The insulation not only needs to be sufficient in thickness but also needs to be continuous. This means keeping penetration through the insulation to an absolute minimum, and if unavoidable then using materials that are less conductive to heat (eg. timber instead of metal) and/or incorporating thermal break to avoid thermal bridges.
Thermal bridges are the points at which a conventional house loses energy. They are often unaccounted weak points in the building fabric, resulting in high local discomfort, moisture and mould, while providing a highway for energy loss between the interior and the exterior of the house that.