Hello everyone. New here but i'll try to be precise so that you can answer my questions accurately. I'm not sure what pictures would help with my question but i would be more that happy to get them for you. I live in oklahoma and we have fairly mild winters. The soil is sandy with rock right below. I am fixing to add on to my house that is about 20 years old with a solid cement foundation with a normal footing. My plans are to add on with post/beam construction. My first question is about the post's foundation. I would like to pour cement piers and attach the posts to the piers. From all that i've seen i should dig 3ft holes at about 16 to 24 inch across. The problem is that there isn't that much soil to dig in. Solid rock about 6 to 12 inches down. The house sets slightly higher than this and so if i brought in fill dirt to mach that which is around the other three sides of the existing house, the piers will still only be 6 to 12 inches deeper. So long story short, can't make the piers deeper than 1ft at the shallow end and 2ft at the deep. I know this rock is hard as well. I built a shop a 10 years back and my father brought out a company tandem axle digging truck with a rock cutting tip and we still didn't make it far. But my question is should i dig through this for the house or be happy that its setting on good solid ground. The shop has headers on top of the posts with rafters setting on top of that. The house will be more solid than the shop. The beams will be a part of the rafters, if you will, there for doesn't need the holes to hold them up right as with my shop. Another problem is if this rock is above the frost line what does that mean for the piers if they are setting on the rock. Is that why they should be deeper? A construction buddy of my father's and my father said to anchor the piers to the rock. I have cad drawings of the add on plans and can take other pictures if anyone likes.
If the rock is not actually a part of a deeper formation that is a problem. If the the rock is a jumble of rock that is above frost depth and you build on top of that rock you will encounter movement caused by freezing. It's a bad situation to build in/on.
You state "solid rock is 6 to 12 inches down". If that rock is really a solid deep monolith that may be something that a concrete foundation can be attached to. Your best bet on finding a best solution for the foundation is a soil or geo tech engineer familiar with the conditions.
What is the difference in price just digging a 'clearance' and coming in with a footing and foundation? If you are on solid rock you do not have to worry about frost heaves unless it gets colder, way colder. Like none of us will be alive colder.
thanks guys
MtnDon
Ok. That makes good since. I had planned on drilling in a few spots while in the planning states to see how deep this rock goes. If i go in and then hit something soft, well i had planned on digging each pear through the rock. But say it stays hard for like 18inches,(longest bit i can get) and check each pier then call it solid and attach the piers to it as if i were attaching a new foundation to an old one. But i do want to be sure about this so what is the best route to go about finding an engineer. I have worked maintenance for years and had to rebuild and redesign so many engineered things i'm sceptical if you know what i mean. I've worked with them and they come out treat you like your stupid and give you help that doesn't apply or is a good idea but would need 9 inch long fingers to do. And i don't mean to bash engineers, they are crucial. My problem is probably that i've delt a lot with young engineers that just don't have enough experience. So how you suggest finding a good engineer(well rounded)? And what to things like that usually cost?
Rick,
Well, If each post holds the weight of walls floors and so on, seems like it would be cheaper to just put a pier under each post instead of haveing a full perimeter footing and foundation. And i'm not trying to be a smart A, i'm sure i just don't completely understand what you are suggesting. What exactly do you mean by a clearance? If i do a complete foundation i'll probably just go with stick construction because of my location. I am going to have to make a few trips with a big trailer and my truck that loves gas to get the heavy timber for this beam construction so the piears help compensate for the drive etc etc. What exactly do you mean by a clearance? And i agree with your statement about frost heaves. If the rock is true solid rock (like Mtndon talked about) the only place that water could get that could freeze and push is the water that seeped between the rock and the cement piers (very little if any). It won't be as if there will be layers of water saturated soil that could expand greatly. And as for drainage the soil is sandy and i'm on the side of a hill. Property drains well. Every time it rains i have to re-do my drive way.
Thanks again guys for your input.
If you do drill test holes and find solid rock, make sure you seal the holes up, you don't want that to be the path for water to get in a freeze and start cracking the rock.
QuoteI am going to have to make a few trips with a big trailer and my truck that loves gas to get the heavy timber for this beam construction so the piears help compensate for the drive
Part of the cost equation to consider is with a crawlspace that girder is not required at the perimeter, the space is perimeter sealed, etc. The initial apparent cost difference might not be as great in the long haul if this can be shallow.