Lessons relearned from Katrina

[RAB]

Lessons relearned in the survivable zones of Katrina.

2 links on this page, many photos, of particular interest are homes with intact roofs – very little shingle damage - that have severely damaged gable end walls.
http://www.apawood.org/level_b.cfm?content=srv_med_katrina&CFID=756193&CFTOKEN=24001114

Ryan B

[jraabe]

Thanks Ryan:

The problems of foam sheathings and under-nailed sheathings and roof materials certainly shows up at times like this.

Just doing the conservative double wall framing (siding over plywood or OSB) and nailing it off with plenty of regular galvanized nails (as called for in all of my plans by the way  ) would have saved many of the buildings in these photos.

[trish2]

John:
How would your double wall system hold up in a "7" earthquake?  Beside the standard bolts to the foundation and other code requirements, what do you suggest to strengten buildings in earthquake zones that is over and above code?

[John Raabe]

Here's what I wrote on another thread on "Understanding structural sheathing and bracing":

For 99.99% of its life a house only has to deal with its own weight and perhaps some snow in the winter.  These are all downward loads - what we call simple static loads.
 
It's the sideways and upward dynamic loads that happen so very infrequently that can spell doom for a house. The extent to which you need to design and build for this varies considerably not only by the big picture earthquake, wind and water forces of your region, but by the very local sheltering or non-sheltering aspects of your site.
 
There are a few simple concepts that will help tie the structure together inexpensively:
 
• Try to get a two stud bay (2'-8" or 4' wide) panel of structural sheathing for the full height of the wall at both sides of all major corners. Nail this well to studs, plates and sills. Have horizontal panel joints meet over solid framing and nail both sides of the joint. You are building a box beam and adhesives will add even more rigidity.
• Use metal hardware such as straps, framing anchors and bolts to tie the wood framing to the foundation, the floor framing to the walls and the walls to the roof framing. You want these parts of the structure to work together and reinforce each other - especially at the corners. (http://www.strongtie.com/)
• Check that all roofing, siding, sheathing and framing is installed with the right type of fasteners and at the right spacing. Many of the Katrina houses failed because framers and roofers used short staples or too few nails to keep things from blowing away. Nails are cheap insurance - use lots.

For heavy earthquake or wind bracing an engineer will do some very plan specific things such as:
• install extra heavy hold down bolts at the foundation and tie these up into double stud posts in the wall
• use plywood on interior walls
• tie interior walls that cross long exterior walls into the foundation (perhaps with a new footing wall)
• strap all of these strengthened walls into the ceiling and roof... and other tricks of the trade.

A local engineer can analyze your specifc building and site for tailored bracing details. (In most high wind and earthquake areas such a review is required as part of the building permit process.)