net]
Sent: Tuesday, June 10, 2008 8:01 PM
To: Debbie Scarcella
Cc: Sallye Clark
Subject: ZPC Meeting of June 13, 2008
Debbie,
I will not be able to attend the ZPC meeting on Thursday due to attending my daughter's graduation in Boston.
Nevertheless, I wish to offer comments on Items #3 and #4 of the agenda.
3. Variances and special exceptions
I am still struggling with item #6 of the Special Exception language. Making it a requirement that the violation must
eventually be cured (even at reasonable cost and at some future time) in order to get the Special Exception seems to go
against the purpose of the Ordinance. I point to the Vanesko steel-frame roof as an example of something that could
never be realistically fixed, yet by all reports (I have heard) was not an issue to anyone in the neighborhoods.
So long as the other provisions of the ordinance are properly evaluated and there is no significant impact on another
person (#5), it seems that #6 could offer two solutions. The first would be the requirement proposed to remedy the
violation at "modest or reasonable" cost whenever possible. Perhaps the reasonableness of the cost dimension could be
defined in either absolute dollars or expressed as a percentage of the fair market value of the structure at the time the
Special Exception is granted. The second would allow the violation to exist on a grandfathered basis under the theory
that it is doing no harm and is too expensive to fix. Once either course is determined, it could not be altered except by
another ZBA Special Exception, which presumably would be very difficult to achieve.
4. Excavations and Underground Structures
I have annotated the Staff analysis included with the Agenda. My comments are obviously without the benefit of
discussion and therefore should not be taken as final. However, I am reasonably resolved that underground space should
not be considered as Framed Area and probably should not count toward the 2 '/z story rule. Please see the attached
document.
Regards,
Dick Yehle
ZPC Commissioner
i
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EXCAVATIONS AND UNDERGROUND STRUCTURES
The key issues regarding excavations and underground structures are as follows:
1. A. Should the underground structure project into the yards and if so, then how
much?
Should the excavation area be allowed to project into the yards? (ZPQ
Table 7-6 of the Zoning Regulations lists those items allowed to project into the
regulated yards. Underground items are not restricted at all as to the limits of their
encroachment into these yards. Conceivably, a basement would technically be allowed
to span the entire building site from property line to property line unrestricted.
For the sake of protecting neighboring properties from damages arising from
subterranean encroachment "standard" sideyard and rearyard setbacks should
apply. An exception might be made for frontyard setbacks, perhaps allowing
development to the street setback line or perhaps only to the allowed front porch
projection.
Excavation should be managed on a case by case basis considering existing
structures, driveways and trees, but in no case be closer than 3 feet to the
property line. While that limitation might impede some underground construction,
it would avoid issues such as already exist with neighboring properties being
encroached by some construction jobs such as brick laying.
B. Should underground structures be allowed on narrow lots taking the 3/7
alternate side yard exception?
'Marrow lots (less than 55' wide) are given an option to use alternate side yards. This is
allowed to encourage rear situated garages. If a structure built underground on a narrow
site is constructed when taking the alternate side setback allowance, should there be
limits and restrictions on the proximity of the basement wall and the excavation to
adjoining property lines.
As suggested in A. above, for the purposes of protecting adjoining properties,
underground structures would not be eligible for the 317 alternate sideyard
exception but could be built with the standard 5 foot (or 10%) setback. The 317
rule could still apply to the above ground parts of the structure.
2. If an underground structure is allowed in the yard areas, should there be special
rules for lot drainage regulations? (BSC)
Chapter 18 provides regulations for building site drainage and controlling the runoff rate
based on a 1" per hour rainfall. Slabs on grade will provide a small amount of pervious
area underneath the foundation for water absorption. If a full basement is built, will this
Note: Comments in Italics are those of Dick Yehle prepared 6/10/08 1
r
impact the drainage in a significant enough manner to require additional drainage
measures not specified in Chapter 18?
The incidental water storage under a slab is too small to be a factor and should
be ignored. Evidence suggests that too much credence is given to the water
absorption capabilities of West U soil. Once the soil is saturated, which is said to
happen quickly.. unpaved areas don't retain much more water than paved areas.
The site drainage rules should continue to be enforced, especially for any sump
pump drainage originating from the underground structure.
3. Underground structures in the 100 year floodplain are strictly controlled.
Should there be additional regulatory language controlling the basements
outside the 100 year floodplain?(BSC)
Enclosed portions of structures located in the 100 year floodplain which are below the
base flood elevation are not allowed unless they meet criteria established in Section R323
of the 2003 IRC and Chapter 18 Article 1X of the city's Code of Ordinances. There are
no similar regulations for structures outside the Floodplain.
Appropriate floodplain rules should apply.
4. Should there be additional engineering criteria for the foundations of
underground structures? (BSC)
Appendix C of the Code of Ordinances deals with the Technical Codes and amendments
to those codes. West U has amendments dealing with requirements for different types of
foundations. Basement walls are not addressed in this amendment. Section R403 of the
2003 IRC addresses some aspects of basement constriction, but does not address
proximity to adjacent sites, depth of excavation, etc.
Standards for basement walls and floors should be developed, to include any
,,ssues with subterranean drainage. There could be issues of sump pump
discharge into the sanitary sewers to consider.
5. Should the area included within the walls of an underground structure be
counted toward framed area? (ZPQ
Framed area definition in Article 2 of the Zoning Regulations lists basements of a certain
depth and less than 8' ceiling height as an exemption to inclusion in the framed area
calculations.
The concept of framed Area is concerned with managing the appearance of bulk
In a structure not its overall si-e. Therefore (the subterranean part of)
basements should not count toward Framed .Area.
Note: Comments in Italics are those of Dick Yehle prepared 6/10/08 1
6. Should the area included between the floor and ceiling of an underground
structure be counted as a story? (ZPC)
The current definition of a story in the zoning regulations would include the basement as
a story for compliance with the 2 !iz story rule. If certain basements do not count toward
framed area, then should they be counted as a story'? Or if we count the basement area as
a story, should it be counted toward the maximum allowable framed area?
As with the Framed Area rule, the 2 '%2 story rule is in part primarily intended to
manage the appearance of size in structures. Space below grade does not add
to size and should therefore not a be a factor. (See #7 for further comments.)
7. What types of uses of an underground structure will be allowed? (ZPC or BSQ
Any enclosure located below base flood elevation is limited to parking access to the
structure, and storage. We could limit a basement to these uses only and not allow any
habitable areas in a basement.
An additional consideration of the 2 ,z story rule is the safety of living areas on
the "third" floor, especially egress. To the extent habitable areas are allowed in
basements, minimum standards for stairwells and windows should apply.
An additional concern might be with parking in basements. Having vehicles
under the house with limited means for emergency crews to access the space
(i. e. realistically only the driveway), could be an issue. Also the standards for
driveway access to a basement garage may need special consideration about
the angle of descent and possibly uncontrolled storm drainage.
Note: Comments in Italics are those of Dick Yehle prepared 6/10/08 3