10/02/2014
For Irish thermal modellers & building fabric designers: update to ISO 13788 (2002)!! The new edition (2012) has now been harmonised as an Irish standard (IS EN ISO 13788). The implications of this are that an increased Rsi must now be applied to junction models (Rsi of 0.25 for all opaque surfaces for condensation/mould growth risk), where the previous edition had no specific values mentioned. This may seem like a minor change, however the increase in Rsi for Frsi calculations makes Part L compliance far more onerous than before, particularly for dwellings. Junctions that previously passed with flying colours may now be non compliant. For example, a standard suspended floor/wall junction which showed temperatures of 16.74 deg. C at the skirting under standard conditions now exhibits a temperature of 13.42 deg. C with the increased Rsi. Getting above the 15 deg. C mark for this junction will require ingenuity, more invasive works, time & money, and the general implications of this change should not be taken lightly! Although it may be standard practice in Passivhaus design to use higher Rsi values for condensation risk, this is normally applied to new-build construction where the issue can be more readily dealt with. For retrofit however, which is where the majority of work will lie for many in the industry for a long time to come, the challenge this presents for Part L compliance should not be underestimated.
For all Psi-Therm users, get in touch with me to receive a new updated boundary condition library reflecting this change.
http://ow.ly/ttVWL
http://ow.ly/ttW4L http://ow.ly/i/4yulf
