Hello folks!
I’m looking to build a garden arbor out of redwood. The plan is to build a fairly wide 16′-20′ width using three or four posts to hold it up.
My question is, how do I secure the posts to the ground? Assuming that I want the arbor to be 7 feet tall, do I sink the 4 x 4 Redwood posts into the ground in 3 feet of concrete or do I attach the posts to a column column base set into concrete?
Also, Simpson makes both column and post bases, it the column base the right one to use?
Thanks in advance!
Replies
I'd certainly set the posts INTO the ground to avoid racking from wind on the structure and plantings that may climb it. I don't trust ANY post base anchors I've seen yet.
7' tall would tell me at least 3' into the ground is a ball park depth. Frost depths ( if applicable) and other variables enter in to the plan.
Firintsnce..I just set a few porch type poles ( Cedar and Locust) in Ky, in solid clay...digging the holes was a PITA, but I got a sound anchorage at 30'' deep, for a 9' tall 6-8'' dia. round pole.
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You gonna play that thing?
http://www.youtube.com/watch?v=32Ln-SpJsy0
Sphere,Then I guess I'll sink them. Thanks! Now to Home Depot to find some nice redwood 4x4s.... HAHAHAHAHA!!!! I crack myself up!
I know redwood is naturally rot resitant but something tells me that anything buried in the ground ought to be treated and rated for ground contact. I'd maybe think about burying PT posts and skinning them for aesthetics.
Red,Skinning some PT posts was one of my original thoughts, but the width of the Arbor is likely to use 3 or 4 posts and that's a lot of skinning! Still might happen though...
I see nine posts for a 16x20
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How cool is this... Piffin answered my post!I'm thinking of a wide arbor only. So I don't think I'd need nine posts. This would be at 16' overall width using, probably using 3 posts (4x6). I'm leaning toward pressure treated now...
three posts?is this a tringular arbour?You mean six posts? Three to a side?That makes the knees a darn good idea
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It might help if everyone was on the same page.A arbor is generally a "flat" structure that you pass through.http://www.gardenstructure.com/s/garden_arbor_plans_designs.htmlA pergola is more of a rectangular structure forming a "room".http://www.gardenstructure.com/s/pergola_plans_pergola_designs.htmlAlthough I see some structures, such as the weddign pergola, that I would call an arbor..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
There is really only a structural diffence made in modern commercial marketing, Bill.In essence, an arbor and a pergola are one and the same.In origin, an arbor is a tree, then the name is applied to any shady place formed amongst the trees, sometimes naturally formed and sometimes helped by weaving growing vines etc.Then man comes along and imitates that in a construction sometimes of stone or other materials and designed more carefully and he gives it afancy romantic name, calling it a pergola.But it is all the same structure.
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and there is nothing special about piffin answering a post. he has done it about fifty thousand other times. That probably deflates the value...;)
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Something has to resist moment or the structure falls down. You can either design joint above ground to handle the moment, or you can embed the posts, so they do it.
If you go with embedded redwood posts, be sure they are heart wood, and not the pithy outer wood. The heart wood stands a chance of not rotting, the outer wood will rot.
Jigs,I plan on setting posts in concrete, but I guess that the rot problem is the point at which the redwood comes out of the ground and is susceptible to rot? I do plan on using nice heart redwood for this. I'll look into treating the wood near the base as well.
in most parts of the country, encasing the post in crete will accelerate rot rather than slow it, because you are holding water too the wood instead of letting it drain away.The rot zone tends to be most active about 6-12" below the surface of the soil when buried, but in crete it is 2-4" down.The location is according to where moisture, temperature, and micro-organisms are at peak.I lean to burying PT and wrapping it. 4x4 posts that are nice looking are rare, but if you want rugged look that would be fine.If you want a crete base and longevity I would attach to crete above ground 2-3 inches with a Simpson post anchor and design the structure for wind resistance with diagonal kickers called knees. These can be artfully done, and with such a large span they would help resist the vertical loading also.
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I would do this as a skinned job. I'd dig deep and plant 2" pipe in cement below frostline - about 3' here. Pipes about 6" shorter than finished arbor heigth and filled with cement at least 2' above the ground. While that was curing I'd go to a real lumber store and find some good looking boards - picked for figure, etc.. Bore some pt blocks to fit over the pipe and build the posts skinning the blocks with the boards. Top 5" of pt unbored with a 'wheel' of 3/4 ply fitted into the hole as a stop so the post does not make ground contact.
Depending on the work you put into it this may be bigger than a 4x4, but it also won't look like a 4x4. It will also outlast any 4x4.
2" pipe that high would be some pretty expensive steel. ever tried something like that with PVC?Also, concrete would be better than cement, no?
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Cement by it'self has very little strength. It is just a binder for the aggregate which does have the strength. A stick of 2" galvanized could do all three of his posts and wouldn't be much more expensive than the wood considering he is looking at putting 1/3 of the wood in the dirt and would save that much. This also allows interesting wood that is less than premium price to be used for the skin.
He also didn't offer situational details for wind loading, footprint for lateral load sharing, etc., so I'm assuming it needs all the help that can be built in.
PVC would need to be 4" and filled with concrete 10 x dia above the bend tangent to equal 2" sched 40 stiffened with mud. I've seen that done as a post for a rock pillar.
Frostline??? I think I saw frost on the ground twice, maybe three times this winter. I didn't even know what that meant until I was watching Hometime¯ a few years ago when they were digging in the fall in Minnesota.Anyway, I'm now leaning toward pressure treated 4x6 for the posts, 3ft in the ground and 7ft above.
Regardless of the wood you use DO NOT GO TO HD!!! (sorry to shout, but...)
All their PT is the lightest possible level of saturation of the treatment - OK for outside exposure but not recommended for ground contact. You need to go to a real lumber yard to get the 0.40 stuff for burial.
Depending on just where you are in the greater Bay Area... Piedmont has a great selection of rough redwood, but it's getting really pricy. Golden State has all the grades of PT, not sure about their redwood; may have cedar as well. If you can afford them Truitt & White have just about anything you'd need.
As others have said, definately avoid the concrete. Check out a crew installing a telephone pole sometime - tamped dirt is all they use. In heavy clay I'd just do the dirt. If there is some level of drainage I like to put a few inches of clean gravel in the bottom of the hole and then up the sides of the posts abut 6". Helps the water drain away.
Thanks Wrudiger,Any way, don't get me started on talking about the quality of HD lumber. I had a rant on the Knots forum about having to re-glue the plywood laminate on one 4 x 8 sheets after cutting it (faster and cheaper than trying to return it). After that, I went back to using A1 grade maple plywood even for my painted project! Also, that's why I joked about going to HD to buy my posts earlier.
Assuming average soil, set the posts into the ground using well-compacted crushed rock, not concrete.