The Forestry Forum

Hi,

My neighbor is building a lean to off the side of a monoslab garage.  My thought is sonotubes would stay put while the garage rises with the frost and that could be bad.  But than again the garage is 30x30 and I doubt it is going very far.  BUT would he be better pouring little pads at ground level to support his posts???

Up in New Hampshire sonotubes might rise if they are not very deep, or even if they are as concrete will transfer heat or cold very quickly. Put insulation in the bottom of the hole to keep the ground down there from freezing.

Check if the garage was insulated under the concrete slab and out to two feet. Insulation will keep the ground from freezing generally by trapping the earth's heat in under the slab.

Pads at ground level would freeze the ground around them and heave I would think.

Routestep,  This garage was on the property when they bought it and is a mix of old barn beams with some BIG steel plates thrown in covered in odd bits of plywood.  I think it was built on the cheap and I doubt it is an insulated slab.

My feeling is  the slab will rise and fall, but how much at 30x30 size?  Does it make sense to try to have the footings for the lean too try to rise and fall too?

There is a lean too already there, and it is on cinder blocks on grade, but they want to go much bigger with this new one.  The old one just hangs off the eave but the new one I think should run from the peak if they want any pitch.

It is the concrete tubes sticking out of the ground acting as cold sinks that will move not the slab.  Keep the tubes at ground level and insulate around it at least 2' out at the surface or just bellow, a covering to protect the foam.  I would not bother with insulation on the bottom of the tube, unless it is very shallow.  frost will grab the sides of the tube.  Use the new ones, the black plastic ones with the big foot on the bottom.  They are tapered for a reason. 

With a structure covering a slab it will be far less susceptible to frost damage, if at all.  It also has a lot to do with soil types and drainage.  It is similar to the condensation issue, where the night sky allows heat to radiate off a surface, hence dew on the windshield, the windshield got colder quicker.   Over time the exposed slab will store the cold and frost will build.  A covered slab has removed this from the equation.

Is this slab moving in the winter?  If so what does it look like?


Tim