One of our friends asks about a project they have trying to increase the height of their basement ceiling. The problem they are having is that they are in a very rocky are and the foundation was built around boulders or ledge that the original home builder decided was too difficult to remove and this resulted in a basement that isn’t really usable.
This situation is pretty common in older homes and I have seen outcrops of stone even in suburban areas where a builder just didn’t want to remove the material because it would have meant blasting at that time. Today there are a number of ways that you can deal with this situation short of blasting but often you might see the need for blasting.
In my opinion if a contractor was to run into this situation the best way to cure it would be to raise the foundation instead of trying to build around a large boulder. However in some cases it is not just one stone that needs to be moved and often a contractor will dig down to remove the topsoil and find that the entire area is too hard to dig. In this case again raising the home and then back filling around the home with clean fill and then topsoil is the best method. Again this normally happens in older homes because new homes would require a specific height for a livable basement and the alternative is to have a rather deep crawlspace that the home owner won’t like or be able to count as livable area.
How To Remove Large Stone Outcrops In A Basement
The process of removing such obsitcals is not easy. Obviously you can not blast the area with a home already built on it and if the stone is in such a position that removing it could undermine your foundation then there is no use in trying.
For most people the best situation is to raise the home with the use of jacks and then place new foundation blocks or pour new knee walls or full walls if it is a stone foundation. This will provide the desired height and may even increase the height of the basement to a grand level in some areas. The method to raise the home is not that hard to do you just need a lot of pump jacks and you slowly raise the entire home an inch at a time around the whole foundation while bracing it. It is the same process as moving a home.
If you really want to continue then the process would require drilling holes into the stone and then using the same tools that stone cutters use by placing wedges in the hole and causing a fracture by hammering on them. You will need some serious equipment to do this work and not all stone takes well to being cleaved.
A large rotary drill and you will want a water mister to keep the dust down even in an unfinished basement.
Drill the holes and place your feathers and wedges and then hammer the wedges into the hole. The steel will cause a small fracture and then you can use a crowbar to complete the process.
Jack hammering alone is not a great idea but it is a good tool to have to chip away any areas that are not substantial.
If you find your home is in this situation and you really want to go through the process of increasing the height of your basement then you should seriously consider raising the home. The process normally only takes a day or two to stabilize the home at the new height and then a new foundation wall can be installed and cured in a few days depending on your situation.
In some areas this is very common and maybe 10% or more of the homes will have this situation so you might be better off just leaving the home as is and a new buyer down the road will understand. If you are doing the work because you expect to stay in the home then raising the home is your best bet if the outcrop or height problem is throughout the basement and you can’t live with it.