Any suggestions for improving insulation of a unique concrete building?

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 –

地热供暖——它有效吗?它能省钱吗?

这些方法可以提高建筑的效率，而不会造成结构损坏的风险。最重要的是，你最好咨询结构工程师，以提出最好的行动方案。希望这能有所帮助，在阅读完这些页面后，请随意抛出一个后续问题，这只是开始的第一个地方。

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