Is there a regulation for thermal bridging condensation risk? | Part L

by Bregs Blog admin team

Open letter Part L

BRegs Blog on November 20th 2014

We received a recent query to the BReg Blog on 20th October 2014:

I have seen several posts on condensation risk analysis and Regulations compliance.

Correct me if I am wrong but no REGULATION is concerned with condensation risk due to thermal bridging. Part L is concerned with limiting heat loss. Part F with limiting moisture in the air that might contribute to condensation. The TGD is addressing matters outside of the regulations.

That’s my learning from the RIAI design certifier course and my defence in court. Wish me luck.

We asked Simon McGuinness to help out with an answer. Here is what he said:

“There is no REGULATION covering any of the following either:

  1. Backstop u-values
  2. EPC or CPC targets
  3. Window area/u-value limits
  4. Y-factors
  5. Minimum/maximum air change rates
  6. Minimum vent sizes and locations
  7. Location of openable windows or mechanical extract vents

If your correspondent expects to be able to ignore these provisions of the TGDs on the same basis as he proposes to ignore fRsi, he will find himself in deep water.  As a compliance strategy it is delusional.

Building regulations are become increasing complex and it is inevitable that they will become more like enabling legislation, setting out broad strategic goals which are then backed up by technical guidance, standards, codes of practice, and the like, to afford practitioners adequate means to demonstrate compliance to the satisfaction of the courts.

I doubt if the RIAI training advised members to ignore fRsi, in fact I know that it is a matter that is exercising RIAI who are drafting an advice note for members on the subject.

Let me put it this way: in a court of law there is no legal difference whatever between the fRsi requirement (0.75) and the EPC requirement (0.6). Neither are mentioned in the relevant Statutory Instrument. Both have a numerical calculation methodology proscribed in the TGD and a threshold value that must be attained.  Why should one be considered irrelevant and the other mandatory?

An fRsi failure in a block of apartments could require a partial rebuilding of the block and the temporary rehousing of its occupants for a number of years. It will also result in a large claim for damages.  That could be significantly more costly than an obstetrics failure which results in an infant being born with brain injuries as a result of the negligence of a doctor.  Do architects really want to carry the kind of PII cover that obstetricians carry?  Failure to calculate the fRsi for a curtain walling system could require the complete replacement of the curtain walling, necessitating a new planning permission, all at the architect’s expense – don’t laugh, there is just such a case pending at the moment.

There were 9,500 members of the Irish defence forces: a maxim total of less than 19,000 ears in all. A fraction of their owners were awarded damages by the courts. By comparison, there are 1.3million houses, each of which may have 40 linear thermal bridges, any one of which could exhibit mould as a result of an fRsi design (or construction) failure. All it takes is for one homeowner to be awarded damages as a result of mould appearing in a new house or apartment and queues of litigants, and lawyers, will form outside the Fourcourts.

It is difficult to see a way back into practice after an unsuccessful defence of an fRsi claim, and the shock to the PII market, should a flood of litigation appear, could even undermine the viability of the construction industry in Ireland.

These regulation are unprecedented, no other country has enshrined three dimensional numerical mesh calculation in its building regulations for surface temperature calculation. But it is there for a reason: fRsi > 0.75 is both necessary and justified as we seek to build to the nZEB energy standard.  We should be grateful to have regulators who understand the importance of these issues and have had the courage to legislate to keep people safe.  We now need the professions to step up to the plate and upskill to cope with the liabilities they are accepting by signing design certificates. ”

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.

Other posts of interest:

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

Design Certifiers – 3 things about certifying Part L… 

Why the design certifier and architect need third party building fabric assessments

Opinion piece: new building regulations and materials risk analysis

SI.9 and Part L | Specialist ancillary certifiers Part 2

SI.9 and Part L | Are specialist ancillary certifiers needed? Part 1 

Dispensations and Transition Arrangements

Practical Post 10: No retrospective compliance – BC(A)R SI.9

Practical Post 13: Duties & conflicts- BC(A)R SI.9 

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