A new house is being built near me. Right now, the foundation is poured. It will have a full basement - with 3 “escape” windows.
When I look at the foundation, it is divided into 4 separate “areas.” The main area (with the escape windows) is what I presume will be the finished living area. On the front of the house, a rectangle sticks out, which I presume will be the front porch. There is another rectangle at the back of the house, which I presume will be a screened porch or something. The left side of the house has an area that will be the garage - you can see the cutouts for the garage doors.
What surprises me is that the 3 areas - the front and back porches and under the garage - all appear to be full depth, but they do not have any connection to the basement living area. I would have expected the porches and garage to be built on slabs with footings, rather than full depth excavated foundations.
Will these 3 areas then have to be filled and compacted? In my ignorance, I would think such fill to be less stable than the existing earth. Or does that not matter because the porches and garage will be built upon beams?
From what I’m reading, the footing needs to be on ‘undisturbed’ earth. Further reading suggests that if they dug out the footprint of the entire house, including the porch and garage, the footing has to go all the way down there, otherwise they have to worry about the backfill settling over time.
I’m sure that is what happened. They had the big excavator on site and just dug out the whole footprint. The extra full-length walls struck me as an unnecessary expense, but minuscule porition of what will be a pricey house.
What struck me as curious was that the garage floor will be poured over a filled vault. The porches will not be bearing as significant loads. How well can 8-10’ of fill be compacted?
Those areas are usually filled with gravel, which is pretty good at self-compacting if you spec the right stuff.
How far north do you live? Frost depth and undisturbed soil are the two criteria for footing location. Along the Ohio River the frost depth is only 30" from finished grade to the bottom of footings, but it’s not uncommon for you to have to go deeper to get to undisturbed soil. Near the Canadian border the frost depth is more like 60", so even if you have undisturbed soil very near the surface you still have to dig down pretty far. At that point the marginal additional cost of a full-depth basement is pretty small, and it’s easier (often cheaper) to form all the footings and foundations on a flat plane versus stepping up and down.
Could the entire basement be usable area, and the section with the windows a bedroom? I think egress requirements differ for a bedroom versus a den or media room, for example.
My basement is fully finished, but only the bedroom has an egress window.
It might just be cheaper to have the people putting up the footing/foundation forms to do it for that area as well. Then you don’t have to worry about compacting 8ish feet of dirt and gravel.
I believe the OP is talking about something like this. You can see two areas that have no obvious way in/out from the rest of the basement.
Foundation depth has to reach the frost line for any structure. That depth depends on your location. Local requirements vary for the entrance to a garage which may have to go deeper than the frost line. It’s generally worth it to go full depth on any portion of a foundation even if it has lower loading requirements such as under a porch so that it can become fully loaded enclosed space in the future.
Doesn’t make a lot of sense to have totally inaccessible areas created by a foundation, but they could be intended as crawl spaces with access in the framing above the foundation.
Thanks very much. The answers - and that photo - very much describe what we are seeing. Although the foundation areas go down to apparently full basement depth (site is fenced and can’t see the bottom from the sidewalk.)
Thank you for dispelling my ignorance WRT foundations/backfill.
They tore down a rock-solid little ranch, and are likely going to put up a lot-line to lot-line white with black trim farmhouse on steroids - as has been so common around here. Basement looks >8’ deep - then they’ll wonder why they get water! Will likely go for $1.7 mill or so - so any addl cost of excavation/fill will be a negligible portion of that.
Don’t they typically cover the outside wall of the foundation with a waterproof coating or membrane? I think it’s easier to prevent water infiltration during construction.
There is some black substance sprayed onto portions of the foundation near me. I presume waterproofing. I believe it is on the insides of the “porch/garage” areas. My guess was because those areas would not be getting floors. I’ll check later today or tomorrow.
I just flashed back to a childhood memory: sneaking into a home construction site and drawing & writing on the tarry black foundation spray. I also rememder it was often muddy/flooded down there and a dump for everything.
Protip: Rocks and sticks and grass will stick to the goo, elevating the prospect of a mixed media composition.
It’s basically an unsecured trench and could have easily entombed two to four kids in one fell swoop of a collapse. It probably wouldn’t make a sound.
Just walked past. When they tore down the old house, they created a pile of rubble - seemingly bricks and limestone lintels - at the front left corner of the property. Later, during excavation, they created a second pile next to it, with some of the excavated (top?)soil.
Today I saw an excavator at work. As I walked past, the 2 piles were gone. The topsoil seems to have been used to fill against the front foundation wall. The side I could see - with the escape window tunnels - was still exposed. The bricks and rubble filled up approx 1/2 of the space under the garage. Is this the sort of correctly spec’ed self compacting fill? Not sure what - if anything - was under the rubble. The other spaces - the main basement area and under the front porch - had a nice layer of clean gravel.
Oh yeah - in the front right corner of the lot, where the rubble pile had been, there is now a hole - maybe 10’x10’ and 6-8’ deep. I’ll note that our city has had a lot of flooding issues in the past - compounded by the many teardowns building larger homes with larger footprints and deeper basements. I’m pretty sure the city requires some remediation efforts, so this might be a french drain or something along those lines.
Backfilling with rubble is fine under the garage floor or other slaps if it’s been compacted well. They should wait a while before final filling, either watering it down or waiting for rain. The excavators may use the shovels to compact the fill or vibrating compactors may be used. The final fill under a slab should be somewhat cleaner material. Any concrete slab has to be poured over a layer of gravel, not directly on dirt, the concrete will ‘grab’ the gravel and it will form a hard layer under the slab that prevents the concrete from crumbling on the bottom.
Protection of the concrete is the main reason sealant is applied now because the concrete is so good and leaks are unlikely but exposure to dirt, water, and cycles or freezing and heating will cause exposed concrete to come apart bit by bit. In the olden days of my youth many foundations were made from somewhat permeable cinder blocks and the sealant prevented water infiltration. Concrete blocks and poured foundations have replaced those old blocks and water infiltration will require a crack or hole in the material, which without sealant will eventually happen. Even with sealant it still can so many foundation interiors are now coated with sealants also, though usually not the black tarry type stuff used on the exterior.
They must’ve brought in some rubble from another site, because now it is piled a good 6’ above the level of the garage foundation wall. And another pile in the front of the lot.
The “vault” in the front right corner has been squared off and lined with some heavy duty landscape fabric. Pretty sure it is stormwater control. Will check the local ordinance for more details.
FEET. Perhaps 4, but it is a LARGE pile, well above the level of the foundation. May not be evenly distributed throughout the entire space, so perhaps it will be leveled and compacted.
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Will likely go for $1.7 mill or so - so any addl cost of excavation/fill will be a negligible portion of that.