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Seismic upgrade of 16 y/o home, II  Rate Topic 
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 Posted: Sun Aug 19th, 2007 04:13 pm
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georgewa
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Dear Howard:

Still trying to figure out if we need to doing anything  to seismicly upgrade our 16 y/o 2 story wood frame house in the SW Washington area near Portland, OR now that we invested a lot in other upgrades -siding, roof, painting, heating/ac. It was built to code then and inspected 15+ times by the records we got, has a poured concrete foundation on level ground with 1/2" anchor bolts every 6' on the ext walls. The walls are t1-11 covered with cedar siding.

We had a structural engineer review the original plans and come up with a retrofit design.  What he did was run  the calculations and said this is what we would do if it was built now . He said we don't positively know what they did when they built it, so there you are. I came back and said, how does this help me. His reply was " I probably wouldn't do anything more if it was my home." This was echoed by the cty building inspector who also added " If you really want a perfectly built home you will need to build a new one." Two other structural engineers I've spoken with said if the house is that age and built to code you don't need to do anything. None of the engineers actually have seen the house, only the plans and detailed pictures which is probably fine.

Another contractor who does seismic retrofit work in Seattle inspected our place yesterday and said they usually focus on better securing the foundation and sill plate because if the house can be kept on the foundation, the rest of the problems can usually be fixed and the cty will not condemn the home. What he uses is the Simpson HFA-6 L bracket and mounts one side to the foundation and the other to a 2X4 ' piece of 3/4' plywood that has been nailed to the underside of the floor boards and the gap between the sill and foundation. He thought we needed this since the 1/2" bolts are at 6' intervals rather than 4' (actually 6' is 2003 IRC code for a 2 story) and we have round washers rather than 3" sq plates. He also wanted to secure the posts to the beams and the posts to the pods with Simpson hardware. The estimate for both was $5-6000. I told him that IF the job was going to be done, I'd probably do it myself.

I remembered what you have said about the L anchor brackets failing previously (?Northridge) so this option does not sound the best though it avoids messing with the sill plate itself which will be difficult to work with in our home because of the tight spacing; the floor boards are mounted  directly on the sill plate; the 4X8" beams are sitting in U shaped cutouts in the foundation wall with a 2' crawl space. The Simpson plate  with the wood block to fill gap between the sill and wall I recall is your 1st choice (Harlen is apparently out of business).

So what is your opinion? Would you add sill/foundation anchors as your first step ( to compensate for not having 3" plates on the anchor bolts and living in a D earthquake zone) or leave all well enough alone ( have 4 people saying do this) or do something else first?  If you are ever be in the Portland, OR area , we'd  welcome you to do a home inspection and do you ever do phone consultations .  Thank you.

Walter

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 Posted: Mon Aug 20th, 2007 02:36 am
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Bay Area Retrofit
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Hi Walter,

Sounds like a can of worms.  If anyone knows anything about building codes they will know how your house was built because it must have been built according to the code in place at the time of construction.  This code required a 1/2 inch bolt every six feet and round washers, not plate washers, were required.  The fact you have round washers is not a big deal.

Sounds like the contractor does not understand much about effective retrofitting techniques.  I have never heard of using the Simpson HFA as he is intending, nor will the manufacturer vouch for its effectiveness.  Putting steel on the post to girder connections is a total waste of money. 

You do not have cripple walls.  The only thing I would do is install Simpson L90 shear transfer ties to connect the end joists to the mudsill and perhaps insall some Simpson UFP10 in these locations to make sure the foundation to mudsill connection is equal on all sides.  Make sure all the connections are equal in strength on all four sides of the house. 

After the Northridge earthquake the code changed so that the end joist to mudsill connection is now stronger than is required when you house was built. 

Forget about most engineers.  They do so little of this type of work that they are pretty much worthless.   Part of the reason they went to college was so they would not have to crawl around under houses. 

Read over the Homeowners Guide in the PDF Downloads section of the website.  It explains all the principles you will need to know.   

This kind of job is not expensive. 

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 Posted: Tue Aug 21st, 2007 01:09 am
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georgewa
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Thank you for getting back to me. That was very helpful.

To just double check as I recall your website pictures, you would prefer the UFP10 to the FAP?

Looking at the L shaped  HFA6 or 8 which Simpson lists as retrofit anchor, the cutouts at the bend kind of turned me off, but the numbers Simpson lists for allowable loads (which I don't know how to interpret by the way) when you look on their website under /connectors/FA-FAP-HFA-FJA-FSA.html the numbers don't look all that bad.

Also, when you look at the City of LA Approval report exp 3-1-2006  for the FAP, FA6, they mention the following comparison that was also a little surprising:

                                  FAP                FA6

Min yield strength      33,000psi       28,000psi

Min tensile strength    45,000psi       38,000psi

When it comes to placing retrofit anchor bolts in the side of the foundation particularly near the corners/ends ,  how close to the end would you go ? Would you prefer to use the epoxy method rather than the expansion type bolts? When you have the situation of a 28" high crawl space, floor boards mounted right on top of the sill, how do you avoid drilling right next to an existent 1/2" anchor bolt in the foundation?

On a different subject, what is your opinion about home auto gas cut-off valves? Which one would you recommend? Northridge? Little Fire Fighter?

Thanks again.

Walter 

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 Posted: Tue Aug 21st, 2007 01:18 am
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Bay Area Retrofit
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Thank you for getting back to me. That was very helpful.

To just double check as I recall your website pictures, you would prefer the UFP10 to the FAP?

Yes, rated loads for the UFP10 of 1340 pounds exceeds both of these products and are easier to install. 

Looking at the L shaped  HFA6 or 8 which Simpson lists as retrofit anchor, the cutouts at the bend kind of turned me off, but the numbers Simpson lists for allowable loads (which I don't know how to interpret by the way) when you look on their website under /connectors/FA-FAP-HFA-FJA-FSA.html the numbers don't look all that bad.

That is correct, but they are a lot more trouble to install. 

Also, when you look at the City of LA Approval report exp 3-1-2006  for the FAP, FA6, they mention the following comparison that was also a little surprising:

                                  FAP                FA6

Min yield strength      33,000psi       28,000psi

Min tensile strength    45,000psi       38,000psi

This is probably the strength of the steel.  These numbers don't mean anything.  The only thing that matters is the amount of lateral force it took before this hardware failed.  This is listed under the F1 column in the catalog.  The failure usually is in the wood but in the UFP10 the failure was in the steel, which is why it has the same strength when installed in redwood or Douglas Fir.  The two pieces of hardware you are talking about have lower values under the F1 column than the UFP10.  Besides difficult installation, this is why they are inferior.   

When it comes to placing retrofit anchor bolts in the side of the foundation particularly near the corners/ends ,  how close to the end would you go ? Would you prefer to use the epoxy method rather than the expansion type bolts? When you have the situation of a 28" high crawl space, floor boards mounted right on top of the sill, how do you avoid drilling right next to an existent 1/2" anchor bolt in the foundation?


Just keep the bolt 6 inches away from the ends.  Don't worry about hitting existing bolts.  It rarely happens.  Use epoxy bolts if you have the money, but wedge anchors have all been tested and will do just fine.  They are a lot less trouble to install. 


On a different subject, what is your opinion about home auto gas cut-off valves? Which one would you recommend? Northridge? Little Fire Fighter?

I believe that if you house is propoerly retrofitted there is no need for a gas valve.  The little firefighter is a good valve. 



Last edited on Tue Aug 21st, 2007 07:53 am by Bay Area Retrofit

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