How to spec/price a suspended slab

vtjon · Oct 30, 2019

I've posted a few times about planning my build. Due to the grade of my lot, I am planning to have a walk-out basement with a suspended slab on top. I am having a hard time getting a price on this work (the framing/decking). I am GCing the project myself. Hollow core pre-cast slabs are not going to be practical in my situation since I am so far from a manufacturer though I won't know this for sure until I figure out a price of cast-in-place.

I have been working with a local building materials supply house on all of the materials. They distribute a suspended slab system for a company that makes the light-gauge steel joists plus the decking. I have been waiting over a week for a general price. I'm assuming the joist company does some in-house engineering to come up with the specs.

I found a distributor and a delivered price for the decking. I can't seem to find the joists. Even if my building supply house comes back with a price, I'd at least like to shop it. Is my only option to get an independent engineer to do a complete spec? I realize before I go with a system I'd likely have to have it engineered.

I do have an L&W Supply house about an hour away. They seem to target commercial (as do a lot of these systems) but they claim to distribute the MARINOWare steel framing products.

Any ideas as I feel stuck and want to get moving on my permit application and build?

firebirdparts · Oct 30, 2019

That's how I did it. Engineer --> Drawings --> Steel erector --> ordinary concrete. I have bar joists. I don't know much about the steel business, but I would assume that they just order bar joists from out of town. They made some stuff for me. I did not want a clear span. I have a 2 post lift on the 2nd floor so I wanted a post right in the center of the building. They made that locally.

readhead · Oct 30, 2019

How big is the garage? I have done quite a few of these and the usual system consists of steel beams and decking. If it is an average size garage we can usually do an install in one day. A lot of the systems like you mentioned are expensive and labor intensive. Stick with simple. Talk to your engineer and move the job along.

sberry · Oct 30, 2019

Beam and deck would be simple.

vtjon · Oct 30, 2019

It will be a 28' x 40' garage. Although I've been calling it a system, it's not a fancy system. The manufacturer is a somewhat local cold-formed-steel manufacturer and they make a variety of building products including joists, beams, posts, decking, etc. I actually expect this to be the cheapest because freight will be cheap especially if they do all of the necessary engineering for me. This manufacturer is who all of the local builders use though suspended slabs aren't overly common around here.

I wasn't expecting to need an engineer originally and I haven't engaged one yet. I was trying to avoid an engineer specing everything and telling me to go buy from this manufacturer anyway. I guess I should just try to push my building supply sales rep a little harder.

LX-Markham · Oct 30, 2019

Is this being done with a building permit? Or no permit?
Because the building department is going to require an engineer for a structural slab.

strutaeng · Oct 30, 2019

I don't believe there are going to be any "guestimates" here without framing plans at the minimum.

There are many structural systems out there: form deck on metal joists (cold-formed or open-web,) form deck on steel beams, composite deck with steel beams, etc. even composite deck on open-web joists!

For economical design, it is hard to beat open-web steel joists. They are not the "best" in many cases. They are widely used for roofs, but can be used for floors too, but at tighter spacing.

I can't recall your garage size from the other threads, but steel can easily span 40-60', so very doable, whether with joists or beams.

Good luck

Edit: was posting before 2 last posts. Didn't read those.

OP: Does the manufacturer have an engineer? I know around here open-web joists are engineered, much the way wood trusses are. You would just be responsible for specifying deck to span between joists. Pretty easy to find tables on this.

vtjon · Oct 30, 2019

This will be a permitted build. This manufacturer has a joint engineering firm so I expect it to come as a package. I've expected this to work like roof trusses do where the manufacturer does the engineering. I might be just getting impatient and will unnecessarily cost myself money by not waiting on this particular company.

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strutaeng · Oct 30, 2019

vtjon said:
This will be a permitted build. This manufacturer has a joint engineering firm so I expect it to come as a package. I've expected this to work like roof trusses do where the manufacturer does the engineering. I might be just getting impatient and will unnecessarily cost myself money by not waiting on this particular company.

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I see.

What are you doing for your roof? Maybe you can design something where the floor members and roof members are installed at the same time to take advantage of the crane?

vtjon · Oct 30, 2019

strutaeng said:
I see.

What are you doing for your roof? Maybe you can design something where the floor members and roof members are installed at the same time to take advantage of the crane?

I'm hoping to avoid the crane. It will have a hip roof to match my house. The truss company cuts and labels everything though there are only 4 (I think) actual trusses. If it works out right, I hope to have the trusses delivered to the top of my walls from the building supply house using their boom truck.

I think the floor joists will all be lightweight/guage and can be handled by hand mostly since they are I beams. The downside of this is I expect them to be every 16 inches.

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strutaeng · Oct 30, 2019

vtjon said:
I'm hoping to avoid the crane. It will have a hip roof to match my house. The truss company cuts and labels everything though there are only 4 (I think) actual trusses. If it works out right, I hope to have the trusses delivered to the top of my walls from the building supply house using their boom truck.

I think the floor joists will all be lightweight/guage and can be handled by hand mostly since they are I beams. The downside of this is I expect them to be every 16 inches.

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I'm not certain for sure how steel erectors around here install open-web joists. I know for most all steel beams they are using cranes, unless it's some specialty retrofit job.

For example, 16K2 joist to span 28' feet weighs around 5.3 lb/ft, so about 150 lbs each. I would expect these to be on the 2'-3' o.c. depending on loading and deck capacity.

Steel beams are most always much heavier for the same capacity as open-web steel joist. For a 28' span, you are looking at a W14x22, so 616 lbs each! Obviously, spaced at wider intervals.

firebirdparts · Oct 30, 2019

So, about the engineer, package deal, all that. I think, if I had just walked into the steel fabricator's office and told them what I wanted, they probably would have done it. So I think you will be fine doing that. However, using the engineer, I have some "eloquence" under my lift, and so I like that.

After the floor was poured, I realized that the floor itself weighs 60,000 pounds. Live load is not a big deal.

Voi · Oct 31, 2019

If you read through the Concrete Bunker thread in the Gallery section you'll see that the originator of that thread used an insulated concrete form for his suspended slabs.

I believe the product was Lite Deck.

According the local contractors here these products come in cheaper than other options. I've never gotten far enough in the process to price.

vtjon · Oct 31, 2019

I finally got a price. It's worked out to about $11/sqft ($12500ish) plus rebar and 4"-5" of concrete and finishing. This price is getting close to what I can have the hollow core plank delivered to me including renting a crane, crew and grouting. I would probably save some on my foundation since they don't have to form 6 beam pockets and only would need to form a ledge.

I found a dealer to deliver the decking to me for $3800. Now, the decision is if I can get engineering, beams (from a different provider and heavy steel vs light-gauge) and crane/crew to erect the beams for less than $9k.

brownbagg · Oct 31, 2019

oh you need to hire this out to a license contractor, i see so much bad here

spudley · Oct 31, 2019

Hmmm... since you originally wanted just a single story 28 x 40, could you just use the lower section for a garage; parking/auto repair/etc, and the upper section for storage/woodworking/etc.
You wouldn't need a concrete deck at all and could frame the floor with wood products.

vtjon · Oct 31, 2019

spudley said:
Hmmm... since you originally wanted just a single story 28 x 40, could you just use the lower section for a garage; parking/auto repair/etc, and the upper section for storage/woodworking/etc.
You wouldn't need a concrete deck at all and could frame the floor with wood products.

There is poor driveway access to the bottom side. You can't drive into the rear and the slope makes it impractical for a side load. There will be a double door down there in order to get mowers, UTV, etc in there. Although I plan to be here for a long time, I'd like the top to function as a car garage for resell purposes. I could cut my footprint down even more, but it feels like not a great trade-off for a few thousand dollars. That said, maybe I should try to price out a 28x30.

I don't have an overall budget per se, but as I've gotten over $50k, I have to give everything due consideration.

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spudley · Oct 31, 2019

vtjon said:
There is poor driveway access to the bottom side. You can't drive into the rear and the slope makes it impractical for a side load. There will be a double door down there in order to get mowers, UTV, etc in there. Although I plan to be here for a long time, I'd like the top to function as a car garage for resell purposes. I could cut my footprint down even more, but it feels like not a great trade-off for a few thousand dollars. That said, maybe I should try to price out a 28x30.

I don't have an overall budget per se, but as I've gotten over $50k, I have to give everything due consideration.

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I thought that the lower access might be an issue. Oh well.

What ever you do, don't build smaller. No one ever in the history of man has ever wished they built a smaller garage. I went 24 x 40 due to lot constraints and I can just get my F150 inside. Wish I could've went at least 26' with 28' being ideal.

firebirdparts · Oct 31, 2019

Hmmm. When I did it, 15 years ago, the steel was only about $4000 total. You may be okay. I have two further comments.

#1: I had a ton of money invested in the bottom floor, all the stuff holding it up. I don't regret it. I'm just saying the foundation and basement was pricey. The cost per square foot for the 2nd floor is lower. Frame buildings are cheap; larger footprint is probably cheaper per square foot than 2 story.
#2: My floor is extremely strong and seamless. I would be curious to know whether a hollow core assembly would be as good, living with it. I never considered it.

Quick240 · Oct 31, 2019

firebirdparts said:
#2: My floor is extremely strong and seamless. I would be curious to know whether a hollow core assembly would be as good, living with it. I never considered it.

I have a hollow core garage (8" slabs with 3" topping). We did make saw cuts in the topping, but I honestly don't know if it was even necessary -- very solid.

vtjon · Nov 1, 2019

Just more updates - got a specific price on the hollow core planks with a 3" topping. If I factor in less concrete, grouting, crane rental, labor to help set, etc. I'm around $2500 less vs a suspended floor system even having the planks delivered to me. This avoids me having to set a bunch of beams and metal decking for a suspended floor.

I am concerned about the plank weights (and lengths) and getting them from the road to my build location. These particular planks are 8' wide and will weight over 14k lbs a piece. On the upside, it'd only be 5 planks. I could have them cut down to 4' widths for $1800. I will have to have a crane on site to unload from the trailer too.

I might be the first residential property in my county to use the planks. The manufacturer will provide engineering so that will be helpful. I am also in the process of contacting a structural engineer locally for some basic consulting on all of the options.

Still undecided, though leaning towards the planks. I think the planks will make it easier to build this time of year (and even later once I get started). Hope to have a site visit with the crane operator next week to see what's practical.

strutaeng · Nov 1, 2019

Cool, thanks for updating us. Probably best to order to the correct length from the precast plant.

I've got a project from the 70s were they used hollow core planks. Very economical and was innovative back then. Typical uses are office and commercial, but have also been used in residential.

This particular client has stated that the is the least like floor framing (bldg. has concrete pan joist, planks, steel beam/composite, maybe even another framing system.) But this has to do with tenants moving in and out and busting thought the planks. In fact, I have to look at one this afternoon.

Should not apply to you, but know where the tendons are before coring though slab :lol_hitti

spudley · Nov 1, 2019

vtjon said:
Just more updates - got a specific price on the hollow core planks with a 3" topping. If I factor in less concrete, grouting, crane rental, labor to help set, etc. I'm around $2500 less vs a suspended floor system even having the planks delivered to me. This avoids me having to set a bunch of beams and metal decking for a suspended floor.

I am concerned about the plank weights (and lengths) and getting them from the road to my build location. These particular planks are 8' wide and will weight over 14k lbs a piece. On the upside, it'd only be 5 planks. I could have them cut down to 4' widths for $1800. I will have to have a crane on site to unload from the trailer too.

I might be the first residential property in my county to use the planks. The manufacturer will provide engineering so that will be helpful. I am also in the process of contacting a structural engineer locally for some basic consulting on all of the options.

Still undecided, though leaning towards the planks. I think the planks will make it easier to build this time of year (and even later once I get started). Hope to have a site visit with the crane operator next week to see what's practical.

8' wide is a pretty big piece. I believe my Spancrete panels were 40".

For the foundation, I know we used 10" block walls with a solid block top course. They craned the panels right off the truck into place on the walls. Each panel bore slightly less than 6" on the wall and my mason came back and placed another course of 4" wide block around the edge. Poured 3-5" of concrete and framed the garage a week later. No issues 35 yrs later.

Good luck bud, sounds like things are coming together.

vtjon · Nov 1, 2019

More updates - got a price on one of the ICF suspended slab forms (similar to Lite-Deck). This would definitely be the easiest to install (maybe). While the styrofoam forms are relatively cheap, there is a lot of rebar in the call out - around 4,500 lbs worth. While I'm not sure how much rebar sells for, but even at $0.75/lb, that's a substantial cost to consider. I'd also have to rent shoring (which is apparently hard around here) and have the slab and shoring independently engineered.

On the hollow-core, 4' panels do seem more common. I get the impression this manufacturer targets mostly commercial so that's why they sell larger panels and you have to pay to have them ripped down.

ConCretin · Nov 1, 2019

I wouldn't be so quick to discount LiteDeck. It can easily be installed by hand without hoisting equipment. The shoring is very simple and doesn't require any real engineering. You could use some lumber and then incorporate it into the structure. Reinforcing consists of a couple bars every 2' in the 'beams', which shouldn't be a big deal. I can see it being the most cost effective option.

With that said, one thing I like about using precast plank is the opportunity it provides to incorporate waterproofing. A simple membrane between the plan and the topping slab provides a waterproof floor/ceiling and protects steel in the underlying structure from corrosion.

All else being equal, precast plank would be my first choice, followed by Lite Deck or equivalent and finally slab on metal deck. Each of these systems is pretty well proven at this point but I'd place a priority on water tightness and minimizing the amount of steel that must be protected from corrosion.

I'm pretty sure each of these systems will require a center beam and posts so some hoisting will be required for each.

vtjon · Nov 1, 2019

LLWillysFan, I appreciate your insights on all of my posts.

So far, all these solutions are clean span at 28'. The only one to require a crane or hoist will be the planks. The beams and metal decking I think can be set by hand because it's light guage and not I Beams. I am confirming the weight but it's the main reason everyone uses that particular system in my area.

I'll give the ICF system a little more consideration including rebar costs.

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1rahamay · Nov 2, 2019

You should absolutely engage a structural engineer and architect to design the structure and price it out based on a set of plans that are approved by the building dept. until you do that, I think you are spinning your wheels and run the risk of getting in bed with a supplier or steel erector who then will have the upper hand when you find out your design doesn’t pass through plan review.

I’ve seen some bad ideas in this thread but it sounds like you’re seeing it a bit clearer now. To try to design a 2nd floor parking deck without a structural engineer or without a crane or without shoring engineering to curtail costs is insane. Consider the cost of a worker dying on your property due to you not following standard procedures.

Quick240 · Nov 2, 2019

I agree with getting an engineer involved. My original house plans didn't include any of that, but it cost me less than $300 for the draftsman and engineer to provide the addendum with the modifications and all the engineering details. Their new page mainly involved thickening the front and back garage foundation walls to 12" (instead of 8") with a 4" reverse brick ledge for the slabs to rest on, beefed up some of the footings, and added more rebar.

vtjon · Nov 4, 2019

LLWillysfan said:
I wouldn't be so quick to discount LiteDeck. It can easily be installed by hand without hoisting equipment. The shoring is very simple and doesn't require any real engineering. You could use some lumber and then incorporate it into the structure. Reinforcing consists of a couple bars every 2' in the 'beams', which shouldn't be a big deal. I can see it being the most cost effective option.

With that said, one thing I like about using precast plank is the opportunity it provides to incorporate waterproofing. A simple membrane between the plan and the topping slab provides a waterproof floor/ceiling and protects steel in the underlying structure from corrosion.

After meeting with crane operator, it looks like precast plank is out. Due to the length of my footprint, it would require a pretty large crane to reach the backside. A large crane could damage my driveway on the way in plus having to ferry the planks from the front of my property.

I did some additional calculating on the ICF floor (including the shoring and engineering) and it might be a little cheaper and potentially easier than beam and pan. What is the best way to waterproof the LiteDeck type systems? The quote I got from the ICF dealer called for 5000 PSI concrete but I think I'd have to worry about the edges.

All in all, I'm now back to deciding if it's worth $10k-$11k (+ the extra DIY labor required) to add a basement to this garage. On one hand, I think yes, it's worth it, on another, where does "just another $10k" end.

ConCretin · Nov 4, 2019

Unfortunately there is no practical way to integrally water proof an ICF or a 'beam and pan' system. Precast plank are inherently structural with a non structural topping slab, which allows the introduction of a waterproofing membrane in between. ICF and slab on metal deck are more like forms and depend on the concrete for structural strength. As such, they don't allow a membrane to be incorporated.

This leaves you two options. A surface applied traffic bearing membrane similar to an epoxy floor in application and cost or go without waterproofing. Concrete is reasonably waterproof by nature and with some attention to joints and potential cracks, it's doable.

With regard to the fundamental question of value, Your lower level is relatively low cost per sf. If your need the space - and who doesn't - it probably makes sense. The other consideration is obviously the cost to fill the space in. This will significantly eat into your $10-11k savings.

paredown · Nov 4, 2019

vtjon said:
After meeting with crane operator, it looks like precast plank is out. Due to the length of my footprint, it would require a pretty large crane to reach the backside. A large crane could damage my driveway on the way in plus having to ferry the planks from the front of my property.

I did some additional calculating on the ICF floor (including the shoring and engineering) and it might be a little cheaper and potentially easier than beam and pan. What is the best way to waterproof the LiteDeck type systems? The quote I got from the ICF dealer called for 5000 PSI concrete but I think I'd have to worry about the edges.

All in all, I'm now back to deciding if it's worth $10k-$11k (+ the extra DIY labor required) to add a basement to this garage. On one hand, I think yes, it's worth it, on another, where does "just another $10k" end.

Hopefully not badly!

I'm reading this with interest, and still thinking about my two floor dream garage.

My goals are more modest though--I would have to do the in-bank wall as a retaining wall, probably parged concrete block on the side walls (stepped down with grade) and then wood framing for the rest (and not clear span, so posts where needed).

For mine, the 'second' floor would be the workshop, so it needs to be framed heavier than a house, but not crazy overbuilt, since I have no plans to sneak in a big Bridgeport mill or anything like that--definitely not carrying the weight of cars.

In Seattle when we lived there, we did have a garage that was built out over a grade that fell away--but they did not leave the space below usable. Since the garage was integrated into the house structure, they had massive piers and posts to hold the whole house up (earthquake standards make it pretty strict)--and the garage deck was wood framed (like a deck), plywood, membrane and then a skin coat of concrete.

scottydosnntkno · Nov 4, 2019

vtjon said:
After meeting with crane operator, it looks like precast plank is out. Due to the length of my footprint, it would require a pretty large crane to reach the backside. A large crane could damage my driveway on the way in plus having to ferry the planks from the front of my property.

I did some additional calculating on the ICF floor (including the shoring and engineering) and it might be a little cheaper and potentially easier than beam and pan. What is the best way to waterproof the LiteDeck type systems? The quote I got from the ICF dealer called for 5000 PSI concrete but I think I'd have to worry about the edges.

All in all, I'm now back to deciding if it's worth $10k-$11k (+ the extra DIY labor required) to add a basement to this garage. On one hand, I think yes, it's worth it, on another, where does "just another $10k" end.

You have to look at the overall cost and what you get for it based on your site conditions.

If your 10k factors in the poured walls, footers, icf, concrete, forms etc etc etc look at it as your getting 1200sq ft for 10000 or less then $10 ft which is dirt cheap for new construction, and usable basement space.

We build our customs at 200/ft living and 70/ft garage space.

If your 10k is just the suspended slab and icf, you also have to factor in the actual basement slab since you now have two slabs, poured walls vs trench footers, etc which can add more cost. But if you have the site slope to do a drive In basement you might already be doing poured walls anyways. We do a lot of houses with poured garage wall footers with 5-7’ of fill in them

vtjon · Nov 4, 2019

LLWillysfan said:
With regard to the fundamental question of value, Your lower level is relatively low cost per sf. If your need the space - and who doesn't - it probably makes sense. The other consideration is obviously the cost to fill the space in. This will significantly eat into your $10-11k savings.

The $10k-$11k difference factors in the fill and having to pour to slabs. It doesn't include any basement finishing or basement electrical which would all be minor. Basically, no $9k in fill or labor to spread but use that $10k plus another $10k for a suspended slab. This suspended slab also makes things more complicated in general as we know from this discussion. I'm somewhat concerned that my regular concrete flatwork guy could be out of his depth finishing a suspended slab.

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vtjon · Nov 4, 2019

scottydosnntkno said:
If your 10k is just the suspended slab and icf, you also have to factor in the actual basement slab since you now have two slabs, poured walls vs trench footers, etc which can add more cost. But if you have the site slope to do a drive In basement you might already be doing poured walls anyways. We do a lot of houses with poured garage wall footers with 5-7’ of fill in them

The base cost includes poured walls, footers and as much as 8' of fill in some spots. This is where I've started. It could end up with less once we start building but I doubt it. It's around $40/sqft but that includes me doing everything once a contractor getting it to a slab. Of course, with a suspended slab, that drops to about $29/sqft but with a lot more diy work, headache and risks.

I had another topic on fill alternatives. Someone today recommend crushed concrete with guidance from a geotechnical engineer but my excavation contractor recommended against using it because you'll spend the savings in all the extra compacting and oversight.

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vtjon · Nov 5, 2019

I just thought I'd post more thoughts on this. I seem to have come full circle today.

Assuming it can be engineered, I am leaning heavily towards using grade beams and fill dirt (instead of #57) as Larry described in my post on fill. This would avoid me having to be concerned about the contractor compacting the #57 fill correctly (even though people claim it's self-compacting). I have to talk to the engineer to see if a 28' or 32' span is practical for this. Including the additional rebar, concrete and engineering for the beams, I should come out ahead (maybe $5k). If I have to go a 28' span, I might go 44' deep.

In looking at my numbers, my 32'x40' slab on #57 fill is estimated around $54k. This is a worst case number. If I do 28'x40' on a full basement, it's $65k in a best case scenario that includes a lot of DIY labor (rebar setting, foundation drain tile, beam/form setting) and hopes that I don't need rock chipping and crazy excavating. I would like to get a lot of this build accomplished this winter as I'd like it mostly finished by spring (might be impossible anyway). I think the suspended slab system would make that harder.

While I have time for some DIY labor, I think I would be best served by reserving that labor for stick building.

I tend to over-research things like this so I thought I'd share my thought process. I'm going to ponder this more tonight and likely engage the engineer tomorrow.

larry4406 · Nov 5, 2019

Keep us posted on what you decide and obviously include a build thread (with pictures...).

You have a couple threads running. Perhaps at least put links in them to each other to help the next guy.

scottydosnntkno · Nov 5, 2019

If your alternative is to bring In that much fill, then I’d say it’s a no brainer to do the panels and have a full basement below.

Your already doing the poured walls. Adding an internal brick ledge would be no additional cost.

For your flatwork guy, he shouldn’t care whether he’s pouring on grade, compacted fill, or a suspended slab. 3” of concrete is 3” of concrete on a flat surface.

Transporting the slabs up the driveway, worst case you rent a skytrack for a day for $1000. Or less than $1/ft so the crane can hoist them in place.

If your actually, true costs to do a grade beam slab with fill vs a suspended slab and poured basement floor below are actually only $10k, then you better jump on it. Even at 20k, your adding double your first floor space for 1-2$ a square ft which is dirt dirt cheap in construction.

With engineered, suspended slabs there’s really not more risk. The slabs are engineered, you put them in place, concrete over them and all is fine.

With 8’ of fill, you’ll forever be wondering if any place sunk or wasn’t compacted or is your slab going to crack etc et. Spancrete has been around FOREVER. Every single parking structure uses it and that sees a lot more stress and dynamic load than your garage everwill.

Quick240 · Nov 5, 2019

vtjon said:
After meeting with crane operator, it looks like precast plank is out. Due to the length of my footprint, it would require a pretty large crane to reach the backside. A large crane could damage my driveway on the way in plus having to ferry the planks from the front of my property.

Could they cut the panels in half at the midway point and use a steel beam to support them? That would cut the weight per panel in half, possibly allowing for a smaller crane?

vtjon · Nov 7, 2019

LLWillysfan said:
Unfortunately there is no practical way to integrally water proof an ICF or a 'beam and pan' system. Precast plank are inherently structural with a non structural topping slab, which allows the introduction of a waterproofing membrane in between. ICF and slab on metal deck are more like forms and depend on the concrete for structural strength. As such, they don't allow a membrane to be incorporated.

This leaves you two options. A surface applied traffic bearing membrane similar to an epoxy floor in application and cost or go without waterproofing. Concrete is reasonably waterproof by nature and with some attention to joints and potential cracks, it's doable.

As of now, I'm back on plan to do a basement with a 'beam and pan' system. Hollow core isn't practical due to crane access and, while ICF is cost competitive, I think having a system that everybody locally is familiar with will be helpful.

All 4 walls will be poured concrete walls with beam pockets. There will be two ways to pour the slab. We can have have the slab overlap the entire foundation wall or we can have a ledge inside plus the pockets (with a 8-12" stem wall to build on). If this was slab on grade, the ledge would be the best choice. With a suspended floor, it seems like you would have less chance of water getting through the edges of the slab if it was over the entire foundation wall. The downside of this you have to form the edges and I lose some wall height that I was going to pick up from the stem wall.

In either case, I will seal the floor and edges. I don't expect to be washing out the garage very often nor commonly parking cars with rain/snow.

Thoughts on the best route?

strutaeng · Nov 7, 2019

vtjon said:
As of now, I'm back on plan to do a basement with a 'beam and pan' system. Hollow core isn't practical due to crane access and, while ICF is cost competitive, I think having a system that everybody locally is familiar with will be helpful.

All 4 walls will be poured concrete walls with beam pockets. There will be two ways to pour the slab. We can have have the slab overlap the entire foundation wall or we can have a ledge inside plus the pockets (with a 8-12" stem wall to build on). If this was slab on grade, the ledge would be the best choice. With a suspended floor, it seems like you would have less chance of water getting through the edges of the slab if it was over the entire foundation wall. The downside of this you have to form the edges and I lose some wall height that I was going to pick up from the stem wall.

In either case, I will seal the floor and edges. I don't expect to be washing out the garage very often nor commonly parking cars with rain/snow.

Thoughts on the best route?

Are you talking about doing a structural concrete slab? You span with beams across your basement walls and one-way concrete slab spans perpendicular to those beams. Big $$$ for formwork.

Or, are you talking steel beams? Same scenario for beams, but use form deck (or composite deck.) This option is more economical. The detail at the perimeter can be done one of several ways.

How to spec/price a suspended slab

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