Let’s establish the situation; MBIE has proceeded with changes to the roof, window, wall, and underfloor insulation requirements by issuing the new edition of Acceptable Solution H1/AS1 and Verification Method H1/VM1 for housing and small buildings. The new insulation requirements aim to reduce energy needed for heating residential homes by approximately 40% over the minimum previous requirements. In this article, we will just be talking about insulation for concrete Raft foundations and how these standards relate.
The effective date for the new acceptable solutions and verification methods was 29 November 2021. The new documents have a transition period of one-year ending on 3 November 2022, except for the verification method H1/VM3. This verification method can be used starting on 29 November 2021, but designers can also still use an alternative solution to demonstrate compliance with the Building Code.
Additionally, the new window insulation requirements in the warmest climate zones will see a different approach with an interim increase in 2022 and an additional increase in the following year. This means by the end of 2023, all parts of the country will have a similar minimum level of window insulation requirements. More on this in the document.
Climate zones
It is important to first understand the zones; the changes to climate zones will better reflect specific weather in different parts of New Zealand and will no longer be “one size fits all”. The aim in making these updates is to make sure homes and buildings are more suited to the climate where they are being built.
The six climate zones are based on thermal modeling of buildings using NIWA climate data files for 18 different climate stations. We only need to focus on the 6 zones shown here, download zones.
Insulation R-values
The proposed R-values in the consultation document are construction R-values for roofs, walls, floor and windows. Here we focus on the requirements for concrete Raft Floors which can be broken into 2x categories; Floors with Underfloor heating systems and floors without. Each have 6x climate zones of NZ and minimum R values to reach accordingly, please refer to the zones diagram to find your minimum R value requirement. For example zones 1-4 are required to reach R1.5 in their (non heated) foundation performance for all of North Island and some Northern & Western areas of the south island.
R Values Verification:
Relating this to your design; so how do we measure the R value? The thermal resistance (R-values) of insulation materials may be verified by using AS/NZS 4859.1. & ISO 13370: 2017 Thermal performance of buildings. It is important to note any testing of foundation insulation levels must be done to a level compliant with the verification methods mentioned here. QPOD contracted Sustainable Engineering Ltd. to perform thorough modeling and testing of the QPOD and associated Quickset insulation systems. The results are published and available in our Sustainable Insulation Methods Manual.
We have also made it easy to determine what system you need to achieve your minimum requirement R Value according to zone with The R Value Calculator, here you can input the area and perimeter of your foundation showing you the R value according to slab insulation system type.
PASSIVE HOUSE Ψ AND FRSISlab Passive House calculations of Ψ are in accordance with ISO10211:2017 with Passive House Institute (PHI) modifications and fRSI criteria. These use EXTERNAL DIMENSIONS and the heat loss at the sill plate (which should not be neglected) is included in this Ψ calculation. NZBC has no official requirements for a particular fRSI value but NZGBC Homestar V5 does have requirements Intended to parallel the Passive House requirements. In PHPP10 these will be calculated via a moisture balance for each specific building to allow lower fRSI values to be used as less conservative criteria are appropriate with more detailed knowledge of the building ventilation rates, loads, and heating set points.
FRSI REQUIREMENTS FOR NZ REGIONS FOR PASSIVE HOUSE
This map shows the three different fRSI zones at the weather station altitudes. The climate zone and thus the fRSIrequirements also vary with altitude as the average temperatures typically drop by 0.6C per 100m of elevation gain. In general thesezones can be used without considering the elevation change. Illustration: Sustainable Engineering Ltd. fRSI requirements from PHIPassive House Standard Building Criteria.
In Closing:
It is a challenging subject that the industry is fast trying to get a grasp of, what we have included here narrows us to a concise view of what we see as the important factors in determining your design requirements and suggesting best practice solutions for foundations of the future.
Here we have combined the resource files and links for download or further investigation.