Page 61

new build between our passive house and the detached house modelled by the department. The Part L compliant house accepted an air permeability of 5m3/hr/m2. This roughly translates to an N50 of 5 air changes per hour (ACH). By contrast the passive house standard requires an onerous maximum air leakage of 0.6 ACH. Mark Baker of Baker & Co is the only person we will work with when it comes to airtightness. In addition to working with Pat for over twenty years, we have found Mark’s advice and experience crucial in getting down below 1.0 ACH on several projects now, while his supply-andfit price is always the same as it would cost us to buy the materials. On this project Mark’s tender price worked out at one per cent of the total build cost, which the client accepted as a marginal extra expense. Still, we found that during construction achieving the required levels of airtightness was not easy, and the cost of works was harder to quantify beyond the cost of the airtight barriers. Any good builder practices attention to detail, but getting down to 0.6 requires you to take this to a whole new level. Pat spent an inordinate amount of time with trades discussing the details required for complex junctions. Every service penetration to the house had to be identified and planned for. It was harder to timetable the trades at first fix while preserving the integrity of the airtight layer. The trades required far more supervision and support than normal. This ensured that when we came to the final test, there was no problem in reaching 0.6 ACH. Still all of this represents a cost to the client that many could argue is not there when the air permeability allowed is 5m3/hr/m2. It should be borne in mind, however, that there is a consequence for this level of air permeability. When I entered 5m3/hr/m2 into PHPP the projected heating bills of the client more than tripled, going from €400 a year in oil to €1,400. So the counter-argument could be made that by sticking to 5m3/hr/m2, you’re paying for an Arated house but in reality you’re getting mediocre energy performance. Another extra expense we incurred related to the requirement for renewables under Part L of the building regulations. Under the new Building Control Act, the local authority requires a Part L compliance report at commencement stage. This involved Mark Shirley of modelling the house in Deap to evaluate it for compliance. As this was a passive house which worked in PHPP, I didn’t foresee any problems in Deap. I was wrong. Mark’s evaluation showed that while it passed the energy reduction requirement with ease, comfortably achieving an A2 rating, it failed to comply with the carbon reduction requirement. The house did have an oil boiler but it also had 40 solar tubes, which we assumed was enough to meet the 10kwh/m2/yr target for renewables. The reason for this failure, Mark explained to me, was that the house was simply too energy efficient. Due to this, there wasn’t enough demand for the solar to satisfy the 10kwh/m2/yr target. Mark presented us with three options: make the house less energy efficient to increasing heating demand, add solar photovoltaic panels, or ask Kildare County Council to use their discretion in the matter. We went for the third option at first, but got no response.

It certainly didn’t make sense to us, the client, or Mark Shirley to make a house less energy efficient in order to achieve Part L compliance. Did this not go against everything Part L was put there to achieve? PV came in too expensive, but working closely with Mark we found that an additional 80 solar thermal tubes (a total of 120 solar tubes) was the most costeffective solution for compliance. It was still an extra unnecessary expense of approximately €2000. Other clients could easily have opted for higher fuel bills to save that few thousand during construction. My fear is that this is exactly what will happen if this issue is not addressed. In the end, the house we built fulfilled passive house requirements without any significant difference in costs to one that was merely Part L compliant. In fact, I estimate a house built to the department’s Part L spec would have cost €310,000, whereas built to the passive house standard, this house came in at €290,000. And in terms of running costs, health and comfort levels it is worlds apart from a house that has only ticked the appropriate boxes in Deap. The biggest obstacle to building a passive house is no longer cost – our own building regulations now put standard building costs around the same as passive house – but lack of awareness. We were aware of the cost-effectiveness of using alternative building methods to those suggested by the department’s guidelines, and of the value of the passive house approach as better building practice. The problem is we’re in the minority. My big fear as we move forward is that unquestioning conformity to common practice and Part L requirements will lead to a major lost opportunity — where houses are built for the same budget as a passive house, but without any of the benefits.

SELECTED PROJECT DETAILS Architect: DH Architectural Contractor: Pat Doran Construction M&E engineer: Target Zero Civil & structural engineer: Tanner Structural Designs Energy consultant & airtightness testing: Mechanical contractor: Seamus Byrne Heating & Plumbing EPS insulation & passive slab supply: Airpacks Insulated sills: Passive Sills Roof insulation: Baker & Co Electrical contractor: Erne Electrical Airtightness products: Siga Passive slab design: Viking House Windows & doors: Munster Joinery Bi-fold doors: Lakeside Windows Roof window: Velux, via Chadwicks Oil boiler: Grant Engineering, via Chadwicks Solar collectors: Joule, via Chadwicks MVHR system: Versatile MVHR contractor: Flynn Heat Recovery First fix carpentry & roofing: Christy McMahon Carpentry Second fix carpentry & stairs: David McDonnell Carpentry

Want to know more? Click here to view additional information on these projects, including an online gallery featuring illustrations, photographs, and project overview panels. This content is exclusively available to our digital subscribers. u

ph+ 61

Profile for Passive House Plus (Sustainable Building)

Passive house plus issue 11 (UK edition)  

Passive house plus issue 11 (UK edition)