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Re: Styrofoam seal at plywood shear wall sill plate

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There goes that whole rigid diaphragm of wood walls idea....add a new factor in the in-plan ewall deflection calc for rigidity...crushing of the styrofoam

Delta_sty =  e^log23 * (coeff. per ASCE 7 section 128.1.5.a exception #3 ) x E of styrofoam x Phi

-gm

On Jan 23, 2008 11:07 AM, Gaines, David <David.Gaines(--nospam--at)hdrinc.com> wrote:
Sasha,
 
I looked at the product info from your link. That's an interesting idea to seal the air gap over rough concrete at the sill plate I'm not sure how important that is when you consider there's an exterior stucco finish and interior plasterboard and baseboard floor trim to limit air flow. Funny thing, the image they show of the installation is one of a sill plate below an elevated wood floor, where air flow is a good thing. It has nothing to do with air flow into the occupied space above the sub-floor sheathing. Limiting air flow would have more value on a concrete slab on grade rather than a wood floor.
 
I'd suggest that if the floor slab is that rough they should get the contractors to finish the concrete slab better. It's not clear from your description exactly where they are using this around the windows. The window and door application is not illustrated in the brochure at this link.
 
The capacity of anchor bolts in a wood sill plate is found in a specific table for wood on concrete. It may be necessary to develop testing for anchor bolt capacity with a smooth Styrofoam material in between. I am not entirely sure about the source of these anchor bolt capacities.
 
The brochure doesn't say how thick the material is or how much it compresses over time. I would ask the manufacturer about long term settlement or shrinkage of the material. If it settles or shrinks your anchor bolts will come loose. Any holdown anchors will come loose. Loose holdowns will allow the wall to flex before it holds. Wall displacement at the holdown probably isn't good for the wall finish or the plywood shear wall sheathing.
 
These are all things you might consider. As I said, I don't see any information on how this product is used around windows and doors.
 

Dave Gaines, P.E.

Structural Project Engineer
HDR ONE COMPANY | Many Solutions
251 S. Lake Ave, Suite 1000
Pasadena, CA 91101
T: 626.584.4960
F: 626.584.1750
email: david.gaines(--nospam--at)hdrinc.com

 


From: Alexander (Sasha) Itsekson [mailto:sasha(--nospam--at)enginious-structures.com]
Sent: Wednesday, January 23, 2008 10:32 AM
To: seaint(--nospam--at)seaint.org
Subject: Styrofoam seal at plywood shear wall sill plate

Dear list:

 

I came to inspect sill bolting installation at one of my projects and found that the contractor (he is a licensed architect too) installed a 1/8" Styrofoam seal.  This material is usually used around windows at in concrete buildings.  The architect/builder thought that he is improving things by installing at all the exterior walls. 

 

Is there any concern about the sill plate shear resistance with having this new slip surface and a small gap?  Please let me know you thoughts.

 

 

Here's the link to the product info:

http://www.dow.com/PublishedLiterature/dh_0032/0901b803800329ac.pdf?filepath=/PublishToInternet/InternetDOWCOM/styrofoam/pdfs/noreg/179-07153.pdf,/PublishToInternet/InternetDOWCOM/styrofoam_old/pdfs/noreg_old/179-07153.pdf&fromPage=BasicSearch

 

Alexander (Sasha) Itsekson, SE

Enginious Structures, Inc.

Oakland, CA

www.Enginious-Structures.com

 

 

 

 

 




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-gm