I am thinking of doing a new house built with slab on grade, mostly, but a small 8-foot basement for mechanicals in part of the footprint. The attached .gif pic shows a simplified arrangement to help frame my question. To help understand the pic, the house footprint is 26′ x 54′, with a 10′ x 12′ bumpout along the back wall. I rendered it with hidden lines dashed, so you can see the 4′ frostwall foundation around most of the perimeter. The mechanical room basement is the deep small part along front middle, and its footprint is about 11′ x 15′. The letter “A” is adjacent the detail I am questioning here. It is where slab on grade floor meets the woodframe deck capping the mechanical room. If you want your finished flooring (hardwood in my scheme), to be continuous across such a junction, what do you do to maintain continuity, and ensure that there is little enough movement to avoid problems with the finished floor?
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I am not a builder. But I have a slab on ground with 4 ft frost walls.
But my question is why partial basement? If you are going to the trouble of digging this out and then complications of access and matching up the flooring, etc then why not just a conventional basement and get the extra space for little cost?
As to your question I am think of putting some hardwood floors down on my slab, but I have existing flooring that it has to meet up with (and cabinets and doors and stairs) that means that I would use a low profile engineered floor.
But you are starting from scratch. I would plan on laying 3/4" ply over the slab and just continuing over the joist in the "basement" area. Then you can do a nail down to the plywood.
Also I would used I-joist or other engineered joist so that they won't shrink when they dry and use hangers so that they are referenced to the top of the slab, and not a ledge on the side of the walls.
I am looking at cost comparisons, and here is the initial view. The bumpout in back would be slab on grade either way, so that is out of the analysis. If I do it with a full-depth foundation, I will have the following as more stuff to pay for: 1200 sf of foundation wallforms, 200 cy excavation, 15 cy concrete w/ rebar, and 1200 sf of wood floor frame and deck. The slab on grade is a wash as I see it, because it is either in the 1400 sf of full depth foundation as basement floor slab, or split between my little 160 sf mechanical room basement, and the main floor house slab. I think there is some real savings here. The house design does not allow any space for the water heater and furnace, and in my partial basement hallucination, the gear is in the hole. BTW, my method for placing a wood floor on concrete will be to use the Sika AcouBond system, which floats the floor atop a 5mm or 8mm foam mat, through which oblong "towers" of a one-part flexible urethane adhesive bond the wood floor directly to the concrete (and wood deck section). She floats, in other words. Works for engineered flooring or solid wood, and might be right for you. Total thickness is that of your flooring product, plus either 5mm or 8mm, depending on which mat you use. Go to Edelweiss Flooring's website for details.
To accomplish this, theoretically speaking, you need to either project the framing out over the slab or project the slab out over the frame hole. You could form to support and pour an integral slab for the floor with reinforcement. Now you've got your bomb shelter.
If it were me, I would build it with a framed floor after excavating the whole hole. Then that brings the question back up of why not a full basement but you are sold on this already. It just doesn't gel for me. I am questioning why a house would be designed with no locations for utilities placement. Perhaps the better post Q would be to put up the design for review and comment unless copywrite protection and site rules would conflict.
Interestingly, I just did an inspection of a very small house that was built almost that way. It was a true slab on grade with a dug and poured plumbing room about 6x8
BTW, a slab on grade is a slab ON grade. This is a frost wall foundation with a concrete floor..
Excellence is its own reward!
I don't understand why anyone would choose a slab over a full basement. The difference in cost really isn't a factor with today's interest rates. Skimping on other things like flooring, countertops & landscaping can easily give you the extra $$ you need for a full basement. Change that other crap later.
My brother lives in Raliegh, NC and I can't believe how few houses down there have basements. Where the hell are you gonna store all that crap you wife buys?
Mike O.
I think I can ponder my way through the slab/floorframe/deck flush-up detail. It will probably involve some kind of ledger block along the top of wall forms to create a ledge for a rimboarded wood frame. I will probably waste some sketch paper doodling around to make it so that rimjoist shrinkage doesn't lower my deck too much. But back to the design. I am trying to see if one of the FH plans offered for sale can work out as a spec house on some land I am looking at. See it at http://www.orderhomeplans.com/main.asp?hspos=FHB2NET&action=plandirect&planid=19769&hsgv=1&sessionid={DF38C3A9-920F-4A83-B2A4-86AE9FE9868B}
It was built with a full basement somewhere near Providence, RI. I am trying to work out a lowest-cost estimate, thus the slab and spook-hole foundation. A couple of high end specs have been built in the village, one less than 1000 feet from the potential site for this, that have had frost-protected slab foundations, and little mechanical room spook holes like this one, to house heaters and pumps and the electrical panels. So ignore my sketch detail showing a frost wall with footing. If we do it with the partial basement spook hole and slab, the edge will be like what we call here the ">
As for the storage aspect, and the losing of it by not doing a basement, this is proposed as a spec house in an vacation community, and will likely be used as a weekend house. Nobody cares about storage in a weekend house, other than requiring a place to stuff the skis in the off-season. The plan has a detached garage, with full-depth bay by about 9 feet wide, and that is more than enough for all the potential bikes, skis, and hiking boots.
Oops, forgot the pic. Here ya go.