The Trent Forensics Zero Carbon project requires a net zero energy and carbon performance in order to be certified by the International Living Future Institute’s Zero Carbon Certification program. For a large institutional facility to reach that goal we needed to ensure both high levels of thermal performance and air-tight construction. Endeavour was hired to be the on-site air tightness consultants for the project to ensure this goal was met.
Thermal performance is pretty easy to achieve: add more insulation. With energy modelling by ZON Engineering, we were able to determine that we required R-24 under the slab, R-40 for our foundation and exterior walls and R-100 for the roof. Getting there only requires adding enough insulation material to meet the requirements.
The “unseen” aspect of thermal performance is air tightness. All the insulation in the world won’t help energy efficiency if the building enclosure is leaky! Imagine a well-insulated building with a window left open… it will be colder in the winter than a poorly insulated building with all the windows closed. It seems obvious to close all the windows, but what if you can’t see any of those “windows”? Most buildings have a lot of air leakage through abundant small gaps and holes in the building enclosure; at seams between foundation and walls, between wall and roof and all through the building where materials converge and holes for services are intentionally made. Surprisingly, these can add up to be the equivalent of an open window, or two!
High performance buildings must be air tight to achieve goals like net zero energy use. The Trent Forensics Facility had a target of 0.6 air changes per hour at a pressure difference between inside and outside of 50 Pascals (expressed as ACH50). It takes special attention at all phases of construction to ensure a high degree of air tightness.
For this project, we relied on sheet barriers to provide the main air tightness barrier. This included a 10-mil poly barrier under the foundation slab, Intello Plus “smart” barrier on the interior walls and ceiling and Mento 1000 for the exterior walls.
Applying sheet barriers is the easy part. The real work in achieving air tightness is ensuring all the connections between barriers and all the junctions and penetrations are properly sealed. This involves using tapes like Tescon Vana and gaskets like Roflex.
In order to ensure that the building will meet its air tightness requirements, ZON Engineering performed an initial air tightness test when the enclosure was complete but the finishes were not yet applied. This gave the team at Gerr Construction and ourselves the chance to inspect all the barriers while the building was depressurized and fix any leaks we found. This test resulted in a score of 0.33 ACH50, well under our target.
A final air tightness test was performed when the building was complete. An initial reading of 0.92 was above the intended 06, but we found issues with the seals and glazing in the doors (which were not yet finished), and when we sealed those with tape we achieved our intended 0.6 ACH50 result.
The team at Gerr Construction deserves much credit for taking on their first air tight building and achieving a very high goal! And the building is now ready to meet the Zero Carbon Certification.
