When we bought the house, we needed to replaster it internally completely (the interior walls were a mixture of old fibrous plasterboard sheets, plywood and cardboard). This meant that we could insulate the walls from the inside rather than having to remove the weatherboards. We used the amount of insulation that was recommended at the time: R1.5 fibreglass batts and sisalation. We had access to the roof space, and fitted R2.5 fibreglass batts.
When we extended the house, we put sisalation and R2.5 in the ceiling, and also R1.5 and sisalation in the walls.
We have also insulated under the raised floor in the extension (about 72 sq. metres). This is over one metre off the ground at the rear of the building, and produced quite a bit of heat transfer through the polished floorboards. This has been
a bit of a problem in winter, and much more of a problem in summer. On a day with a hot northerly wind, the floorboards became noticeably warm. The problem was finding an insulation solution that doesn't act as an attraction to nesting rodents,
nor a moisture trap to warp the floorboards above. We ended up going with a solution from Ecomaster called ecoUnderfloor. In our
setting this was a combination of polyester batts between the floor joists, and then a perforated double-sided aluminium foil air-cell cover to stop rodents and keep the batts in place. This provides approximately R2.9 insulation. So far, it
seems to be keeping that end of the house noticeably warmer in winter and cooler in summer.
We should have over-insulated the walls (R2.5 or higher) and ceiling (R3.5 or higher). We should also have fitted double glazing for all the windows. We investigated the cost of doing this, and just couldn't afford it at the time without going into lots more debt. But there really isn't a good solution for retro-fitting double-glazing to existing windows, and so we would still need to spend a large amount to replace the existing windows (there are a lot of them). It would have been cheaper to just go into debt upfront, and I'm not sure how/ife we're going to resolve things now. At present we compensate for the lack of double-glazing by having curtains with pelmets on the inside to stop heat loss in winter and canvas blinds on the outside to stop heat gain in summer. We'd probably need both of those even if we did have double-glazing. But they'd work better.