Pier foundation for a carport

[handirifle]

I have a steel 18' x 18' car port, that is currently sitting on a slope and the dirt, no foundation. Hopefully sometime this year I will get the chance to make some improvements. I want to move the carport from its current location, grade the site level, as it is FAR from that now, and build a foundation to raise it about 2 feet above current height. I plan on a floor base of decomposed granite or similar. Maybe just some sort of small crushed gravel, compacted.

I have a friend that will have access to about all the 8" diameter treated logs, I need. I am thinking of sinking them in the ground at least 2' possibly 3'. The frost line is no real concern here, as water lines are safe 12" underground. More than likely, if I can rent an auger, I will go for 3' just for extra strength and stability. Although we do not NORMALLY have high winds here, storms can always bring nasty surprises, so wind making any movement would be my reason for 3ft depth. I am thinking if I go to 3ft I can get away with 4" or so of gravel on the bottom, and hard pack earth around the pole. For reference, we get about 20" or so of rain a year. I have seen 40" before though.

I plan then to create a mounting surface to mate the logs to the base piece of steel the runs the length of each side at the bottom of each steel rib (correct name?) for the carport. Not sure how just yet, which is the reason for the post. Looking for suggestions on that. I want to raise it because I want to semi enclose the carport, with swing open barn door type doors (very light weight) just to keep things out of view, and I wanted the higher straight wall to make sure my tractors ROPS clears the top rail I plan on running from side to side.

What would you guys suggest to use to connect the logs to the base plate with. I was thinking possibly a 2x8 bolted to the tops of the posts, but wasn't sure that would hold up to hefty winds.

I plan on placing a log in the ground that will sit under each of the steel ribs of the carport. Oh, let me add, the foundation will only be under the walls and it will go across the rear, but supporting nothing for the carport. it will just make enclosing it easier.

Educate me please. Any and all suggestion or criticisms of my idea are appreciated.

 

[davedj1]

Sounds like a lot of work but should work just fine. I would dig a ditch, stack the timbers (8x8 or 6x6) and be done. Or dig ditch, form up and pour concrete with pt top plate.

 

[Illini22]

I'm looking at xarports too, and was also debating concrete (cost) versus sinking some posts and bolting it to the bottom rail. I think we would need quite a few piers to secure it, which makes pouring a pad more attractive.

 

[KYErik]

You could buy some flexible metal "hurricane straps" to attach the horizontal sill plate to the vertical sunken posts. As long as you attach the carport/top board through the side grain of the wood of the sunken posts, it should hold. I would not expect nails/screws to hold going down though the end grain- this would be an issue if you ever had a big wind and some serious uplift. It would also be great if you could bolt a treated 2x8 etc along the side of the top of all of the sunken posts to keep them all tied together

 

[flusher]

Here's the foundation I had to use for my 20x36 ft carport (9 ft sides)



Dug trenches for nominal 12"W x 18" deep footings. The driveway is sloped so the concrete is about 24" deep at the low point.

Embedded pairs of J-bolts in the concrete for hold-down straps and to be extra safe used a bunch of wedge-anchor concrete bolts also. Needed to design the foundation/hold-downs for 80 mph wind conditions per the county building code for a carport this size. There's something like 15,000 lbs of uplift force on the canopy in that wind condition. I poured about 6.25 cubic yards of concrete to make a ~20,000 lb anchor. So far it's still standing.:thumbsup:

Good luck.

 

[handirifle]

I was hoping to save some $$$ by not using concrete. I was wondering, now that you bring it up, if the piers should be anchored in concrete? I am sure there is no such thing as being tooo strong.

Eric
if I strapped the bottom sill to the posts as you mentioned, do you think a 2x8 would suffice for the sill? The carport has a strip of steel, no idea how thick cause it's mostly covered in dirt, but I doubt it is more than 3/16" thick, most likely less. Anyway that is what connects the main beams of the carport together, and keeps it anchored to the ground. Mine also has a wood structure attached to one side that I store firewood in, but it was not part of the carport itself.

 

[handirifle]

Flusher
Are those the hold down mounted every other post? Hard to see them clearly. I'm going out to see exactly what the bottom sill is, that is currently used.

 

[handirifle]

OK am officially embarrassed now. I had always ASSUMED (you know what they say about assuming) that is was just flat metal, but I got a shovel out and dug down. Lo and behold, it's 2x2 steel tubing. I hope it isn't rusted, since it's all underground. I have found a lot of things on this place like that since I bought it. It's when I go to re-do or move something I see just how mickey moused it was.

The good part is when I get ready to move the car port out of the way to make the new foundation, the base tubing will hold it together better. My plan, might be crazy but will try it anyway, is to place a 20' beam in front of the port, attached to the sides and base, and drag it from current location till I have room to work on the foundation. I MIGHT go sideways with it, just enough to get ample work area, but doubt it.

Whoever put it up before did ZERO ground prep before setting it down. So now, I have to move everything and do it right. There is probably 12" difference in grade from front to back.

 

[KYErik]

I think the sill (the board laying flat on top of the posts) should match the diameter of the posts. The more straps you put around the carport base rail and sill and attach to the posts, the better. I'd at least put them near each of the carport posts.

 

[flusher]

Flusher
Are those the hold down mounted every other post? Hard to see them clearly. I'm going out to see exactly what the bottom sill is, that is currently used.[/QUOTE]

Sorry. Here's what they look like.

There are five J-bolt hold downs and five wedge anchor bolts on each footing to keep the carport from blowing away. The installers put in the anchor bolts in about 15 minutes total. Spaced them approximately evenly.

Good luck

 

[handirifle]

KYErik
I agree, the more the better., The last thing I want to see in a windstorm is my carport headed to the land of oz. I am thinking that I might go one of two ways with this now. I could put the round concrete forms in the ground, and fill them with concrete, instead of the posts, using a similar system to flushers. Or, if I put the posts in the ground, I could use a 2x8 to connect them but anchor the bottom sill of the carport to the posts with an upside down "U" going over the carport sill and down the sides of the posts 10" or so, and lag bolted in with about 4" lag bolts, 2 per side?

I dunno, maybe I ought to just pour a footer, and lay concrete blocks all around to get the 2 foot wall. That was one of my original thoughts. It's just that the costs on these ideas keep going ever upwards and makes me wonder if I can do them at all.

 

[handirifle]

Let me ask this. If I were to use concrete blocks for the wall, if they were set, say, 18" underground, on a gravel base, would that suffice, or does it NEED to be on a concrete footer, underground?

I am thinking that if I built it like that, it would be 3-4" of gravel, with the blocks locked together with rebar, horizontally and vertically, and the vertical rebar sections back filled with concrete. I would then anchor it like flusher did. I could do the blocks in stages that way and not have to pay the horrendous delivery fees the concrete trucks charge. I live about 30 min from any concrete source, on country roads.

I did a project similar to this for a small retaining wall in my back yard, except I made a footer for it, but I am thinking that if the blocks are buried 18" underground and extend 2 ft above ground, that might just do it.

Thoughts?

 

[tmc_31]

I built a carport a few years ago for my dad. It was similar sized, 20'X24' I think. On his I had 4-4"X4" steel posts with 3/16" wall on each side of the carport. Each post was set in a 18"X36" deep pier and backfilled with concrete. 8 piers total. The roof frame was built of 6" purlin that was screwed to the top of the posts. A R-panel roof was laid on top of that.

If I was in your shoes, I think I would drill 3' deep 18" diameter holes at each post location. Set a 4"X4"X3/16 steel post in each hole and concrete them in place. The posts can be cut off so that the tops are level all around and so that they will raise the carport to the height that you want it. You said that the bottom rails of your carport were 2" square tubing. I would weld a steel cap on top of each post to seal out the rain and then weld a 2"X2"X4"X3/16" angle iron on top of that so that you can screw your existing rail to the top of the posts. Then I would grade between the piers and lay a concrete block wall to meet up with the bottom of your rail.

If this concept interests you, feel free to ask any questions you may have.

Tim

 

[tmc_31]

Let me ask this. If I were to use concrete blocks for the wall, if they were set, say, 18" underground, on a gravel base, would that suffice, or does it NEED to be on a concrete footer, underground?

I am thinking that if I built it like that, it would be 3-4" of gravel, with the blocks locked together with rebar, horizontally and vertically, and the vertical rebar sections back filled with concrete. I would then anchor it like flusher did. I could do the blocks in stages that way and not have to pay the horrendous delivery fees the concrete trucks charge. I live about 30 min from any concrete source, on country roads.

I did a project similar to this for a small retaining wall in my back yard, except I made a footer for it, but I am thinking that if the blocks are buried 18" underground and extend 2 ft above ground, that might just do it.

Thoughts?

It depends on how much the ground moves where you live, and if it heaves much when it gets cold. Where I live the ground is pretty stable but I still would want a 18" deep steel reinforced concrete footer under that block wall. That said, if you set the carport on very stable piers, the worst that could happen is that your block walls might crack. I think the carport would stay put.

Tim

 

[handirifle]

Well the ground around here doesn't heave really at all. I mean a water line 6" deep would never freeze. We just don't get sustained cold.

If I did do a footer, not sure how deep it would have to go.

 

[KYErik]

KYErik
I agree, the more the better., The last thing I want to see in a windstorm is my carport headed to the land of oz. I am thinking that I might go one of two ways with this now. I could put the round concrete forms in the ground, and fill them with concrete, instead of the posts, using a similar system to flushers. Or, if I put the posts in the ground, I could use a 2x8 to connect them but anchor the bottom sill of the carport to the posts with an upside down "U" going over the carport sill and down the sides of the posts 10" or so, and lag bolted in with about 4" lag bolts, 2 per side?

I dunno, maybe I ought to just pour a footer, and lay concrete blocks all around to get the 2 foot wall. That was one of my original thoughts. It's just that the costs on these ideas keep going ever upwards and makes me wonder if I can do them at all.

"More expensive" is typically better/stronger, but we all have to work within a budget. I think any of these ideas would work fairly well. If you have many trees near this structure, you might try to save some money on the base since an extreme wind storm would likely result in it being damaged by a falling limb.

I would guess that 6-8 steel posts, set deep in concrete and firmly bolted to the base would be the strongest AND most economical method to keep it from blowing away and sunken wood posts would be the cheapest retaining wall.

 

[handirifle]

I built a carport a few years ago for my dad. It was similar sized, 20'X24' I think. On his I had 4-4"X4" steel posts with 3/16" wall on each side of the carport. Each post was set in a 18"X36" deep pier and backfilled with concrete. 8 piers total. The roof frame was built of 6" purlin that was screwed to the top of the posts. A R-panel roof was laid on top of that.

If I was in your shoes, I think I would drill 3' deep 18" diameter holes at each post location. Set a 4"X4"X3/16 steel post in each hole and concrete them in place. The posts can be cut off so that the tops are level all around and so that they will raise the carport to the height that you want it. You said that the bottom rails of your carport were 2" square tubing. I would weld a steel cap on top of each post to seal out the rain and then weld a 2"X2"X4"X3/16" angle iron on top of that so that you can screw your existing rail to the top of the posts. Then I would grade between the piers and lay a concrete block wall to meet up with the bottom of your rail.

If this concept interests you, feel free to ask any questions you may have.

Tim

TMC
I am interested in this idea. I think I will give up on the wood posts, for a number of reasons, possible rotting of the wood being one of them. I hate to redo stuff I have put a lot of time into.

You gave the dimensions of the angle as 2x2x4 x 3/16" is the 4" the suggested length of each piece? As for grading, I would most likely grade the entire area before I did anything else, mainly because the whole area needs to be graded. There is too much slope. I would leave some slope for drainage.

n my mind, I would dig out holes and put concrete forms down, so that they would top out just slightly above grade, for drainage, with the posts set in them. I think I might invest in a steel top that connects all the posts together, to control any shifting. If I did that, I could get away with 4 piers per side, and clamp them to the post caps similar to how flusher did.

I will have to do a cost comparison, for that method compared to block walls. Steel prices have gone astronomical around here, so that can change things up a lot.

 

[Ted Summey]

I built a 24x30 shop building with two 12x30 sheds on either side. It is a metal building built with the 2"x2" galvanized tubing like you describe for your carport. My shop had to be engineered for 140 mph wind loads and for some astronomical snow load. The sheds are on 8" of crush and run gravel pads ( the main shop is on concrete). The plans required and engineer's certification/ stamp.

I tell all of this to say that the sheds are anchored with 36" long by 4" auger type mobile home anchors. The bottom tube is drilled and the top of the anchor is bolted to that tube. The building is 9 years old and has withstood both high wind of 60 mph and snow loads of 10 to 12 inches.

 

[tmc_31]

handirifle, yes I was recommending a 4" long piece of angle iron. Four piers on each side should be enough to support a 18'X18' carport. If you have more posts than that and you want to run a full length steel cap over the top of the square steel in the piers, I suggest that you use something like 4X4 angle or Jr. I beam so that your intermediate posts are supported.

Tim

 

[handirifle]

Ted
That is kinda how it's built now, but I want to raise that bottom section by 2', for added wall height.

I have asked the various car port companies about just getting longer wall pieces, but they say the new pieces need to be 2x3" and the roof needs to be trussed differently, so that is why I came up with sitting the existing design on top of my own 2ft wall.