APPROVED BLD2021-0520+Letter_fron_Arch+1.6.2022_3.03.22_PM+2607748REVISION
Jan 06 2022
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
January 5, 2022
Kyle Jones
Senior Project Manager
Ameresco Inc
222 Williams Ave South, Suite 100
Renton, WA 98057
Dear Kyle:
BLD2021-0520
AMMR - FOR
STEEP STAIRS
■ See AMMR Request
Form for approval by
1 L. Bjorback 1 /28/2022 1
' City of Edmonds ■
Building Division 1
K PUX
Interdisciplinary Design
3131 Elliott Avenue Suite 400
Scattic, .AJA 98121
P 1206.286.1640
www.kpg.com
■ Revised plan sheets ;
include A-4, A-5, A-7,
1 A-8, A-9. '
Plans for renovations at the Edmonds WWTP include a new stair system between the utilidor
landing and the new upper floor level. There is a 138" (11'-6") vertical distance between those
levels. Current approved plans for that area show an alternating tread stair. The stair is shown
on pages A-4, A-5, and A-7 in the approved construction drawings.
The horizontal space available for a stair run is very limited at this location. Large equipment
sizes, specific connection requirements, and existing and new structural elements constricts the
useable space. Plan views of the levels in questions are shown below.
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New Upper Floor at Alt Tread stair Utilidor Platform at base of Alt Tread stair
An initial version of this design showed a steep stair between these floors (8-5/8" risers and
10-3/8" treads). This stair was flagged as non -compliant during plan review. In the final for -
construction drawings, an alternating tread stair was shown. An alternating tread stair is a code -
compliant means of allowing a steeper ascent angle per IBC 1011.14. The alternating tread stair
had individual risers of 7-1/4" and treads offset 5", for an effective riser height of 14-1/2" and an
effective tread depth of 10". Section views of these two different stairs are shown below.
Proposed Steep stair
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Current approved Alternating tread stair
The stair in question provides a convenient means for staff to traverse between the utilidor
and solids handling floor levels, occasionally carrying tools or parts for equipment. Staff and
management at the WWTP are concerned about the practicality of the alternating tread design.
They can be challenging to learn how to use them. Hand -carrying items interferes with proper
use of the handrails. Staff and management would both prefer a steep stair at this location. This
AMMR is for a code exemption for a steeper than the IBC 7" maximum riser height in lieu of an
alternating tread stair or ladder.
The reasoning to limit riser heights comes from several factors. Steeper stairs are more
difficult to traverse, slowing travel speeds in an emergency. Overly tall stair risers are physically
challenging for some occupants, further reducing travel speed and increasing the odds of a fall.
As the number of occupants goes down, and the mobility of those occupants remains high, it can
be considered safe to allow steeper stair runs.
One example of steeper stairs allowed is in the OSHA regulations covering stairs used to access
equipment and work platforms. OSHA chapter 19.25 regulates the construction of stairways used
for these purposes. See OSHA Regs here Those regulations allow for a steeper, narrower stairs
with less hand and guardrails because of the low occupant counts and their better -than -minimal
mobility.
Given the low load and reasonable mobility of the occupants in this space, it is reasonable to
compare this exiting situation to the equipment access stairs under OSHA regulations. This
proposed steep stair at this location will meet all OSHA rules for stairs, providing an acceptable
level of safety. There are several factors that make this modification NOT reduce occupant
safety:
1- This is a second exit from the space in question. IBC 1006.2.2.1 requires
two exits from incinerator rooms. One of those exits is allowed to be a fixed
ladder or alternating tread stair. The proposed steep stair will be only one of
the two required exits. There will remain a fully IBC -compliant stair in the NE
corner of the basement that will accommodate typical day-to-day travel.
2- There is a very low occupant load in this area. Occupant loading per IBC
Table 1004.5 is 7 for each floor. Such a low occupant load reduces the chance
of overloading and crowding this part of the exit system.
3- There are no members of the unaccompanied public here. Only trained
staff will be traversing this area. Having occupants familiar with this facility
reduces the chance of dis-orientation during an emergency.
Attached are revised drawing sheets from the April permitting set showing the proposed steep
stairs. A-4 shows the lower landing, A-5 shows the upper level and stair plan, and A-7 shows the
stair in section. The stair is shown clouded in blue on all sheets. Upon approval of this AMMR,
these changes would be incorporated into the construction documents and used as a basis for
final detailing and approval of the stairs in question.
Based on the above, it is this architect's professional opinion that allowing the installation of a
steeper stair at this location complies with the intent of the building code. A steep stair meeting
OSHA standards will not adversely impact occupants' ability to exit the building nor unacceptably
reduce the safety of the exiting system.
Please contact me if you have any questions or feedback. I look forward to your favorable reply.
Yours,
X),� 4,� �,
Bryan Schutt, Architect KPG
WA license number 12404
Enclosure: 3 drawing sheets