Breaking the Mould | Joseph Little Architects


15 September 2016

Industry expert and BReg Blog contributor  Joseph Little published an informative series of articles in Passive House + magazine in 2009 on mould growth, ventilation and condensation problems in buildings.  ‘Sick building syndrome’, consequent occupant health problems and long-term damage to building fabric are issues that have long affected Irish construction.

Due to technical conflicts and deficiencies in our current building regulations, specifically for ventilation, many experts consider ‘sick building syndrome’ to be the next potentially widespread defective issue facing the building industry; the next ‘pyrite’.

Inadequate technical knowledge, ‘traditional’ detailing coupled with poor workmanship particularly in the speculative development sector are at odds with more technically demanding building methods such as timber frame projects. Timber frame has the potential to be a viable and efficient way to accelerate projects off-site, but requires a high level of precision not only in design, but also in execution and workmanship on site.

‘Design and build” procurement models where the builder/developers are contracted to provide design, build and certification of projects has been a major problem in the past with very poor outcomes. The industry awaits a government audit into a number of so-called ‘rapid’ build timber framed schools completed less than 10 years ago which have been plagued by serious building defects. Timber frame estates figure prominently in lists of known defective residential schemes.

Our current privatised system of building control involves very little state involvement and scant enforcement of standards.  Remarkably bulding certifiers can still be direct employees of contractors and developers. Despite onerous and costly administrative procedures introduced in 2014 the occupant and purchaser still have little or no legal rights in the event of mould and condensation problems arising in new homes.

The following series of 5 technical articles by Joseph Little are well worth a read; we have included links to each complete article along with the respective executive summary.

“It should be obvious at this stage that the external envelope of any building (be it wall, floor, roof etc) is a place of seasonal, and at times weekly, change in temperature, moisture content and vapour movement.  In certain cases of inappropriate knowledge, installation or materials the thermal performance of the insulation can change and so to can the likelihood of that building element hosting mould growth…

Designers and builders need to build with far more awareness of moisture movement.  We need to build resilient systems – be that a wall, a ventilation system or the building itself.  We need designs that can accommodate things going wrong and can ensure structure and the occupants’ health are safeguarded.  The only answers are more education and understanding among designers, more understanding and care among builders, and a better selection of materials.  In some cases it may mean clients need to pay more, in others no cost difference: but the pay-off for their health should be clear.

In Society at large, particularly now with the HES Scheme about to part-fund private sector thermal upgrade programmes, we need a public awareness campaign to emphasise concerns wider than chasing the lowest, cheapest BER rating.  Our leaders could also learn from the approach of local governments in south-east France where free house surveys for sick clients are seen as another aspect of treating their illness and preventing more ill-health.  When justified the surveys lead to grant aid for specific healthy house upgrade works.  It’s a great example of all sides working for the common good.  What value meeting important carbon-cutting standards if we do it in such a way that we go further up the world’s allergy or asthma tables?  Who’ll thank us?”

Making the right choice… Financial cost is always an issue in Irish construction projects and can only increase in significance in the current straitened circumstances.  This is only right, but our plea to homeowners embarking on an energy-efficient upgrade is that they would give greatest weight to long-term value, long-term costs and long-term benefits.  A great example of this can be seen in the comparison of drylining and external wall insulation.  Most forms of drylining are cheaper to install on ‘day 1’, per square metre of prepared surface, than external wall insulation.  While this article has discussed in detail hidden long-term costs that must be considered, such as the dependability of the thermal upgrade, mould potential etc, there are also other hidden financial costs.

Drylining requires that occupants move out and rent or stay elsewhere, that they put furniture and paintings etc in storage (even if still on site) and re-decorate after.  External wall insulation on the other hand requires that scaffolding be erected (some external wall insulation installers do this: some leave it to the general builder).  For a proper installation with minimum thermal bridging, windows should be unfixed and moved to the outside line of the original wall, drainpipes should also be moved out, roof eave fascias need adapting and any concrete paving surrounding the house should be cut back to ensure the insulation clads the full height of the relevant external walls.  This may sound expensive, but that view may be countered by the shorter construction time, the fact that the occupants can often remain resident, and the fact that the only re-decoration needed inside is the cladding of the widened internal window reveals with timber liner boards.  However the final, and perhaps most persuasive hidden cost in this comparison, may be the remaining size of the house.

Take a typical Dublin 3-bed semi-detached house with hollow block walls, a floor area of ~100m2 and overall internal dimensions of 10m x 5m.  It has an external wall perimeter of 20m per floor, giving 40m over two floors.  This excludes the party wall of course.  Assume the external walls are built of hollow block with sand-cement internal plaster and pebbledash outside.  A best practice, healthy approach to drylining these walls (to achieve the 0.27 U-value target of the ‘Home Energy Saving’ scheme) would be to use 80mm of ‘Warmcell 100’ or equivalent blown cellulose insulation (λ-value of 0.035), continuously sealed with an intelligent vapour control layer (to surrounding structure), and a 38mm service zone filled with hemp or sheep’s wool with a plasterboard finish.  This buildup can be 130mm thick.  The floor area lost would be 40m x 0.13m = 5.2 m2 of lost floor area, which converts to (5.2 x 10.76 =) 56 ft2.  Assuming a conservative average value of €250 per ft2 for residential floor space (the value could be double this in certain parts of the city) means that this ‘lost’ floor area has a value of €13,988. [10]

Where the discussion is about insulating inside or outside the deciding question could be ‘can we afford to lose further value by losing space in a market already falling?’  An alternate response to this news, wherein the thinnest or cheapest drylining is selected, would be a mistake if those installations have dubious credentials, don’t allow a proper airtight installation, or result in poor thermal bridging or health.  As with almost anything it is better to do a little work well than a lot badly…

Finally the right thermal upgrade and heating system are those that suit your specific lifestyle and your house’s construction while safeguarding health and the greater Environment on into the future.”

“It is still not clear to the author, or to many others, why Agrément certificates with the current level of detail are supplanting a wide number of excellent ETAs in relation to EWI for use under the HES scheme. We want clever systems, more choice and good prices. Besides references to Irish regulatory standards and codes, Agrément certificates do not appear more detailed or ‘local’ than ETAs. If the case for local and installed value is to be convincingly made Agrément certificates need to be more useful to installers and more specific to Ireland by referencing a wealth of local information, such as the impact of severe weather conditions on the system assessed, and information and issues that will impact upon performance. It would be very useful if they could, for instance, allow easy calculation of Psi-values and provide equivalent details to the ACDs for that construction system.

The regulatory requirements for conserving fuel and energy in relation to thermal bridging in dwellings are currently inadequate, however a great opportunity exists in the upcoming review of Technical Guidance Document L to put this to rights.  The marked shift to a refurbishment-focused building industry and the ambition in the HES scheme to raise the thermal standards for refurbishments to new-build levels make this all the more urgent.

In the context of climate change… A key part must be integrated guidance, another must be wide access to good products. It will not be easy but working together we have a good chance of reducing the carbon emissions of our housing stock to zero, not by 2020 but perhaps by 2035, and creating a large number of jobs and a more sustainable society in the process.

“Numerical simulations can create hundreds of pages of data.  It’s obviously critical that the key elements (that one is interested in examining on any particular occasion) are extracted from the ‘noise’ and correctly interpreted…

A reasonable understanding of the scientific units, material data and the vapour mechanisms involved is necessary to use the software and to understand if what is being outputted reflects a mistaken initial input or a key finding.  Software with a good user interface, an extensive help file and an online forum, such as WUFI Pro has, will do a lot to guide and educate the user.  They also have courses: the first English language course in using WUFI was delivered last year in the Fraunhofer Institute in Holzkirchen, near Munich.  This writer attended.  However courses have been run in various European countries, North America and Japan for many years.  Alternatively you may wish to visit the WUFI website <> and download the free trial version of WUFI.

It is this writer’s view that those creating codes of practice and regulations, NSAI Agrément, and architects who wish to control their specification closely need to learn and use numerical hygrothermal simulation.  Outputs from simulations shown in the next ‘Breaking the Mould’ article will show why it’s so important.  The technical department of all insulation suppliers need to move to supplying condensation risk analysis based on numerical simulation also.  In fact, when standards are fully adhered to, they’re obliged to use numerical simulation in the case of drylining.”


Everyone wants to reduce energy demand by insulating as highly as possible, but insulation without due regard to structure or health, or without full understanding of the changes the act of insulating creates, can only cause problems.

Given the volume of refurbishment work expected to commence it is hoped that government bodies, the utilities now entering the refurbishment market under the EDRT [9], and professional institutes will quickly engage with these concerns and contribute to the creation of a detailed, practical code of practice for refurbishment of dwellings.  A key initial step is a general acceptance that current guidance on refurbishment is inadequate.

Testing of, for instance, three competing impregnation treatments and a range of typical blocks, bricks, renders, plasters and insulants by an independent third party is needed to form a basis for all simulations and assessment of Irish buildups.

With use of new test data the simulations presented in this article would then need to be revised and significantly expanded on as a way to explore the most appropriate, healthy ways to carry-out energy-efficient refurbishments.

One striking conclusion of this comparative series of simulations is that higher and higher levels of external insulation appear to create healthy and ever more stable conditions within the wall buildup, while even relatively modest levels of internal insulation face tougher conditions and either failure or are bordering on doing so.  An equally significant conclusion is that the right treatment of the external face appears to allow the installation of internal insulation without risk of growth in internal moisture levels.

Organisations need to be prepared to revise old guidance based on the new results.  It is suggested that SEAI re-examines the insulation performance associated with the internal insulation grant.  This work is clearly not conclusive but simulated walls internally-insulated to 0.27 W/m2K clearly failed in more than 35 simulations.

About the author:

Author Joseph Little is expanding the range of services his environmentally-focused architectural practice provides to now include technical support to other designers and builders, starting with thermal bridge assessments.  Visit ‘Building Life Consultancy’ at for more info.

Other posts of interest:

The Latest Homebond House Building Manual: A Critique | Joseph Little Architects

Notes from the (thermal) edge: Part L Compliance (2 of 2) | Look Back 14

Does the Minister want a cut-price building control service? | Simon McGuinness

Part L | DECLG slowdown: Better building or more red-tape?

Does the Minister want a cut-price building control service? | Simon McGuinness

Building Regulations Reform & the Housing Crisis | Irish Examiner

Developer makes 27% profit in 6 months: warns against state housing.

Simon Carswell: Politicians, Construction industry lobbying and banking | look back 10

Beware profit-driven lobbyists when it comes to housing policy | Dr. Lorcan Sirr

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