HomeMy WebLinkAboutEngineer Report 08.21.17 - South DeckPATTILLO ASSOCIATES ENGINEERS, INC.
S T RU CTURAL C ON SU LTANT S
1215 grand avenue, post office box 751 glenwood springs, colorado 81602
phone (970) 945-9695 e-mail: info@paengineers.com
August 21, 2017
Margaret McNulty
513 91h Street
Glenwood Springs, CO 81601
Re: McNulty Residence
0420 County Road 122, Garfield County
To Whom It May Concern:
Our office has reviewed the construction assembly details provided by the contractor,
Dan Friel, regarding the recently built south deck at the subject property.
understand that the plan dimensions of the deck are approximately 8 feet north -south by
24 feet east -west with components as follows:
1. The deck surface was built with preservative -treated 2x6's, laid flat and spaced
for "drip -through" drainage.
2. The deck joists are preservative -treated 2x10's, Hem -Fir or Southern Pine #2
grade or better, spaced at 16 inches on -center, spanning in a north -south
direction approximately 8 feet between a treated ledger board attached to the
house and an edge beam. The ends of each deck joist are connected with metal
joist hangers, designated LU26 or larger.
3. The deck edge beam consists of a series of three double 2x10's, also
pressure -treated, spanning in an east -west direction between concrete pier
supports. Each edge beam spans not more than 9'-0" and is attached to the
concrete piers with an embedded metal 4x4 post base connection.
4. The concrete piers and footing were monolithically cast with three #4 vertical
bars that extend from the bottom of a 24 -inch diameter pier stem. The overall
height of each pier is 1'-8" with about 6" of the stem extending above grade and
14 inches of buried depth. elow each
5. It was reported that the bearing soils ilsthat were built footing from the le el of he ally
compacted layers of native clay o
excavated area for the modular house foundation.
All elements for the deck framing, including decking, joists, connections and edge beams
are hereby verified as adequate for support of residential live loads (40 psf) or snow
loads (50 psf for this site). However, there are two issues of concern. First, it was
determined that the 2x8 floor joists for the house are not sufficient for the support
of
additional loads imposed by the deck ledger. Second, although the maximum pr
essure
imposed by the deck piers is relatively lcght (about 750 pounds er ted bearing soilspthe 14 inches of bury for
re foot) which
should be easily supported by properly p
the piers, from finished grade to bottom of footing, is less than the stated 36 inches of
frost depth required by Garfield County.
McNulty Residence
August 21, 2017
Page two
Our first concern, about the lack of adequate building structure to support deck loads,
can be mitigated by providing solid shimming between the bottom of the modular floor
joists and the top of CMU perimeter foundation. Although the foundation wall was
designed as an isolated independent retaining wall element, it also has adequate strength
to support the imposed loads from the house roof, house floor and new deck with no
adverse effects. With shimming in place, the foundation wall will relieve loads from the
house framing system, and all will remain compliant with building code requirements.
The second concern about lack of frost protection may be alleviated by realizing that the
deck foundation only supports an ancillary portion of the house, and any small seasonal
movement due to frost heave will be readily absorbed by the deck structure with no
adverse effects to the house or to the finishes of the deck. In my experience, structural
damage due to frost heave is extremely rare, and in more than 35 years of engineering
practice in this region of Colorado, I am not aware of any problems that have been
caused by frost heave of isolated deck footings or landscape structures, such as retaining
walls, even when footings have been observed with less than one foot of earth cover.
Thus, in my opinion there is little risk for damage or distress associated with the 14
inches of frost cover provided for the deck footings of this particular building.
This completes my report. Please contact me if you any questions or require further
information.
Sincerely,
Robert M. Pattillo, P
Principal Engineer
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Email copies: Meg McNulty (ro minnneonrn amail.crnn)
Wendy McNulty (wend a qututercirch8 _com)
Dan Friel (dan@frielconstruction.com)