This document provides design specifications for gutters, downspouts, catch basins, and a grease trap for a two-story building. It first calculates the roof area and rainfall flow rate to size the gutters at a minimum depth of 67.7 mm. Downspouts are designed to drain the gutter volume in 5 seconds using 3-inch diameter pipes. Catch basins are sized based on drainage areas and a 5-minute holding time. Culvert pipes for the catch basins should be a minimum of 2 inches. Finally, the grease trap volume is calculated based on either the sink volume or a flow rate times a 5-minute holding time.
1. Design of Gutter, Down
Spout, Catch Basin, and
Grease Trap for two storey
building
Engr. Marlon D. Mata, RMP
Master of Engineering in Mechanical Engineering (CAR)
Instructor, Dep’t of Mechanical Engineering
Cebu Technological University-Danao City Campus
Philippine Society of United Master
Plumber (PSUMP) – Cebu Chapter
3. Gutter Designing
Solving for Area of roof;
Area of roof = Total Roof Area – Total Area of
Spaces
Area of roof = [8.65m*9.32m]-
[(4.35m*4.85m)+(1/2*1.08m*9.32m)]
Area of roof = 54.5 sq.m
4. Gutter Designing
Solving for Volume flow rate of rainfall;
Volume flow rate of rainfall = [Area of roof, sq.m * Rainfall
Intensity, m/s]
Where,
Rainfall Intensity on Super Typhoon Yolanda is 11.1” in 12hrs.
(11.1”/12hrs) x (1’/12”) x (1m/3.28’) x (1hr/3600s) = 0.00000653
m/s
Volume flow rate of rainfall = [54.5 sq.m x 0.00000653m/s]
= 0.000356 cu.m/s
In GPM,
0.000356 cu.m/s x (35.29cu.ft/cu.m) x (7.48gal/cu.ft) x (60s/1min)
= 5.64 GPM
5. Gutter Designing
Sizing of Gutter;
Volume of Gutter = [Volume flow rate of rainfall, cu.m/s x
Holding time, sec]
Advised holding time in gutter is 3 mins or 180 sec.
Volume of Gutter = (0.000356 cu.m/s) x (180 s)
= 0.06408 cu.m
Length of gutter: 7.57m
Assume Width of the gutter: 5in or 125mm/1000 = 0.125m
Minimum depth of gutter= 0.06408 cu.m / (0.125m x 7.57m)
Minimum depth of gutter = 0.0677m x1000 = 67.7 mm ~ 3 in. or
more.
7. Down Spout Designing
Drain Volume flow rate of DS = Volume of Gutter / Drain Time
Drain Volume flow rate of DS = 0.06408 cu.m / 5sec
= 0.0128 cu.m/sec
0.0128 cu.m/sec = (Area) x Velocity
where, Velocity=√(2 x 9.81 x 0.2 m)
Terminal Velocity= 2m/sec
Area = (0.0128 cu.m/sec ) / (2m/sec)
Area = 0.0064 sq.m.
8. Down Spout Designing
Area / no. of Down Spout = 0.0064 sq.m. / no. of downspout-
designer’s call
At number of downspout =2
Area / DS = 0.0032 sq.m./ DS
Solving for Diameter of Down spout;
D = √[ (4 x Area/DS) / 𝜋]
D = √[ (4 x 0.0032 sq.m ) / 𝜋 ] = 0.064m or 2.5”,
use ( 3”∅commercial size)
11. Catch Basin Designing
Formula for Catch Basin Sizing;
Volume of Catch Basin = (Designed Area x Rainfall Intensity x
Holding time) / No of. CB
Where,
Advised Holding time is 5 mins.
Rainfall Intensity = 11.1”/12hrs or 0.4mm/min or 0.0004 m/min
Designed Areas;
A= 21.1 sq.m.
B= 54.5 sq.m.
14. Catch Basin Designing
VCB3=VCB4= (54.5 sq.m x 0.0004m/min x 5min) / 2 catch basin
= 0.0545 m^3. or 1.923 ft^3 ~ 15 in^3 (inside)
15.
16. Catch Basin Designing
VCB5= (75.6 sq.m x 0.0004m/min x 5min) / 1 catch basin
= 0.1512 m^3 or 5.34 cu.ft. = 21 cu.in.
21 in
21 in
21 in
17.
18. Catch Basin Designing
At standard flow velocity in culvert pipe = 0.75 m/s or 45 m/min.
Solving for minimum diameter,
RI=Rainfall Intensity
D = √( (4 x Total Designed Area x RI) / (𝜋 x std.flow velocity))
Then D for CB1 and CB2,
D = √( (4 x 75.6 x 0.0004) / ( 𝜋 x 45))
D = 0.02925 m ~ 2 in. (minimum)
Therefore, use standard size 8 in. for culvert and 6 in for PVC.
19. Grease Trap
Volume of GT = Volume of Sink (residential) or
Volume of GT = Volume flow rate of grease water x holding time
Where, holding time = 5mins or more
20. Grease Trap
Volume of GT = Volume of Sink (residential)
Example: 0.60 m x 0.40 m x 0.20 m
Volume of GT = 0.048 cu.m
Volume of GT = Volume flow rate of grease water x holding time
Where, holding time = 5mins or more
Example:
The Volume flow rate of grease water is = 1 cu.m/min, Find the
Volume of grease trap ?
Volume of GT = 1 cu.m/min x 5 min = 0.2 cu.m
