Since the new H1 regulations first came into effect on 3 November 2022, designers have been looking for a way to build cost-effective wall structures and insulate walls to the required R2.0 for housing and buildings under 300m² or up to R3.2 for buildings over 300m² under the H1 Schedule Method. Kingspan Insulation NZ Ltd understands the demands of cost-efficient and effective insulation and has sought to increase Construction R-values and address thermal bridging issues.
Kingspan Kooltherm K12 phenolic rigid insulation board offers high R-value to thickness ratios and when used as continuous insulation, mitigates the potential of thermal bridging from framing.
Thermal bridging occurs when the building’s frame creates a bridge or connection between a structure's inner and outer faces, often due to gaps in the insulation layer or where elements such as joists penetrate through. A research project funded by the Building Research Levy in 2021 (The Wall Research Project) found that the percentage of timber framing in the walls of new buildings is often higher than those assumed in compliance calculations. It was discovered that the average timber wall framing is 34%, which is 14%-18% higher than generally assumed. The maximum timber framing found in this study was slightly over 57%. When modelled to accurately reflect timber framing percentages, thermal bridges can significantly cause heat loss, accounting for as much as 30% of total losses.
Additionally, as the inner surface of a construction where a bridge occurs will be cooler than the surrounding area, it can allow condensation to form. This can potentially damage the surface or lead to mould growth which can present health risks. To achieve the new minimum Construction R-values of R2.0 using traditional glass fibre or polyester insulation, it is likely that wall framing will need to move towards 140mm framing. Consideration could be given to an additional layer of internal continuous bulk insulation, however, overall thinner construction and increased internal space can be achieved using Kooltherm K12 Framing board as an external continuous insulation layer.
Insulating the exterior of the frame with continuous insulation helps mitigate thermal bridging and increases the overall Construction R-value of the wall. Kingspan Insulation NZ commissioned WUFI hygrothermal modelling, showing that wall constructions with Kooltherm K12 rigid insulation sheathing a 90mm deep timber frame, resulted in a lower mould growth index compared to conventional wall constructions with just bulk insulation between studs. Wall constructions with a Kooltherm K12 rigid continuous insulation have reduced heat loss through thermal bridging and a lower likelihood of mould growth inside the wall cavity.
Maintaining a 90mm wall frame and using continuous insulation on the exterior side of the frame alongside in-frame bulk insulation can achieve an increased Construction R-value and cost savings. This not only offers higher thermal efficiency for the wall construction but in the H1 Calculation Method for thermal design, it can increase design flexibility in the overall thermal envelope of the home.
