BLD2020-0992+GEO LETTER+9.25.2020_3.45.45_PMRobert M. Pride, LLC Consulting Engineer
September 2, 2020
Mr. Rob Williams
7725 168t' Place SW
Edmonds, WA 98026
Re: Geotechnical Recommendations
New Deck Structure
7725 168t' Place SW
Edmonds, WA 98026
Dear Mr. Williams,
As required by the city of Edmonds I have made a site inspection and performed
geologic research for this residential site. It is understood that a new deck structure will
be installed on the west side of the house as a second story addition. This deck will
cantilever three feet out beyond the final deck support and will be adequately designed
for structural support. The existing concrete slab on the west and north side of the
residence will remain as constructed, and there are no signs of settlement or lateral
movement of this slab.
There is a steep slope extending down to the lower west side of this property, and the
top of this slope is setback 25 feet from the west wall of this house. Based on
topographic contours this slope has a 3H:2V gradient (equal to 66% slope) and shows
no evidence of prior instability or landslide movement.
Geologic research showed that this area of Snohomish County is underlain by pre -Fraser
deposits consisting of fine to medium grained silty sands. Field observations and
subsoil inspections showed that these soils were medium dense to dense and they have
stood without any slope instability problems extending down below the rear west side of
this property.
Geotechnical Recommendations
Construction of the new upper deck structure will be supported by the exterior second
story walls of the house, and there will be one post supported by a concrete pad footing
on the southwest corner of this deck. It is recommended that this footing extend down
18 inches below existing grade, and can be designed for a bearing value of 1500 psf.
Estimated settlement of this footing will be less than 1/4 inch because a majority of the
deck loading will be supported by the adjacent house structure.
Recent observations of the existing residence foundations and the rear yard concrete
deck slab showed no evidence of any settlement or lateral movement. The underlying
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13203 Holmes Point Drive NE Kirkland, WA 98034
glacial soils will continue to provide excellent support to this structure as well as the new
deck footing.
It is recommended that a field inspection be made to confirm adequacy of the bearing
soils for the new deck footing pad, and an appropriate field memo will be prepared for
submittal to the city of Edmonds.
Please call me if there are any questions.
Respectfully,
of Was.01
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Robert M. Pride, P. E.
Principal Geotechnical Engineer
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13203 Holmes Point Drive NE Kirkland, WA 98034