HomeMy WebLinkAboutLot Certifications - 01/22/2020 (2) 7200 South Alton Way, Suite C400
Centennial, CO 80112
303-740-9393 x Fax 303-921-7320
3930 Sinton Road, Suite 219
Colorado Springs, CO 80907
719-593-2593 x Fax 303-921-7320
X 2900 South College Avenue, Suite 3D
Fort Collins, CO 80525
970-491-9888 x Fax 303-921-7320
MEMORANDUM
To:City of Fort Collins, Bldg Dept.
From:Rebecca Brush, PE
Date:01-21-2019
Subject:1624 Remington Street – Drainage Certificate Supplement
Certification of Lot Grading - Supplement
Item:
3.Not all elevations are within 0.2’ of the approved grading plans, the drainage patterns are similar
to the existing condition with less actual new impervious area than proposed, and the as-built survey is in
conformance with the attached stormwater approved grading plan and drainage analysis memo dated
October 13, 2017.
4.All grades surrounding structures are at least 6’’ (0.5’) below TOF, except at the concrete patio off
of the west side of the secondary structure near the middle of the south property line where the grades are
+/- 3’’ (.25’) below TOF. This is a small portion of the site that is already covered in gravel and the
grades drain away from the buildings.
5. Due to the existing flat nature of the site and the proximity of the two structures, there is a
minimum grade of 3.5% away from the structures within the first 5 to 10 feet. The area with this
minimum slope is covered in gravel and flagstone.
6. Due to the existing flat nature of the site and the proximity of the two structures, there is a
minimum grade of 0.6% in the swale between the two structures. The area with this minimum slope is
covered in gravel and flagstone. All other areas meet the minimum requirement of 1%.
8.All downspout locations are shown and runoff is directed into swales around the building, there
are two point at which runoff is directed to the southern property line with no apparent property line
swale, the as-built survey is in conformance with the attached stormwater approved grading plan and
drainage analysis memo dated October 13, 2017.
11. It is industry standard to certify the grades prior to landscape installation. The landscaping was
not complete at time of survey. Landscaping or temporary seeding/erosion control should be installed as
soon as possible to prevent erosion of the bare soil.
12. The site was not at the stage of “final clean-up” at time of as-built survey for the drainage
certificate, but the final grades and exterior elevations had been set.
A Subsidiary of Westrian
FINISH FLOOR
DINING ROOM
EL:4989.20
FINISH FLOOR
BEDROOM
EL:4987.82
FINISH FLOOR
SHED
EL:4988.03
AIR CONDITIONING PAD
DOWN SPOUT
LOCATION
DOWN SPOUT
LOCATION
DOWN SPOUT
LOCATION
DOWN SPOUT
LOCATION
GAS MAIN
AIR
CONDITIONING
PAD
FOUND IRON REBAR
PROPERTY CORNER
N: 1449282.247
E: 3118023.857
EL: 4986.55
FOUND IRON REBAR
PROPERTY CORNER
N: 1449332.315
E: 3118023.889
EL: 4987.40
REMINGTON STREET
DRAINAGE FLOW ARROW
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WOOD FENCE
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WOOD FENCE
CONCRETE PATIO
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LIVING ROOM
EL:4987.28
FINISH FLOOR
ENTRANCE
EL:4989.66
FINISH FLOOR
LIVING ROOM
EL:4989.59
FINISH FLOOR
MASTER BED
EL:4989.59
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7200 South Alton Way, Suite C400
Centennial, CO80112
303-740-9393 x Fax 303-921-7320
130 East Kiowa Street, Suite 400
Colorado Springs, CO80903
719-593-2593 x Fax 303-921-7320
2900 South College Avenue, Suite 3D
Fort Collins, CO80525
970-491-9888 x Fax 303-921-7320
MEMORANDUM
JR Engineering, LLC has completed a weighted imperviousness based storm drainage evaluation for
the 1624 Remington Street project. The following is a summary of the findings and determinations
made while performing an analysis of the proposed home addition and new garage remodel space in
order to determine the site’s ultimate drainage characteristics based on a direct comparison of
weighted impervious surfaces in their existing, Phase 1 and Phase 2 states. It is important to note three
things while reviewing this memo. First, we believe that this project will not be required to provide
water quality or detention facilities, based on the gross addition of only 769sf of new impervious
surface. Second, this analysis has been performed using a “weighted impervious area” calculation,
which is the square footage of each impervious surface type, multiplied by the surfaces weighted
impervious coefficient values for infiltration characteristics of different materials (< 1). The
impervious coefficient values were derived from Urban Drainage and Flood Control District’s Table
6-3 “Recommended Percent Impervious Values”. Lastly, the construction will be done in two phases.
The first phase includes removal of large existing flagstone areas and a green house, and the
construction of a garage addition and installation of a hot tub. Phase 2 involves the construction of a
home addition, which will utilize roof slope and a gutter system that reroutes rooftop stormwater run-
off to Remington. The sites Existing Condition, Phase 1 and Phase 2 improvements may be seen on
their respective maps within Appendix C.
The existing 1624 Remington Street project site is located along the east side of Remington Street
North of Parker Street and south of Prospect Road as seen on the vicinity map in Appendix A. The
property currently supports an existing 1-story home, which covers an approximate footprint of 880 sf.
Just east of the house lies an existing one car garage, a small greenhouse, and further east a shed. The
site is composed of type C soils and generally, slopes from 0 to 2 percent towards the lot’s southern
property line. The existing site also contains a large amount of flagstone paving, a wood deck and a
gravel parking area at the northeast corner of the site. A specific breakdown of weighted impervious
areas can be found on the Existing Condition Map within Appendix C. The portion of runoff that
flows off of the front half of the existing home and front yard sheet flows west into the curb and gutter
along Remington. All stormwater runoff generated from the east side of the existing house roof peak,
to the eastern property line at the alley, sheet flows to the adjacent southern property line and the
alleyway.
To:Mr. Shane Boyle, PE
From:Tim Halopoff, PE
Date:October 13, 2017
Subject:1624 Remington Street Project – Weighted Impervious Drainage Analysis
Phase 1 construction will include removal of all the flagstone surfaces, removal of the greenhouse and
removal of the concrete slab near the rear shed (shed will stay). Phase 1 work will also include the
addition of 497 sf of gross rooftop surface. All of this may be seen on the Phase 1 Plan found in
Appendix C. This proposed Phase 1 garage addition, along with the removals, essentially adds no
new, net impervious surface to the site, because the weighted imperviousness of the improvements of
Phase 1 are less than that of the existing garage, outdoor impervious hardscape (flagstone and concrete
pad) and the small greenhouse that are all being removed. The summation of newly added impervious
areas can be found within the Phase 1 table located on the Phase 1 map in Appendix C. It is important
to note that the densely spaced flagstone is assumed to have an impervious value of 0.8 due to gaps
between the stones. Considering all weighted impervious areas before and after Phase 1, there is less
weighted imperviousness following Phase 1 construction than in the existing condition. Therefore, it
follows that Phase 1 should have no negative drainage impact to the southerly neighbors.
Phase 2 involves the construction of a home addition, which may be seen on the Phase 2 Map in
Appendix C. Runoff generated from the proposed home addition will be routed north via rooftop
gutters, then routed west, along the north property line to the curb and gutter on the east flowline of
Remington. The existing condition shows a portion of the current home's rooftop flowing south to the
adjacent neighbor's property. Phase 2 improves the existing drainage condition to the southerly
neighbors, by rerouting much of that portion of the homes runoff over to Remington Street. The net
new imperviousness from the existing condition to the end of phase 2 is 769sf, but because of the
rooftop flows being rerouted to Remington, instead of the rear yard, this project should have no
adverse impacts to downstream neighbors.
Finally, this Drainage Memo demonstrates two key points with respect to this site's storm drainage
and the downstream neighbors. We have shown that Phase 1 adds no new, net weighted impervious
area draining toward downstream neighbors. We have also shown that Phase 2 prevents any adverse
drainage impacts to the southerly neighbors from new impervious area, by rerouting the house addition
rooftop flows, north and west to Remington. Thus, the 1624 Remington Street improvements have
been strategically phased and designed to mitigate the potential for adverse drainage affects to
adjacent downstream neighbors.
Sincerely,
-
.o 37953 .
Timothy J. Halopoff, PE /ONAC~
970-817-1010
07200 South Alton Way, Suite C400 0130 East Kioa Street, Suite 400 1812900 South College Avenue, Suite 3D
Centennial, C080112 Colorado Springs, C080903 Fort Collins, C080525
303-740-9393 . Fax 303-921-7320 719-593-2593 • Fax 303-921-7320 970-491-9888 • Fax 303-921-7320
7200 South Alton Way, Suite C400
Centennial, CO80112
303-740-9393 x Fax 303-921-7320
130 East Kiowa Street, Suite 400
Colorado Springs, CO80903
719-593-2593 x Fax 303-921-7320
2900 South College Avenue, Suite 3D
Fort Collins, CO80525
970-491-9888 x Fax 303-921-7320
Appendix A
1624 REMINGTON HOME ADDITIONS DRAINAGE MEMO
Project No. 39761.00 FIGURE 1- VICINITY MAP
SITE
7200 South Alton Way, Suite C400
Centennial, CO80112
303-740-9393 x Fax 303-921-7320
130 East Kiowa Street, Suite 400
Colorado Springs, CO80903
719-593-2593 x Fax 303-921-7320
2900 South College Avenue, Suite 3D
Fort Collins, CO80525
970-491-9888 x Fax 303-921-7320
Appendix B
7200 South Alton Way, Suite C400
Centennial, CO80112
303-740-9393 x Fax 303-921-7320
130 East Kiowa Street, Suite 400
Colorado Springs, CO80903
719-593-2593 x Fax 303-921-7320
2900 South College Avenue, Suite 3D
Fort Collins, CO80525
970-491-9888 x Fax 303-921-7320
Appendix C
Know what's
Area ID Area (sf) % Imp.
Existing
Weighted Imp.
Area (sf)
Ex. House 880 0.9 792
Ex. Deck 218 0.75 163.5
Ex Flagstone 548 0.8 438.4
Ex Sheds 514 0.9 462.6
Misc. Flagstone 89 0.8 71.2
Total 2249 1927.7
Existing Condition
Phase 1
Know what's
Area ID Area (sf) % Imp.Net Weighted
Imp. Area (sf)
Garage Addition 911 0.9 819.9
Hot Tub Area 64 0.9 57.6
Shed Removal -414 0.9 -372.6
Ex Flagstone Removal -637 0.8 -509.6
Total -76 -4.7
Phase 1
Know what's
Area ID Area (sf)
Existing Site 2249
Proposed Site 3018
Net 769
Phase 2(All Imperviousness)
Area ID Area (sf) % Imp.Net Weighted
Imp. Area (sf)
Home Addition 154 0.9 138.6
Deck Removal -218 0.75 -163.5
Roof Overlap -175 0.9 -157.5
Phase 1 Removal Net -4.7 --4.7
Total -243.7 -187.1
Note: This table only includes areas that will flow towards
the southern adjacent neighbors property and not areas
flowing out to Remington.
Phase 2(Impervious affecting Neighbor)