H1 underfloor Insulation requirements
In new edition of H1/AS1, the schedule method requires underfloor construction R-values to be R2.5 (Climate Zone 1, Climate Zone 2, Climate Zone 3), R2.8 (Climate Zone 4) and R3.0 (Climate Zone 5, Climate Zone 6).
The increased R-values apply under both the schedule and the calculation methods of determining construction R-values.
Why it is good to exceed the H1 underfloor insulation requirements
If using the schedule method of compliance the number in the H1/AS1 document is the minimum R-value and this must be exceeded. However, if using the calculation method or the modelling / verification method it is possible to use a construction R-value which is lower than this number - provided this is offset elsewhere and that the designed home performs at least as well as a reference home. By using construction R-value which is higher than in the table, it provides the ability to use a lower R-value on other elements or to adapt the home elsewhere such as using lower cost windows or using a higher glazing percentage to increase natural light to the home.