Green/Blue Roofing System Question Answered


GWPhius Senior Scientist Graham Wright weighs in on an interesting proposal for a green/blue roofing system and its feasibility for use on a Phius project.

The Question: “…The design team is considering a Green/Blue roofing system. Some of these systems / designs show rainwater being stored underneath the continuous insulation on the roof. We wanted to run these design concepts by you to understand what questions we should be asking and what information we should be gathering in order to model this, whether you have encountered this and have thoughts on how to model / approach this, and/or whether we should steer away from any of these designs altogether.”

The Answer: As far as I can tell, Green roofs and high insulation are not compatible, or, this is a research area.

The concept shown has only a thin layer of insulation. The Opti-Green system in the WUFI database is about R-3 overall. This research paper from 2012 looked at an R-22 roof.  

Green-Blue Roof Graphic

So, first thought: you probably could not do a large area of this and hope to meet the energy targets. It might be OK to experiment with it in a small area. They should ask if what is being proposed has any track record. Has this ever actually been built before in this climate?

Second thought: There is also clearly a tradeoff with the insulation positioned where it is. On the one hand, placing it above the water helps keep the water from freezing. On the other hand, how does the water get up through the insulation to the plants? If there are perforations, then the “fastener correction” calc should be done to derate the insulation. This becomes more troublesome the thicker the insulation is. Also, water flowing and draining away beneath the insulation will defeat its winter performance. This will happen whenever it rains enough during the heating season, and there should be another derating for that.  

Third thought: I think the idea of these is there is an evaporative cooling benefit in the summer. So it might make sense for a cooling-dominated building in the right kind of climate — e.g. one with warm summers but not too dry summers — so you get free rain water and don’t have to pump water up for irrigation. In terms of both energy savings and heat island mitigation, I think a foam-insulated and cool-membrane roof would compete very well with this concept and would be a lot lighter. If they are thinking of doing a whole roof this way, I would suggest doing a comparison to such a baseline case on both cost and simulated performance by WUFI Pro.


The article about green roof modeling mentioned in the WUFI help is here

Energy and Buildings

Volume 145, 15 June 2017, Pages 79-91

Energy and Buildings

A hygrothermal green roof model to simulate moisture and energy performance of building components

D.Zirkelbach S.-R.Mehra K.-P.Sedlbauer H.-M.Künzel  B.Stöckla

NESEA Passive House Tour, Part 2

Hi everyone, hope you got a chance to read part 1 of the virtual NESEA Passive House tour. (Remember, if you’re going to NESEA and you want to join the actual tour of Passive House products that I’ll be leading on the BE12 trade show floor, be sure to sign up for my workshop.)

We left off with the excellent options from Zehnder and Ultimate Air. To finish that discussion, The UltimateAir RecoupAerator  is the only American-made high-performance ventilator on the market that meets Passive House efficiency requirements. It is very affordable, but does have some more maintenance needs. This unit also has the best humidity recovery in ERVs, which is especially interesting for the humid North American climates (of course, it works just as well in the dry climates). One unique feature: the designer has a limited ability to dial in the humidity recovery level according to climate. Very cool!

Now, on with the tour. We touched on airtightness when talking about the excellent 475 product suite.

What about the rest of the envelope? Aren’t we talking super insulation? What about walls? NESEA has a range of Passive House walls on the floor. Here are the highlights: GreenFiber, National Fiber and International Cellulose Corp. are classics when it comes to super-insulated wall systems. Not only was cellulose used in the very first projects in Canada when Passive House principles were invented in the 70s (yes, we do have long-term experience with these wall systems, this is nothing new!) it also rates high in the context of the embodied energy discussion. Given the amount of material required, it’s a valid discussion.

I lean to using materials with very low embodied energy as sound good practice for Passive Houses. Cellulose has one of the lowest embodied energies and is only beaten by — you guessed it — straw bale. Cellulose is also a safer choice when it comes to the hygrothermal wall performance of a super insulated wall. Super insulation means very little heat loss from inside into the wall, therefore less drying potential for the wall and colder exterior sheathing surfaces, which is potentially a higher risk for condensation. Cellulose can mitigate some moisture that might occur, is more forgiving than other materials and if the wall was designed in a diffusion-open fashion (as it should be for a Passive Home) then potential moisture in the wall will dry out during the in-between seasons.

Another popular insulation choice is foam insulation systems. Icynene Spray Foam and Vantem Panels offer two environmentally sound solutions for those who like to use foam products. Foam is liked in this country for very good reasons: in North America we have many humid climates. If we super insulate, we increase potential for condensation in the wall. Add bad construction and failed air tightness measures and the building will have serious problems. To address these risks, many have come to rely on foam’s benefits of added air tightness, moisture retardation and relatively high R-value.

The 2 lb closed cell spray foam from Icynene has none of the high Global Warming Potential (GWP) blowing agent controversy attached to it. It is water blown, and eliminating the concern. Vantem Panels are another excellent alternative. They use Expanded Polystyrene for their Structural Insulated Panels. The blowing agent of this foam product is pentane, which has a GWP of only 7 (compared to approx. 1000 for the most commonly used high GWP blowing agents). In addition, Structural Insulated Panels (SIP) make it really easy to meet Passive House air tightness expectations. The monolithic panels themselves are airtight, if penetrations are avoided or detailed in a very conscientious manner, then the only connections left to air seal are the panel junctures and corners. An even better foam alternative is graphite-enhanced high density EPS used by some SIP manufacturers. This type of foam yield R-values in the range of 5 per inch.

Now, if you’re building a Passive House, you have all the materials in the shopping cart. Now, what else is missing?

You might want to find an architect who ideally also is a Certified Passive House Consultant, CPHC. To find a professional you have three options: Visit the Passive House North East (PHNE) table at NESEA BE12. It represents the forum of professionals in the Northeast. Also, if you are interested in getting hooked into local Passive House events, meetings and local conferences, get involved in the PHNE local meet up groups. It’s a great place to start for local expertise and advocacy work. These folks can tell you everything about available incentives for your Passive Dream Home, which will make it look even more attractive. (Massachusetts and the Northeast are ahead of all other regions in that regard — NESEA might be able to take credit for some of that too!).

If you want to go mod (modular) you’ll find the modular homebuilder who built the very first modular Passive House in the US! Check it out, stop at the Preferred Building Systems booth. The modular project is the Charlotte Habitat for Humanity Home in Vermont. Preferred Building Systems was the first one to put a fully certified Passive House together in the factory. That deserves great recognition for the vision and ability to make it happen!

If you want to build your Dream Home in some other part of the country, go to the PHIUS site to find a Certified Passive House Consultant (CPHC℠). You can sort by location to find CPHCs close to you. PHIUS is the leading technical research organization in terms of all things Passive in the United States and has trained more than 600 consultants over the past five years and certified more than 300 are nationwide. PHIUS also offers PHIUS+ project certification, a conscientious Passive House quality assurance protocol that assures that you get what you pay for. You can also take a look at the certified projects (more than 100 are in the review process).

Also visit the Passive House Alliance-US site. PHA-US is a PHIUS partner, a national membership organization providing education, networking and advocacy for the community. It has 11 chapters and affiliates active across the nation with more applications pending. Its members are architects, builders, manufacturers, other associates, advocates and Passive House enthusiasts. PHA-US has kicked the gear into overdrive in 2012. Member benefits are growing fast. National webinars on Passive House topics are being shared between the regional groups, and conferences are planned. To become involved in this exciting national effort to help make Passive House mainstream with US builders, homeowners and government policy makers, join the PH Alliance today.

Finally, some special recognition: Having been a long-time forward thinker and leader in education about the built environment, Yestermorrow Design/Build School is the first educational institution to license the PHIUS Certified Passive House Consultant training to integrate it into its training offerings. Kudos to this pioneer in so many realms of construction and environment.

This past January, Yestermorrow hosted the first inaugural Passive House Consultant class. It was a great success with great feedback; more classes are being planned for next year. Twenty-four students, instructed by myself and Marc Rosenbaum, huddled in for 9 days straight in what was easily the most intense studying setting ever. Fifteen of them took the final exam on day 9 and 13 passed! Watch out for the graduates from this class, they excelled in that learning environment like no others! And, Yestermorrow’s library is unprecedented in regards to items about Passive House history in the United States and Canada from the 70s until now. This organization is a leader in Passive House education.

Thanks to NESEA and all the friends out East that have given me the opportunity to do this review and I hope to see a few of you on the NESEA BE12 trade show floor! Be sure to sign up for my workshop — you need to sign up for the workshop to take the tour.


One-Stop Passive House Shopping: Join Me at NESEA’s BE12 Trade Show

I’ll continue with the climate-focused case studies from the last installment soon. Right now, though, it’s worth giving a headsup on an upcoming conference event.

In the early days of Passive House in the United States, finding Passive House components – windows, HRVs, etc. – was a project in itself. How far we’ve come! In fact, if you’re interested in building your Passive Dream House, you’ll be able to find everything you need on the floor of the NESEA Building Energy 12 trade show floor.

The national conference of the venerable Northeast Sustainable Energy Association, every year BE12 astonishes. This year in Boston will be no different.

Passive House has been at the forefront of recent NESEA conferences. This year, to meet the growing appetite for all things Passive House, NESEA asked me to lead a tour of Passive House products that will be displayed at the NESEA trade show. (You’ll need to sign up for my Tuesday workshop to join the tour.) And so it will be my pleasure to guide the tour, to introduce them to the forward-thinking folks who’ve made available awesomely performing materials and components to the designers, builders and homeowners of Passive Houses. And made the components cost effective.

Some suppliers have been there for decades: Pioneers such as Stephen Thwaites with Thermotech Fiberglass Fenestration. I used Thermotech windows for the first time in the Smith House in Urbana, Ill. In 2002, it was the only North American window I could find that approached the Passive House specifications for the Urbana climate. Little did I know how dialed-in the window design by Stephen Thwaites really was. After 10 years of experience with Passive House construction throughout all different climate zones I have come to appreciate the smart balance applied in this design. A comparison of the energy balance of a certified European window and the Thermotech windows for my house showed that they were performing virtually equally, Thermotech maybe even a little better. How could that be at somewhat higher overall U-values? It is all about the right balance of Solar Heat Gain coefficient and U-value dialed into the specific climate conditions. Thinner frames to maximize the glass area in a high solar radiation climate is where the money is at. Passive House two thumbs up for an excellent North American manufactured fiberglass window perfectly designed for cold and sunny climates.

And then there is Pinnacle Window Solutions, with another classic, SeriousWindows. Serious has been used in many Passive Houses across the nation. It is a North American manufactured fiberglass window featuring excellent U-values well suited for cold and very cold climates. The solution of the suspended plastic film technology instead of an additional glass pane to increase the R-value allows the creation of a window that features essentially quadruple window performance, while maintaining a manageable weight. This is an interesting choice for the cold and very cold and perhaps more cloudy climates in North America. The high R of SeriousWindows comes at a price: the Solar Heat Gain Coefficient goes down the better the R and the visible transmittance is lowered as well. In cold climates with very good solar opportunities, a high Solar Heat Gain window with less R might perform just as well or better. This only reinforces what we have been teaching in the PHIUS trainings: the right window for the right climate. And Serious definitely has a place at the table.

In the last couple of years many entrepreneurs have brought new options for high-performance European Style windows. For example, Intus Windows has been turning heads with amazing Euro-style windows at very competitive prices (typically the Euro style window comes at a price). European Architectural Supply and New England Fenestration, LLC offer more European window varieties from other manufacturers such as Schueco, Macrowin and Unilux, all superb performing windows, all of them featuring thermally broken frames certified for the cool moderate climate through the Passivhaus Institut.

Still another excellent choice: Bieber Windows, and ZolaZola’s booth will be staffed by Passive House veterans Florian Speier and David Gano.

Go and visit — you have to see and touch these windows to understand the quality.

Windows are critical to Passive House construction, and so are systems components for minimized micro-load mechanical and ventilation systems. They put Passive House within economic reach. On this front, too, NESEA will also include many exhibitors. In addition, I’ll give a workshop at NESEA on Tuesday on cost effective integrated mechanical systems for North American climates.

In the early days, I would begin designing Passive House projects by first sketching the continuous air tightness layer. Later that focus shifted slightly toward laying out the mechanical system and the duct system. I am in love with Passive House mechanical systems simply because I never dreamed of being able to design it myself, and being able to really integrate it into the design process. They are in their own right very elegant and if well done one the key quality indicator of a Passive House. Hence, Passive House homeowners are actually proud to show off their mechanical rooms.

My latest interest has shifted towards heat pump hot water heaters as viable Passive House solutions, even in cold climates. Stiebel Eltron, Inc. makes such an appliance. It is a true super-insulated tank a Passive House enthusiast dreams of. Our Passive House builder, who installed it in our last project, was blown away in terms of efficiency and quality. By far the most energy efficient solution on the market, the unit is slightly more expensive than other options, but a good value. Another Passive House two thumbs up. Heat pump hot water heaters are becoming a very interesting solution for integrated mechanical systems designs for Passive Houses. Located inside the thermal envelop in a super low load home (including cooling and latent loads) the contributions to cooling and dehumidification by a heat pump hot water heater can be significantly helpful and in some cases all it takes.

And then there are the mini-split heat pumps. NESEA attracted two significant Passive House players, Daikin AC Americas, Inc. and Mitsubishi Electric HVAC. The mini-split systems are quickly becoming the most popular heating/cooling and dehumidification systems for Passive Homes. Daikin and Mitsubishi are among the manufacturers offering a heat pump slim duct built-in option. The units can be obtained in small sizes for single-zone and multi-zone systems (just what we need for Passive Homes) starting at 6k BTU/h and up. They generally have very good SEER ratings, the slim ducted options have a little lower rating, but are still solid in cold and mixed humid climates with larger cooling and dehumidification loads where integrating the space conditioning in the ventilation system is preferred.

Another interesting product from Daikin is the point source “Quaternity” Heat Pump wall mount unit. The SEER rating is 26.1 and it has an additional feature for warm humid climates where dehumidification might be needed when there is no cooling need: a dehumidification mode only. This unit is available in three capacities, 9k, 12k and 15k BTU/h. The Mitsubishi’s wall units have one of the best SEER ratings (26) and operate down to very low temperatures, making it appropriate for cold and very cold climates.

Mitsubishi has also truly excelled in terms of control of its heat pumps. Recently Mitsubishi introduced wireless technology eliminating the need to run wires and offering a centrally located thermostat just the way we like it.

Wagner Solar Inc and Tarm Biomass offer extremely low source energy heating options for multi-family Passive House projects (we are seeing more and more coming into the certification process). One major challenge of the multi-family typology is meeting the source energy criteria. Both companies sell wood and pellet boilers that offer excellent low carbon heating systems options. One boiler can be used for an entire medium-sized apartment complex if combined with Passive Solar. The Tarm Biomass boilers range from 75-80% efficiency for wood, 85-87% for pellets. Wagner Solar Inc offers a Pellet boiler with the efficiency of up to 93%. Smaller units for single family are available in Europe in combination with a hot water heat exchanger. It’s worth checking on availability of these systems. They are fine low source energy solutions for cold climates with predominantly heating requirements and lots of wood.

475 High Performance Building Supply is bridging the gap with many products not only in regards to air tightness but also over into the ventilation system realm. This Brooklyn, NY-based outfit has an interesting suite of specialty products mainly imported from Europe. They offer airtightness solutions from INTELLO plus and Pro Clima, a wood fiber sheathing/insulation product from Gutex, triple pane skylights from Fakro, and Foamglass from Pittsburgh Corning.  They offer a through-wall decentralized apartment venting solution with a ceramic heat recovery core from Lunos and a compact heat pump by a Swedish company Nilan (not available yet but in testing – coming by year-end according to 475). The configuration is cost effective for cities, as it saves a lot of space by comprising all the mechanical functions of a Passive House into one compact box the size of a refrigerator.

Another high performance ventilator on the NESEA floor is Zehnder America, Inc.; it’s still the only game in town on this show floor in terms of high efficiency heat recovery ventilation. As important as high efficiency heat recovery ventilation is to Passive Houses, we still hope for a little more competition and for the North American ventilation system manufacturers to come up to speed. In the  ventilation systems by Zehnder — integrated solutions for pre-warming the incoming air through ground source heat exchange and fast flex ducting systems – continue to impress. New this year: it received the Home Ventilation Institute Testing stamp of approval. The results show the heat recovery efficiency of this HRV under this testing protocol coming in second with 93% Apparent Sensible Effectiveness (ASE) which is topped by only one other ventilator made and sold in America, the UltimateAir RecoupeAerator with 95%. Zehnder products are a little pricy, but with the ease and time savings of installation and an impeccable maintenance record, it seems a well worth investment.

That’s it for part one of the tour…here’s part two, where we get into some more airtightness and wall system products.