Monolithic Slab or Stem Wall-

[FreshWahoo]

Hi All,
I am getting ready to build a 30'x30' Garage with what will eventually be an apartment upstairs... basically a 2 story building-all block.

It will be sitting at a very low spot, on a very low lot in Florida- and will require at least 2 1/2' of fill. I have had the soil tests, and we do not need pilings.

The engineer that drew the plans, provided a site plan showing stem wall construction, but construction details show a monolithic slab. (The main house is stem wall)

Now that I am putting it out to bid, I am getting lots of questions from the contractors as to which way I want to go..

It seems that Stem Wall would disturb the site less and require less fill, but I've heard it is considerably more expensive... is it?

One other thing I would be interested in some comments.. I asked 2 shell contractors for a number for just the slab and block (Monolithic Slab and 2 stories of block) and they came in between $30 and 40K.. I was thinking I'd be at least a third of the cost there, but the numbers I'm getting from contractors are about $185,000..really? We are talking just a GARAGE... are they just really greedy, or on crack?

 

[Ch3No2]

I did mine in a 6" concrete stem wall for mopping and hosing out.

 

[Musicinabottle]

Stem wall is best for sure and while it would require more concrete and labor to form it up in two stages...... footers then the stem wall, it wouldn't be too much more. Something like that, if you had the right crew, could be an extra 2 days labor. I assume that they are calling for an 8 inch stem wall since it's two story?

 

[ForceFed70]

Stem wall is certainly the better way to go for a couple of reasons. It's also more expensive.

In your scenario the biggest advantage is having that wall above the slab for moisture control (water in/out). You're also less likely to see slab cracking with a stem wall design. The biggest reason stem wall design is used is for frost protection in areas where footings must be below the frost line - not required in your area.

Best place to start would be to understand the cost difference. Is it worth it to you?

 

[matt_i]

Seeing as you have to build on previously undisturbed earth, and you have second floor loads, and you are using concrete block, I would go for the pad footing + stem wall.

You can compact the center of it to build up for a floating floor and achieve proper elevation but then you don't compromise the building's integrity if something isn't perfect.

 

[FreshWahoo]

Stem wall is certainly the better way to go for a couple of reasons. It's also more expensive.

In your scenario the biggest advantage is having that wall above the slab for moisture control (water in/out). You're also less likely to see slab cracking with a stem wall design. The biggest reason stem wall design is used is for frost protection in areas where footings must be below the frost line - not required in your area.

Best place to start would be to understand the cost difference. Is it worth it to you?

For sure! There has been such of range of prices... the verbal numbers I got were a lot lower then what I'm getting now on paper! Nobody has quoted it both ways...


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[FreshWahoo]

Seeing as you have to build on previously undisturbed earth, and you have second floor loads, and you are using concrete block, I would go for the pad footing + stem wall.

You can compact the center of it to build up for a floating floor and achieve proper elevation but then you don't compromise the building's integrity if something isn't perfect.

That makes a lot of sense to me! When one thinks about the amount of fill that would have to come in to level out the lot, it may be a wash (?)... another factor is the concern that covering the roots of our many Oaks could kill them as well.. now I have to force our engineer to redraw that page of the plans!!!



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[James-W]

I have a 24X36 garage with storage upstairs. I have a 6 inch stem wall going down into the ground over 3 feet. The concrete, including the apron, was $7,000 completed, which included the prep work involved. I built the garage myself, with the help of friends, and the total cost for everything (concrete, permits, building materials, everything) was right at $30,000. I had a roofer do the shingles and I had a crew do the siding, wrap the trim with metal, and put on gutters. But my friends and I built the walls, put up the trusses, put on the plywood, and I did the wiring. The city building department said I had to have a master electrician pull the permit for the meter and install the meter base and electrical panel. Well, I actually did it, but the master electrician signed off on it.

 

[FreshWahoo]

I have a 24X36 garage with storage upstairs. I have a 6 inch stem wall going down into the ground over 3 feet. The concrete, including the apron, was $7,000 completed, which included the prep work involved. I built the garage myself, with the help of friends, and the total cost for everything (concrete, permits, building materials, everything) was right at $30,000. I had a roofer do the shingles and I had a crew do the siding, wrap the trim with metal, and put on gutters. But my friends and I built the walls, put up the trusses, put on the plywood, and I did the wiring. The city building department said I had to have a master electrician pull the permit for the meter and install the meter base and electrical panel. Well, I actually did it, but the master electrician signed off on it.

That's helpful! It's a little apples and oranges though, as with Hurricanes and floods we want block all the way up., and have a full second story- just not finished, with rock etc.. you do inspire me to consider having the shell built, and doing what I can- subbing out the rest. The problem is building is going bonkers here, and the GC's are having a hard time getting the subs in.. they would just laugh at me!


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[FreshWahoo]

Stem wall is best for sure and while it would require more concrete and labor to form it up in two stages...... footers then the stem wall, it wouldn't be too much more. Something like that, if you had the right crew, could be an extra 2 days labor. I assume that they are calling for an 8 inch stem wall since it's two story?

The construction drawings show a monolithic slab.. just the site plan shows a stem wall.. both were generated out of the same office. I'd have to presure the engineer to modify the drawings, but this is just one of the issues with the plans..


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[ForceFed70]

That's helpful! It's a little apples and oranges though, as with Hurricanes and floods we want block all the way up., and have a full second story- just not finished, with rock etc.. you do inspire me to consider having the shell built, and doing what I can- subbing out the rest. The problem is building is going bonkers here, and the GC's are having a hard time getting the subs in.. they would just laugh at me!


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If you're going to do a stem wall, why use block? Do you like the look? You can pour the stem walls as high as you like and skip the block completely if you want. Might offset some of the additional cost? Not a lot of extra labor to form the stem walls 9' high vs 3'

 

[FreshWahoo]

If you're going to do a stem wall, why use block? Do you like the look? You can pour the stem walls as high as you like and skip the block completely if you want. Might offset some of the additional cost? Not a lot of extra labor to form the stem walls 9' high vs 3'

No one has mentioned that option.. pour the whole thing? Walls for two stories are more like 20' ( garage doors are 9' tall, plus joists, then the second floor.. it sounds like it would be strong! Exterior will be stucco..


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[ConCretin]

Up here we call them frost walls because their purpose is for the foundation bear on soil below the frost line and thereby resist lifting due to freezing/expanding soils. Since frost is obviously not a concern, I wouldn't spend the extra money for walls.

A monolithic slab with thickened and reinforced edges will have the same or more bearing capacity as a footing and wall. We even use this method up here if we have frost resistant soils underneath. In fact, I have a 28 x 32 garage built this way.

If you are building a wood structure and want to lift it up a bit, add a concrete curb or a course or two of block. It should still save you significant money.

 

[tarmy]

Ummm...what does the geotechnical report call for?

What does the structural engineer say? These professionals, who do this for a living, should be advising you of the options, issues, costs and risk with each type of solution.

Whomever is designing the wind and hurricane load will be very interested in what the whole thing is tied down with...and what to.

I have a stemwall, but am in earthquake country...with snow load. I discussed all of the issues with my engineers. I also lived in West Palm for a while. The engineering co I worked for, that took the liability for the design...always specified the foundation, tie downs, hurricane strapping and roof structure.

Get someone who knows what the hell they are doing. This is the best free advice you will get.

 

[FreshWahoo]

Up here we call them frost walls because their purpose is for the foundation bear on soil below the frost line and thereby resist lifting due to freezing/expanding soils. Since frost is obviously not a concern, I wouldn't spend the extra money for walls.

A monolithic slab with thickened and reinforced edges will have the same or more bearing capacity as a footing and wall. We even use this method up here if we have frost resistant soils underneath. In fact, I have a 28 x 32 garage built this way.

If you are building a wood structure and want to lift it up a bit, add a concrete curb or a course or two of block. It should still save you significant money.

Thanks for the reply.. I’m sure the engineer knows what he’s doing- he’s been to the site and selected the monolithic as the most efficient...
I had considered going frame, and what you suggest makes a lot of sense, but I decided on block due to Hurricanes, our damp Environment and Insects... any of which can be very destructive! I want a bomb shelter!


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[FreshWahoo]

Ummm...what does the geotechnical report call for?

What does the structural engineer say? These professionals, who do this for a living, should be advising you of the options, issues, costs and risk with each type of solution.

Whomever is designing the wind and hurricane load will be very interested in what the whole thing is tied down with...and what to.

I have a stemwall, but am in earthquake country...with snow load. I discussed all of the issues with my engineers. I also lived in West Palm for a while. The engineering co I worked for, that took the liability for the design...always specified the foundation, tie downs, hurricane strapping and roof structure.

Get someone who knows what the hell they are doing. This is the best free advice you will get.

That advice is worth EVEN MORE then I am paying for it! The engineered drawings I paid for show Stem Wall on one page and a Monolithic Slab on another.. and there lies the confusion! I have one contractor going one way, and 2 other going the other! The drawings also show the floor joists on one page as 16” O.C. and 24” on another.. He did some other work for me and I was pleased, but I gave him a deposit in May and just got the drawings a few weeks ago! They are all so busy right now, I think they are all just phoning it in..


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[redneckcharlie]

X2 Why people do two pours is beyond me in residential applications. The footings and slab are always poured together here regardless of footing depth for frost lines. Our typical footings are 18-24” in width and 24-48” in depth. Appropriate rebar is done throughout the depth of the footing. A properly done monolithic pour makes for an extremely strong foundation.

Up here we call them frost walls because their purpose is for the foundation bear on soil below the frost line and thereby resist lifting due to freezing/expanding soils. Since frost is obviously not a concern, I wouldn't spend the extra money for walls.

A monolithic slab with thickened and reinforced edges will have the same or more bearing capacity as a footing and wall. We even use this method up here if we have frost resistant soils underneath. In fact, I have a 28 x 32 garage built this way.

If you are building a wood structure and want to lift it up a bit, add a concrete curb or a course or two of block. It should still save you significant money.

 

[lakeroadster]

.....It will be sitting at a very low spot, on a very low lot in Florida- and will require at least 2 1/2' of fill. I have had the soil tests, and we do not need pilings.

... but the numbers I'm getting from contractors are about $185,000..really? We are talking just a GARAGE... are they just really greedy, or on crack?

Are the contractors also doing the 2-1/2' of fill? To be done right this will be labor intense and require multiple tests to confirm adequate compaction.

Be sure to drill down on the contractors and have them be very clear about how the compaction will be done, and how it is verified.

You'll want a 3rd party doing the compaction tests... not tests done by the folks doing the fill / compaction.

As the ole adage goes.... "You can't build a great building on a weak foundation."

This may prove helpful to you: Proctor Compaction Testing of Sub-Grade Material

Good luck with your project... and keep us in the loop as things progress.

 

[tarmy]

That advice is worth EVEN MORE then I am paying for it! The engineered drawings I paid for show Stem Wall on one page and a Monolithic Slab on another.. and there lies the confusion! I have one contractor going one way, and 2 other going the other! The drawings also show the floor joists on one page as 16” O.C. and 24” on another.. He did some other work for me and I was pleased, but I gave him a deposit in May and just got the drawings a few weeks ago! They are all so busy right now, I think they are all just phoning it in..


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STOP WHATEVER YOU ARE DOING. Get this **** set of plans fixed...and get some quality control review done if you can't do it. The contractors are going to have fun getting extras from you. If the plans are ****...then the clowns who designed this won't take any responsibility when the problems start.

Hell, I am not sure how they can claim to form up something with those plans. Either get the plans straightened out...or get ready for an expensive mess to come. The time you take now will be well spent...

 

[FreshWahoo]

STOP WHATEVER YOU ARE DOING. Get this **** set of plans fixed...and get some quality control review done if you can't do it. The contractors are going to have fun getting extras from you. If the plans are ****...then the clowns who designed this won't take any responsibility when the problems start.



Hell, I am not sure how they can claim to form up something with those plans. Either get the plans straightened out...or get ready for an expensive mess to come. The time you take now will be well spent...

You are so right- measure twice and cut once.. the drawings will be an Addendum to the contract-they have to be compliant, accurate and complete...
This thread started with the question whether I should push for stem wall or monolithic, and how it will effect cost- it has morphed into a conversation about the competence of my engineer.. I’m confident I will eventually get everything corrected before going to contract, but it is trying my patience! Unfortunately I did not find the mistakes until I paid for the plans and started getting questions from contractors.. Rrrrrrrrgggggh!



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[gearhead1]

I had to use a stem wall per the structural engineer, to handle the loads. 36 x 50 with attic trusses. The footer between the roll up doors is even thicker and wider than the rest.

 

[kbs2244]

First of all you are not building a garage.
You are building a residence.
Two very different codes apply.

You may not have a choice.

 

[FreshWahoo]

First of all you are not building a garage.

You are building a residence.

Two very different codes apply.



You may not have a choice.

There are some code issues to be considered.. the city does not want a kitchen upstairs for example, but I have reviewed the plans with the building department and they don't have an issue with either type of construction.. the engineer is well respected...


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