Monolithic or stem wall footer for ICF build.

[imjustdave]

First off I don't want to debate price difference of ICF, SIP, Wood, Brick and such. Wood has gone through the roof as of today, "Covid" and my home is ICF and I enjoy the sound quality it brings I have a highway nearby so noise reduction is nice.

Plan is 44x50 to 40 X 60 shop somewhere in this size range.
In floor heating as working on cars with warm feet is nice.
Frost level is 12 inches Seattle areas has advantages.
Seismic Design Category D-1
Per geotech of the school next door SILTY SANDS, POORLY GRADED SAND-SILT MIXTURES

Ground for the most part has been undisturbed, it was a cow field, sold 10 years ago for homes with nothing ever built on it. top layer has been molested to clear blackberry and such but that was almost 2 years ago now.
I decent compaction, will need to be done, with water once top layer is removed, with overlay of fresh compactable fill. Otherwise Cut and fill is maybe a foot over the entire area.


My designer is giving me the option of monolithic design OR traditional footer.

A lot of my advantages or disadvantages for both revolve more around the work to install it over advantages for the building. Was hoping to see what other may view as good bad ugly for my building?

Pour and finish will be by a crew on the slab. I intend to do a lot of the utilities, Pex, dirtwork myself as I have done this in the past.



Monolithic
Good
1 less pump truck.
easy to backfill after pour. no walls. 5 foot setback on 1 side.
Cleaner site during build, place to store - keep material dirt free.
Might start build this fall and build walls in spring.
should be epic level for wall building.
Easy to move scaffolding around.
Suspect less ICF forms needed as the slab will be above grade.

Bad
Lot a of work to complete before Rain hits every day.
Bunch of inspections as well.
All Utilities need to be run. sewer Water,
Planned on running conduit under slab for electrical, to cross shop floor.
Need to really plan placement of lift NOW vs latter.

Cracking
Need a place to fasten wall bracing - need to watch out for PEX, and mindful of surface damage.
Big floor with rebar sticking up on finishers.
possible damage to floor during build
$$$$ upfront... dislike spending $



Footer
Less work prior to rain season.
Could leave a few utilities till spring - dryer season.
Decent amount of work still to pour but less finish work needed on a footer

Muddy
1 extra pump to finish the floor once building is built.
Maybe not as level

 

[matt_i]

If I understand this correctly the walls of the shop are going to be ICF.

I would not even get a pencil out and draw anything other than a pad footing. That's a lot of concentrated heavy weight just from the wall itself. You didn't say how tall guessing 10-12 feet tall (?) I'm not an expert but wouldn't think you would want to pour more than 8ft tall in one day.

~60 yards in an 8" thick wall * 12' high @ 40' x 60'.

 

[ConCretin]

You've got a good start on evaluating each system especially as it pertains to sequence and constructibility issues. The biggest advantage to a monolithic slab is usually cost. Less excavation, backfill and fewer elements to build. This is mitigated by your shallow frost depth but a monolithic slab should still cost less.

I usually lean towards a monolithic slab for detached structures but with the weight of an ICF structure above, I think I'd lean towards separate footings and slab to allow for differential movement and avoid potential cracking. I don't have any engineering to back that up, it's just a gut reaction.

Btw, you shouldn't expect a traditional slab on grade to be any less flat than an a monolithic slab.

 

[rsanter]

The ICF building we have at work has a monolith is pour.

Love the ICF construction, if I could build my own house out of it, I would

 

[NUTTSGT]

The ICF building we have at work has a monolith is pour.

Love the ICF construction, if I could build my own house out of it, I would

Like Doug mentions, I'd prefer a footer to help absorb the weight on the ICF walls.


However, I wonder if in a region that does not have frost heaving if ther would be a difference ?


rsanter, do you have to worry about frost heaving in your area ?

 

[imjustdave]

I should also add that my designer and engineer specialize in ICF builds. I would expect weight wise for the walls, the engineering should take that into account, I suspect the Monolithic section to be Up sized to deal with this load.24 36 48 wide VS 12 18 I have seen in Monolithic pours in the area. So I'm not concerned with engineering calculation side as much as the long term use of the building and if I'm missing any building construction issue.

Building a 1 sided wall isn't fun, lots of cribbing and or plan to cut it tight and use the ground to hold the outside, but I prefer a smooth foundation over dirt formed. Might try and keep it tight with a slight offset to backfill the forms.

In terms of foundations I'm leaning towards the Monolithic as I feel the entire mass should help hold the building VS smaller foundation stem walls. I know once it's all built the entire building keeps everything up.

 

[imjustdave]

Btw, you shouldn't expect a traditional slab on grade to be any less flat than an a monolithic slab.

Good point, when I was typing this I was looking at Laser Screeding the floor as an option but it's size, and pex precluded doing that cost also doesn't' justify it. But yeah a good crew can and should be able to level off a decent slab.

"lean towards a monolithic slab for detached structures" Why do you lean this way, cost? simplicity? 1 pour VS potentially 3? Even with sidewalks, patios, drives you end up with more pours.

Most home in the area are stem wall with 18 - 36 crawl spaces, almost never a basement, and it's rare to have slab on grade besides the garage. not sure the fixation on crawl spaces.

 

[csp]

not sure the fixation on crawl spaces.

Ease of running electric/water/HVAC plus access for adding/modifying any of those in the future. I'm sure there are other reasons as well, with cost likely to be one.

 

[ConCretin]

"lean towards a monolithic slab for detached structures" Why do you lean this way, cost? simplicity? 1 pour VS potentially 3?

You pretty much summed it up. It's just a simpler, less expensive foundation for a structure that doesn't need to be frost protected. You want to be a little cautious with the soils underneath to make sure you don't get too much differential movement but they typically work just fine. You can even make them frost resistant with the use of rigid insulation.

If you put in frost walls, you still need to keep the slab from heaving from the frost unless you are going to keep it heated 100% of the time and even then you need to protect the edges if you are in a really cold climate.

 

[Pluribus]

Will follow this discussion with interest, as I'm also in Western WA and sort of on hold due to the market/materials for building a shop right now. Used to live down by you and have lots of fond memories of mountain biking at Victor Falls before that area was closed.

Once you get the details ironed out, it sounds like a really interesting build.

 

[MushCreek]

When I built my ICF house, we went with a separate footer and slab, but- That's for a full basement. Having the slab inside of the ICF, and on top of the footer created a brace to prevent soil pressure from moving the ICF walls inward. It is important to make sure that the footer or slab is really level, or you'll fight it with the ICF. The monolithic pours I've seen incorporate the footer with the slab, with the perimeter being deeper to create a footer. The only difference is that it's all poured at once. That's what we did with my barn (not ICF).

You do need to plan and measure carefully for your utilities. ICF requires a high level of planning due to the difficulty of making changes after the fact. It took me half a day to punch a 3" hole in my wall for HVAC lines. I can't imagine trying to move a window! Regardless of the method you use, you want the slab done before stacking the walls. Stacking, bracing, building bucks, and scaffolding would all be a PITA in the dirt. For my bracing, we glued blocks of 2X6 down to the slab with a foam gun, then screwed the braces to the 2x6's. When done, pop the 2x6 off and scrape off the foam residue. I don't know of this is going to be DIY, but if you do, get a good foam gun with the screw-on cans of foam. You'll use many, many cans of foam!

 

[Tduby]

If your footer only has to be 1 foot down are you really saving anything by going with floating slab. I’m thinking as a person wanting to do more work myself that breaking the pours into 3 separate jobs makes it easier. Sounds like you could do the footings by yourself no problem. Then build the walls on your time schedule. Then potentially even have the roof on for the floor pour so you can do the pex and what ever work for the floor at your own pace. That’s how I wanted to do it but we needed a 6 foot deep footing so that made the floating slab a better choice.

 

[imjustdave]

If I understand this correctly the walls of the shop are going to be ICF.

I would not even get a pencil out and draw anything other than a pad footing. That's a lot of concentrated heavy weight just from the wall itself. You didn't say how tall guessing 10-12 feet tall (?) I'm not an expert but wouldn't think you would want to pour more than 8ft tall in one day.

~60 yards in an 8" thick wall * 12' high @ 40' x 60'.

Going 15-16 range wall height.
In terms of pour they recommend having 1 pour per floor, as they don't' want a cold joint in the middle of a floor section. So for me Floor to eve height in 1 pour, now you can and should take your time and walk around filling it up in lifts, VS filling an entire section and moving down the wall.

If it was 2 story you would pour to the bottom of the 1st floor and have your in bed supports in the wall and or ledge to support the poured floor in the pour, Then after your floor is installed and or ready to be poured the floor you continue on.

been reading watching a bunch of videos they make it look really easy. I'm sure the first pour is stressful but they make it look easy.

 

[MushCreek]

You do the pour in a series of lifts, usually about 3' at a time. Work your way around, and by the time you get to the first corner, it's set up enough for another lift. It is easy, if you know what you're doing. You need to vibrate the mix with a pencil ********, especially around door and window bucks. Overdo it, though, and you can get a blowout. The pros keep supplies handy to quickly patch the wall in the event of a blowout- otherwise, you have a serious problem. There are tricks of the trade, too, which is why I hired a crew to fill my forms. If the guy filling knows his stuff, and the pumper operator knows his stuff, it's a smooth operation. My crew had three guys- one with the pumper hose, and the other two running around with vibrators and just generally keeping an eye on things. It made it easier when they trued up the walls, too.

My guy rented me the adjustable bracing and staging, and his crew filled the forms. He also taught me a LOT about ICF, and wouldn't take a penny over and above what I paid him for his part in it. He's a local builder, and all he does is ICF. Just dumb luck that I found him- he only lives about two miles away!

 

[imjustdave]

If your footer only has to be 1 foot down are you really saving anything by going with floating slab. I’m thinking as a person wanting to do more work myself that breaking the pours into 3 separate jobs makes it easier. Sounds like you could do the footings by yourself no problem. Then build the walls on your time schedule. Then potentially even have the roof on for the floor pour so you can do the pex and what ever work for the floor at your own pace. That’s how I wanted to do it but we needed a 6 foot deep footing so that made the floating slab a better choice.

I'm not sure what I gain with a footer in terms of strength, quality ETC over a Monolithic slab... That's the real Q basically today. Does one have an advantage I'm not thinking about or seeing today?

How it's constructed is epic different, I suspect the cubic foot yardage to be about the same at the end of the day.

To me a finished slab 20+ feet long is a nice base to build from, especially when I know that base is thick.
A 3 to 4 foot by 12 to 24 inches foot chunk of footer is cool too but, it's not nearly as big or massive, once built it's a complete system. I'm guessing at the engineering needs for dimensions.

Sounds like flexibility for plumbing is one as I can modify once I see some walls up.
Flexibility in doing smaller chunks of the work.
Finish work is at the end less damage.

 

[Firebrick43]

The biggest advantage to a frost wall is that you can pour the slab separate. IF you PREP right and cure right it can be crack free(no concrete is truest crack free but some you can see them). Because the slab is not restrained it can shrink away from the walls. Both my 28x50 basement and 28x30 garage are crack free with no saw cuts.

A monolithic slab is going to crack as by definition is restrained at the perimeter and varies in thickness, both guaranteed to crack.

Also most don’t recommend pouring more than 12’ in any one day. I couldn’t imagine working at that height on the bracing/scaffold. The second pumper on my job was ran by an inexperienced operator and he yanked the hoseman off the wall. The hoseman had the smarts to react fast enough to hang onto the hose until the pumper operator set him back on the scaffold. We did have to restrain the hoseman from beating the pumpers ***.

If you do plan on pouring that height, amvic, logix, and buildblock have stronger walls to deal better with the high hydraulic pressure. Also they make a ******** that attaches to a drill and is pressed on the outside wall. My distributor stated that they worked nearly as well without as much of an issue of high hydraulic pressure caused by a Pencil ******** hitting rebar.

 

[Tduby]

I'm not sure what I gain with a footer in terms of strength, quality ETC over a Monolithic slab... That's the real Q basically today. Does one have an advantage I'm not thinking about or seeing today?

About the onny real advantage is it sounds like you can get down to virgin undisturbed soil with out having to compact and fill for a traditional footer and then your free floating slab can be on compacted fill where it can move independent.

Ultimately I think the difference between the quality of strength between the two is so close it doesn’t matter. If you want a nice slab to build from then that is more important to you and you should do it that way.

Having done a floating slab prep by myself it was a lot of work to form up, insulate, put pex, plumb drains, and get ready for a pour and I get hit with rain and had to fix some form work.

If I could have had a 1’ deep footer could have did the footer in a day poured the next. Layed out the stem wall in a few days or in your case the whole wall in probably a few more days poured then with drainage and rock as fill inside worked on the interior utilities then poured the slab with very little risk of damage from a washout.
I have no experience on ICFs but I don’t see a poured slab as that much of a bonus building the walls but I could be wrong and would defer to anyone on that.