Can I safely insulate between the firewall of an occupied house and an empty building?

Question

I have a 2-story house that is 70+ years old and brick. It is a city semi-detached row home, meaning one wall is open to the elements. But the real problem is at the firewall where it is attached to an empty building. I've had problems with moisture (water) on the side where the two structures are attached. I know there is space (about 6 inches or so) between my brick firewall and that of the building. Can some type of insulation be put into that space to cut down on: a) the moisture traveling between the two and b) to keep my heat from escaping through that wall. I notice that the wall is always cool to the touch so I imagine because there is no balance of heat from the other side since the building is empty and abandoned.

HELP!

Answer 1

1- Use mineral wool blanket for thermal insulation , also it is acting as fire rated material
2- If you can't stop water leakage , use water proofing sheets as used for roof

Answer 2

USA Check with the owner of the empty building, and ask them to repair the water problem. It is coming from the top, or from a leak in the roof. Insulation will not stop a water leak - it will only compound the problem. The water must be stopped from the top where it is entering. A good metal flashing at the roof over the building firewall might be a good start. Once the water problem is solved, yes, you can insulate the space in the fire wall to reduce your heat loss. Do not use expanded polystyrene foam insulation, as it is flammable. Use a polyisocyanurate, or a fiberglass. You might want to consider insulating the wall in your part of the building - on the inside of your side of the brick fire wall. That will hold more heat in your place than insulating the space between the buildings. But, you must stop the water first. Check with a roofer.