Building Footings on Rock

[whit]

I have been walking my property looking for the best place to build a small shack say 5X10 or 8x8. I can build up to maximum of 50 sq/ft without a permit in my area. I know, that's not too big. I just want a small little place to go so I can enjoy the property, get in from the rain and the bugs, before I build something bigger say in 10 to 20 years. I hate the idea of the land just sitting idle. The property is in the Ottawa area, Canada. We can get down to about -30 celsius/-22 Fahrenheit in the Winter on the coldest of days.

Here's my situation, I have a lot of rock on the property and there is an area at the back nestled in with some pines that is pure rock. I won't be able to dig anything there so can I use Dek Blocks to build my piers? I was thinking of placing the dek blocks on 2x2 pavers sitting on crushed stone or stone dust, say 6 to 12 inches thick. I was thinking of following the plans for building a deck using the http://www.deckplans.com/ but maybe with not so many blocks. I built my backyard deck this Spring using this method. We'll see how it handles the Winter thaw.

So back to my question, Has anybody used this method and what do you do on rock with no possibility of digging?

Thanks,

Cheers

[MountainDon]

The main deficiency using something like dek blocks on pavers and gravel/crushed stone, is that there is no uplift resistance. A big wind for example could move the building. Good solid rock could be drilled to place rebar at angles. The rebar would be cemented/grouted/epoxied in place and concrete poured around them in forms to provide a solid level block at each corner. Then build on that and the wind can blow all it wants.

[MountainDon]

More to come on this in a little bit. Good info from an engineer. PEte

[MountainDon]

Here's some free and IMO invaluable information on this from an engineer...  Thanks to PEte

It has to be good competent rock, not a bunch of big boulders which are just tough to dig around. It should not be all cracked up (many faults), with frayed surface, etc. or this must be cleaned up and taken into account in your design. You don't want to place your footing or pier on a significantly sloped surface of the rock, or the rock should be flattened out, or keyed into, and you want the concrete to conform to the clean rock surface for proper bearing, not a sliding action under load. Just dowel four vert. rebars into the rock, full height, and use some closed ties, round or square, to tie the vert. rebars together up to the top of the pier. These could be two inverted U shaped bars with the four ends epoxied into the rock. Simpson, USP or Hilti, and other suppliers have strength and embedment length info. There are also undercut and expansion anchors made for this purpose. Then a sonotube or wooden form, fairly well conforming to the rock at the bottom, and anchor bolts or some such for your beams at the top, complete the job.

With proper anchorage at the foundation, make it as big a footprint as you can and two stories high with a sleeping loft.

Does your bldg. dept. say max. 50 sq.ft. shed or 50 habitable sq.ft., and does habitable mean you need waste disposal provisions?

Is a permit that outlandish to deal with if it means a more useable building for the next 10 - 20 years?

Don't use deck building details for a habitable building.

[whit]

Thanks MountainDon and Pete for all of the great info. These are not boulders but a 12 foot high slope of solid rock. No power up there so may not be able to get rebear drilled in but could definitely chisel out and clean the surfaces out. I get the fact that you want to take into consideration any hight winds and anchor the building. Duly noted.

To go bigger would require permit, spetic, well, a surveyor to mark out the building and I would have to build a minimum of 645 square feet. I can't afford another mortgage right now that's why I am looking at 10 to 20 years to build.

[UK4X4]

Just hire a generator and an SDS drill or rotary hammer drill

I have one of these and love it for UK work- especially on my 110 year old kiln fired brick house
http://www.google.com/products/catalog?rls=com.microsoft:en-us&oe=UTF-8&startIndex=&startPage=1&q=bosch+sds+drill&um=1&ie=UTF-8&tbm=shop&cid=15486161558147399476&sa=X&ei=V_aeTvfgLMHV0QGY3ay9CQ&ved=0CCwQ8gIwAA#
A standard hammer drill does not compare !

[whit]

Thanks for the link UK4X4. That's something I am going to consider.

I have thought about a bit more and wonder if I could also do this.

Build a pad of crushed stone, stone dust and layer it with patio stones (2x2) and sit some dek blocks according to the builders cottage plans for the pier footings. I could bore some holes into the rock and bang my rebar in. Layer with the stone materials, run the rebar through my patio stones and up through the deck block and bend them there.  Here's a graphic of what I am talking about:



We have a shed up at another lake built like this on a thick pad and it's pretty solid.

[whit]

If you follow this posting of a 10X10cabin, you can see on the first page that he just set some dek blocks on some 2x2 patio stones. I would of dug out the footings a bit, layered them with crushed stone and set my patio stone and dek block on top of that. Because I want to build on rock, I think I will need the pad as well so that I can get things level.

http://countryplans.com/smf/index.php?topic=7815.0

[UK4X4]

you loose a lot of the rock - footing bond that way

I'd just build a form to the height you want with the rebar-allthread and expanding bolts inside
fill with concrete and your done

then just use a simpson beam or post holder on top