The new standards as released by MBIE around R-Value requirements does demonstrate a marked increase in R-Value requirement where in cases additional insulation is required for a large part of New Zealand.
To start, we’d refer to the method of calculating area to perimeter ratio which is outlined in our calculator. It is largely dependent on the shape and design of your foundation. Essentially, if you have a large proportion of perimeter ins and outs to your slab and complex shapes, this will ultimately reduce your overall R-Value substantially over a standard rectangle or square slab which will perform much better.
In any case, the minimum R-Value for the new standards released is 1.5 for most of the North Island, and higher for parts of the South Island. This value increases substantially when underfloor heating is to be specified in the project. Please refer to zones and minimum R-Value requirements map.
The H1 requirements allows R-Value to be calculated one of two ways:
We reference F.1 Methods for determining construction R-values for slab-on-ground floors:
F.1.1.1 The construction R-values for concrete slab-on-ground floors, including floors of basements that contain conditioned spaces, shall be determined using:
- a) The performance tables described in Section F.1.2; https://www.qpod.nz/determine-qpod-compliance-to-h1-as1/ or
- b) The calculation method in Verification Method H1/VM1 Appendix F. http://www.qpod.nz/qpod_calculator
As a raft foundation we can refer to the tables referenced MBIE Release H1/AS1 for floor type concrete raft foundation. MBIE have supplied 4 table variations including masonry veneer, standard veneer & edge insulation options for multiple different perimeter framing widths.
Resources referred to in this article a follows: