20111026095732174.pdfJune 1, 2008
To: Edmonds Building Department SOLTNER GROUP
architects
Re: Drainage Calculations for:
Mariner Condominiums, Building B
555 Alder St., Edmonds, WA, 98020
Building Enclosure Repairs
00
To whom it concerns: W
This document contains roof drainage calculations for the building B roof 6P
areas. These calculations were established using appendix A-7 of SMACNA 0 N)
0)
(Sheet Metal and Air Conditioning Contractors' National Association, Inc., CYI
Fifth edition. 0
co
These calculations determine the required length for the scupper(s) in the
described location.
A rainfall intensity of 5 minutes exceeding only once in 100 years was
determined from Table 1-2, column B for the Seattle, Washington area.
IPH (Rainfall Intensity) - 3.3 inches per hour
H (head of water) - I
Constant - .0104
SF - Drained roof area in square feet
GPM (GALLONS PER MINUTE) = (.0104) IPH x SF
Calculations are as follows:
Total square feet of roof - 1,575 sq. ft.r.
.5 (1575) = 788 (2 scuppers equally dividing roof drainage area). 0
Z)
SF = 788 CD
G)
GPM = (.0104) (788) (3.3) = 27.04 0
0
D
Per table A7-1, a scupper with a width of 10" is capable of draining up to 29.3
GPM. A 10" scupper will be used with a 3" downspout at both ends of the
butterfly roof.
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Stairtower and elevator penthouse roofs at the southwest corner:
Total square feet of roof - - 106 sq. ft.
Only one scupper will be calculated for the full load. The smaller roof drains
onto the slightly larger one below (stair penthouse). This scupper size will be
calculated. The roof above will utilize the same size scupper and downspout.
GPM = (.0104) (106) (3.3) = 3.64
Per fable A7-1, a scupper with a width of 4" is capable of draining up to 11.0
GPM. A 4" scupper will be used with a 3" downspout at both scupper
locations in this area.
Stairtower penthouse at the northeast corner:
Total square feet of roof - - 116 sq. ff.
Only one scupper will be required to drain Phis small roof area.
GPM = (.0104) (1 16) (3.3) = 3.98
Per table A7-1, a scupper with a width of 4" is capable of draining up to 11.0
GPM. A 4" scupper will be used with a 3" downspout at this scupper location.
Roof deck area at penthouse:
The roof will be drained at the north and south ends of the structure into
sumps as shown on the roof plan and elevations.
The roof drainage area is divided slightly unequally, with the south side having
more drainage area. The calculation will be done for the south side, and
scupper sized equally at the north side.
South side drainage area (SF) - 1368 sq. ff.
GPM = (.0104) (1368) (3.3) = 46.9
Per fable A7-1, a scupper with a width of 18" is capable of draining up to 53.4
GPM. An 18" scupper will be used with a 5" downspout at these locations on
the north and south of the roof deck.
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