The R-Value of bulk insulation is reduced if it is compressed. The allocated space for bulk insulation must allow the insulation to be installed so that it maintains its correct thickness. This is particularly relevant to wall and cathedral ceiling framing whose members can only accommodate a limited thickness of insulation. In some instances, larger framing members or thinner insulation material, such as polystyrene boards, may be necessary to ensure that the insulation achieves its required R-Value.
Some insulation manufactures now offer standoff for insulation at the roof line to allow for the extra thickness of insulation typically required since BCA2010
Care should be taken when installing insulation to ensure a continuous envelope between a conditioned space and either the outside environment or a non-conditioned space. Draw the thermal envelope boundary in plan and section to identify the relevant wall, roof/ceiling and floor components of the building that require insulation. The drawing will bring to light any discontinuity in the insulated envelope which can be resolved in the design details rather than during construction. (Application Solutions will mark up the relevant drawings as part of their compliance assessment report).