Window layout for 20x30 1 1/2

[Micky]

The good news is that I got my foundation poured before the snow came.  Now I have all winter to finish my planning.....

I am looking at the window layout and have a couple of questions.

1 - I am trying to get a symmetric look on the front of the cabin.  This would be the front door centered on the wall with windows flanking on each side.  Since this is the side of the cabin facing the water, I also wanted to maximize window area.

I was told that I need to keep 2'8" without windows on each corner for the shear wall.  Is this a rule I can break?  If so, what are the tricks?


2 - Is in possible to incorporate the pop-out window seat in this cabin like you talked about on the 2 story model?  Do I just use floor joists that are a couple of feet longer and add a header to treat it as a window opening?

Thanks
Micky

[borgdog]

My understanding, and I'm not an architect or an engineer, but unless you want to spend a lot of money on an engineered sheer wall smaller you are best to stick with the 2'8" minimum, some standard engineered kinda thing (like my highly technical terms there   )

I've seen several that size with two large sliders 6 foot wide should work nicely on the front, lots of glass, maximizes space.  Or one of them could be replaced with a tall window that would give pretty much the same look.

Dan

[Ryan B]

First - swing by your local lumber yard and pickup a copy of the "Simpson Wood Construction Connectors" catalog. Find the pages on shear walls for illustrations (most code books have similar illustrations but Simpson's show more detail. Also you can go to www.simpsonstrongwall.com for the same illustrations.
Second – Read below

The term shearwall is a slight misnomer; actually these walls should be called deflection reduction walls or force reduction walls as they pick up the load that can deflect your wall.

For most walls (and other house components as well) excessive deflection has been tested and seen over time to be ¼" in 96". That's a ratio of 1 to 360. As an example: a simple door will stick if the jamb moves 1/8" or a sliding window will stick with 1/16" frame movement. These are all examples of failure in deflection. The higher you can get that ratio within financial limits the better off you will be.
 
If you have wind at your site that strikes your cabin perpendicular to your window wall this will produce a force that that wall will have to resist.

A common default value for wind is 15 lbs per sqft.
For common applications the force resistance of a wall is 250 lbs per foot.

Common deflection reduction walls (oops shear walls) mentioned in code books start with a 4x8 area near each corner with a common nailing pattern, stud layout and sill bolting spacing. Quite simple and economical!
Smaller width deflection walls will need more detail and in turn cost more.

In your case a 24" shear wall can be obtained for not much more cost - Yes you would have to retrofit hold down bolts and the extra framing will take longer.

Deflection limits are specified as the ratio – full load deflection/Span length. Common design ratios are 1/180 - 1/360 - 1/480 or .0055 - .0028 - .0021
Examples:
A house ridge beam 180" long should not sag more than 1" under load (180 x .0055 = 1").
Wind deflection ratio for skyscrapers = 1/200 – 1' of movement per 200' of height is acceptable.
Old plaster on cantilevered ceilings should have deflection ratios higher than 1/480 due to their brittle nature.
Boeing 777 rear doors will open but not close under full fuel and passenger load due to excessive deflection.

You're on the right track with the bump out window seat, keep in mind the costs and time for floor detailing (insulation and critter proofing) and small roof area that the bump out creates. And of course fabric selection for the seat cushion.
 
Ryan B

Ps. Standard values are given based on UBC, IRC and common building practices

[John Raabe]

This is a very good overview. Thanks Ryan

Micky: Also keep in mind that the braced wall panel (4' wide) or alternative braced wall panel (2'-8" wide with extra holddowns) can start anywhere within 8' of the corner. Thus you can do large windows from both sides opening up the corner and still brace the wall prescriptively with panels on either sides of the windows.

Your general idea on the pop-out is correct. You can cantilever the joists 1/4 of their backspan and treat the opening with a header. The pop-out design in the 20' wide two-story plan is a bit more complex as it braces off the wall and can be done on stair landings and places where the joists don't run the right direction.

PS - Ryan posted a good link to details in the Referral Link section. Here is one on how to build the alternative panel:
http://www.iccswwc.org/documents/R602.10.6AltBracedwallpanel.pdf