4 Hurdles to Hitting Passive House Performance & How to Overcome Them
Passive House performance is the future of building. As with any trip there are obstacles. Yet professionals new to Passive House can be disoriented and may not readily see them. What's going on?
The Passive House Paradox
On the one hand Passive House is simply a rediscovery of basic building science with a more rigorous arrangement of what builders have always done. It's an invigorating back-to-basics approach.
On the other hand, Passive House is a revolution in approach, where the goal of human comfort results in great energy efficiency. It's a transformative revelation.
Back-to-basics and transformation. It seems paradoxical. And these fundamental re-discoveries and revelations challenge our typical project delivery thought processes. So in this new world of Passive House, it is easy to confuse priorities. But we can figure this out.
4 Fundamental Obstacles to Success
- Certification not a goal (The Context is not properly set.)
- Insufficient professional training (The Preparation excludes team members.)
- Starting without integrated & optimized modeling (The Process is short circuited.)
- Components specified are of inadequate quality (The Tools are not carefully selected.)
With these identified, let's dig a bit deeper.
1. Certification not a goal
A Passive House is a predictable product. The predictability is based on, and allows for, the full integration and optimization of the building design. The context for making this predictable product a reality is certification. And like consumers looking for Certified Organic or Fair Trade product labels, the certification provides a signpost the public can recognize.
Certification to the Passive House Institute's Passive House Standard, prevents the accumulation of lazy compromises that result in a loss of predictability and in customer dissatisfaction. PHIUS certifies to a similar but different standard that also strives for Passive House performance, called PHIUS+.*
Then again, certification isn't the point - if you have the discipline and track-record of delivering Passive House performance, you don't need it. Yet if this is one of your first few Passive Houses or your first of a particular use group, then it really will prevent death by a thousand cuts. Get the design pre-certified ensuring that what is going out to bid is designed to hit Passive House goals. Then institute the final certification process during construction and ensure that what is built matches what has been designed.
PHIUS is the sole certifier of the PHIUS+ standard. There are seven Passive House Standard certifiers operating in the US and Canada - all members of the North American Certifiers Circle - to work with. Make certification a goal.
2. Insufficient professional training
How often do we unnecessarily struggle to get something done right simply because we didn't take the instructional webinar, the few day course or even just read the directions? With a bit of specific training, what previously seemed baffling and ridiculous, becomes logical and effective. The same is true for Passive House and the professionals working on it.
The architect, MEP engineer, structural engineer and contractors must all get trained. It would also be good to have the developer or building owner, the real estate broker, the landscape architect - every professional tied to the success of the building - get some specific training.
There is a five day Tradesperson training for general contractors, carpenters and site managers. (It is also a good introduction for non-architects/engineers). For architects and engineers there is an eight day Consultant/Designer training. These trainings are regularly held by the Passive House Academy and Passive House Canada. PHIUS also conducts builder and consultant trainings. Get the whole team trained.
3. Starting without integrated & optimized modeling
Do you set out on a long trip without mapping it first? Without looking at current traffic conditions? Without rechecking traffic conditions as you drive? If so, you might make it in the time and effort you hoped, but it's more likely you won't. And for Passive House to be predictably cost effective** and optimized you need to engage the map before you set out and recheck it as you go. The map is the model. The pre-design and schematic design phases need to incorporate PHPP and/or designPH modeling. PHIUS works with Fraunhofers's WUFI Passive modeling program. Assumptions can be easily and quickly tested, and adjustments made as you move through the design process. Early integration avoids surprises and enhances predictability. The PHPP is the benchmark for Passive House performance and can be purchased online at 475. Do a PHPP or designPH model on day one.
4. Critical components specified are of inadequate quality
High Performance goals often require that critical components also be high-performance. Substituting common materials at these critical locations may provide a temporary work-around but is not a robust solution and they should not be relied upon. Reliability of critical components is crucial for long-term robustness and they need to perform as advertised. For a variety of products the Passive House Institute has developed stringent component certification criteria. Passive House Institute certified components are listed in a database. And while some may cost more initially, the optimized performance achievable can make them affordable, in installation and operation. We outline three areas where we've seen particular component shortfalls:
Airtightness & vapour Control Materials
Source: Ecological Building Systems
OSB: OSB has failed in Passive House airtightness tests in America. OSB manufacturers don't control for airtightness and don't report airtightness. Leaky OSB is such a concern that GreenBuildingAdvisor wrote a blog post specifically on it. We want our OSB to be dry to avoid moisture damages but it is at its leakiest when dry. Use OSB with great caution.
Gypsum Wall Board (GWB): The material is airtight but the installation won't be a season or two later. GWB regularly stops and starts, making air barrier continuity exceedingly difficult. GWB joints when used as an airbarrier crack with the seasonal movement of the building and as a result require continual maintenance. And GWB is a sacrificial material - it gets beat up under normal usage - and we shouldn't use sacrificial materials as critical control layers. See 5 Reasons Why Airtight Drywall is Obsolete.
Spray Foam: Spray foam is sold as an airtight material - open cell over 5" thick and closed cell at any thickness. While the material itself might be, like GWB certainly is, the installation of spray foam, as with GWB, will fail over time. And on site manufacturing of this highly toxic and sensitive material is prone to defects - often covered up by GWB before the defects reveal themselves. For Passive House performance the unpredictability is not acceptable. Use it as an insulation if you must, but use it as an airtightness measure only as a very last resort. (See: Is Foam Evil? A New Paradigm of Foam - Less is Best)
Much better to use materials specifically designed for the task at hand: See INTELLO Plus: airtight in the lab for ASTM 2178 and onsite, and The Pro Clima SOLITEX Mento Difference.
Connections:Common caulks, sealants and cans of Great Stuff spray foam are often used in typical construction to connect sheathing, membranes and seal around penetrations. We see Passive House failures in the lack of continuity in these connections or their inability to fully seal penetrations. Because these connections need to last the life of the building - or its performance profile will dramatically change - durability of these seals should be part of the design, connections need to be durable, flexible and easily verifiable. One can avoid such problems by installing the best tapes, that have been rapid age tested for over 100 years and EPDM pre-cut gaskets: KAFLEX for wires and ROFLEX pipes and ducts - all part of ProClima airsealing system. Additionally, please make sure the window installation is as good as the window. (sealed on both side and insulated in between - see: How to Prepare for High Performance Windows)
Plywood:Good track record for airtightness. Unpredictable for vapour control. The manufacturers don't control product for either aspect nor do they report testing for it. As insulation levels rise we need a more reliable solution. See Why The vapour Curve Matters.
Latex Paint: Latex paint is often considered as a contributor to making drywall a class III vapour retarder in common construction. Again, in its measured effectiveness, the data is non-existent or imprecise and unreliable (ranges from perm 8 to 25+). And even if it worked as reported as a material (latex paint manufacturer's do not provide a perm rating), a painted interior GWB surface typically has so many holes, any reliability of vapour retarding can be effectively undermined. See Air & vapour, Part 2: The Importance of Air Tightness.
Airtightness and vapour control is what we specialize in providing the Passive House and high-performance markets. Manufactured by Pro Clima, we offer a complete system of airtightness and moisture control - designed and tested to the most stringent and specific requirements.
Common buildings have ineffective exhaust-only ventilation equipment. (See BSC BSI-012: Balancing Act - Exhaust-Only Ventilation Does Not Work)
In Passive Houses we need continuous, distributed and balanced ventilation that has very high levels of heat recovery. Many of the units on the market today fail Passive House requirements for the basic reason that the heat recovery is not high enough. Unfortunately the traditional American testing protocols have allowed US manufacturers to hide these results - not accounting for airstream mixing (cross contamination that degrades air quality as well) and contributions of motor energy. These uncertainties can result in discomfort and significantly higher power usage - reducing predictability. Andrew Peel and Tomas O'Leary wrote an informative paper on the on the subject: Mechanical Ventilation of High Performance Passive House Buildings in North America.
We are proud to offer the Brink FLAIR ERV - HRV.
Windows and Roof Daylighting
Windows and roof daylighting are in many ways the most complex and therefore, the most critically important, functioning to provide: very good airtightness, high insulation values, thermal comfort, passive heat gains and visual connection, all in a predictable balance. Windows are fully integrated into the thermal enclosure. A poorly performing window or skylight can counteract all the good work done to the enclosure elsewhere. On the other hand, very good quality windows and skylights can actually enhance and make more economical the rest of the work of the enclosure - lowering insulation level requirements for example - in a more predictable manner. 475 is happy to provide unit skylights and glass roofs by Lamilux. We also offer Passive House compatible flat roof unit skylights by Lamilux and pitched roof skylights by Fakro.For critical components specify high-quality materials.
We can make affordable and predictable buildings that perform at Passive House levels today. If you address these obstacles head-on you will too. We are here to help - please don't hesitate to contact us.
* Passive House as it is understood the world-over today, was developed and formalized by the Passive House Institute, an independent research institute, in Darmstadt, Germany as the Passive House Standard over 25 years ago. Today there are several derivative standards that include Menergie-P and PHIUS+, that strive for Passive House level performance but have developed their own proprietary programs. Today in America, Passive House and PHIUS+ are the two dominant programs.
** Cost effectiveness and affordability are critical and can also be seen as obstacles to achieving Passive House performance. Size of project and size of budgets are huge factors. When projects and budgets are smaller, it can be more difficult, and as project size and budgets grow it is easier. Another big factor is familiarity of professionals: architects, engineers and contractors, as well as availability of components. As professionals gain in experience, the costs flatten. For example airsealing to 0.6ach50 need not cost more than hitting 3.0ach50. And windows, the biggest single upcharge historically are fast falling in price. So this cost curve is dynamic and what seemed unaffordable a year ago, may be affordable today. But where we see a history of delivering Passive House projects at cost parity or even for less money - is when Passive House is integrated as a basic goal on day one, and everything is on the table for optimization. And frankly, if at the end of the day, the optimization comes up short and you only reach a Low Energy Building or a very good Net Zero Energy Ready building, there is no shame in that - we simply need to push as far as we can....and then some. :) This subject is certainly worth more discussion and we'll be providing a blog post about this specifically in the near future.