Bedrock above the frost line

[WoodSprite]

So after three years of hard work, we're finally starting the foundation.  Don't ask.  Reminiscing about the well-drilling several years ago, we recall that the drillers hit bedrock three feet down.  Our frost line is four feet.  I know this is a question for our inspector, but are we looking at drilling into the bedrock to anchor our piers?

(Please say no...)

[Squirl]

I have not checked with the building inspector yet (I think we have the same one), but I was looking to buy homes in this area before I bought land.  I commonly found foundations right on top of the bedrock.

[WoodSprite]

Thanks for the speedy response Squirl.  I'm sure that was a great selling point - a house literally "built upon the rock". 

But my question is, but how are the piers anchored?  Surely they're not just cemented to the rock?  Will we likely be required to drill rebar, at least, a foot into the bedrock?

[Squirl]

I could not tell from what I saw.  I have no expertise on this subject. 

[rdzone]

The experts on this forum will answer, but from what I know you will be required to drill into the bedrock, epoxy the rebar pins in the holes and then form up your foundation.  Sorry I know that isn't what you wanted to hear.  

[muldoon]

the point of getting under the frost line is avoiding the heave / shrink / swell properties of soil and clay from moving your piers.  Seems to me that bedrock would not exhibit these problems and would be a fine anchor.  I imagine you would still want to actually anchor to it though, ie a rebar tie or the like. 

[rwanders]

There is bedrock and then there is bedrock-----all make excellent foundations but drilling into it can vary from hard (granite) to easy (sandstone). Depth and rebar size depends on what you are building but none should be more than you can handle with a good hammerdrill whch can be rented if you don't want to buy. Add a little epoxy and you are ready to pour footings.

[WoodSprite]

Thanks to you all for the responses - even if they weren't what I wanted to hear, they certainly confirmed my instincts.  I'd much rather hear it now, here, rather than from the inspector, after we've put a lot of work and materials into something difficult to undo.

In case it's of interest to others, I'll post a follow-up when we get an answer from Harry, our inspector.

[glenn kangiser]

The rock is likely harder than the concrete so not much need to remove it unless the inspector insists for some reason.  If drilling hard rock with a hammer drill to epoxy pins, get a rather large one.  The small ones will have a very hard time.

Ask the inspector about the epoxy - he may want to watch or have you get a special inspector at your expense.  Clean the hole - blow - brush- blow - brush blow - then epoxy.  Drill size about 1/8 larger than the rebar or anchor.