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Re: Two conditions in residential construction

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Dennis,

How do feel about a contractor designing and building a residence without
the service of an engineer (in seismic zone 4) under the following
conditions:
1) The design meets the statutory definition of conventional framing (were
talking California here).
2) It's one story.
3) In lieu of a soils investigation, he uses code values (natural
undisturbed soils ) for the foundation design.
4) The building/grading official waives any requirement for geotechnical
after performing a field inspection prior to issuing a permit to build.

Clearly this house may not win any architectural awards, but would this type
of construction be considered substandard from an engineering perspective?

Steven A.
Los Angeles



Dennis Wish wrote:

> I wanted to read a few responses before I sent mine. I agree with the
> majority, but want to make a few points very clear. Let me start with
> the Let-in strapping first and work backwards.
>
> You did not indicate what seismic zone (or wind zone) you are in. Let-in
> bracing is still allowed in all but seismic zone 4 as a braced wall
> panel material. However, you designed this project and it was not
> permitted as a prescriptive design in compliance with the 2000 IRC or
> the 97 UBC Section 2320. The builder has no right to change the details
> you designed for lateral bracing and you have the right to stop the job
> and make him replace the work he did.
>
> In Seismic zone 4 (or D per the 2000 IRC) let-in braces are used as you
> indicated - to keep the walls plumb until sheathing is nailed in place.
> The builder may also choose to sheath the wall flat and without diagonal
> bracing and tilt the wall up in place. In this manner, the shearwall
> sheathing is used to assure that the wall is plumb (although I don't
> recall seeing a framer actually do this inasmuch as most low cost labor
> is paid by the total length of studs laid up each day).
>
> With regard to issue one - rock foundation; this is not a typical case
> in most regions and as others noted, you have no idea who much of the
> outcropping exists to secure the foundation to. I am concerned that you
> are using an unreinforced foundation as this will not help to resist
> uplift on panels in high risk areas - but again, you have not indicated
> where this is being constructed.
>
> In my opinion, a home is only as good as the foundation it is
> constructed on. If the site condition does not comply with the worst
> case code condition and is considered anything better (including the
> assumption that you are building on bedrock) then it is best to leave
> the liability for the foundation to a geotechnical firm who should be
> advising you as what is appropriate.
>
> Don't be afraid to be conservative - your client will most likely bitch
> and moan as the builder accuses you of over-designing. This is normal
> since the owner and the builder do not understand the principles of
> mechanics and the requirements of the code. I can guarantee you this, if
> you give in, the client will seek you out with a vengeance at the first
> crack that appears and will probably hire another professional to
> evaluate your work so as to find flaws in what you have done. The first
> big flaw will be that you did not stop the job and demand the contractor
> to do it your way.
>
> Regards
> Dennis
>
> Dennis S. Wish, PE
> California Professional Engineer
> Administrator - The Structuralist.Net
> Website:
> http://www.structuralist.net
>
> Professional Forum:
> http://www.structuralist.net/cgi-local/yabb/YaBB.cgi
>
> Public Forum on Housing:
> http://www.structuralist.net/cgi-local/yabb2/YaBB.cgi
>
> -----Original Message-----
> From: Albert Meyer [mailto:Ameyer(--nospam--at)martinaia.com]
> Sent: Thursday, December 06, 2001 10:34 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Two conditions in residential construction
>
> I have a few questions regarding some conditions that occasionally come
> up
> in residential construction that we deal with, and I thought I'd solicit
> some opinions on two of them that have come up recently.
>
> 1) A contactor building a single family home encountered "rock" when
> excavating for a basement foundation, and where we had specified an
> unreinforced 36"x36"x14" concrete footing, a footing with a 10" depth
> was
> placed.  The wants to know if this is OK.  There is no soils report, as
> is
> typical for this type of job, and neither he or I know what type of rock
> is
> on site.  Many take the attitude that "Oh it's only a single family
> home,
> it's fine", but what would you do?
>
>         Would you say: Hire a geotech to ascertain the allowable soil
> value,
> use this value to determine what minimum footing size is required and
> check
> to see  that the footing works for both bending and punching shear?
>
>         Or: Remove the existing footing and excavate to the required
> depth
> and replace the footing?
>
> 2) A contractor has elected to not provide the required shear wall
> sheathing
> on some interior unit separation walls of a multi-family dwelling, and
> has
> instead installed diagonal straps on the walls.  No special nailing or
> attachment at the ends of the straps has been done nor was specified by
> the
> "other" engineer they hired to provide them with an alternate detail.
> It is
> my feeling that diagonal straps on wood frame shear walls are not a
> practical solution since even though you can specify a strap that works
> for
> the tension load you generally can not provide the attachment required
> at
> the end of the strap unless you provide a large solid sawn post (not
> typically available in this area) or a Parallam post and or solid
> blocking
> appropriately fastened into the corners of the shear panel.
>
> Am I being too conservative the issues here?
> Does any one else do diagonal strapping on wood shear walls and if so,
> how?
> Any and all opinions are gratefully appreciated!
>
> Albert J. Meyer, Jr., P.E.
> Martin-Espenlaub Engineering
> (215) 665-8570 Tel
> (215) 561-5064 Fax
> ameyer(--nospam--at)martinaia.com
>
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