Whether something is cost effective is directly proportional to energy prices - hence rising prices suddenly reduce payback periods for energy saving. Sealing

Whether something is cost effective is directly proportional to energy prices - hence rising prices suddenly reduce payback periods for energy saving. Sealing houses up without accounting for moisture can cause issues, but it's not insurmountable. Rather than ventilating through accidental means, you seal the house until ventilation needs to be intentional - and then you can do it using mechanical ventilation with heat recovery - which effectively keeps 80% of the heat in the air and transfers it to incoming fresh air. Equally insulating without moisture management can cause issues - but as long as the insulation is designed with vapour barriers and ventilation in the right place, it's perfectly doable. The problem is that it's very easy to do it wrong, and not realise until years later all the timbers are rotting because of condensation. I'd argue that (at least in the UK) we have far too many old houses not to deal with them. Space heating accounts for 27% of our national energy consumption. So much energy, which could be useful, is just wasted. I can't speak for your situation, but the costs you suggest for external wall insulation seem very high - eg https://www.checkatrade.com/blog/cost-guides/external-wall-insulation-cost/ https://www.checkatrade.com/blog/cost-guides/external-wall-i... suggests it's more like £6-£20k depending on house size. Speaking as someone working in the energy industry, we are a very, very long way from zero carbon energy. Renewables only work intermittently - we don't have a solution to fill the gaps in dark winters or calm days. Batteries are at least a couple orders of magnitude too small, pumped hydro needs very specific geography, and all other energy storage methods are unproven or highly inefficient.