old-iron-habit
Senior Member
- Joined
- Nov 22, 2012
- Messages
- 4,233
- Location
- Moose Lake, MN
- Occupation
- Retired Cons't. Supt./Hospitals
On a hospital project I am consulting on an interesting conversation took place today. This is not in my juristiction but it is something I have never came accross before. There is a section of the new hospital that can not be built until next spring because of access issues with the existing hospital. The contractor is allowed by the licensing authorities to put the foundations in but can not build on them until spring. Code does not allow hospital patient windows to be blocked (physically or view) while they are occupied. The contractor wants to put the foundations in this fall to save time but the footing will set on solid slate rock that was blasted to a depth of 2 to 5 feet below slab on grade. Two inches of sand below the footing is required for separation from the rock. The frost depth in this locale can be up to 8 ft dependent on the winter, 5 to 6 feet is normal. While discussing this today the structural engineers started getting concerned about frost mitigating into the footings after the facility is completed. So finally, heres the question. What is the thermal properties of rock as compared to gravel or other soil. Normally we would put 4 inches of styrofoam horizontal out from the footing to a width of 8 ft. and with the footing exterior insulated it would never freeze beneath the footing when the building is heated because of the thermal properties of the ground. Does rock transfer heat or cold different than soil? Would frost travel deeper in rock, would thermal ground heat come up more or less? Thanks in advance for any thoughts or theories.