Help designing my Shop/Shed foundation
Hi Guys,
I’m looking for a little help deciding which way to go with a foundation for a shed/shop building I’m putting on my property. I am building a 16′ x 32′ gambrel roofed building with a full loft. Two choices I’ve come up with for the foundation are:
1. 12″ sonotube piers 36″ below and 12″ above ground every 8′ with steel saddles imbedded in the top of the pier to carry 4×4 treated sills running horizontally from pier to pier (which would support the 32′ walls. I figured I could clear span the 16′ dimension and not need any piers in the middle of the foundation if I used 2×10 or 2×12 joists. Could I use non treated lumber for the floor joists/rim joist given that it will be a minimum of 12″ above grade?
2. Concrete slab on grade 4″ thick. My question here is do I need to pour footings around the perimeter of the slab or would a 4-6″ mesh reinforced slab carry the weight of the building?
I’m a woodworker/furniture maker in my free time so I do have a decent understanding of wood and framing, but I’ve never done a foundation before and I could use some advice. I live in Oklahoma and the frost line here is fairly shallow, certainly less than the 36″ I’m planning if I do the sonotube piers. Soil is clay mostly.
Thanks in advance for any help with this guys, I surely have found some very good advice on this board in the past!
Jeff
Edited 7/19/2008 3:56 pm ET by JeffScott
Replies
The easiest and probably the best method is a monolithic slab also called a turned down slab. It's 4" reinforced in the middle and 12"-16" deep around the perimeter.
This is accomplished by first grading the site level and then digging the perimeter down to the chosen depth. Form the perimeter, then hire a good concrete finisher and his helper to handle the pour with you as second helper.
As the name implies, it's all poured as one slab.
agree but I would do 18 inch on side and increase slab to six inch, because mine is four and it flex too much under loads, beside if you want a car lift twenty years from now it be ok
agree but I would do 18 inch on side and increase slab to six inch, because mine is four and it flex too much under loads, beside if you want a car lift twenty years from now it be ok.
I should've mentioned those options. Having worked with a tight budget on my own place for so long, I tend to think about the $$ too much.
And my budget is tight, $5000. I think the lumber cost, windows and a door will be around 3000 to 3500 so that doesnt leave a lot for foundation, but i know that the foundation is the most important aspect to get right the first time.
I did my whole shed for $6000 and its 36 x 30
Another budget minded option, one that I've used for slabs of this kind, is to limit the the thickness to 4" reinforced with 4X4 welded wire and pay a few dollars more per cu. yd. for a stronger mix.
Another important matter is proper curing. The highest strength is attained when the temperature of the concrete low. During hot summer weather this is usually accomplished by keeping the surface wet for several days. A sprinkler is a good method, particularly when the sun is high, if you have the water supply to keep it going.
If you go with a slab, the concrete cost alone will probably be over 1k.
roughly 12 yard at $90 a yard $1080 no labor, no wire,rebar, no equipment, bob cat, back hoes
It's a home workshop shed, right? You're not planning to park a truck or backhoe in there or install industrial-grade stationary tools like 48" planers?
If that's the case, a framed wood floor over a gravelled crawl will be more than sufficient. It will also be much less costly than a poured slab, since in your climate you shouldn't have to go deep on the footings.
I would recommend you pour a perimeter footing. It will be easier and possibly less expensive than piers. The standard here on sand is 24" wide; on clay you may be able to go narrower. Check with a local concrete contractor; he will know. He will also know where the frost line is.
On top of the footing, either lay up a few courses of block, or pour a stub wall, just high enough to get you a foot or two above grade. This should be eight inches thick. Block out two window openings in the forms before you pour, one each on the facing walls that run perpendicular to the prevailing winds; this is for seasonal ventilation.
If you can't get a transit-mix truck in there, you can hire a small concrete pump for the two or three hours that pour will take. If you can't even get a 10-wheeler past your sycamore to deliver the gravel, hire a slinger truck to shoot enough ¾" washed gravel into the foundation to cover the soil 3-4" deep; rake the gravel even, then lay 6-mil polyethylene sheeting over it as a vapour barrier.
Now frame your floor on top of the walls, like you would for any house, and go on up from there.
I should mention that since you're on clay, you may have drainage problems in the event of heavy rain or flooding. Depending on ground slope, etc., you could occasionally get a bit of water in the crawlspace, and if it doesn't have a way to get out, it will cause problems. On clay, it won't soak into the ground very quickly.
Think about providing a way for that water to get out of there. Two choices come to mind: Either grade the whole site so that it will surface-drain towards one corner, and put a thru-footing drain there (a 4" or 6" piece of PVC pipe), leading to an exterior french drain and daylight. If you forsee a real problem, go whole hawg and install a french-drain grid inside the foundation leading to an exterior perimeter drain, again through the footing. (The gravel goes over the french drain pipes, of course.)
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Is this going to be insulated and heated? Where do you live?
If you live where the frost goes fairly deep, my advice applies.
Either slab or piers will work. If you go with a slab, unless your soil is sand or gravel, you will have to haul in and compact granular fill. If you are heating it, you will want to insulate under the slab. Not only will the slab need a thickened edge (ours are 18"), but we also run 4 pieces of rebar around the perimeter.
Your pier plan sounds OK, but you will want more than a treated 4x4 between the piers. That really wouldn't do you much good. You could build up a grade beam out of 2x12's or use engineered lumber. Then the joists could be hangared off of the beam.
The "steel saddles" in the top of the piers are a bitch too pull off to wind up with parallel beams. Not saying it can't be done, but if this is your first time, it's unlikely. Might be easier to just set a j-bolt and bolt a post base onto the top of your pier.
I would think you'd want a bell footing of some kind on your piers, but since I have no idea of your soil conditions, I can't even hazard a guess.
What I described is a "floating slab". You can also have frost footings under the perimeter of a slab.
Edited 7/19/2008 11:03 am ET by Marson
Welcome to BT jeff.
as to do I need to pour footings around the perimeter of the slab , short answer is yes, some methods already posted.
Location, etc: click on your own name in the heading, a profile screen comes up that asks for location, etc. The location part is very helpful for those who reply.
I used a monolithic slab with thickened edges on compacted fill and am happy with this. If you have the space I would suggest that you have a wider width to your shop, 24' or more will allow you to manouver longer lengths of wood or other material.
Any good shop needs a basement.
Our shop/show room has a basement. In fact, the shop is in the basement, and the show room is above. There is an over head door on the back to drive into the shop if needed. There is also a garage up top with a 4" slab pored on two layers of 3/4" pressure treated ply on top of 14" open web trusses with a span of about 12'. There is a car parked in the garage. It hasn't cracked in 22 years.
Dig a hole in the ground and it will fill with water!
I don't like basements up here in canada. Think there should be more slab on grades! My 2 cents!
Where's Peterborough? You some sort of low lying flatlander?
I thought all Canuk's dug down. Lookit Toronto, or Montreal. It's so damn cold there, that they build two, three levels down.
Peterborough is 1 and a half hours east of peterborough.
Yes we do build down, but I'll bet 70% of all basements have mould,, if you look close enough. Basements suck. But maybe I'm just radical!
Ever dig a hole at the beach? It fills with water! We get loads of snow,, and every spring it melts. Then the calls start,, my 100 year old house has water in the basement. I think slab on grade is super managulistically cool, and would love to see a shift in the paradigm.
Just my ideas,, thought I'd share!
Ever dig a hole at the beach? It fills with water!
The lot I recently bought on Lake Michigan has it's building site 120' above the lake level. All sand. Think that'll fill with water when I have the basement dug? They are saying the water level is up 6" from last year...
Now you got me worried!
For that size building, you probably have to pull a permit. What does the local code office say? Many of them now have web sites with boilerplate applications for projects like detached garages. They show you exactly what's needed for a foundation, depths, rebar, etc.
OP is in Oklahoma (it's in post #1), and probably has a frost depth of 3-6"
OP confused me with 48' piers (36'-0" down and 12'-0" up), so I was picturing a gambrel-roofed pole barn with a loft--a tad mind bogling in tornado country.
I'm going to guess this is rural, so there may not be an AHJ at all.
So, my bias would be to a slab as that will be easier for DIY work (not augering holes for 12" diameter sonotube 48" long, plumbed and squared to a grid, and then getting concrete set in every one to the same mix/strength). Compacted pad; turn-down edge 18" minimum into undisturbed soil and a 6" slab (to get 5"). Bar schedule to suit, too (2 #4, cont. T&B, stirruped #3 @ 24" OC; slab #4 @ 12" OCEW). Spec 3000psi crete and hope to get 2400-2800 if field-mixed.
That deep turndown is for more ground adhesion to resist wind lift. Heavy slab to cut down on needing intermediate beams; but also for future loads (like lifts, cranes, spaceship gantries, no telling what in a century or two).Occupational hazard of my occupation not being around (sorry Bubba)
A little more information. I live in Oklahoma and the soil is all clay. The reason for the 16 x 32 footprint is because that is the biggest size building I can put in my yard given the setbacks and easements. I have spoken with the city and I will have to pull a permit but they don't seem to care how big the building is as long as I provide a plat drawing showing the placement and square footage of the building. As far as direction on what they would like to see in the way of construction technique the guy only offered the 2006 International Building Code book as a guideline. Great. I've read through some of it and its a little daunting for someone who hasn't done this before.I plan on visiting with one of the city inspectors and picking his brain on what he likes and would pass. I do live in a subdivision and this would certainly be one of the largest sheds in the neighborhood so I also plan to visit my neighbors and get a feel for their opinions. There is no homeowners association but I do need to get a copy of the deed covenants from the county to double check. Most people around here just throw up sheds left and right that should be permitted and are not. I'm trying to play this by the book.I like the idea of a slab foundation, thats what my house is. I am not planning on heating it other than a window a/c and heater unit maybe. Funny thing is the city told me I could do all my own electric and plumbing myself! I'm sure it would have to pass inspection but I thought that was interesting.I could excavate the site with a small track hoe or bobcat but it may be hard to get a ready mix truck on the lot due to a sycamore being somewhat in the way. That's why I was leaning toward the pier and beam foundation because I could pour that myself with a 1 yard trailer of concrete from one of the local companies.I appreciate all the suggestions you guys have given me so far, it's a great help to me. I have a lot of time right now to think about this as I am home in bed recovering from surgery :-)Jeff
I recall seeing a goodly number of tension slabs coming into popularity down there a few years back.
Cables run thru conduit to threaded rods which could be tightened and released as needed.
I'm not sure about OK, but here, all slabs get put on compacted sand/gravel fill. Sounds like you might have tough site access, so the slab would be problematic in terms of getting fill back there. I would probably just rent a mini excavator and put in piers. You could also auger them--a rental center near me rents the Toro "dingo" which comes with an auger attachment that is pretty slick. As someone else said, getting piers in the right spot is no small job. Another thought is helical piers. They look sort of like a giant drill bit which is drilled into the ground, and you wind up with a pipe sticking out of the ground with a flat plate on it to which you can bolt a post base. No hole, no backfill, no lawn disturbance. They work well in clay. The nice part is that there is no guesswork involved. X amount of torque results in a pier which can support y tons.
Jeff,
I thought I could build the same size and shape building for $5,000, too... but the concrete slab was $4.50 a sq. ft. and with four runs of 1/2" rebar in the footings and 3/8" in the slab and porch, the final cost was about $3,500. Plus, I found that adding an 8'x32' porch along the side length (front), the concrete floor was only $500 more than pouring piers and using pressure treated lumber and decking with my labor. The whole slab has now been poured 16 months and not a hint of problems.
If you are going with a 19ft. tall two story, you'll need heavy footings to carry the down loads and the side loads from the wind..... and if you ever wish to have a rollup door in one end, an extra beam about 12" behind where the front car tires will set will prevent any cracking under a parked load....
With my "shoestring" supply gathering, it will be insulated, a 17,000btu heat/cooling electric wall unit, wired, shingled, sheetrocked, finished inside and the Hardiboard siding painted for under $12,000.
Here's some shots of how my slab was poured...and where I've stopped awaiting insurance claims after an April golf ball size hailstorm....
Good luck with your project, Bill
Edited 7/19/2008 10:15 pm ET by BilljustBill
Thanks Bill and everyone else for your opinions and suggestions, it's very helpful. That's a very nice looking building Bill.I plan to use the building as a woodworking shop and the heaviest piece of equipment I have is a 500 lb. Powermatic table saw. I'll never put any kind of vehicles in it, just hobby stuff and woodworking. It should look a lot like Bill's with a large second story loft area to put all the wife's stuff up there out of the way of my stuff ;-)The slab idea looks the most promising but also a budget buster so I may have to think about this a little more. On a side note I was at Home Depot tonight looking at a large gambrel shed about 16x20 that was all sheathed and floored with OSB and they wanted 9k to build one!I should probably start contacting concrete contractors and get some bids. I've finished a 10 x 30 ft driveway before, my first such concrete project and I know that you have to work fairly quickly or the redi-mix driver gives you dirty looks! I would like to do as much of the work as possible to save money but I'm unsure if I'm up to the whole task.Oh and as far as drainage, the yard slopes away from the house and drops about 1.5 ft. from house to the far side of the shed about 26 ft. away from the house. I know clay doesn't drain fast and I would have to keep the crawlspace open to allow drainage. And I never had considered wind load and I should have because we routinely get 60 mph winds here in the spring.Lots of good advice guys, thank you very much!Jeff
Jeff,
It took me almost a year to collect most of lumber and sheet goods from cull carts at Lowes. One small load at a time. Because of 15 sheets for $60 of radiant barrier Kool-Ply roof decking, I did have to buy the other half the 5/8 radiant roof and porch decking, and price matching of four 5/8" side sheathing for the bottom floor and 12 sheets of 1/2" OSB with radiant barrier.
Here's what my year of collecting "inventory" looked like before I thought I'd have enough to complete the building...the rollup door is 8'x8'.... On the side shelving is enough tongue & groove Western Red Cedar (cull cart) to do the underside of the porch on the diagonal...just the retail cost of the cedar would have been over $1,000...
Don't forget to add a 220v floor plug or two for your saw, and other 3hp+ tools in the future.
Bill
Edited 7/20/2008 1:15 am ET by BilljustBill
Wow that is some impressive stockpile there! Ok I have to ask a dumb question though, what is a "cull cart"? Is is an area with clearance or seconds material? Sounds like you got the same hail storm we did except that we only had golf ball sized hail. Roofing companies up here are waaaay busy. I'm on the list for a new one, hopefully they'll get to me soon.Jeff
Now REZ might jump in here, too, as I understand from his postings, he lurks in the isles of the box stores looking for bargains more than I do....
There are boards in every shipment of lumber that have defects. I suppose it's because of lability, but rather than cut a 10ft down to a good 8' or a 16' down to a solid 10', the employees cull the defective lumber and put it on one of the blue lumber carts at the back of the store. When the "Cull Cart" gets full, an inventory sheet is run on its content and then the whole cart is usually sold at 10%-15% of the retail price.
The fellows at HD and Lowes have commented that about 1/4 of a brand new opened lumber bundle qualify for the cull cart from the beginning.... To see that, all you have to do is look at the endgrains of the stacked lumber. There is such a high percentage of lumber that shows center-of-the-tree growth rings; the most unstable part to be used for projects in softwoods or hardwoods...
One morning I visited Home Depot and found 32 sheets of Hardiboard siding sheets showing where a pair of forklift arms broke/skinned a pair of 1/2" deep edge-scars on one side of the panels. All 32 were marked down to $10 a sheet. The Hardiboard 1x3" batten strips easily hide that nicked edge anyway. Then one evening at Lowes a few weeks later, there were 16 sheets with some corners broken. Since the gambrel roof needs the end walls to taper in anyway, when the manager marked all 16 sheets for $20, I had my building's siding needs solved....
The key is knowing what your future projects will need as well as what can be used for upcoming house upgrades, and a dry place to store it until you get to it... With my lumber storage getting full, I stored all the sheathing, decking and the Hardiboard siding on my 5x8' trailer wrapped with HD's transport plastic sheeting, plus tightly tarped down for the fall and winter storms...
A word about the roofing shingles. As of Friday, our insurance company is now paying $170 a square for 30yr shingles. The 40yr "Impact Resistant" shingle from GAF/Elk sells for $201 a square. My insurance company looked at my policy and said that if I put on the 40yr, class A shingle, it will save me $400 each year on my homeowner's premium cost. I'll break even on the upgrade cost in 6 years, and still the savings will continue until the next wind/hail damage... FYI Here's a shot of the hail storm that day...
Good luck with your shed, the fellows on the forum have been great at answering any question I've asked. They make it a good and safe place to ask just about anything!!!
Bill
Edited 7/20/2008 6:42 pm ET by BilljustBill
Edited 7/20/2008 6:48 pm ET by BilljustBill
I shall start diligently looking for bargains since I usually visit Lowe's once or twice a week (i live 1.5 miles from it). I'll check into the 40 yr shingles and see whether I can save some money too. Don't you just love hail? $5000 damage to my car last time and $7500 to my house. I can almost deal with the tornadoes just spare me from the hail!! Thanks a lot Bill.Jeff
I agree with the monolithic thickened slab edge ... should be fine for the local BO, too. I've used it on a garage in a far north climate. 4" slab w/ 12-16" around perimeter ... You could probably do 12" maybe even less. #4 bars around the perimeter and 6x6 wwm in the center and down under the rebar around the perimeter. Great slab!! Install the anchor bolts and you should be ready to go. One pour, minimal excavation.