# To bury or not to bury.



## ghar23 (Jun 14, 2013)

Hi everyone,

I have 6 6x6 posts for a pergola....

The more I read about how to put the posts, the more I am not sure what to do.... 

Top 2 choices are as follows....

1. Dig holes and pour in concrete footing to about 2 inches above grade. Set a metal base anchor/mount (Simpson CB66 is most popular suggestion) before concrete sets in. Attach the posts to the base mount. Advantage - Lasts longer because post is not in contact with soil/concrete so moisture is not an issue.
Disadvantage - There may be some lateral load balancing/movement issues (Although I heard with knee braces you can minimize them) and/or it might be a little shaky (wow, don't want that !!)

2. Dig holes and fill bottom 2" gravel and then bury the post in there and pour cement. Let it set. So basically the post is buried 3-4 feet under ground in cement.
Advantage: Minimal lateral movement. Very sturdy and does not shake.
Disadvantage - The wood will rot under the ground because of moisture and the structure may not last more than 10 yrs.

I live in the north east by the way, so I am not sure how deep should I dig the holes....
For (1) above I need only 6x6x8 posts, for (2) though I'll need 6x6x12 posts.

What are you opinions about the 2 approaches above ?


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## Gene Howe (Feb 28, 2009)

We put a 28' long by 16' wide roof over our deck. We used 12 ea. 12' redwood 6X6s and anchored them as you describe in option #1. Our deck is approx. 4' above ground level and not attached to the house. The interior posts (4) are bolted to 2X6 floor joists under the deck planking and 2X6s running length wise on either side of the posts just under the roof joists. The posts closest to the house are bolted to the 2X8 skirt AND the 2X8 joists. The outer 4 posts are 2' away from the deck and are not laterally braced at all, except for the double 2X6s that run under the roof joists.
We are subject to 30-50 mph winds each spring and have noticed no movement at all. 
you don't mention how you will build the base for the deck. Ours has 9 ea. 2' dia. concrete piers with pressure treated 6X6s mounted on CB66s, which support the 2X8 floor joists. 
It's pretty solid!


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## <*(((>< (Feb 24, 2010)

The original post is about building a pergola not a deck, so the lateral ties between the posts are I'm assuming going to be 8'+ off the ground, so there would be lots of leverage. I think the pergola would have some wobble to it by your #1 idea of mounting the posts. But this can be overcome by the use of some corbels in the corners where the posts meet the horizontal stringers on the top of the pergola.

I'm in the process of building an elevated playhouse with a sandbox underneath for my kids in our back yard and I used sonotubes dug and set 2-3" below frost line (here it is 24") and simpson anchors on top to anchor the 4x4 posts I used. I knew ahead of time that the anchors are only for verticle loads and don't have next to no lateral stability. And even after adding the floor at about 4' off the ground the structure still had a fair amount of movement to it. I the added kickers that come down on the post about 16" and attach to the horizontal floor structure at each post, for a total of 8 kickers and now the structure doesn't move at all, I can push on it and there is very little movement.

The biggest improvement of the stability of the playhouse was in the kickers. There is great strength in triangles. If I were you I would try and find a way to use the #1 idea, as it will last a lot longer, I would do some searches for pictures of pergolas and see the different styles of corbels, kickers whatever you want to call them people have done. A lot of them look really nice.

Playhouse isn't complete for those who are wondering, I'm still working on it.


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## ghar23 (Jun 14, 2013)

Awesome guys, appreciate your responses.
This is exactly what I was looking for.....

Gene you seem to have an awesome deck, as the other poster said I am building a pergola, a light weight at that.

<*(((><, Great playhouse you got, what you said kickers, is what I meant when I said knee braces, So I will have it two per corner and 3 on the 2 middle posts. I am in the northeast so the frost line is like 42 inches, so I need to dig really deep. I am wondering now that maybe I can do with 4x4 instead of 6x6, as it will be just 10-11 ft between posts.


Thanks for your responses guys.


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## Steve Neul (Sep 2, 2011)

I think the real answer to your question is a regional one. You might get better answers from your local city hall where they issue building permits. They often have literature there with specifications. 

In my area the soil is sandy and doesn't hold moisture. I normally use a tractor with a post hole digger and put a 12" hole about 3' deep and then dig a square hole 18"x18"x 3 1/2" around the hole and put a form in flush with the ground to pour the cement in.


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## Jordan_SD (Jun 14, 2013)

In South Dakota (similar weather to you probably) I dig holes 36 inches deep and fill with concrete, then use the metal post plates that keep the 4x4 one inch above the concrete top. This is code in my area for normal decks that are less than 4' off the ground. For a pergola I would do 36" holes with concrete just like a deck.


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## Gene Howe (Feb 28, 2009)

That's going to be one sweet play house, Luke.
Since our roofed deck is not attached to any other structure, I figured it would be sorta like a pergola, construction wise.


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## ghar23 (Jun 14, 2013)

Another question, I know the posts have to be pressure treated, does the wood for the pergola beams rafters and slats needs to be pressure treated also ?
Also, how many years should the post last if its buried in concrete in the ground ? This is in the North east. What are the options when its time to replace the posts ? I know its going to be ugly, but just thought of asking.


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## Pauley (Jan 21, 2012)

Here in New Hampshire, it should be 48 inches to be below the frost line...


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## SteveEl (Sep 7, 2010)

Is there a way to use Option 1, but stiffen the base with sexy native rock masonry, and hidden rebar/wire mesh ?


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## ghar23 (Jun 14, 2013)

I have scoped out the project. I am concerned about the warping of the pressure treated wood. Can someone give me some pointers on how to buy ?
My local lumber yard will deliver it home, can I send back some wood after inspection on delivery ?
I can go to Home depot also, but no matter where I go the wood is going to be wet. How do I minimize the probability of the wood warping as it dries ? 
Thanks guys.


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## against_the_grain (Aug 15, 2010)

I would go with option #1. Seems you have already decided to go that route. I put some fencing up about 10 years ago and went with option 2.

The downside with option 2 is obviously no easy way to replace or repair rotted wood. So far , mine are holding up. The gravel in the bottom helps to wick water away from the post. Results will vary depending on how well drained the soil is. Timbers treated for placement in or underground should last for years.


As for wet wood. I usually bring it home and let it dry out in the shop some. At least a few days before using it. Let air circulate all around it so it loses moisture evenly.

I also hand pick the pieces myself as there are usually quite a few culls in HD's inventory.


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## bzguy (Jul 11, 2011)

Wood posts soak up water through the end-grain like a virtual straw.
Was born in NH, snow, rain country.
Can't tell you how many outdoor posts I've seen there rotted out at the bottom only.
I'd raise the concrete bases as much as possible and slope the top edges to shed standing water.
Leave a small space to keep the post from contact with inevitable water on top of base.


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## ghar23 (Jun 14, 2013)

against_the_grain said:


> I would go with option #1. Seems you have already decided to go that route. I put some fencing up about 10 years ago and went with option 2.
> 
> The downside with option 2 is obviously no easy way to replace or repair rotted wood. So far , mine are holding up. The gravel in the bottom helps to wick water away from the post. Results will vary depending on how well drained the soil is. Timbers treated for placement in or underground should last for years.
> 
> ...





bzguy said:


> Wood posts soak up water through the end-grain like a virtual straw.
> Was born in NH, snow, rain country.
> Can't tell you how many outdoor posts I've seen there rotted out at the bottom only.
> I'd raise the concrete bases as much as possible and slope the top edges to shed standing water.
> Leave a small space to keep the post from contact with inevitable water on top of base.



Yeah I am going with option #1 even if its a bit more expensive because a fence post.... you can put another one and repair or fix, but with the pergola its probably a pain with the structure on top.

Thanks for the the responses, but basically I'm a novice with wood working and I cannot tell a good cut lumber from a bad piece so I am looking for simple non technical tip(s) on identifying bad wood so that I can send that back before I install it and then realize after a few days that its warped or whatever the issue is.


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## bzguy (Jul 11, 2011)

Boy, good luck there.
Once it's out in the sun and rain, all wood will move.
I'd look at the end grain and try to find pieces of the heartwood, center of the tree.


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## against_the_grain (Aug 15, 2010)

Usually there are bad timbers on top as customers sort through the stack. I look for wood that is fairly dry but not too dry. You can tell
how wet or dry the wood is by how light or heavy it is and obviously
sometimes you can feel the moisture. A board that is really a lot lighter than the rest is dry, and I stay away from those also.

Stay away from wood with sap lines running along the length. Look for pieces that are fairly straight obviously and have good grain integrity. Some lumber that is cut by a branch will never dry straight. You can tell by the how straight the grain is. Heavily knotted wood I usually stay away from also.

Watch for splintering and chunks of wood missing.


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