Any suggestions for improving insulation of a unique concrete building?
This is a c1915 2 storey house made of concrete located in Nova Scotia. The walls are about 8" thick solid poured concrete on the ground floor, and 4" on the second floor. Both stories have had an exterior skin added by applying bi-sected hollow blocks which gives a few inches of air gap. Interior was plaster and lathe, then strapping and gyproc was added. Over the years the inner walls have moisture damage.
For the past 20 years it has served as a museum and is closed for the winters. The past 15 years it has been unheated in the winters, but we have been advised to maintain at least a baseline temperature well above freezing. We are planning a "rehabilitation" project which will include replacing the interior walls. We are wondering what to use, and if it might be helpful to blow in rockwool or flax wool to the cavity under the outer skin? The concrete needs to breath, and we dont want to introduce condensation moisture problems when we start heating again. Any advice (short of destruction!) would be appreciated.
Insulating old buildings made of concrete and stone has to be done with caution. The advice you received to keep it above freezing is likely to prevent further damage from moisture within the wall freezing. The problem with adding interior insulation, is that the exterior structural walls will then be exposed to moisture and freeze every winter since you are preventing heat loss. This would be contrary to the advice you received to keep it warm.
For typical homes in situations like this we advice people to insulate the exterior of the walls to protect the stone or concrete wall from freezing and cracking. Is that an option? If so read on here –
How to properly insulate the exterior walls of old homes
If as a heritage project insulating the outside is out of the question, I would honestly consider putting that investment into an extremely efficient heat source instead in order to reduce energy consumption. Heat pumps are on average about 3 times more efficient that other heating systems read here –
All about Heat Pumps for efficient home heating
Geothermal heating systems are generally an expensive option, but it may be a great solution in this case, you can read more here –
Geothermal Heating - does it work and will it save money?
These are a couple of ways you can improve the efficiency of the building without putting it at risk of structural damage. And above all, you are best to consult a structural engineer to come up with the best course of action. Hopefully that helps, and after a read over those pages please feel free to drop a follow up question, this is just the first place to start.