OBC: Stop the Foot Dragging on Air Leakage Testing

Waiting for the Building Code to incrementally ratchet up efficiency every 5 year cycle is too long a wait for high performance housing. The new 2017 version of SB-12 still has a prescriptive package (A1) that merely permits a fiber insulated 2×6 stud wall cavity without air leakage testing – that’s so 1980′s! We’ve had the materials and building science know-how since the 70’s, and with the proven processes of the Passive House approach to designing and building the most efficient buildings, there’s no excuse for not building high performance homes – now.

The good news is that all homes permitted after 2016 will require a ventilation system that has heat recovery. This has been a long time coming and these balanced ventilation systems (HRVs and ERVs), it only makes sense to make the house as air tight as possible. This ensures the Heat Recovery Ventilator earns its keep; there’s no sense installing an HRV in a house with excessive air leakage. Though SB-12 does give a trade-off if the home meets a prescribed air leakage target of 2.5 Air Changes per Hour at 50 Pascals (ACH50), air leakage testing can be used as a trade-off for skimping on other parts of the building envelope. It’s a quirky trade-off that I suspect few will take up, at least that’s our hope.

SB12 table

SB-12 has the same air tightness (ACH) requirement than the 2012 ENERGY STAR for house labeling program. The above table is flexible in that any one of the three limits ACH, NLA or NLR will suffice.

An updated version of CSA F280 was introduced in 2015 for sizing Part 9 building’s mechanical systems. The updated standard arbitrarily defaults air leakage at 4.8 ACH50 for calculating the size of the HVAC equipment AND it reflects the impact the HRV has on heat loss. CSA F280 permits the designer to build a better house by lowering the proposed building’s air leakage rate, but the house has to tested to meet that air leakage rate. The idea here was to stop over-sizing HVAC equipment and design a house with perfectly “right sized” mechanical equipment.

How leaky is a typical new house in Ontario you ask?

We don’t know, but what we know is that we’ve tested new homes that were more than 7ACH50 which is pathetic for a new home. That’s almost twice the default air leakage rate CSA F280 assumes and could lead to discomfort issues at the very least on very hot or cold days where the HVAC system may be undersized for a more air tight house.

Sportscanoe

Ridiculous right? We agree, if you size the motor on a racing car for racing, it might win the race. Unquantified and uncontrolled air leakage in a high performance home with a “right-sized” HVAC system is like strapping a canoe on a Formula 1. Don’t do it. Just because the building code allows you to not test and energy optimise the design, doesn’t make it right. Energy optimise the design with simulations and test your homes to minimise air leakage.

So What’s Holding us Back?

The biggest hurdle to overcome is designer and builder training.  Often we tend to think of large tract builders as the lowest common denominator for building quality, but ironically, a high percentage of new tract-built homes are tested for air tightness as part of the ENERGYSTAR labeling process.

We’re certainly not saying that tract-builders build the best thermal enclosures, but what’s certain is that all trades need air barrier training and it needs to start early in school. Ontarians specifically, aren’t able to divorce the 6mil poly from the air barrier and we all know that putting the air barrier outside means better odds of making those air tight goals a reality.  The confusion between polyethylene vs outer breathable air barrier membranes or continuous foam insulation needs to end and it needs to be taught to architects, carpenters, designers and building officials.

Exterior Air Barrier

Can you spot the air barrier? (Hint: it’s blue, vapour-open and is doing double duty as sheathing membrane.)