The growing ambition of sustainable building in Ireland has never been more thoroughly embodied than in the recently completed St Mary’s Credit Union, Navan, Co. Meath.

Central to the building’s design, engineering and construction is an approach that is holistic in the truest sense, driven by architects Gaia Ecotecture’s belief that the building—linked to the original credit union built by the firm in the late 1980s—should act as a living structure; its elements interacting dependant on the needs of the building’s users and the challenges and benefits thrown up by shifting weather conditions and natural resources.

The attention to detail inherent in this holism has created a building that is innovative in so many regards that focusing on any one aspect of the building—such as the fact that this is Ireland’s first 5-storey timber frame building—would do the building as a whole an injustice. In recognition of this fact, the building has been selected amongst a handful of cutting edge projects around the world for presentation at the World Sustainable Building Conference in Tokyo.

Embodied Energy and Lifecycle Analysis

We’re blessed with an excellent client—an articulate and careful management team from the board, to the executive, to the building committee, to the general manager. They had put their trust in us in the late 80s, and we’re very pleased that they came back to us. As an owner-occupier to the building, they were open to the persuasive argument of prolonging life to first replacement, keeping down the use of external energy sources such as grid electricity and gas, and investing in energy producing devices such as double wall and box windows, photovoltaics and solar thermal. The payback period on these devices is fully justified commercially speaking through lifecycle analysis when you have an owner-occupier. A pernicious problem is that developers, who “lash the thing up”, sell it quickly, and turn their money over, couldn’t care less, and the unfortunate tenant is left with low performance fabric, which if they have a repairing lease, rapidly becomes an ‘albatross’ that they have to pay for. We were in the position here that the owner-occupier is responsible for the maintenance costs, and there are excellent studies by our own cost managers Gardiner and Theobold, et al which show that the life cycle running cost of a building greatly exceeds its first capital cost, with conventional building. The cost to the organisation is minimised by intelligent investment in quality.

The fact that we now apparently need four planets to maintain our profligate life style means that if you’re conscientised about your children or your children’s children, you have got to move towards making buildings on the Factor 10 principle—that we use less of everything, much more efficiently. Factor 10 is by no means out of the question. If you look in ‘Green Design; Sustainable Building for Ireland’ you’ll see that locally produced air dried softwood has embodied energy of about 110, on a scale where aluminium is in the region of 75,600, KwHrs / cubic metre and concrete products based on conventional Ordinary Portland Cement and steel (103,000) are up there in the mega numbers. We’re dealing here with step changes in building culture. If we accept the word of the UN Environmental Programme team in their annually updated GEO 2000 reports we need to change. This Credit Union building goes as far as possible, in a streetwise and alchemically alert way to bring down embodied energy. It’s not fundamentalist—where we need steel we use steel. We’ve used a ‘filigree’ of galvanised steel, with zinc cladding elsewhere in the building with flashings and so forth where it is appropriate. Those relatively small volume materials carry an embodied energy burden, but they’re applied intelligently, to do the task for which they are best suited. The vast bulk and mass of the building is timber, and this timber is in fact protected by the high embodied energy materials on its external face.

Navan Credit Union

5 Storey + Roof Timber Frame

Years of research have gone into this timber structure. We trawled Europe and North America for the most advanced timber technology. We’ve gone to see the leading people in Austria , Germany , Switzerland , and Scandinavia , and to cut a very long story short, Projekt-Holzbau Merkle in South Germany had previously earned their credentials with a colleague of ours in GAIA International, Joachim Eble. With their engineers, Pirmin Jung, we worked through a design process within the terms of Eurocode 5, BS 5268 and the German DIN standards amongst others to develop the design. The key point of the structure over five stories, of course, turns on the connections. The delightful engineering involves tiny amounts of steel used to form the connections, but this steel is totally submerged within timber, so that the timber itself is acting as an insulant to the thermally vulnerable steel, in terms of fire protection. The building is being presented at the Garmisch conference later this year by Pirmin Jung, and there is great interest in the building. We devised the basic structural scheme but great credit must go to Pirmin Jung’s team for detailed analysis and shop drawings.

The lift shaft itself is engineered in timber. There was a proposal to use concrete which we discounted. In other projects where concrete and timber have been used together with less than total success because they are two disparate materials. They behave entirely differently, and if they’re used in conjunction it can cause great problems with settlement, expansion and contraction.

Navan Credit Union

The timber engineering aspects need to be treated with great caution. Every building of this kind must be closely engineered. The fire safety aspects, moisture content, density and stress grading required engineering of a very high calibre from Jurg Stauffer of Pirmin Jung’s office, working in close collaboration with the architects. Readers of this article cannot take it that they can, in cavalier fashion, build to five stories. This building is a hybrid between a frame structure and a skin or panellised structure. The wall panels came complete with sealed insulation, preformed windows and so forth to infill around a skeletal frame. It’s a hybrid interaction between frame and skin, rather like the bones, cartilage and ligature of our own bodies. We’re not just skeletons—we work with a tenuity of skin and tissue, and this building is rather similar in its concept to that. An additional key point is racking (lateral) stability and strength. In certain very extreme weather conditions—the ‘Clonee tornado’ or the recent ‘Katrina’ hurricane, are cases in point—there can be negative uplift forces on the substructure. So there are holding down bolts at certain points to literally hold the building onto the substructure. The dead load of course is much lighter than a conventional concrete structure, thereby significantly reducing substructure, which in this case consists of continuous fluidised augered piles.

Navan Credit Union 4

Projeckt Holzbau- Merkle used the Brettstapel system, with beech dowels at 8% moisture content being inserted, under pressure, through slightly smaller drillings, in the pine laminae, typically at 12% moisture content. In this system, as the moisture contents equalise, the hardwood dowel expands and the softwood shrinks, becoming an integral solid timber construction, with attractive fire safety characteristics, while retaining very low embodied energy. This component is manufactured to a quality control level which allows it to be used directly as a finish, eliminating other materials.

A Kerto stressed skin was also used, a highly engineered timber product that uses minimal amounts of glues but in a very strategic way. It’s basically what the North Americans call laminated veneer lumber (LVL). This is such a huge subject that we’re skimming over here. The use of OSB plywoods, Glulam, Kerto, Steicoflex wood-fibre insulation rather than petrochemical derived insulation—It’s all of a piece.

We would recommend the use of Pirmin Jung’s office. We’ve found them to be among the best consulting engineers we’ve ever had contact with. I say that based on my own experience as an engineer. When I come across really subtle, nuanced engineering I recognise it and the degree of detail they went into was astounding. Every single junction in this structure was modelled in 3 dimensions. The statics and detail stress analysis were of a very high order, and the interlock between Pirmin Jung’s office and Projekt Holzbau Merkle was exemplary. It’s something that has been lost in the building industry. There’s too much of a divide between consultant and ‘on the shop floor’ know-how. In this case, literally, the CAD drawings became the automated cutting software for the components. Due to the fact that Projekt Holzbau Merkle and Pirmin Jung have built up a rapport, we reaped the harvest of a collegiate approach between them. There’s two much of a schism between consulting engineering and actual fabrication. It’s not a culture as it was in the past- Peter Rice comes to mind as a wonderful example.

Passive heating measures

The main passive heating measure is to look at the whole building as a passively heated device, through the use of orientation, shading, and percentage aperture for different elevations. Good uptake of solar heat gain in the morning is delivered into the building for the hours of occupation, or in the alternative, shaded or vented if the gains are unwanted.

The major passive solar heating device is the double façade to the banking hall. The orientation is basically square on diagonal—that is one corner of the building is effectively due south. So you have a southeast and southwest banking-hall glazed timber double wall, and then you have a northwest wall. This is tied into the double ‘box’ windows. The winds in this location are predominantly from the southeast or southwest, with virtually no winds of significance from due south north. So there tends to be suction or lower pressure from the northwest façade and positive pressure on SE and SW ; this helps cross ventilation.

The passive devices are carried forward into what we call the ‘box’ windows, which are twin skins of window with an interstitial space of about 400mm. Both windows are double-glazed with a high glazing specification, and as with the banking hall walls which are 6 meters high, these ‘box’ windows have a subtle system of trickle ventilation. So in deep winter it’s a ‘lockdown’, using trickle ventilation only. By creating a suction effect within the building of so many Pascals you draw air from the warmed cavity into the building. The ventilation air arrives into the occupied zone pre-heated. Conversely in high summer, the outer glazing is opened at the top, so that all unwanted gains are vented off. The cavity must be purged once you pass the acute cold season and part of the shoulder season, because the passive gain device can become your enemy in high summer. The use of external shading and external purging is crucial to the way these work. Afternoon overheating on southern facades would be a huge problem if these design measures weren’t incorporated, including mechanical external shading doubling with overnight security shutters and deciduous shading of what we call the ‘Abraham screen’ to the Peace Garden—a brise soleil screen with Wisteria climbers. In a short time, this will provide shade in summer, and with loss of leaf, will provide light and heat access in deep winter

Solar Water Heating

We have a range of Thermomax panels, and here Mark O’Brien of Energy 365 provided services to the consulting engineer, Brian McPhillips with expert subcontractors Eirbyte and Glas. The basic device is evacuated tube which picks up from the steep south-oriented plant room roof, into a calorifier for hot water to lavatories, wash hand basins and the kitchen. Any excess to that requirement goes into the space heating system as a minor pre heat, so that the temperature difference—or Delta T —for the boilers is somewhat reduced.

Active and Auxilliary Heating Measures

We live in an oceanic temperate climate. In a way you can say that in Ireland we have weather rather than climate. I’ve walked in my shirtsleeves in Dublin at Christmas, and I’ve been very cold in mid-summer. We see auxiliary heating and cooling as being exceptional events that are needed to deal with peaks in the weather, of heat or cold. We see the whole technological approach to this building as hybrid in nature rather than fundamentalist. The passive building idea, where there’s no heating or cooling whatever is a counsel of perfection that can sometimes leave clients physically uncomfortable, while the professionals involved may be feeling smug. So the active heating and cooling systems employed both use state of the art technology. We believe in subtle science. In the case of the cooling system, we’re using gas-fired heat pumps of extremely high efficiency. The Coefficient Of Performance in the heat pumps means that the net efficiency in the whole system is 131%.

The heating system is in a banked series of modulating condensing boilers, which are efficient whatever the load, to take full advantage of the load/ efficiency curve. It’s a commonplace, that if you use a boiler at the low end of its load capacity, it is inherently inefficient. So by having three boilers in tandem, as and when you need to service varying demand, you bring them in, in series. The first boiler is brought as quickly as possible to the peak of its efficiency curve, which is up around 93%, and so on. In a clever, controlled regime you keep these three boilers as close to their peak of efficiency as possible. This is a completely natural-gas based system in both cases, which means the primary energy use is highly efficient rather than having road haulage of LPG or electrical grid losses.

We have found from experience that low temperature hot water systems are the best outcome. We’ve tried various different solutions but we believe in oversized radiator surface with lower circulating water temperature and lower water content. We would like to see the same plant and equipment doing both jobs of heating and cooling, but after careful study it was found that it was more appropriate to have separate heating and cooling circuits in this case. For the future, to keep down installed cost, we believe there’s a very great scope for the same plant within the rooms performing both functions, especially using heat pump technology.

There is natural gas available, at a considerable infra-structural cost brought to the town. We see the building, in urbanism terms, as tied into the organism that is the town, and it is sensible to use the grid supply while it is available.