[Guest]

A question for the people who know such things:
My land has about 8" of dirt over solid bedrock hillside.
Is it possible to somehow bolt my house foundation to the rock? Maybe make holes- somehow (?) - in the bedrock, fill them with concrete, set in bolts, and then fasten the foundation (treated wood) to the bolts? Is this possible without fancy, expensive power tools and/or heavy equipment?
Since there's so little soil and I don't have the money or inclination to deal with a bulldozer and lots of gravel, the building sites aren't going to be very levelable short of blasting rock out, so I'd rather work around the existing conditions if I can.
The slope is not real steep, about 20 degrees at worst.
Thanks in advance for your help.

 

[fordy]

..................I would think at the very minimum you will have to engage the services of a truck with a hard rock drill . Something on the order of those rigs that drill holes for telephone poles. You can buy those hard cardboard forms that slide down into the hole and then rise above the soil . But, you will atleast , have to have a reputable cement contractor comeout and "Shoot" alevel on all the cardboard forms that you have set. Personally, I would get bids on letting a contractor do the complete job if you have NO prior experience doing Such. It might better to let your home float on the Piers rather than having a solid attachment. I say this IF you live in a Zone where Earthquakes are "Expected". On the other hand...if you live in an area where tornado's are common then attachment is necessary. ....fordy...

 

[rambler]

You are going to need some professional help to get this working for you.

To get some advise on what paths you can follow, we'd really need to know the location. Some areas are so tight with regulations you won't be able to do anything; others are affected by wind, or earthquake, or deep frost - each situation is different & advise from one location will hurt you more than help in another location.

In addition to location, what type of bedrock? and is it truely solid, or is it layers, or just big bolders?

--->Paul

 

[Guest]

You already have some opinions, are you ready for another?

I think that you need to have a small concrete foundation to get you above that normal soil line of 8 inches. You really shouldn't have soil and the moisture it holds up against your building on a continual basis.

At the least I would use a drill to set anchor bolts into the rock. A hammer type drill will make this much easier. Renting a larger one from a rental agency would probably be better than purchasing a smaller one. An epoxy is used to set the anchor bolts.

After anchor bolts are in place I really think you need form up and pour a concrete foundation of at least 8 inches to get your building above the soil line. If you use a poured foundation, remember to install anchor bolts holding it to the bedrock as well as anchor bolts for the plate.

No need to get a contractor to shoot the grade/level with instruments. Just use a hose and water level to make sure all points are at the same height.

If you are going to get quite a bit of money wrapped up in your home, then you really should contact an expert and not just use opinions from here.

 

[agmantoo]

Build the house on fabricated concrete piers. Locate the pier positions for the supporting framework and excavate each area. When you are down to the bedrock use a star drill and affix anchor bolts to the bedrock. Get *sona tubes (*unsure how this is spelled) for each pier and mark with a water level the height you want the home off the ground and fill each tube with concrete to that height. Insert anchor bolts in the top of the concrete to anchor the flooring joists and you will have a well secured home.

 

[rambler]

Build the house on fabricated concrete piers. Locate the pier positions for the supporting framework and excavate each area. When you are down to the bedrock use a star drill and affix anchor bolts to the bedrock. Get *sona tubes (*unsure how this is spelled) for each pier and mark with a water level the height you want the home off the ground and fill each tube with concrete to that height. Insert anchor bolts in the top of the concrete to anchor the flooring joists and you will have a well secured home.

That would be one way to do it. Basically you would be making a mobile home foundation.....

The problems: Here in Minnesota where I live, that sure would be a cold floor!

In Florida the hurricanes would easily snap off a couple of lag bolts & roll that house - you would need some real engineering to make those bolts hold in that rock (what if it's soft limestone?) to make the piers a good enough foundation. How many bolts, what size, how big a pier to create the stability needed?

In California, you would have earthquake issues, piers tend to crumple down right quick so probably woundn't work at all - but I'm no expert on earthquake issues. (Well, as most of you should know, I'm no expert on much of anything!)

So, a great idea, but we need to know a whole lot more about this situation - and even then, only a local expert can make it work well. I'm asuming this will be a dwelling housing people, of some value, and a person wants some level of insurance & resale or morgagability on it - the current owner might not care today, but that is being short-sighted, and greatly limits your future. If this were a simple shed rather than a dwelling, it's a lot easier to use free internet advise to plan & build & let things be as they may. But a dwelling, a person really shouldn't cut too many corners on. jimho.

Now, I'm not wanting to be critical of ideas coming in here - love yours & the others, and hope more come. I'm just playing devil's adv. & getting the land owner thinking - at least that's all I intend with this message.

--->Paul

 

[Guest]

Thanks for all the advice!
What exactly is a star drill? How much do they cost? Is an anchor bolt a special kind of bolt or a designation of what a normal bolt is used for? In other words, can I walk into a hardware store, ask for anchor bolts, and be pretty sure to get the right thing?
Tornadoes are definately not an issue here. There is the occasional minor earthquake, and winters get down to 70 below and the frost line goes hundreds of feet down. However this being solid rock, not soil, it isn't going to be moving a whole lot in the freeze/thaw cycle anyhow. There are no building regs in this area, thank God.
The bedrock beneath the soil is solid and continuous, not layers or boulders. The soil on top of it is so shallow that removing it is not so much excavating as raking.
I'll be building with straw bales, so I'm planning a really high foundation anyway to keep the walls well off the ground. Serious insulation will be installed, of course. I'd like to enclose the foundation with treated foundation plywood with rigid insulation stuck on it, and then bank it all around with gravel. I understand that treated wood lasts a lot longer when it's covered with soil or gravel than when it's exposed to the air...is this so?
This will be a tiny little house for one person, and due to it being strawbale and having several other peculiarities of design it will have zilch resale value anyway, except possibly to crazy homesteading type people. With this in mind, I'm building solely to please myself, not any projected possible future buyers.
My thoughts on the foundation, and please correct me if any of this is wrong, are:
1) Concrete has to be mixed just right and handled carefully to do its job properly, which having no experience at all with it makes me nervous, and it is expensive, whereas treated wood is comparatively straightforward to deal with, and cheaper.
2) Being on a slope, there is inevitably going to be some drainage running through the foundation. Concrete, unless sealed, absorbs and wicks moisture, especially sonotubes in their cardboard jackets, but treated wood doesn't. A wet or eroded concrete pier would be a lot harder to replace than a deteriorating piece of treated lumber.
3) As I mentioned, winters get very cold and complete insulation will be necessary. A wood foundation would be a lot easier to enclose and insulate than a concrete pier one, plus wood wouldn't transfer cold like concrete would.
4) In the event of a minor earthquake, a wood foundation, (what I have in mind is sort of like three dimensional box trusses) bolted to the bedrock would probably be able to move and give a little, but concrete would transfer the movement to the structure and/or crumble.
Hope this clears things up as far as the specific situation. Again, thank you so much for your extremely helpful advice.

 

[fordy]

.................After reading thru the posts I think i may have the best\cheapest solution for You. First a star drill is a hardened steel rod that is designed to penetrate either hard rock or cement. You can buy them in most hardward stores . you Hit them with a 2 to 16 pound hammer to "drill" a hole in the rock.
................The best idea I think would be for you to try and locate an Electric Hammer Drill. They come in all sizes . I've seen them for sale in Pawn shops. New, they will cost up to a couple thousand bucks. Both plumbers and Electricians use them to bust up existing concrete when doing rennovations and fixing leaks in Pipes under an existing foundation. Try to RENT one if you can or buy one at a pawn shop and then sell when you get your holes drilled. They get big and heavy but Don't require an Aircompressor like a Jackhammer or Rotary Airhammer drill which is a jackhammer that rotates. VERY heavy to move around and Very hard to keep in one spot while drilling. Almost like Dancing with a 400 pound woman with big Feet.
.................Again, find a electric hammer drill then all you'll need is a generator.......fordy...

 

[brosil]

On bolting, we've been using a product called Chem-Bolts for some jobs. They're kind of pricey and may not be what you're looking for but I thought I'd bring it up. They have a high strength epoxy around the bolt. They cement to the hole very well. Good luck.

 

[rambler]

There are different kinds of anchor bolts. Some have a locking collar on them - you drill a nice hole, put them in, and the 'ramp effect' collar will wedge into the concrete/ rock when tightened. Other types get cemented/ epoxied into a rougher hole. Others are 'L' shaped & get put into fresh concrete as it sets. All do the job, depends on what you are starting with. For wood they even have guns that use black powder to fire a hardened nail into concrete - don't think that would make a founation tho.

A friend of mine put in a wood basement/foundation. It's selling point is that it is a lot easier. Lots of people are sckeptical - they _say_ they last 50 years, but they are only 10 years old or so - how do we know? they use super duper preservitive in them, not the regular stuff from a lumber yard. Replacing a 'bad piece' is not easy, either construction method. I guess I see the wood as far more likely to have a 'bad piece' show up. Wood will want to rot the most where it comes out of the ground. The bugs that eat on it live in that zone where the air, water, & wood meet, inch or 2 below the surface. Deep down the bugs aren't as active.

Concrete is generally much sturdier, less water wicking, and will last 100 years. Wood is easier.

--->Paul