Building Air Tightness (Part 2): Responsibility
Within my previous post, thanks to the folks who took the time to read it, I speculated that our industry is on the cusp of taking up the opportunity of air tightness in buildings.
With a little more leniency within the Green Star Innovation category for air tightness, we could see some great results by those delivering tighter buildings to clients.
With heating/cooling capacity and operational cost reductions, it seems to be a theoretical no brainer. Below is a recap. However, it’s not just theory and technology that matter in the case of air tightness, it is practical experience, skill, understanding and risk.
A Step into the Unknown
At the forefront of many air tightness debates, I can empathise with those early adopters and thought leaders that dare to design to higher standards. Within our warm climate, the jury seems to be still out.
How air tight is tight enough? Moisture, moisture and err, moisture? Is designing air tight even appropriate and when? How climate applicable is air tightness and are Green Star Innovation targets too challenging and a hurdle to adoption? The road to air tightness is paved with unknowns that need greater support and transparency to encourage adoption.
For clients, reading the potential savings associated to air tightness will no doubt make for easy reading. If you truly want a fix to optimise both mechanical services and façades, a sound air tightness strategy could be the holy grail of solutions. The heart is locked in and the pocket will benefit!
A Shared Responsibility
From a designer’s perspective, either Architect or Façade Engineer, detailing of junctions and the understanding of cladding and glazing materiality becomes a major focus and an additional scope item that needs to be understood and addressed by concept/schematic design.
For some construction types, such as curtainwall systems (below), where a homogeneous skin is applied to a building, the risk of leakier buildings are in theory drastically reduced. Where multiple construction types are applied to a design, the risk can quickly increase.
For those in charge of strategy and performance objectives, often the ESD or Mechanical Engineer, the role is often motivational over practical, with the focus being the adoption of suitable performance targets within a Green Star strategy. Once set, these values determine a host of cost implications and concerns that should not be underestimated.
Starting with a Main Contractor, particularly in the Design and Construction procurement model, most have not yet had the opportunity to understand the effort and risk required to meet targets agreed by the design team.
Contractually a mine field, what happens if you don’t meet an air tightness target? And how about the delivery end. With greater levels of planning and trade sequencing on site, site reviews, testing during construction and ongoing site education, what are the real cost implications and risks to delivery?
Embedded within the Main Contractors delivery, do sub-contractors working on envelope elements also share a responsibility for air tightness? Awareness is important but if you puncture or neglect the air tightness strategy, are you fully responsible for ongoing remediation until the air tightness or blower door subcontractor provides a result in line with the performance strategy?
And how about the aforementioned and most fundamental practitioner in this performance equation, the blower door subcontractor. They may very well have there own crosses to bare.
Strategically, following the adoption of a performance target, they must plan and be able to deliver enough equipment to be able to test a building under strict testing procedures. If the building is too leaky, and targets are not met, then they may very well fail to be able to complete the test under contractual obligations.
Check out the chart above for some Australian context, details of actual projects retained for confidentiality. Simply put, early Australian market conditions suggest anyone promising to test larger or complex buildings need to be able to prove they have the fan power to do so.
Referencing the above, if you have a large office and want to test the entire building to meet a good practice target of 5 m3/hr/m2 @ 50 Pa, your blower door subcontractor needs to show he has more than 10 fans to complete a test. That's a lot of fans that very few have the capacity to provide. Even for those that have the fan power, when the construction quality is not up to the mark and the building is leakier than expected, it is likely that they may struggle to be able to meet international testing requirements.
Taking on the Challenge
To revive the ESD adage - you need to get in early - has never been truer. Post schematic design, and you are already on the back foot.
Engage your ESD consultant and get upfront advice from the blower door subcontractor to inform your design as soon as possible....and make sure he has the fan power if you are looking to test a large volume of space.
The same can be said for the Main Contractor. Hold workshops to summarise the value and risk of air tightness to the project. This may alleviate some fears and avoid unnecessary increases in scope items for delivery.
Take on the Green Star Innovation challenge! Green Star Deign and As-built provide points for simply testing and the guys at the GBCA are a flexible bunch that appreciate the difficulties of changing hearts and minds.
In summary, air tightness design within Australian early market conditions is no doubt complicated by delivery but equally so by the acceptance of risk. Take on the risk, and the rewards will follow.