An building can opt for external wall external insulation or internal wall insulation to meet energy-saving and thermal insulation requirements. External wall external insulation can protect the entire building facade and reduce thermal bridges. Technically speaking, it is an excellent insulation method. However, if internal insulation is used, the historical style of the exterior wall will be limitedly preserved, but this is a risky solution from a technical standpoint.
Why is internal wall insulation risky? Internal insulation leads to more severe thermal bridges, which can only make the ends of the beams on the facade colder, potentially causing damage to the wooden beam ends on the facade. However, that is not the main risk. Without internal insulation, the inner surface of the original wall would be at room temperature. With internal insulation, the inside of the existing wall would be very cold. When it's cold outside, less heat passes through the wall. If there is a high humidity level in certain areas, the inner surface of the wall may encounter issues.
Generally, there's a risk of mold growth between existing walls and interior insulation. One solution is to install a vapor barrier, which prevents warm, moist indoor air from penetrating the insulation. Another option is to use non-vapor-permeable insulation materials, though this introduces other issues. When the inner surface of the wall gets wet, it's ideal to use breathable, capillary-drainable insulation materials, as moisture will be transported through the insulation into the indoor air. In such cases, it's best to avoid vapor-retarding constructions. Reducing the thermal flow through the wall also presents other challenges; the reduced flow cools the original wall, meaning it takes longer to dry when the outdoor weather is cold. When it freezes outside, it can lead to the outer wall peeling off and gradually falling. If the wall remains wet for extended periods, algae growth on the exterior wall may occur.
Another solution is to use masonry-type thermal insulation materials for interior insulation, such as Yintong's YT thermal insulation, which can effectively prevent cold and hot bridges, mold, and other issues.