Setting 4x4 posts in footer or on top, ‘joists’ on top of 4x4 with a bracket or through bolted to the side?

Submitted by Bigfornoreas0n t3_yzrc07 in DIY

I’m in the design phase of building essentially a 10x16 carport to store work equipment in that will need to be lifted in and out of my truck. This will be a temporary structure until I can build a proper detached garage/ workshop (5 year plan) It will have 8 4x4 posts 7-8’ above grade and 2x12 joists with a long 2x10 running down the sides. The middle 2 sets of posts/joists will have a 1 ton hoist hanging from it in the center so it can be attached to the front and back of the equipment I need to lift in and out of my truck bed. The weight of the equipment will not exceed 1 ton and once it’s lifted out it will be lowered to the ground (these posts/joists will only be weight bearing for a few mins at a time a few times a week). I’m in the south so it rains often and we do have the occasional threat of tropical storms/ hurricanes but no snow load to worry about. Would my posts be better off set 2’ in concrete or bolted to a plate on top of a concrete footer? Joists mounted on top of posts with brackets or through bolted to the side? Will the 4x4 be sufficient to safely hold this temporary load? My gut is telling me set in concrete and bolt to sides but I know there’s other considerations like wood rot when setting in concrete.

48

Comments

You must log in or register to comment.

blbd t1_ix2ma76 wrote

Posts have better shear resistance set in concrete or with shear resistant brackets. 1 ton is quite a lot of concentrated point load in a hoist system. It's very important to ensure that the brackets connecting that to the lumber distribute the load properly and are arranged with through bolting instead of lag bolting and without an excess amount of wood drilled out to provide adequate load transfer. In addition to that the right amount of wood cross joists and beams or truss system to transfer that load is very important.

Lifting heavy things overhead is a life safety application so it would be very wise to collaborate with a PE in your area to get stamped drawings calculated with an appropriate safety factor for variability and glitches that happen in lumber based construction because a failure could cause serious negative consequences for life or property.

4x4 posts won't really offer the best shear resistance because they will tend to deflect easily under heavy compression. It would be wise to figure out how to cross brace all the posts to their neighbors to increase stiffness.

10

jinbtown t1_ix1low3 wrote

bolt to a plate on top of concrete column or footer.
the structure needs to be rigid to prevent racking or twisting, make sure your fourth wall that you pull into has some sort of shear protection

notch your 4x4's for the cross beam/rafter. the 4x4 will be fine for 1000 lbs per post, but that's a lot of weight for a dimensional lumber rafter, so make sure what you're using is strong enough for a point load of that much weight. Might want to use a knee brace or something to reduce the span

7

Bigfornoreas0n OP t1_ix1n0nk wrote

I think knee braces will be a great idea and cheap insurance. I was planning on there being no walls, open air structure which is why I was thinking of setting the posts in footers to help stop racking.

2

jinbtown t1_ix1p6m9 wrote

totally, and knee braces will help stiffen it! Personally would want more than 2' of concrete setting depending on how high you're going. if you're going 8' up I'd want 4' in the ground

2

Bigfornoreas0n OP t1_ix1qdp1 wrote

I was going to go 8 if sitting on top of footer or use 10’ and have 2.5-3’ in concrete. Should I up those to 12’ and burry more?

0

jinbtown t1_ix1ulej wrote

that's what I would do. for fences they recommend 1/3 - 1/2 of the exposed height, and this is carrying a lot more weight than a fence! the weight being 8' off the ground means there's a lot of torque on those posts if the load gets off center. Make sure that 4x4 is sitting on a proper bell end too - you need uplift resistance since this has a roof and open sides, the wind can produce thousands and thousands of pounds of uplift force on the underside of the roofHave you considered a mobile gantry for lifting stuff? You could make the entire structure floating if you did that

0

dominus_aranearum t1_ix23b98 wrote

> for fences they recommend 1/3 - 1/2 of the exposed height

Fences aren't carrying a vertical load so the recommended burying distance is irrelevant in this case. Fences need to withstand wind forces perpendicular to the posts, hence the below ground support. For uplift, the structure needs a proper footing and brackets.

4

jinbtown t1_ix271xp wrote

Lateral stability is extremely important for posts carrying a gantry. Gantries have 4 feet forming a triangle for this exact reason! You're totally right about uplift which is v important for open structures

1

dominus_aranearum t1_ix27cex wrote

I misread what you wrote. My ADHD meds have worn off for the day and my reading comprehension has apparently been compromised.

3

jinbtown t1_ix27py0 wrote

ugh i feel like an ass, my apologies. edited my comment. thanks for chiming in

3

dominus_aranearum t1_ix2eq0b wrote

No need, I didn't take it personally. I'm one of those seemingly rare people up here that prefers to be corrected if I'm wrong. I'd rather learn something new than get offended. Have a great night!

2

Bigfornoreas0n OP t1_ix1vafi wrote

I did consider it gantry with a metal structure. I think I could nearly build this for the price of just a mobile gantry. And I really need to put as much money into my equipment as possible. I’m budgeting this before buying the equipment to make sure it’s feasible.

1

jinbtown t1_ix278a4 wrote

I pretty regularly see mobile gantries for sale with huge capacities for under $1000 on FB marketplace, maybe try checking there

1

Bigfornoreas0n OP t1_ix1w23n wrote

The new equipment to setup everything in my truck bed will be around 6000, if I start getting up towards 2-3k for this project then I’ll just buy an enclosed trailer and be done with it. I’d prefer to have the truck bed setup overall, especially if I can make it work and save a few thousand.

1

PositiveFalse t1_ix3j1gl wrote

Post & beam construction is a great way to build a structure, open or enclosed! If your five-year plan isn't to enclose & incorporate this current structure, then rethink what you're doing! NOT asking...

Also, 4x4 posts are rarely viable for much more than a deck cover or gazebo. For structural stability - and if it were me and my money doing this - I would purchase a full set of prefab plans that suited my needs, which should include specifications and drawings with footer details as well...

This is a structure that is going to require permitting. And then, in the end, insuring. Relying upon unqualified design work and no specifications is highly unlikely to get anyone to the finish line...

Hoists are a whole other issue, by the way, and really should be investigated separately when an architect or engineer isn't involved. Again, in the end, insurability!

[EDIT] To get a feel for what might be involved, overall, take a look at a more contemporary shelter cover build at a public park. Even if the structure is older and light duty, hopefully it will provide some insight on build quality to better manage your expectations...

3

dxrey65 t1_ix47ob8 wrote

> I would purchase a full set of prefab plans that suited my needs

Worth saying, asking at a county planner about local permits and standards is really basic. When I was looking at building a carport in my area I asked about permitting at the county office and they gave me the pre-engineered plans for a standard carport, which suits our local soil and weather conditions.

That makes their job easier too if people just use their boiler-plate plan instead of guessing and improvising, then having to have an inspector come out and puzzle out the loads and forces for every randomly built thing.

3

PositiveFalse t1_ix52nj4 wrote

Wow! Your municipality seems like a good one, just based on that!

1

LeatherDonkey140 t1_ix20jm6 wrote

Never put posts below grade…..even ptdf….use a Simpson post bases, and figure out another way to provide lateral support(45’ angle brace, pst/beam).

2

but_i_dont_reddit t1_ix3rduf wrote

Just a suggestion:

Design the shelter for weather, use a stand-alone gantry crane to unload your equipment.

good luck!

2

SympathySpecialist97 t1_ix3p91r wrote

The Simpson post bases are designed for uplift, that’s why we use so many in Ca. It does not provide lateral(shear) stability. They make one bracket that is like a 12” sleeve that provides shear as well(they are like 250$ea) and a pain to set, have specific cage requirements. Go to the Simpson website. Good luck!

1

Bigfornoreas0n OP t1_ix5g64k wrote

Thank you for all the feedback! I’m going back to the drawing board and looking at doing a freestanding gantry. The load is just under 1000lbs but has the potential to have up to 100 gallons of liquid. I plan on only loading empty but was going with full as a safety factor. Plan on creating columns and beams out of triple 2x6 and 2x8 beams. Will have knee braces from beams to columns and columns to ground. I will build a shelter around this as budget allows and just cover equipment with a tarp until that time.

1