BRANZ Guideline – H1 schedule method and partially heated floors
The question that has arisen is how does one treat a floor, for H1 schedule method compliance, where only part of the floor area is heated? Typically, this occurs where heating elements are laid immediately below a tiled floor finish.
Replacement Table 3 in the Acceptable Solution H1/AS1 simply refers to heated floors and does not differentiate between heating that is embedded within a concrete floor slab, installed under the flooring or installed immediately below the tiles. Table 3 sets specific R-value requirements.
Because a heated floor system – whether within or on top of the floor – heats the floor and also the attached surface finish, which is then transferred to the space, BRANZ believes the whole floor should have an R-value of 1.9 to comply with the requirements of the schedule method given in Replacement Table 3.
In both the 2004 and 2009 versions, NZS 4218 defines a heated floor as 'a floor having embedded pipes, electrical cables or similar means of raising the temperature of the floor for room heating'.
Section 3.3 of the 2009 edition of NZS 4218 (while not yet cited in the compliance documents) is titled Embedded floor heating and states that 'where building elements form part of the thermal envelope, those building elements shall have construction R-values no less than those in Table 1 of the standard'.
One of the options for demonstrating compliance with clause H1 Energy efficiency is NZS 4218:2004 modified by H1 3rd edition. This document gives the designer three options for determining the thermal performance of buildings. These are the:
- schedule method
- calculation method
- modelling method.
A fourth option is using the building performance index (BPI) given in H1/VM1 1.2 to meet the requirements of H1 clause H1 3.2A (a), H1.3.2C (a) and H1.3.2E.
The BPI method, implemented in ALF3.2 (available on the BRANZ Website), is a specific design tool to determine the thermal performance of the proposed building. When compared to the schedule and calculation methods, it gives a better overall representation of a building's thermal performance by taking account of:
- orientation of the building
- the direction windows face and the actual size of the windows, to determine both the heat gain and potential heat loss
- the presence of thermal mass
- actual construction methods used.
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