Foundation. is 6" slab is really enough?

[agrasyuk]

Hi Members.
I'm preparing to start my L shaped outdoor kitchen build, plans are on file with the village and I will have the permit in a week or so. build is similar to one of the members here: https://community.fornobravo.com/for...819#post261819 - oven will be the corner piece. and the entire area will be covered by rain shelter.

now here is the question. for the rain shelter roof support pillars I will be digging holes >42 deep and pouring concrete piers. village, as well as common sense, ask for foundation to reach below the frost line (42 inches deep) and I plan to go closer to full 4 feet below. I see pretty much all the builds here suggest building on reinforced slab. Obviously this is much easier then digging a perimeter trench for 3-4 cources of concrete block foundation. but somehow I'm not feeling very easy on this.
is 6" really provides sufficient foundation? how does that hold over time?

thanks

[UtahBeehiver]

There are several cold climate builds with 6" slabs. The ground prep is very important, I installed 8" of compacted crushed stone under my 6" pad. The pad also had 8" X 8" wire mesh with # 4 rebar around the perimeter. I am from SLC, UT and we get similar snow and frost condition like Chicago and my build is over 5 years old with no structural issues. Ultimately, you and what the village requires will be the deciding factor.

[agrasyuk]

thank you for the answer. doing lots of reading here and it looks like a thicker aggregate layer with rebar reinforced slab for floating foundation might be passable. thinking about it the aggregate should help to drain the water that could freeze and I don't mind digging down. then again I know for sure there is clay underneath (excavated for deck foundation piers last year).
but then you are right that the village engineer is indeed going to be the final authority answering that question. can't wait...

regards! best

[RandyJ]

The question you have asked is a very hotly contested one. Some insist that you need footings others not. I live just outside minneapolis MN and I did not do footings. I went a foot thick 1 foot wide all the way around my slab and 6 " thick for the rest. I did a 8"x8" grid of 1\2" rebar. But I was not worried about frost heave as where I live it is all sand as fast as you want to dig. If if had heavy clay I would have done footings. My brother in law just had a new side walk and it heaved 2.5" the first winter. I had no movement at all.

Randy

[agrasyuk]

thanks Randy. I did look through several conversations that indeed got hot
while 42" deep trench is lots of work, 7 courses of CMUs below + all the extra concrete i'm mentally preparing to do it. chances are that it will be required by municipality here and it just makes more sense to me (not that I have any experience with foundations). but maybe we could settle on several deep piers (flared out below the frostline). attached is a sketch of what I have in mind building, grill/fireplace on the right will not be a very light structure.

[RandyJ]

The story I hear over and over is that the sonotubes do no good to prevent frost heave. The general consensus is to either go all the way or slab on grade. That is a very nice looking setup you have planned there. I can't wait to see it all come together. It is funny. My city did not want a permit for construction. I think it confused the lead city planner and then he said there was nothing to inspect other than the foundation. I said I was planning a slab on grade and then no permit. Just call the fire marshall and see what he has to say. Good luck.

Randy

[agrasyuk]

for patios and concrete in general our village does require permits, but at least I don't have to deal with HOA. I did receive reply - "climate zone 5 requires 42" below grade foundation" which as I said does make sense to me so I will be doing lots of digging. and I guess my plans did confuse our inspector as well as I received quite a reply letter and among other comments a fireplace construction code that he for some reason believes applies in my case. we had a lengthy phone conversation that was quite a mood killer for me, I simply fail to understand why village would be concerned about dimentions of individual elements. its not like they will need to buy or build it. but there is no point arguing i guess, redid my plans to include floor and section drawings of the 2 fire burning elements (hopefully it will be close to code) and resubmitted this morning. maybe it was my mistake to have have the words "fireplace" there in first place, should have called it a "decorative masonry structure" instead... if all fails I will strip the firebrick from the plans and declare it as covered wood storage area.
on the good news I found and purchased a small concrete mixer of craiglist, can do 2 bags at a time , can't wait start mixing concrete

[RandyJ]

Di you give them a copy of the Pompeii oven plans? I did this when I did mine and it answered a lot of their questions. I was eventually told if it had a proper flu and chimney then it would be considered an appliance and that I did not need a permit??? Oh well I was happy. Also the fire marshall said that I would be exempt from burning bans because of the design.

Randy

[agrasyuk]

Randy , didn't think about it at the time and drawn my own. aside of more details about chimney/roof penetration they largely satisfying the requirements. But as it turns out village engineer had quite a few questions about my wooden structure, beams and spans. I can agree about the concern of snow load, will be adding more support columns and increasing the sizes of members. third time is the charm, hopefully. but that leaves me wondering how some of the structures that I see around here (built without any kind of permit) are still standing for over a decade...

[RandyJ]

I know it makes you wonder sometimes doesn't it.

Randy

[SableSprings]

I remember when I went to our building department to see if I needed a permit for my oven and the den I planned to build over it. The building official was also confused with my oven description, but when I started talking about cooking in it--he broke into a smile and the conversation went like this; "So, it's like a BBQ?" I said yes, then he asked "Will it connect to any other structure?"...no, "OK, are you going to put waterlines or electricity in it?"...no..."OK, you don't need a permit for an outdoor BBQ with a cover". Bottom line is if you are going to ask about permits from administration or building people...only use the phrase outdoor BBQ area.

I also talked to the local fire marshal and he was only concerned that the oven had a cinder screen on the chimney...again, as long as I was talking outdoor BBQ everybody was OK with the project. Randy's suggestion of take a copy of the Forno Bravo plans is a good one for everyone starting a build. No matter what we think of local government/officials, they are in control and you want to make sure you not only keep them in the loop, but don't be a smart-ass when they start asking (what we think) are silly questions. (...kinda like marriage, for a happy one, always smile & nod )

[agrasyuk]

Well, my overstructure didn't pass the review even after 4th attempt either . after which I had a productive discussion with village engineer. Since I'm not licensed architect/engineer my load calculations for the middle support truss cannot be accepted which makes the calculated span to be outside of "prescribed design". This will be resolved my making the overstructure onto a pergola (no wind, nor snow load), but for now I'm differing it till after the masonry work, which I did get permit for

Started digging. Cherry tree that used to stand right in front of the "L" corner is cut down , stump removed (anyone makes smoking pipes here?) And I'm a foot or so deep into the ground. It took quite a lot of wheelbarow runs.

[agrasyuk]

Weekend of digging, getting deeper, the pileup is getting higher. Soil is mostly hard clay, with rocks. pickaxe and digging bar got quite a workout. but we did get rewarded with several good spots of wet silty clay and compared to hard clay it was a breathe. Crew (my dad and nephew) looks with satisfaction at the results of our efforts while smelling nice rib-eyes being grilled for dinner.

[deejayoh]

Looking good. I hope that you saved the wood from that Cherry tree. Great pizza fuel!

[agrasyuk]

Yep, all the wood is saved and stockpiled on drying rack. Should be ready for next summer.

Not yet deep enough to start laying foundation, but I decided to take advantage of material sale and ordered the CMUs + concrete drymix. So this weekend's highlight was moving 400 concrete blocks, 200 sacks of concrete + some odd and ends like rebar, Portland and sand from the driveway where it was unloaded. Quite a workout.