Hi all, we’re building a new home that will feature a walkout basement (partly thanks to input from you folks!). Due to some land features the foundation walls underneath the garage will be 9′ poured concrete. A friend of mine says that if we’re going to have 9′ walls under the garage then we should consider “spancrete” for the garage floor so that we can utilize the space underneath. The builder said a “rough estimate” for this would be about $10K to cover our 3.5 car garage.
We thought our basement was plenty big already (about 1800 s.f.; about 1200 s.f. of which will be finished 3-5 years down the road) but I suppose it wouldn’t hurt to have the additional space…suddenly I’m envisioning a pool table room! 🙂
Any Thoughts?
Thanks, Rob
Edited 10/5/2004 9:19 am ET by strokeoluck
Replies
Hollowcore precast panels are a great way to do a structural garage floor.
Make sure your builder is quoting the package the way it should be done, which is this: Hollowcore planks, with a thin slab topping (2-1/2" minimum thickness), slope for drainage (out the doors is fine), and topped with a waterproof deck coating. Sika and Sonneborne make them. They are elastomeric two-part moisture curing urethanes, going on with a notched squeegee and then backrolled, 40 mils wet for the primer, 40 mils wet for the topcoat. You will want to sprinkle sand or granulated rubber particles into the topcoat before the backrolling, to embed a grit to the surface, for a non-slip feature.
If you are in a heating climate and will consider the space under the garage as heated space, you can tapcon 2" furring strips to the ceiling below, do rigid foamboard in between, and gypboard the ceiling. We did exposed conduit runs on the surface of the ceiling afterward and fastened rows of tube lighting. It is a shop space for me.
Thanks! We're in Michigan. Any idea of the cost over/above normal.
I remember hollowcores for a two car garage being about $4500, but that was 4 years ago. You will need a small crane for an hour or two to get them off the truck and set. Edgeforming for the topping slab will cost about a two-man crew day, plus materials. Figure maybe ten yards of crete for the pour, at $85 per yard delivered, then 75 cents per square foot for placement and finishing.
You might be looking at $750 for the Sika or Sonneborne deck coating materials, which you can do yourself, or pay your GC about 6 hours labor, tops, to apply.
Builder got back to me tonight and said it would be about $10k to do our 3.5 car garage w/spancrete. Given that we already have ~1800 s.f. in the basement - and no plans to finish the walkout for at least 3-5 years - I think we're going to take a pass on the spancrete.
On the one hand I think "boy if it's 'only' going to run us another $10k, let's do it!" but then I have to slap myself and remember that we're saying that w/just about EVERYTHING! Nothing gets cheaper during this process...
- Rob
Here is the site for the Sonneborn product you can use.
http://www.chemrex.com/productcatalog/detailpage.asp
The concept is a good one. In fact my basement is under the garage and higher than the first floor or my house. I am on a hill side.
But around here it is all done with pour in place concrete over temporary supports. But then I do have a steal beam and post in the middle. That is the way my house was built in 79, but a couple of neighbors have done additions in the last 5 years and they where the same way.
But if I were doing it today I would seriously look at doing it with ICF's. Now they also need temporary support, but they will span 30 ft or so. Have channels for utilities. Have insulation. A lot of heat is lost out of the top of concrete ceiling even with a garage above. And it comes with attachment points for doing your finishes, don't have to drill a thousand holes in the concerete.
JLC or FHB had an article on exactly this within the last few months.
I'm envisioning a pool table room!
A 3.5 car garage puts you in the right sorts of room for a pool table. The recommended minimum is 10' plus length & width (for 5' all around--so you don't need a stumpy stick or three). So, for a 60x120 pool table, you want a 15' x 20' room.
You might wander down to the billiards store to get the sticker shock out of the way, though. Table is just the start, you need the table light, a rack for the sticks, all kinds of things they will be only to happy to provide a quote for . . . <g>
A "plank" (of concrete) floor is an elegant way to make the span.
http://www.polysteel.com/litedeck.htm
Used this on my house, back and front porch about a year ago. It's outstanding stuff. Mine spans about 15', but you can get bigger spans and still park a car on it. It has the insulation value already built in, though up North I would add more foam to it.
I posted pictures of it a while back, you can probably find them. If not, let me know and I can send you some more. I could probably also dig out my bill if you want me too.
I gained a 400 sq ft storage room under my back deck and 3 extra feet for the TV under the front porch.
Note that my back porch did form a couple of hairline cracks that leaked ever so slightly. > 1/4 cup per day of rain. I caulked the cracks the problem went away. I also laid down EPDM membrane (not glued or anything, just laid down), before putting finish stone work on my porches.
MERC.
The lite deck forms are actually what I used when I did my garage with shop under.
We shored with temp studwalls at the 1/3 span points (24' overall span), edgeformed, reinforced with big rebar in the beams, and poured.
With the foam insulation already there, and the integral c-studs of steel embedded in the form bottoms, we gyprocked directly to the bottom, then surface-applied lighting.
For a finished room, you would want to rout in grooves for the electric wiring, before rocking.