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