Bigger Supplies Needed.

I have sussed out internal insulation. One of my worries is that inside rooms are relatively humid, especially in winter. If the insulation is good enough, then the inside of the outside wall could be below 12°C for significant parts of the year, and with humidity that could mean mildew, in places you can no longer get to. Which is something I would want to avoid, since it poses a health problem. How did you deal with that?

Just a vapour barrier (or vapour check) on the warm side of the insulation. It doesn't have to be 100% as the outside walls usually are a little vapour permeable anyway - just as long as moisture generally doesn't build up faster than it can escape. If using PIR or PUR the insulation boards are foil faced so just some foil tape over the joints is usually sufficient. If using 'fluffier' insulation then a plastic sheet. Preferably make some provision for services (cables, back boxes, pipes etc) to the inside of the vapour barrier so it doesn't need to be pierced repeatedly (e.g. 25mm battens to form a service void, or sections of slightly thinner insulation for allow for 'chases') - although I did see that the Germans had developed a "sealed" version of their back boxes to allow cables to run behind the vapour barrier.  I recall some "robust details" somewhere - and  most insulation manufacturers provide details on how to use their products.

   - Andy,

I have sussed out internal insulation. One of my worries is that inside rooms are relatively humid, especially in winter. If the insulation is good enough, then the inside of the outside wall could be below 12°C for significant parts of the year, and with humidity that could mean mildew, in places you can no longer get to. Which is something I would want to avoid, since it poses a health problem. How did you deal with that?

Just a vapour barrier (or vapour check) on the warm side of the insulation. It doesn't have to be 100% as the outside walls usually are a little vapour permeable anyway - just as long as moisture generally doesn't build up faster than it can escape. If using PIR or PUR the insulation boards are foil faced so just some foil tape over the joints is usually sufficient. If using 'fluffier' insulation then a plastic sheet. Preferably make some provision for services (cables, back boxes, pipes etc) to the inside of the vapour barrier so it doesn't need to be pierced repeatedly (e.g. 25mm battens to form a service void, or sections of slightly thinner insulation for allow for 'chases') - although I did see that the Germans had developed a "sealed" version of their back boxes to allow cables to run behind the vapour barrier.  I recall some "robust details" somewhere - and  most insulation manufacturers provide details on how to use their products.

   - Andy,