Subject: Field Observations - Stupid things I've seen
Date: Sat, 26 Jun 1999 14:23:36 EDT
I liked this thread and thought that it would be interesting to accumulate a
thread of construction defects caused by both conventional construction and
by contractors who don't read plans.
Here is my contribution which occured this week.
I received a call from my client - an architect, who designed a small 100 sq.
ft. addition to a home for a special client of his. I engineered the project
and provided all the appropriate details for the project.
The architect phoned to say that the contractor replaced a steel post with a
wood column and requsted me to approve the change since the steel column was
only intended to support a glass to glass connection acting as a mullion.
There was no sufficient load to the column that a simple 4x4 wood post would
not handle. On top of this, the contractor put in a 6x6 wood post and secured
it to the foundation with a Simpson HD10A (I don't know why).
I had to drop my wife off at the Palm Springs Airport and the job was nearby
so I decided to stop by and take a look. I ended up writting up an
oberservation report and this is what was included:
1. The new 6x6 post with an HD10A was approved - overkill, but acceptable.
2. The building inspector failed to notice that the contractor moved the
entry door over 12"' and reduced the only shear panel on that wall from 3'
wide to 2' wide. The panel was 12 feet tall but was tied to the header at the
adjacent door. The wall above the headers for the entire length of wall was
indicated to be sheathed in plywood - which was not done. So here I was with
a 12' tall x 2' wide shear panel with 8700 pounds of uplift (this is a 90mph
wind zone) which was calculated at the net height of 9' taking the sheathing
3. The framers placed all of the rafter blocking outside of the plane of the
wall - not above the top plate as I indicated on my details. Instead they
installed a hurricane clip to each rafter and nailed it to the plate. I do
not consider this to be an adequate shear transfer (certainly not in
compliance with the code) and the deflection in the hurricane clip would
certainly be a strong argument for a flexible diaprhagm.
I wrote up the observation and called the head building official to discuss
what his field inspector missed. I asked if the head building inspector would
verify that the work was completed per my report rather than have me drive
the 35 miles back to the job. The head building inspector thanked me for
bringing this to his attention (the city is known for being tough but he was
not aware that his field inspector missed this one) and told me that he would
personally take care of it.
The toughest part was trying to make a retrofited tension anchor (holddown)
work for the 8700 pounds when the best I could do with a Simpson SET adhesive
was about 6500 pounds. The capacity of the bond needs to be reduced almost
50% for it's proximity to the edge of slab. I finally had no choice but to
take into consideration the existing HD10A which was only 12" away. I also
drew upon some engineering judgment:
There is an existing home on two sides of this addition. The actual new
addition juts out only three feet from the existing structure. I disregarded
the existing structure because the architect did not provide me existing
information or a full plan of the home. Therefore, I isolated and designed
the addition as if it were free standing and separate from the main residence
- a good conservative approach. I know that the existing structure will
absorb most of the shear if this wall proves to be inadequate in uplift, and
after seeing the home would conclude that the HDA's were probably
overdesigned from the start (had I known). Therefore, I had the contractor
install a new HD10A and embed it 11" into the fndt (18" deep).
No matter how well the job is detailed or design, I have yet to meet a
contractor that is willing or able to sit shotgun and protect a shearwall
from the nimble fingers of a sub-contractor who wants to bring his utilities
up through the mudsill. The cutouts are very liberal and the GC rarely
repairs the cuts properly.
I'd like to read others who can provide stories of construction abuses.
Dennis Wish PE