HomeMy WebLinkAboutAV 91-12; Hill Residence; Administrative Variance (AV) (5)September 10, 1993
TO: Planning Technician II - Lynch /
FROM: Assistant City Engineer @w
ENGINEERING REPORT FOR ADMINISTRATIVE VARIANCE 91-1 2 - HILL RESIDENCE
I completed my review of the August 19, 1993 engineering report for the Hill
residence which was prepared by Mr. John Vernon. As presented, the report did not
comply with the report requirements outlined in my letter to Mr. Hill dated August 3,
1993. Specifically, the report did not include a scaled site plan of the property, a
discussion of the adequacy of the existing installed subsurface drains or, a discussion
of the potential reasons why the surface and subsurface treatments failed to resolve
the drainage problem absent the installation of the side yard roof structure.
Despite the report omissions, there appears to be adequate information for me to
render a professional opinion on the mechanism of failure and therefore, I do not
recommend that we request any further revision or addendum to Mr. Vernon's report.
It had been previously stated by Mr. Hill that installation of the retaining wall, concrete
surfacing and subsurface drains did not resolve the problem of the water seepage into
his residence. It was further stated by Mr. Hill that construction of the side yard roof
between his house and retaining wall together with the installation of a roof drain
gutter effectively eliminated the problem. The question thus raised is what protection
did the roof provide that the concrete surfacing did not?
Based upon the site plan included in Mr. Vernon's engineering report, it is apparent
that there was a critical flaw in the design of Mr. Hill's subsurface drainage system.
The pipe beneath the concreted area of'the side yard which carries the surface
drainage from the back yard and the side yard (prior to construction of the roof) is
constructed using perforated pipe. Therefore, much of the water which enters into the
pipe is distributed directly into the ground adjacent to Mr. Hill's house. During a heavy
rainfall, the small size and relatively flat grade of this subsurface pipe could easily
create a situation of pressure flow potentially forcing even more water into the ground
than occurred prior to the concrete surfacing of the side yard.
It was apparently Mr. Hill's intention to utilize the perforated pipe to intercept the
underground flows prior to their reaching his house. For such a design to work, it is
necessary to utilize a drainage system separate from the system used to convey the
surface drainage. Had such a dual system been utilized, I am confident that the
drainage problem would have been resolved to a greater extent than is presently
enjoyed by the Hills. As it presently exists, the roof structure only diverts the side
., I'
September 10, 1993
Hill Residence
Page: 2
yard rainfall flows from the subsurface drains. The rear yard drainage continues to be
carried within the perforated pipe and presumably percolates into the ground next to
the house. This may be the reason for the continued existence of subsurface water
found in the sprinkler valve wells by Mr. Hill.
Mr. Vernon's report does include a recommended alternative for an 8 foot deep french
drain with an accompanying curtain wall that would completely resolve the Hill's
drainage problems without need for the side yard structure.
In my opinion, the roof structure was clearly not the most economical solution to the
Hill's drainage problem. The roof structure was 'necessary' to solve the Hill's drainage
problem solely because of the improper installation of the subsurface drainage system
constructed by Mr. Hill.
DAVID A. HAUSER
Assistant City Engineer
c: City Engineer
Assistant Planning Director
John Vernon, Property Development Engineers Inc.
Mr. Steve Hill
attachments - Letter to Mr. Steve Hill dated August 3, 1993
Letter report from John Vernon dated August 19, 1993