Every egress window installation is unique. The block is different sizes, hardness, and your horizontal cut may or may not end up on a mortar joint. Recently I installed an egress window in a limestone foundation. Although I have installed 100’s of egress windows, this was a distinctively different experience. To begin with there is no information online that was helpful, which is my reason for writing this article. Unlike a block foundation that can be cut from both sides with a partner saw, or a poured concrete foundation that can be cut with a diamond tipped chainsaw, I could not use either of these options. Every tool rental store I contacted expressly forbid using there chainsaw on limestone foundations, and after cutting it with my partner saw I can see why, it really did a number on my blade.
The best advise I can give is to cut the opening from the outside as deep as your partner saw will cut, for me that is about 4 inches. Once the limestone has been scored as deep as it can be, starting at the bottom, remove the pieces that come free. Once this done, you can take a sledge hammer and break the limestone off as long as there is nothing supporting it underneath, and there is a score cut in at least 1/3 on the stone. This will get you through about 90% of the foundation. Inevitably there will be a large stone that will need to be cut by bringing the partner saw into the opening and horizontally cut the stone as best you can, then bring out the sledge hammer to finish the job.
Simply put, these are very difficult and time consuming foundations to cut and install egress windows. I would not recommend attempting this if it is your first egress window. If you are determined to do it yourself, make sure to take your time, and use the saw as much as you can in order to minimize damage to the rest of the foundation, particularly if there is a one piece stone header running along the top.
Edit 8 DEC 2009
I just completed another egress window in limestone foundation. This time after cutting the limestone with my partner saw, I used my demolition hammer with a 2 1/2 inch chisel bit and I was done in about 20 minutes. Even if I encountered a large stone as long as it was scored the demo hammer made short work of it.