I want to build a 3 season porch off the side of the house. I live in Northern VT on a lake so it gets pretty cold with a bit of snow. My question is which would be better, sona tubes for the foundation or just bite the bullet and do a foundation wall. I'm estimating I need 10 or 12 sona tubes. I have been looking at the big foot sona tubes or the other plastic ones that come with the rebar pre cut in them. Which would be cheaper and is there a big cost difference. The porch will be 14 ft by 20 and I envision it as a 3 season porch with the possiblity at some point going to 4 season. I do plan on insulating it to keep the cold to a minum. Any guide or thoughts would be appreciated. Dave
If your planing on going to a 4 season porch I sure would want a full foundation.
One to stop to stop the air flow under it, and two to fully support all that weight.
I'd bet it would be no more expencive then all that work, concrete and expence of the big foot tubes.
I'm located in Massachusetts (near Cape Cod) and sunrooms on sonotubes are common in this area. The reason is cost. Your 14' x 20' sunroom would typically have three sonotubes (10' on centers) with bell footings sized for the bearing capacity of your soil, and the weight they must support. Floor joists are typically attached to the existing dwelling with use of a ledger board. They are typically constructed as a hybrid post and beam structure with walls framed in as needed based upon size and location of windows.
With that said I prefer like stated above to have at minimum a cast-in-place concrete foundation to support the sunroom. This can be a full depth basement or frost wall (minimum frost depth, 48" in Mass). The reason is most people after using their sunroom during the warmer months miss its use during the winter and want to go to a year round occupation. A foundation under it makes this a lot easier and less costly.
Even though these are three season rooms not intended for use during the cold New England winters we do have minimum insulation requirements in Mass. You may want to check with your building department and find out what requirements you will need to comply with. This link will provide you with information on codes in Vermont http://www.reedconstructiondata.com/building-codes/vermont/
Verify the code information with your local building department.
Thanks all for the input. The contractor I'm talking to says there wouldn't be a big difference in cost and in fact that wall would be easier to do. He is against soon tubes because of the swing in temperature and heavy snow we get in northern VT.
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