LEED can learn lessons from Passive House
It looks like no single green home certification system will give a homebuilder the whole picture on a home’s performance.
Zack Semke of Seattle-based home builder Hammer & Hand writes in his blog that the discipline of Passive House can address issues with LEED certification. The result is a whole picture of a high-performance home design.
In his blog, Semke writes:
"The Passive House building standard wears blinders. Its sole laser-like focus is on building energy performance and durability.
So most Passive House practitioners recognize that broader sustainable construction approaches like LEED, are naturally complementary. Passive House brings depth, promising revolutionary reductions in the carbon footprint of our built environment. LEED brings breadth, addressing environmental concerns like toxicity, renewable materials, water conservation, stormwater management, waste reduction, access to alternative transportation and much more.
To truly build "green," we understand that we need both depth and breadth."
He talks about the company’s experience in building the The Karuna House, the first building in the world to achieve the trifecta of LEED, Passive House and Minergie-P-ECO certification.
“The broad green mandates of both LEED and the “ECO” portion of the Swiss certification Minergie-P-ECO ensured that the Karuna project team look well beyond energy performance in its definition of sustainable construction.
But the Karuna House also proved how powerful Passive House’s advanced understanding of building performance can be for LEED practitioners and their projects. Because just as Passive House is “blind” to broader sustainability issues, LEED has its own blind spot: it can’t see thermal bridges, at least not without help. Thermal bridges are elements of a building (steel beams, building junctions, window-wall interfaces, etc.) that allow heat energy to escape across the building envelope. And while they may sound wonkish and technical, thermal bridges demand respect: they are anathema to high performance building, providing an escape route for energy to heat (or cool) to circumvent super-insulated assemblies and for moisture to penetrate walls and wreak moldy havoc."
The Hammer & Hand team found that the LEED tools for determining building energy performance for LEED projects – the HERS Index as modeled by REM/Rate for residential projects, and eQUEST for commercial projects – generally ignore thermal bridges.
“We could have built a Karuna House full of thermal bridges and it still could have achieved LEED Platinum status. But it would have failed Passive House and Minergie-P certifications miserably.
"Because Karuna’s purpose is to provide lessons for green builders, I’ll close this post with a few findings from the project that we think are relevant to LEED professionals, Passive House designers and builders, and the green building community as a whole:
"Not only are the broad scope of LEED and the singular focus of Passive House complementary, a paired approach is actually vital in achieving a truly “green” project. The Swiss Minergie-P-ECO designation recognizes this, with its "P" roughly equivalent to Passive House and its “ECO” similar to LEED.
"Effective energy modeling is vitally important in the design process of high performance building and tools borrowed from Passive House, like the Passive House Planning Package (PHPP) and WUFI-Passive, can help LEED projects eliminate the thermal bridge blind spot.
"As code bodies reach for increasing levels of building energy efficiency, the success of future performance-based code will depend on the same comprehensive energy modeling borrowed from Passive House that LEED projects can benefit from.
"Our big, collective goal – averting catastrophic levels of climate change through meaningful reductions in building greenhouse gas emissions (as called for by the 2030 Challenge) – therefore depends on better modeling that takes things like thermal bridges into account. Fortunately those tools are readily available, and improving in accuracy and ease of use."
Photo courtesy Hammer & Hand.
Read more about Passive House.