Construction & Contractors/Building on limestone in Prince Edward County, ontario
We are having a home built in Prince Edward County in an adult lifestyle community. This is an established subdivision that has seen ongoing building for many years.
The latest phase in this development is now just being being serviced and in installing the services, the builder has encountered limestone about 3-4 feet below the surface. The first basement to be dug also shows limestone at about the same depth so I expect it will have to be excavated to get the required depth.
Given the above, I believe that when they excavate for our house they will encounter the same subsurface.
My question is regarding the suitability of building on this type of bedrock and what measures should the builder be taking to ensure the footings are suitable. I suspect this is not the first house they have built here with the same issues but in reading other articles about limestone I do have some concerns.
Also, is the area around Wellington in Prince Edward County a place where radon gas is a concern. I understand that further to the east in the county radon may be present but am not sure if it is around Wellington. Also, if radon is present, is having limestone under our foundation good or bad.
Thank you in advance for any advice you can offer about the foregoing.
Get a copy of the soil/foundation report and review whether it considers the possibility of limestone bedrock. You can then contact the soils firm that did the work with any specific questions.
Limestone can make great foundation material as long as it is intact and does not exhibit karst (dissolution) features. If dissolution is present or suspected it is best to completely clean the foundation to reveal any voids and be sure those are backfilled with concrete or grout. If dissolution is suspected additional foundation reinforcement may be warranted to ensure that the foundation can bridge any voids that may develop during the service life of the structure.
If the foundation is only partially on rock and otherwise on native soil, diffential settlement becomes a possibility. Again, this is an issue to take up with the builder's soil and foundation firm.
I can't fully speak to the radon gas issue because your question is very specific to a certain area that is outside my area of practice. Naturally-occurring radon (there have been documented instances of man-made radon hazards when uranium mill tailings were used as one of the components of construction concrete, but that cat is now out of the bag and I don't think anyone would be that stuipd any more) generally is an issue where trace amounts of uranium-containing minerals are present in the subsurface. One would not expect this in terrain underlain by carbonates, but if sandstones are present that may hold trace amounts of uranium-containing minerals, or if there are intrusive igneous rocks (chiefly granites) that may hole primary minerals containing trace amounts of radon that are present at shallow depth, then radon accumulation is a possibility. The local soils firm may have more specific information. I would check with local health authorities also about known radon occurrences; they may be wielling to perform air sampling at existing residences in your area.