Spancrete Vs engineered poured floor

[aventino68]

Building a 50' x 34' garage and since we're needing foundations I figured excavating further and putting in a 7' high basement underneath and internal lift for cars. Pondering concrete flooring and about to get engineer and architect to look at load calculations and get a plan finished. I'm curious to see the cost of using spancrete vs Bracing and pouring a concrete floor. Don't want any additional support walls when we're done, the precast spancrete goes 35ft but how would that compare with an engineered poured in place floor.

I suppose my question is, do you pay a lot more for precast concrete because it gets finished so quickly? Has anyone else done similar and weighted up the cost of both?

 

[strutaeng]

I doubt anyone here can give to hard numbers on this. You'd have to post plans.

Typically, precast is more economical than cast in place concrete. This is on commercial projects. Precast will involve a crane, but erection is faster. Faster erection is less money vs. a lot of labor for CIP.

I would contact a concrete contractor that has done both types of systems for some rough numbers.

Even then, the two systems are not true apples to apples, even though they are both concrete.

Cast in place would probably involve beams and slab to make that span work. That may be post tension territory...

 

[ConCretin]

To add to what strutaeng said, the CIP version would probably be more expensive due to the spans involved. You'd be looking at integral beams or PT, both of which would add to the cost if you can even find someone to do it.

The planks are prestressed and can span longer distances. You probably know this, but the planks have camber so you'll need a topping slab to provide a smooth, level surface. You should also pay attention to a waterproofing system to keep water and salt(?) out of the space below and to protect the floor system itself. You can use a membrane between the plank and the topping slab or a surface applied coating.

 

[stillnostrebor]

I've worked in the Prestressed Concrete industry for 30 years, so...

The above poster pretty much nailed it from my experience. Cost will be directly related to proximity of your site to the precaster, as freight is the great equalizer in our world, and access/availability for erection equipment to install the precast components.

Waterproofing the slab is an issue as noted, and can be achieved a number of ways, but be sure to involve a PE that understands these systems as often the topping slab is a composite part of the design and cannot be divorced from the deck surface by a membrane.

 

[readhead]

You could look at beams or bar joists and decking. If you are willing to have at least one post it will reduce the cost quite a bit no matter what system you are looking at.

 

[SGKent]

a smaller basement is also an option. That would reduce the span.

 

[scottydosnntkno]

A friend of mine just built a house that used spancrete under his four car 26x45 attached garage. Similar to my new house it was built on a hill so the garage already required full height 9’ poured walls even going with a typical slab setup. The price difference was $15,000 just counting the spancrete for 1170 ft of space. I spent $6000 filling my garage with 1x3 so really it was like 9000 or $8/ft. Super cheap for a lot of added space. The spancrete rests on an internal brick ledge that’s already there to support the poured in place slab.

 

[MattRMagnum]

Building a 50' x 34' garage and since we're needing foundations I figured excavating further and putting in a 7' high basement underneath and internal lift for cars.

Sorry for the mild derailment, but have you looked at the costs of in-ground lifts? They were all 2-4x the cost of an equal quality above ground lift when I was looking (my garage has a service pit that I contemplated getting one for).

Definitely worth building a basement none-the-less, but I'd sooner say make sure the concrete above it is 4" inches thick, and put a standard lift in.

 

[Kmp259]

I have a shop built 30x100 with a basement...and 15” spancrete and 4” poured on top of the spancrete.....

We pull many large trucks in all the time to do maintenance on them......very strong floor....

 

[Showkey]

One change.......don’t build a 7’ basement.......extra cost to make it 8-9-10’ the added space and function is well worth the cost. 7’ leaves very little or no head room after HVAC and other utilities are hung.

Local builder did this exact plan, basement under the garage in the the last two parade of homes. It was done with spancrete and poured floor over the top. Both were attached to the home about 38x28’. Basement ceiling were 11” in both cases. Made for an awesome basement shop.

 

[aventino68]

Thanks for all the responses. I'm still waiting for the plans, I did a basic set of measurements and put in a bunch of cars to scale and can't seem to get any narrower than 34 ft and still get cars manoeuvred easily onto the lift. Turning circle etc becomes a problem. That's where the 34ft came from. I'm running with the tallest bendpac hoist they make (and tallest on the market) and that's 89.5" so with my 7 ft basement and 6" precast floor I'm at 90" and then a layer of floor/sealant on top and I should be close. I have nothing down there apart from car storage, no HVAC etc since its a separate building away from the house and with lighting up high on walls it'll have a clear ceiling in basement.

I wanted to go 8 ft but since its just storage and I'd have to add a foot to the hoist bases and a foot to the hoist ramps to get the hoist level with the garage floor it didn't seem worth it. And then there's clearance with 17" high ramps and getting cars on the hoist when in basement. The inground lifts I loved but they were crazy expensive (7x cost) in comparison to a 4 post hoist. Bend pac do make a 3 car high 4 post hoist that has the height but they don't do custom and I want in-between the 3 car and 2 car.

For transport costs I'm about 2 hours away from the nearest hollow section precast floor manufacturer I think. I'll need to see how best to seal the floor, seems as important as putting it in.

 

[Showkey]

I assume you have limited space in the property ? The economics only works if the goal is maximizing the sqft on limited foot print on the property.

 

[aventino68]

I assume you have limited space in the property ? The economics only works if the goal is maximizing the sqft on limited foot print on the property.

I'll look into the economics more. I'm not too limited for property size but don't want the workshop to dwarf the house. I'm new to basements and thought since we had to do the footings for the building it was cheap space to get a basement.

 

[readhead]

Considering what you will have to spend on the floor it isn’t cheap space. It can be a lot less expensive if you are willing to have some posts.

 

[aventino68]

Just to update basement under garage idea, stretched garage and will run an extra Bay with two hoists and get 4 car storage in there instead. Will landscape in front of it and hide a large portion of the garage with hedge/trees. Wife didn’t want my garage dominating the house in size, but didn’t want it too far away from the house either. House has an attached 3 car as well. Engineer basically said cost was either a little more or more likely a lot more depending on the excavation and issues that may pop up so as helpful posters have said, if you’ve got the space above ground it’s cheaper not to dig down.

 

[Armorpoxy]

Hi
While we are not concrete foundation experts, just make sure whatever you do has a waterproofing membrane specified since if you want the basement to not get water in from dripping cars there needs to be a membrane since what you have is really not a floor but a 'roof you park on' hence roofing type embedded in the floor.

We get a lot of calls about leaking garage floors to space underneath...