Cavity walls or external insulation?

Is this new build or current? External insulation will give much better insulation values as it will fully envelope both skins of the walls. The idea is to allow the walls to absorb the internal heat and disapate it later on. New building technology is pointing this way now. If it was my build, i would do both. The downside is, 1 cost, 2, depending on the thickness of the external insulation used, it will increase the depth of your window reveals. Im pretty sure theres more pro's and cons to be added. " You can never have too much insulation" HTH Gareth

Your Question is easy the answer not so, Factors involve Use of extension Are the walls equally exposed to the weather? How heavy is the roof You can choose timber frame for optimum insulation effect. However a sheetrock wall has limitations when fixing things to it. And can create nightmares for bathrooms if not installed correctly, leading to damp. Thermal blocks with added insulation as an internal wall with a cavity and a common brick outer wall rendered, is a good strong and energy efficient wall. But you lose on internal dimensions. Other options are also possible and you must choose. Costs vary greatly depending on supplier, contractor and market changes. Don’t just discuss cost of materials with your builder but also consider time, as some methods cost less because they are easier and less weather sensitive. Methods and material costs often balance out. The cheaper materials don’t mean a cheaper build. How much insulation and where, is less important than good method. Good cavity ventilation is vital to effective walls. Good hunting.

i will try to keep it really simple external insulation - most expensive way to insulate as the tech is new and not common in small extensions cavity construction- allows you the most versitility and will cost less than external there is a third option that is internal insulation- this is usally the cheapest option.