Timber Frame Carport Project

[pmsmechanic]

The reason I do not like crushed rock inside a hole with a post is that it gives water a place to go to. Virgin soil around the hole is harder and then inside the hole. By creating gaps inside the hole with rocks, you provide a place for water to gravitate to, and remain for extended periods of time. If there was no rock in the hole, no water would go into the hole.

I agree with you on this. My theory is that at least with crushed rock the water can also percolate back into the soil. When there is cement around the post it's like setting a post into a bucket of water.

I got the idea form the power company's around here. They set power poles into the holes with crushed rock. I said if it was good enough for them it was good enough for me. And I really like the self tightening properties of crushed rock.

 

[Dougeye]

For drainage to work their has to be a path for water to drain. Putting gravel in a hole is just like putting gravel in a bucket. The water just sits there with or without the gravel. But if you fill that bucket with concrete, or compacted soil, then water does not go into the bucket. The gravel just allows the water to remain in a hole longer that it should never have been in there to begin with.

When I auger a hole for a post I end up with an open top cylindrical hole that is similar to a bucket pushed into the ground. But your analogy doesn't work, because my augered hole is only the same as a bucket if the bucket has holes in the sides and bottom. If I auger a hole in the wet season, say 2 feet deep, it will slowly or quickly fill with water up to the level of the water table at the time. If it's the dry season, and the water table is lower than the bottom of the hole, any water that I might put into the hole will run out, either slowly or quickly. The speed the water enters or leaves the hole is determined by the permeability of the surrounding materials, but nothing that I've ever encountered is absolutely impermeable like an intact bucket, not even a really heavy clay.

So I don't see what difference it makes what you backfill the post hole with, concrete, crushed rock, the spoil from the hole, water is still going to come and go depending on the rising and falling water table. Water molecules are really small and they get into everything that is not totally impermeable. You'd think a vehicle's hydraulic braking system would be impermeable, but water still gets in there.

Tell me why I'm wrong about this.

Wood posts will last decades if the conditions are favourable. I have a good friend who grows hay in the desert (rattlesnakes, cacti, sage, very gravelly soil, less than 10 inches of precipitation a year) alongside the Nicola River in south central BC. He has stacks of wood posts that we've pulled out of the ground after they were pounded in more than 40 years ago. When I go there, I always bring some back because they are nearly as good as new. I use them to replace the rotting posts on my place that were pounded in only 14 years ago.

 

[s219]

In some parts of the US that have well drained soil, you can use pea gravel (or similar) to backfill the posts and it will help longevity. But here in VA with our clay soil, when you auger a hole in, it is literally like a bucket. It will hold water. Pea gravel won't really help in that case. Concrete (wet or dry mix) will at least "plug" the hole and displace water.

There are parts of my property where I can hit sand about 1-3' down, and those areas never hold water and post holes drain well. But where I am doing this carport, and most other parts of my property, the clay is bad. I have one area to the side of this carport that is wet and muddy, and I am thinking about seeing if I can drill a deep hole with the auger, then go further with my handheld post hole digger to see if I can hit sand. If I could get down to the sand layer then I could fill the hole with #57 gravel and it ought to help drain the area. I know the sand must be 4-5' down or more.

 

[ChuckT]

It's been my experience and observation that wood posts set in holes will rot at ground level more oftener than below grade here in Florida.
I've tried no adds, dry concrete mix, wet concrete, gravel at the bottom and forming the concrete to a collar at slump angle above grade.
Under the _best_ conditions they all work but if I were working a post construction I'd use sonotubes and post anchors. Anything else has a shorter life span.

 

[EddieWalker]

When I auger a hole for a post I end up with an open top cylindrical hole that is similar to a bucket pushed into the ground. But your analogy doesn't work, because my augered hole is only the same as a bucket if the bucket has holes in the sides and bottom. If I auger a hole in the wet season, say 2 feet deep, it will slowly or quickly fill with water up to the level of the water table at the time. If it's the dry season, and the water table is lower than the bottom of the hole, any water that I might put into the hole will run out, either slowly or quickly. The speed the water enters or leaves the hole is determined by the permeability of the surrounding materials, but nothing that I've ever encountered is absolutely impermeable like an intact bucket, not even a really heavy clay.

So I don't see what difference it makes what you backfill the post hole with, concrete, crushed rock, the spoil from the hole, water is still going to come and go depending on the rising and falling water table. Water molecules are really small and they get into everything that is not totally impermeable. You'd think a vehicle's hydraulic braking system would be impermeable, but water still gets in there.

Tell me why I'm wrong about this.

Wood posts will last decades if the conditions are favourable. I have a good friend who grows hay in the desert (rattlesnakes, cacti, sage, very gravelly soil, less than 10 inches of precipitation a year) alongside the Nicola River in south central BC. He has stacks of wood posts that we've pulled out of the ground after they were pounded in more than 40 years ago. When I go there, I always bring some back because they are nearly as good as new. I use them to replace the rotting posts on my place that were pounded in only 14 years ago.

Your example of how quickly and easily water travels from the undisturbed soil, into the hole is better then my plastic bucket example of why putting gravel in a hole is a bad idea. The simple fact that water travels to the void, also known as the path of least resistance, means that just by digging the hole for the post, water will want to go into that hole.

Putting gravel into the hole with the post allows water to remain in the hole longer, and it does nothing to slow the water from going into the hole. Gravel does not force the water out, it gives it an area to remain in the hole.

For wet areas like you described, concrete will keep water out of the hole because it is denser then the soil that is allowing water to travel through it.

 

[oosik]

I have two carport structures. One really large and tall for the tractor. One is four stall and "normal" car sized. I used treated 4x4 posts on all of them. So far, after 39 years, only one of the treated posts has required replacement. The remainder are all rock solid. The unique one rotted off right at ground level. Why - who knows. It was replaced eight years ago and is still solid.

I dug each of the holes with a manual post hole clam shell tool. I put a single shovel of gravel in the bottom of each hole. I don't think it made a hill of beans difference. Just made me feel better.

This is the larger single stall for the tractor.

 

[JJT]

Very nice, everything I build is timber frame, 30+ yrs of experience. And 6/12 pitch is my favorite, right at the limit for what you can walk/work on. Wish I was closer, I'd help you make some sawdust.

 

[Rustyiron]

s219, There's special satisfaction cutting you own project. (as you know):thumbsup: Very nice job!
I got a mill last summer and only have one small building "under my belt" and around here any groundwork (footers/foundations) is not worth doing until spring as the ground is frozen hard several feet, but your project has me chomping at the bit. The first project will be like yours, for my mill.

 

[skipmarcy]

I did my 32x32 carport in 2014 with 8x8 treated #1 posts. I did the holes with my 12" auger and a lot of hand digging and poured a concrete bottom maybe 4" deep. At the bottom of each post I cross-drilled a 1/2" hole and stuck an 18" long piece of 1/2" rebar thru it and placed the posts in the holes and did some scab framing to get the posts in place - the wobbled-out 12" hole really helped to accurately place the posts. I then poured approx. a 5" - 6" deep plug of concrete around the bottom of the posts, encasing that rebar within the plug. I then refilled the holes with the clay dirt we have and hand-tamped with a rock bar as I went - these holes were as deep as my auger would go, approx. 4'. My thinking is/was that the concrete plug on the end of the post would help keep it much more stable in high winds etc. I've done this type of post setting for my 2 sheds out back too, the oldest being 14 years old. Luckily no post rot yet. You have to really look for true #1 lumber anymore but I was lucky to find some when I needed it.

One thing while building that carport that my wife & I will always remember was while at the stage of framing the posts getting ready to pour the plug concrete I went out to start work and found a baby skunk had fallen into one of the larger diameter post holes. Mama was looking all around the area for the little one with a second little one right behind her every step. As I said above, these holes were close to 4' deep and the 8x8 post was taking up a fair portion of the area inside so it was pretty tricky getting that little guy to stand on the blade of my garden hoe and lift him up & out without getting shot. All came out OK though and mama found the errant one and dragged him off thru the woods in the back yard.

 

[s219]

Wow, a skunk down a hole, that sounds like a dicey situation! I have been covering my holes with boards just for that reason. Although it didn't stop my daughter from falling in one time (she was 5, and a real string bean). Then after telling her to be careful I almost dropped a foot in.