It’s natural for people to look for cheaper ways to do things. In the case of air tightness testing, what may seem like a cheaper and seemingly more economical way of testing has many more strings attached. This article is written to help builders, ESD consultants or interested technically minded people to understand the complications of moving away from a whole building test to reduce cost.
When we consider air tightness testing to be done for whatever the reason, the first question we need to be asking ourselves is “What is the aim and purpose of this testing?”
- Are we testing to understand the overall permeability of the building envelope?
- Are we testing to understand the quality of the installation of the facade compared to factory facade testing, or to understand how much the core and facade leaks?
- Are we testing for confirming weather protection from ingress of water during extreme weather events?
- Is it needed for all of the above?
Before we discuss the testing options, it is crucial to understand that the Australian construction industry has yet, not come to grips with the principle of a ‘building as a system.’
Any building, large or small, needs to be considered as a complex piece of machinery with thousands of components and a range of mechanical systems, all working together- hopefully- in harmony.
As the building is a system, changing one element will have an immediate impact on another part of the building and can often influence its (energy) performance and/or indoor air quality.
Compare a building with the engine of a car. Make changes to the air intake, and it will immediately affect the performance of the car as well as its fuel consumption. If the intent is to improve the fuel consumption of the engine, it is highly likely that just changing the air intake is not enough. Maybe the spark plugs, the carburetor, and the timing belt need changing at the same time to make the engine work better.
Improving the airtightness of a building is the same. Testing and sealing one part, or compartment, of a building, can be counter-productive. As the building has many different components and other areas might include elevator shafts, different ductwork, external doors, or a leaky roof section, just testing one part will not tell the complete story of the whole building. Sealing one compartment will often result in unbalanced mechanical systems and poor air quality in other parts. In other words, you cannot just change the spark plugs and ignore the rest of the engine and still expect optimal performance.
In the following article we discuss the various ways that people may think of airtightness testing:
- Compartment blower door testing
- Guarded compartment blower door testing
- Whole building blower door testing
- Facade and Compartment Testing
What types of testing can be performed on a building?
Compartment Blower door testing is testing a part of the building envelope, but it is unknown whether leakage is coming from inside of the building envelope or from the outside. Only the surface area connected to the outside are to be used to describe the m2 leakage rate. Facade testing is also considered compartment testing. Results include leakage internally and externally via the external surface area. For example, an intermediate floor can only use facade surface area, and the floor surface area should not be used. Compartment testing should include multiple different types of areas, top floor, ground floor and intermediate. This method of testing is not detailed in any international standards.
Guarded compartment blower door testing is where a compartment is tested, but surrounding compartments are pressurized at the same pressure to cancel out leakage going internal to the building envelope. Only the surface areas connected to outside are used to describe the m2 leakage rate result. Guarded blower door testing includes multiple different types of areas to be tested, top floor, bottom floor and intermediate levels. Up to 20% of the building. Guarded blower door testing can experience similar flaws to compartment testing if it is not planned out well. Core leakage can also be inadvertently canceled out and not measured. Guarded blower door testing may require many blower door fans, and it is spoken about in international standards.
Whole building blower door testing, enables the builder to focus only on the building envelope and enables a way less complicated and much more reproducible test methodology, but in most cases requires more fan power.
The building envelope is what creates the magic, go to this link to find out what the building envelope includes.
The Pros and Cons of compartment and facade air tightness testing…
Obvious issues with the facade and compartment testing:
- Firstly, It may seem cheaper, but in the long run, if you are aiming for a target, it ends up costing more in undertaking works that do NOT improve the overall airtightness of the building envelope connected to the outside.
- Air leakage occurs in the enclosure/compartment, which has been built around the facade. Only the surface area connected to the outside can be used to report on the leakage rate. The issue with this type of testing is that it includes additional air leakage data not relevant to the external building envelope and therefore creates an additional barrier for the builder to pass a particular target that may be set for Green Star points or specification, which is not ideal.
- Air leakage occurs inside the detail of the facade design, into the building envelope, or behind the plaster around columns
- The energy efficiency benefits of air tightness are not realized with the effort exerted by both testing contractor and building works because key parts of the building envelope are not included in the test methodology.
- The performance of the building after the build is constructed may be disappointing, which may trigger the owner of the building to conduct a full building test, and if the leakage is not favorable, it may be necessary for the builder to conduct costly remediation works, which could significantly affect the profitability of the job.
- More surface areas in compartment zones, other than the building envelope surface area, becomes a precedence of work, which should be duplicated on all other floors that aren’t tested.
- One way to potentially do facade-testing work is to undertake the testing with guarded pressurized enclosures, surrounding the facade detail to be tested. Is it worth undertaking this task considering all the effort of the temporary enclosures? No!
- As soon as trades or the builder know that a particular area is earmarked for facade or compartment testing, trades will put extra effort into that area to make the result perform better than what it otherwise would have been
The only benefits of compartment testing.
They are pretty good ones though:
- Testing smoke walls is a fantastic option for compartment testing! Smoke walls are designed to create an airtight barrier and prevent smoke from passing through one building compartment to another. Today no one knows if smoke walls work.
- Smoke testing, for improving people’s knowledge of air tightness. This type of testing uses a (theatrical) smoke machine to demonstrate an air leakage path in a building envelope.
- Water ingress testing while depressurizing a part of the facade to a required pressure.
Facade and Compartment Testing
This curtain wall will perform very well in a whole building air leakage test, while it will fail in an in-situ facade test. This system creates an efficient air barrier at the red dotted line as shown, and the minimal air is expected to get to the outside of this curtain wall detail.
During an in-situ facade test, however, the cavity highlighted in purple will be acting as a path to the area outside of the temporary test chamber/ enclosure created for the facade test. It is not part of the air barrier by design; however, the construction of the temporary test chamber can only be sealed to this capping element. Unless the builder seals up the joint where the blue dash is circled, it is not possible to isolate this air path.
Window facades are tested to require 1.6l/s/m2@150pa, which is equivalent to 2.8m3/m2@50pa. If a builder is aiming for 5m3/h/m2@50pa, then they are allowed to give away 2.2m3/h/m2@50Pa for the facade to roof detail and all other penetrations into the core.
By the time the small enclosure has been passed, this money could have gone towards actually getting the building tested in full, with a much greater understanding of the air leakage of the whole building envelope.
Because air leakage locations are unknown, this type of testing ends up costing builders bucket loads of money upon dead money fixing the building envelope for the enclosure without improving the overall air tightness of the building.
From a builders perspective, you want fewer surface areas to deal with, and you want all the surface area to be counted in a test to ensure that you test less often, and get the result you need sooner rather than later.
Stakeholder potential outcomes with Compartment/Facade testing
Bill payer/Building Owner
With compartment testing, the actual leakage rate of the whole building is not tested, the builder may not have sealed up the building to any particular level that may have been required, and the owner/client paid for something that added zero value.
In order to test a building compartmentally and achieve points for Green Star, the floor will have to be caulked and sealed in every single little nook and cranny, and the builder could be held accountable to duplicate these works on every other floor in the building, in order for there to be any benefit for energy efficiency of the building envelope. Trying to achieve 5m3/h/m2@50Pa, realistically the builder may actually be achieving something like 1m3/h/m2@50Pa if you test the whole building.
The real value of air tightness is getting a building to an airtight state, so that actual savings are achieved. Testing alone does not add any value.
If a compartmental test is suggested, which on face value looks like a cheaper alternative, in reality, it is a riskier and potentially more expensive option, which provides little value for all parties, especially given the amount of risk that is involved.
Internal building envelopes are extremely complicated with ducts, risers, smoke seals, window details and lastly but not least, elevators shafts.
The less risky and most cost effective solution to air tightness is focusing on the whole building envelope, with less surface area to deal with, to get the whole building to an airtight state.
This is why the correct methodology for air tightness should be considered if there is an ambitious target (5-10m3/h/m2@50Pa) that needs to be met. If a target is below 5m3/h/m2@50Pa is required, a whole building testing is the only option.
- Full building test, and invest into getting the building to a more airtight state. A building that may need 12 fans to test to a target of 8m3/h/m2@50Pa. If the builder can achieve 4m3/h/m2@50Pa the fans required go down to 6. It ends up being a cheaper test.
- Guarded blower door testing of a percentage of the building, while separating areas using HVAC zones. When testing compartmentally or with guarded blower door testing it’s hard to know if there is opened ductwork going up or down the building, which could be contributing to air leakage in the building envelope. Troubleshooting then becomes a requirement to understand if the compartment is closed off sufficiently or if the floor is just generally leaky.
* Compartment/facade testing should NEVER actually ever be considered, due to some extra additional works that need to be undertaken to achieve a targeted leakage rate.
Case study of a building air tightness tested in Melbourne
|Level 1 Compartment 3 Fan *||3.7m3/h/m2@50Pa||Building/floors in fire mode, bathroom ventilation taped up|
|Level 2 Compartment 3 Fan *||18.1m3/h/m2@50Pa||Building/floors in fire mode, bathroom ventilation taped up|
|Level 3 Compartment 3 Fan*||19.8m3/h/m2@50Pa||Building/floors in fire mode, bathroom ventilation taped up|
|Level 4 Compartment 3 Fan*||18.4m3/h/m2@50Pa||Building/floors in fire mode, bathroom ventilation taped up|
|Level 5 Compartment 3 Fan *||5.3m3/h/m2@50Pa||Building/floors in fire mode, bathroom ventilation taped up|
|Average Whole building Testing with compartment testing *||13m3/h/m2@50Pa||Average Leakage rate in a case study|
|Whole Building Blower Door Test, 5 Fan Test||5.2m3/h/m2@50Pa||Building in fire mode, all dampers closed off|
^ The table above shows a recent actual case study of a commercial building air tightness test in Melbourne. Note the huge difference in leakage rate from overall leakage from a compartment test compared to a whole building airtightness test.
Guarded blower door testing can be extremely problematic and complicated, and it’s important to ensure you get an experienced contractor to conduct this type of testing on a super large building. Ductwork and elevators complicate the testing methodology significantly.
Whole building testing enables you to confidently take ventilation and HVAC out of the air tightness test and just focus on the airtightness level of the building envelope to the outside environment.
The most cost effective procedure for air tightness testing is to include the building envelope sealing strategies in both the design and construction process. Sealing should be integrated into these processes to achieve a high level of air tightness with a minimum of effort and cost. Once completed a building can be tested with fewer fans and minimal expense.
Authored by Joseph Cheung & John Konstantakopoulos
With contributions by Jan Brandjes