4x4 base for a 6x6 post?

[Wakahisa Shinta]

I've been "commissioned" by my parents to build a pergola/patio cover on a 12' x 16' concrete slab. At the time the slab was poured, they were advised to put down Simpson 4x4 post bases. IMHO, 4x4 posts are small for this size pergola, so I made a Sketchup model with 6x6 posts to show them. They like it. All is well there. But...
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My dad took a grinder to the far-corner (relative to the house) post bases and filed them into oblivion a while ago! He left the two bases next to the house in tact. Why? No idea! The two remaining bases were put into the slab too deep, only about 1/16" of the 1" standoff portion is above the slab level.

Option 1: Use the two existing post bases. What would be the best way to cut two parallel slots in the 6x6 posts (picture)? Circular saw followed by some hand sawing to square up the slot?
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Option 2: Use new 6x6 post base and 5/8" concrete anchors. This requires the grinder to cut away the base vertical tabs. The standoff plate needs to be drilled through for the anchor bolt and filed down flush to the concrete slab.

I'm leaning toward #2. More work, but will place the posts off the ground, out of contact with standing water (if there is any).

What you think?

[Bradley Gray]

I like #2. I would likely use tap-conns to fasten the new bases to the slab instead of a 5/8" anchor.

[David Gutierrez]

+1 option #2 is the right way to do it..

[roger wiegand]

Do you know that the footer under the concrete slab is adequate to support the load you're going to put on it? If not you might have to put additional concrete under there anyway. I'd avoid the typical Simpson style deck post supports if at all possible. They would not be in keeping with the elegant pergola you've designed. I'd use a hidden system, perhaps as simple as a piece of 3/4" rebar epoxyed into the concrete slab and the end of the post. I've no idea what the earthquake structural requirements might be where you are though, I usually only have to worry about frost heaves.

[daryl moses]

I vote #2 as well.

[Chris Padilla]

What kind of wood are you thinking? Redwood? It is nice 'n plentiful in our neck of the US. Ipe is really nice but A LOT more money. I'm currently working on a small bench/arbor/pergola thingy (http://www.sawmillcreek.org/showthread.php?232414) right now.

I agree with Roger...skip the ugly Simpson ties unless you have a plan to cover them up.

You might flood test the slab and see if water pools anywhere to see if you even need to really worry about it. Sealing the end-grain of the 6x6s really well (like with epoxy) might be enough protection. Besides, it doesn't rain in California anymore...does it?! :D

[Wakahisa Shinta]

Thanks everyone! You're right; might as well do it right. #2 it is!

The wood is redwood. It's plentiful here in Northern California. There are a few lumber yards selling it within one hour away. They don't charge much for delivery either.

Chris, it rained here two days ago! Poured down 1" where I am at. Let's hope for more!

I am still pondering hardware options. My father was a marine officer, so he likes industrial looking things. He doesn't mind the exposed hardware. My mother is the opposite. I'm going to build it leaning toward her taste with some consideration for his. :)

I like the post base with a single vertical tab in the middle. The one where you cut a slot in the middle of the post. Once done, all you see is just the bolts. I saw a video of a timber-frame structure using this, but can't remember the URL any more.

Can anyone point me toward examples/sources of less conspicuous hardware for this type of structure?

[Chris Padilla]

Yes, rained 1.25" here in the South Bay where I'm at, too. I was kinda of kidding there...yes, I hope for more, too!

Do some searches on 'black iron hardware' and/or 'rustic hardware' and 'wrought iron hardware' you'll find some interesting (albeit spendy) items.

http://www.wildwesthardware.com/ is one I found.

[Gene Davis]

Just use pressure-treated 4x4s and wrap them. You can detail the wrap so the bases get completely hidden.

I use 3/4" rough-face western red cedar for the wrap, and biscuits and waterproof Titebond for the assembly. The wrap stops before the bottom, where it mates to a base-wrap part. You can replace the base part readily if needed. Not so easy with the wrap.

[Eric Schmid]

Simpson makes a wedge post base like the one you are looking for. It uses pins instead of bolts to attach at the post.

Nice design!

[Wakahisa Shinta]

Gene, 4x4 posts would not have enough stock for the way I designed the joinery for the beams and rafters. The posts are notched full thickness of 1.5" for each 2x material. A 4x4 post would leave .5" of wood left in the middle. A 6x6 post leaves 2.5" of wood in the middle. Thank you for the Sketchup model you posted. Below is a jpg of my joinery study. Though not modeled, the knee braces' tenons will be secured with wooden dowel, likely white oak.

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Eric, glad you like my design. I found the post tie. It's model CPT66Z, included with 3 pins as you mentioned.