Slab floor question

[JMartens]

My wife and I bought a barn we are transforming into a house. Posted a build pic in the gallery so I won't go into the details of the build.

We are getting everything prepped for concrete flooring and I'm looking for some opinions on the slab style.

The excavator recommends digging a trench around the inside perimeter to get the slab below frost line to keep the floor from heaving. I'm leaning towards bringing in the rock, packing it and pouring up to the skirt boards. I would insulate up the skirt boards and under the perimeter of the slab before pouring.

The barn is 30 plus years old and solid and square. The concrete that was in the barn was just poured on the soil and was in great shape. Even after digging out the inside of the barn it is still the high spot where the barn sits and the undisturbed dirt has been packed by tractor traffic and hay 4 tall for decades. The drainage around the barn is good and I'm not worried about moisture getting under the barn.

I've read as much as I can find it seems like a 50-50 split. What say those with pole barns?

Obviously it is gonna be much easier and cheaper to not try to trench around every post. I'm also a little Leary about disturbing the posts as they are set in concrete and stood for 30 plus years.

Not discounting my excavator as he is awesome on the dirt moving and his concrete finishing is great and that is why I chose him. I know his way will work but not sure it is necessary and his primary focus is residential construction and traditional foundations and not pole barns.

Looking for some opinions before I make the final call next as to the way we are gonna do it. This is my retirement home (god willing) so I want to do it well but budget is not unlimited so I need to balance cost versus performance.

 

[Kaizen]

definitely go down 2 feet and pour a footing/foundation wall. If you just pour a slab and build on top of it I think you definitely increase you tile and wall cracks. Right now the piers for the posts are down that deep hopefully in concrete and the freeze thaw slips up and down around it.
This is a unique set up you have and maybe pouring a very thick pad with rebar would eliminate it but if you DO end up with a problem you'd have to destroy the place to fix it. I might even think of pouring under the exterior walls and use it to support those walls. would be a pain but definitely very strong.
I know its a lot more money but I'd try and insulate with 4 inch under the slab and lay in pex for heating. A slab that size once heated up will radiate equal heat for days. With a roof that big you can use some hot water solar or even the pond with a heatpump if its big enough.
Those posts are beautiful but if you are pouring around them I would be concerned they will rot out very quickly as they don't look like pt. I'm sure they look fine now but the concrete causes moisture on the. maybe insulate around them will help.

 

[finn]

Another vote for the insulation below, and perimeter, as well as the pex.

 

[JMartens]

No doubts about insulation. I don't remember which member posted the phrase "pay for insulation once or heating and cooling for the life of the building" but I am a believer in that one. At a minimum the whole slab is getting vertical insulation around the perimeter and 4 foot in horizontally. Walls are spec'd for R40 and ceilings R60.

 

[MagKarl]

In my opinion, a guy could make a good argument that with good drainage and dry ground to start with, along with a slab that's heated above or within the living space, the ground under the slab may not have enough moisture or actually get cold enough to heave.

 

[Old Moparz]

My garage is a pole building & just has a slab with uniform thickness throughout. I'm in NY & we have a frost line 4 feet deep & I was concerned about heave as well. It's been okay since 1997 except for the front, right corner of the slab that developed a hairline crack. If I get a stretch of cold below freezing that lasts more than 8 to 10 days, it pushes the slab up under the overhead door & binds the deadbolt lock.

I've since relocated the deadbolt lower on the door & the movement of the slab has never caused any other issues. If however, I had the chance to do the slab pour over I would probably still do it the same way except I would excavate deeper in the one area for more stone. My slab is poured over well compacted gravel & a processed, crushed, stone material that ranges in thickness from 4 feet to about 1 foot where the original grade of the property is. The area where I have the heave problem is the 1 foot thick stone material close to the original grade.

If you're in MO your frost line won't be too deep so I would consider digging down to it like your guy suggested. Insulate the heck out of it & pour since you're using it as living space, not a shop. On a personal note, I would rather have a crawlspace with a floor joist system & not a slab. I like the idea of raising the living space well above the surrounding grade & being able to access the floor from underneath.

 

[yeldogt]

I'm trying to uderstand how this slab would be any different than one with a typical foundation. The foundation is for the buildings support on a conventional ... not the slab. the block or concrete at grade would be the same temp as the ground.

Digging down a bit and installing vertical foam and then backfill with a proper stone base -- horizontal foam and VB under the slab. With proper base -- without moisture what could happen?

I have done two barn conversions ... both in PA. One was an existing 100 + year old dairy barn the other was one that we relocated as an addition -- became more of a timber frame rebuild. I had foundations rather then poles --

On the dairy barn we had foam up against the old rubble foundation on the inside, backfilled with stone and did a proper slab.

I will give you one piece of advise -- insulate the whole slab. And make sure it has a proper base and perfect vapor barrier.

In PA with have radon -- so I take even more precautions .. and I always add drains .... but you are on grade.

 

[rburke65]

Foundation....don't know. But I would also vote for the pex and insulation both under and along side the perimeter. You will only stone chance to do this right.

 

[wssix99]

I'm also a little Leary about disturbing the posts as they are set in concrete and stood for 30 plus years.

Digging up to them on one side shouldn't be a problem since you won't be disturbing the soil underneath.

You should replace whatever you dig out with gravel because you can compact it properly, (with a vibrating compactor) it will be a lot less expensive than a deep concrete slab, and will get you the depth you need down to the frost line.

+1 on the other comments regarding insulation and adding pex in the slab. Even if you don't think you want a radiant floor, (you will...) putting the pex in the slab is cheap.

We just did this in our new house and added pex in the slab just in case we found that we needed the radiant floor. 2 months of the cold weather - and we've already tapped out. The radiant hookup starts next week!

 

[JMartens]

What diameter and spacing is recommended for the PEX?

 

[yeldogt]

You will get various opinions. I'm in the closer camp -- as I want to use lower temp water and no hot spots. You need to start with a load calculation on the building and then go from there. Many around me in PA use 12" ... I have done 6" and 8".

 

[Kaizen]

What diameter and spacing is recommended for the PEX?

really depends on your layout and length of the runs. 1/2 inch I think is 500 ft max run but you have to check on it. there are a lot of things that come into play which is your temp zone, concrete thickness, insulation value of the rest of the building, the temp of the water. make some calls to pex people and have them spec it out. whatever you run think about running 2 in case you have any issues on the live loop in the future. of course double the cost.

 

[rburke65]

No expert here.....repeat....no expert here..... I believe the school of thought is to run the pex closer at the perimeter of the slab..... 6" .... for the first 2 runs and then 12" apart there after. Your square footage will be pretty close to the total pex length. Half inch diameter runs no more than 300' and try to keep the runs the same length. Did I say I was no expert? Ok....just checking.

 

[wssix99]

What diameter and spacing is recommended for the PEX?

I wasted a ton of time worrying about this. Best to find who is going to install it and what system they are going to use. The answer is academic from that point. (Different systems will have different requirements.)