Advice on building a ramada

October 11, 2009 10:30 AM

Construction newbies would like to build a backyard ramada. We're thinking of an open structure, similar to an arbor. The plan is to use 4 4x4 posts set 8 feet apart. The roof will be a slatted top with a 1 foot overhang. Since this is termite country, I'd like to anchor the posts in a cement footing using a J-bolt.

My question concerns the size and depth of the cement tube forms. Do you recommend an 8 inch or 12 inch form and to what depth should we dig the post hole? We will have a motorized posthole digger, but we will be digging in caleche.

posted by TorontoSandy to home & garden (3 answers total)

Your local hardware store (where, presumably, you would buy the supplies for this project) will have someone there who knows local code in addition to how deep/large your holes should be.
posted by JV at 11:11 AM on October 11, 2009

What you are building I know as a pergola.

Generally you want to get below the frost line with footings. I'd just phone the city building department and ask as I've found hardware store employees less than authoritatively knowledgeable about stuff like this. If frost isn't a concern then you only need to go far enough down to allow the soil to provide horizontal support against wind loads. Again your city building department can give good advice on this even if you don't pull a permit.

A 6" sonna tube is more than sufficient as a footing for this project though you may need to bell out the bottom of the hole depending on the load bearingness of caleche (I don't know what that is) and uplift resistance required. You should set the tube so that you can have the wood posts high enough above the ground that any termite tunnels won't be hidden by skirting or foundation plantings. If I didn't have to worry about frost I'd go 16" down and 8" up with the last 4-6 inches down being flared out.

Consider using a post base instead of a j-bolt to attach the posts to the concrete. Post bases provide a capillary break, are quite a bit stronger and depending on style are adjustable.

You said you're a newb so I'll throw out a caution: The structure needs to be diagonally braced regardless of what you attach the posts to the footings with. Pergolas lacking diagonal bracing generally have the posts themselves extend into the ground. By using a j-bolt or post base you gain durability and easy of maintenance but the trade off is you have created a hinge point at the bottom of the post that will allow your structure to collapse if it isn't braced.
posted by Mitheral at 12:07 PM on October 11, 2009

2nding the building inspector. They're the ones you have to please, not us or the hardware store guys.
posted by electroboy at 2:18 PM on October 11, 2009