Part L compliance – Who wants a building control service provided by cowboys?

by Bregs Blog admin team

Cowboy Up

by Simon McGuinnes architect, on 14th October 2014

Part L compliance – Who wants a building control service provided by cowboys?

The following opinion piece relates to Part L  compliance under SI.9 . Part L of the Irish building regulations is  “CONSERVATION OF FUEL AND ENERGY – DWELLINGS” (Part L Download HERE and the TGD Part L Download HERE).

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Let me state at the outset that I believe the fRsi regulation is not a mistake but is actually a carefully drafted text by an expert who understands the risks and the complexities and is primarily interested in ensuring the health of future occupants of compliant buildings.  It is both correct and justified. It is also extremely onerous.

The TGD Part L, Appendix D, section D4, page 61 clearly states that we must prove DESIGN compliance for ground floor junctions by numerical calculation in 3D using validated software.  Other details can be modelled in 2D using similarly validated software. [Blog Note extract from TGD in bold, italics]

D.4 Calculation procedures

The calculation procedure to establish both temperature factor (fRsi) and the linear thermal transmittance (ψ) is outlined in BRE IP 1/06. Details should be assessed in accordance with the methods described in I.S. EN ISO 10211. These calculations of two dimensional or three dimensional heat flow require the use of numerical modeling software. To be acceptable, numerical modeling software should model the validation examples in I.S. EN ISO 10211 with results that agree with the stated values of temperature and heat flow within the tolerance indicated in the standard for these examples. Several packages are available that meet this requirement.

There is currently only one independent Thermal Modeller approved by NSAI for the entire country.  I am reliably informed that he has not undertaken 3D fRsi calculations for any Assigned or Design Certifier since BC(A)R SI.9 was introduced, leading me to conclude that in all probability, few of the certificates signed for domestic buildings (or extensions) issued to date are valid.  He has, apparently, quoted for this service several times but not once was he contracted to undertake it.

This is a very dangerous state of affairs that demands immediate action on the part of all three professional bodies whose members are entrusted with responsibility for certification under BC(A)R. Ignorance of the law is no defence so, at the first sign of mould, the assigned certifier and the design certifier could find themselves  in court and be unable to defend themselves against charges of negligence.

Mould is becoming a significant issue of building failure as a result of the introduction of Part L 2011 with its high U-values for flanking elements.  This focuses the surface condensation problem on the linear joints between the flanking elements as these become the lowest temperature surfaces.  Such linear corners, with their associated low air movement conditions, are ideal locations for mould growth. Old assumptions that inadequate ventilation is the cause of mould have been thoroughly sidestepped by the fRsi regulation: this is strictly a design compliance issue, not a use issue. You cannot blame a user for your design decisions.

Unfortunately, there is no alternative to 3D modelling to prove that the fRsi  has been achieved.  There is no rule of thumb.  The Accredited Construction Details (ACDs) cannot be relied upon to achieve the fRsi because the scope of what they cover is too broad, even very slight (trivial) variations in dimensions or material conductivities will result in breeches of the fRsi.  DIT have modelled several examples of  ACD-compliant junctions which fail the surfaced temperature test.  Furthermore,  the limits on ACDs are such that the applicable range of U-values is often breeched to achieve the EPC and CPC performance indicators required in DEAP.  If you exceed the approved U-value range – the tabulated ACD psi-value in Appendix D cannot be used and even the erroneous assumption of fRsi compliance falls.  This is not an accident.

I would therefore strongly advise anyone considering signing a design certificate for a domestic project to pay the €3,000 – 4,000 for an fRsi compliance check of all the junctions before putting pen to paper.  Once signed, if mould does appear, there is no defence; you are liable for the full cost of remediation including relocation of the occupants.  If you are quoting fees for a house or an extension, add the fRsi compliance check cost to the fee quote and make the ancillary certification by a NSAI approved Thermal Modeller conditional on the issue of the design certificate.  The way the TGD is formatted indicates that fRsi compliance applies equally to material alterations and extensions in addition to new build, so there is no escape.

Now that you know what is required to achieve compliance, will you ever again sign a certificate of design compliance for a residential project without an fRsi check? There is a word for a person who signs such a certificate: a “cowboy”.  I am sorry if that hurts, my intent is not to hurt but to warn colleagues of significant risk that they may ignorantly fall into. I didn’t write the regulation; I just read it, understand it and agree with it, but only after significant personal upskilling in this highly technical area.  Irish Thermal Modellers are the most highly qualified in the world: they need to be, Irish building regulations in relation to fRsi are by far the most onerous in the world.  That is why there is an NSAI Register of Thermal Modellers (the only one in the world), why they need to undertake a postgraduate course of study and sit an exam to gain access to the register, why they have to have PI cover and why they have to pay a fee to have their work audited annually.  This is not the work of a Government intent on ignoring fRsi. You should not ignore it either.

In all likelihood, the fRsi regulations currently applying to residential construction will be extended to all construction once the revised Part L (Non-Residential) is published.  It is right that occupants of hospitals, offices, schools, etc. should not be exposed to dangerous moulds.  Even if you don’t do residential work, now would be a good time to begin the journey to understanding fRsi.  It is a fundamental technical requirement of the delivery of the European nZEB building standard.  The Irish government is to be congratulated for staking its claim to the nZEB territory in this most exportable of high-level technical design services. The projected demand for these services is breath-taking.

But to return to present realities, I find it worrying that my professional colleagues in the Surveying, Architectural and Engineering professions who undertake residential work may already have signed compliance certificates under S.I.9 without fRsi assessments undertaken by a competent Thermal Modeller.  I also find it strange that there have been no warnings from any of the professional bodies to their members advising of the risks they are taking in such projects, and only high-level admonition for those colleagues who decline to take such risks with their PI cover.  Clearly, something is wrong with the system of professional oversight and support.

In spite of the former minister’s ham-fisted attempts to cap the fee for building regulations certification, there is an onus on professional certifiers to ensure that the letter of the regulations is applied fully, regardless of the cost.  If the minister wants to revise the regulations to make them cheaper to implement, then that is entirely his prerogative.  It is decidedly not for certifying professionals to second guess the written regulations and opt out of any they find difficult. That is the road to perdition.

Simon McGuinness is an architect in private practice, a passive house design consultant and a part-time lecturer in digital analysis and retrofit technology at DIT.

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