Greetings!
New guy here; live up in the boondocks of Northern California.
Bought 1/4 acre on a dirt street two years ago; old trailer-house, decent garage and all utilities.
The idea is to build a new house and then dispose of the trailer.
Now it gets sillier. I have a mind to build the house after my own head and do a lot of the work myself. Mind you, we are talking about a 720 Sq.ft. cabin (legal minimum) — not the Taj Majal. I also want the place to be fire proof, rot proof, termite proof and earthquake proof. And simple to build. (And super-insulated and more… but one thing at the time.)
I once read something about “rubble on grade” foundations. This would NOT be the more common “rubble trench”, but a full size pad of compacted rock placed directly on the grade, with the concrete slab then poured on top. Like a highway; or maybe a railroad track, where the rock is known as “ballast”.
The soil is expansive clay — big cracks in summer, slick mud in winter. The grade slopes a little bit, so I foresee good natural drainage out from the rubble pad. Frost is not a factor — we get only a touch of night frost.
Any thoughts? Any knowledge? Experience? Advice? Anything at all???
Most cordially,
Elliot
Replies
I also want the place to be fire proof, rot proof, termite proof and earthquake proof. And simple to build. (And super-insulated and more... but one thing at the time.)
Steel framing, stucco, and borate treated cellulose insulation will do all that.
a full size pad of compacted rock placed directly on the grade
No matter what base you decide on, you HAVE TO TAKE THE TOPSOIL AWAY!
Stockpile it, 'cuz you'll use some of it later. Sell the rest.
Put stakes at the planned corners and remove the topsoil 10' past the stakes. Level the clay inside the corners and 2'-3' outside. Slope the clay away from the house at 1/4" per foot to the edge of the excavation.
The base fill. Plan ahead. You will want the bottom of your siding (stucco) to be 6"-8" above final topsoil grade, (check with your AHJ. Termites, ya know?)
After the house is sided, measuring down from the bottom of the siding, you should have;
You should have two drain zones. 1 schedule 35 pvc at the perimeter of the house and 1 schedule 40 pvc at the perimeter of the excavation. both laying on top of the clay pan under the Engineered Fill. If you get a lot of rain or snow. Otherwise just the one next to the house. Run them to Open Air down slope. You should put gutter drains next to the footing perimeter drain. Don't forget cleanouts for 'em.
Water and freezing temps in the clay under the house is your enemy.
Water and freezing temps in the clay under the house is your enemy.
Water and freezing temps in the clay under the house is your enemy.
Just my opinion, worth what you paid, though.
SamT
Wow, thanks Sam!
That's a nice detailed recipe. Just the kind of advice I need. I'm printing it out.
The two feet of Engineered Fill, sloping out to ten feet past the house, is exactly what I had in mind. I even expected to compact it in many layers -- which you reminded me are called lifts. So I must be thinking basically correctly.
But I wonder if I can simplify your recipe thanks to the local conditions? There is no top soil. None. And no frost to speak of -- maybe 25 F for a few hours at the worst. Even this time of year we have 50 F during the day.
The big hazard is indeed the clay-and-water. We get not a drop of water for eight months and the clay dries out and shrinks. You can lose your shoes in the cracks. Then the winter storms blow in and dump heavy rain and the clay expands, breaking any concrete slabs that are not isolated from the movement. My thinking is to let the house float like a boat on top of the EF. Does that analogy make sense? And with no top soil to remove, the EF would serve as its own drain to Open Air, eliminating the pipes. Does that sound realistic? The floor of the house would wind up 2' 6" above the existing grade. The sloping EF outside the house would be covered with landscaping and patios.
As for the rest of the house, I am definitely going with steel and concrete. Possibly a Heritage Steel kit, if they can tailor one to the small size. No wood at all. And for insulation, I'm partial to rockwool, which is what I "grew up with" in Europe. With massive insulation and concrete block "thermal mass" in the walls, I should not need hardly any heating and cooling.
Building my own house will be my biggest project ever. But I've done a bit of other fabrication, so I know I can do it if I only learn-learn-learn first.
Sure appreciate your time, Sam!
Any additional information and suggestions are of course very welcome.
Most cordially,
Elliot
Elliot,
No topsoil = no drains?
EF is not waterproof, it lets water run right thru.
You want to keep the clay under the house at the same moisture content year round. So you want a vapor barrior on top of the clay that extend maybe 5' past the house. Tape all the seams. How deep does the clay dry and crack? That's how far beyond the footings you want to extend the VB.
Now put the first foot of EF down with the drainage slope out the the edge of the VB. Put another layer of plastic over the base bed you now have extending out 8' past the footings.
Add the next foot of EF.
The first layer of plastic (the VB) is to moderate the soil moisture content under the house. The second layer is to channel water away from the footings. EF is pretty good about resisting frost heave, but I wouldn't want it sitting in a big puddle.
SamT
""EF is not waterproof, it lets water run right thru.""
Right, that was the idea. But you say I need to keep water AWAY from the clay, and keep the clay at an even moisture level year round. Oh boy, that would be wonderful. I just didn't think it was possible. But now a perimeter drain makes sense to me. I failed to grasp that part earlier.
""EF is pretty good about resisting frost heave...""
That's what I was hoping -- your frost heave being equivalent to my water expansion.
I conclude that EF (or equivalent that I can get here) is usefull for my purpose, but that it is not a cure-all and that I need to control the moisture in the clay with drains and barriers also. Sounds like a plan! Thanks!
Elliot