Expert: Dave Johnson - 1/24/2008

Question
Dave, Thank you for your time.  I want to build a one story observation platform made of wood about 9 feet in height.  I am trying to find out where I can find information or purchase plans to determine the type of wood, size of the bolts, depth of the foundation, height of the guard rails and the degree of slope for the stairway? I am using it for up to 4 adults to use to oversee a nature area. Any advice? Thank you

Answer
Hi Christian,
First, I think if you go on line and ask for "plans for observation tower/platform" you may get what you want.
I would use pressure treated lumber...only because it will last a lot longer.
Foundation depth depends on what climate you have. Here in Maine, we go down 4-5 feet. In warmer climes I've seen them built on-grade.
Guardrail height should be 40" to 48".
1/2" bolts are more than enough.
Outdoor stairs are normally 11" tread (min) and 8" rise (max).
The posts can be 4"x6" minimum and need a cement "cookie" under them 6" thick and 18" diameter on undisturbed earth.
Floor framing should be 2"x8" and decking 5/4".
Railing...4"x4" posts and 5/4 railing.
Diagonal post bracing ...4"x4".
4 adults would be fairly comfortable on an 8'x8' platform.

Please mail me again if I can be of any more help...
Dave