HomeMy WebLinkAboutStructural Engineer's Report 03.18.20186SGM
MEMORANDUM
TO: Jaime Araujo
FROM: John Partch, PE
DATE: March 2, 2018
RE: 3911 CR 100 — Structural Review of Addition
RECEIVED
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
We have reviewed the framing and foundation of your unpermitted addition to the
residence at 3911 CR 100 for conformance with the structural requirements of
the Garfield County Building Department and the 2015 International Residential
Code (IRC). Design Criteria and assumptions used in our analysis are:
1. Snow Load: 40 psf
2. Seismic Zone: B
3. Wind: 115 mph, Exposure C
4. Assumed maximum soil bearing pressure: 2000 psf
5. Dimensional lumber: Hem -Fir #2 or better
Dimensions and layout used in our analysis are based on the sketches and notes
you provided and our site observations. Exact dimensions, attachments, and
other details of the construction will all need to be further verified if we are asked
to verify full compliance.
Our analysis of the structural compliance of the addition as constructed is
1. Roof structure:
a. Roof sheathing is reported to be 5/8" OSB, which appears
adequate.
b. Roof rafters are reported to be 2x6's at 16 inches on center. The
required snow loads exceed the capacity of the 2x6's. The roof
rafters appear to be supported by the hallway walls in most of the
addition, except for at the living and kitchen area. In this area, the
2x6 rafters span over 13 feet without support and are at 50% of the
required capacity. With support at the hallway walls, the rafters are
within allowable limits.
2 Exterior walls:
a. Sheathing and lateral bracing appears adequate within the
prescriptive requirements of the IRC.
118 W. 6th St, Ste 200 Glenwood Springs, CO 81601 Phone: 970-945-1004 Fax: 970-945-5948
b. 2x6 stud framing appears to be at 16 inches on center which
appears adequate.
c. Window and door openings appear to have been constructed with
(2)-2x6's placed flat over the opening. Capacity of these to act as a
header to carry the vertical roof loads is limited to a maximum of 4
feet rough opening.
3. Interior walls: Interior hallway walls are required to function as a
structural bearing wall if the roof framing is to be within code for support of
roof snow loads. Walls appear to be 2x4 studs at 16 inches on center with
gypsum wall board. Analysis results with this assumption are:
a. 2x4 stud framing appears adequate
b. Door openings for bedrooms appear to have (2)-2x4's placed flat
over the opening. The capacity of these to act as a header is
roughly 60% of that required.
c. Support of the roof framing between the living room and the hallway
is required to get the roof framing into code conformance. A
header beam would need to be added.
4. Floor framing: Floor framing appears to consist of OSB sheathing on
14 inch I -joists with (3)-2x12 beams at the perimeter and one intermediate
beam.
a. Thickness of floor sheathing was not verified. It should be a
minimum of 5/8" to conform to code.
b. I -joists are adequate to carry floor loads, in addition to bearing wall
loads of hallway loads above.
c. Connection of I -joists to the main residence appears to consist of a
2x12 ledger attached with intermittent powder actuated fasteners.
The number and spacing was not verified, but they appear to be
nowhere near adequate. Anchor bolts would be required to bring
the connection of the ledger into code conformance.
d. The (3)-2x12 beam at the perimeter of the floor framing appeared
to be spliced intermittently. Structural beams typically are required
to be spliced at supports only. The capacity of the beam with a
minimum of two unspliced sections per span is within code
compliance. Splice locations will need to be verified to ensure this
is the case.
e. The intermediate (3)-2x12 beam that supports floor framing on both
sides is at about 50% of the required capacity to support the floor
and roof loads. Additional posts would be required to support this
beam. Connection of the beam at the house also needs to be
verified and anchor bolts likely added to the ledger board.
5. Foundation: Foundations consist of 8x8 pressure treated posts
embedded in the ground. The posts are reportedly supported on a
concrete pad and backfilled with concrete. Depth of embedment is
reported to be 3 feet.
118 W. 6' St, Ste 200 Glenwood Springs, CO 81601 Phone: 970-945-1004 Fax: 970-945-5948
a. Minimum required footing size at the 8x8 posts should be a 20 inch
diameter concrete pad a minimum of 6 inches thick. The existing
posts observed appeared to have less than that size of concrete
backfill around them. Verification of the typical footing size will be
required and a geotechnical engineer will be required to verify
whether the soil bearing capacity is adequate.
Our preliminary structural analysis indicates that the addition will need a
significant amount of work to bring it into code compliance with the structural
portions of the building code. The roof framing will need to have additional
support at the living room, structural headers will need to be added over windows
and doors and across the living room area, additional support posts will need to
be added in the crawl space area, with additional footings, and the footings for
the exterior walls need their size verified and a geotechnical engineer will be
required to verify whether they are adequate with the soil conditions at the site.
Additional building code requirements beyond the structural aspects will also
likely require building modifications, such as ventilation and insulation, electrical,
and plumbing requirements. These aspects are beyond the scope of this initial
structural analysis.
118 W. 6'h St, Ste 200 Glenwood Springs, CO 81601 Phone: 970-945-1004 Fax: 970-945-5948