How Much Insulation Do You Need in a Passive House?

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Passive house has a reputation for requiring ungodly amounts of insulation. It grew out of the superinsulation movement after all. If you're familiar with any passive house projects, you may be thinking about double-stud walls that are a foot thick or regular walls with 6 to 12 inches of rigid insulation on the outside. But how much insulation can you use and still meet the requirements of the Passive House Institute US (PHIUS)?

In 2014, PHIUS announced  their new adaptation of the passive house standard that came from the Passivhaus Institut (PHI) in Germany. A lot of scientific work went into developing the new standard, including modeling a test home in the various climate zones of North America. Dr. Joe Lstiburek's compay, Building Science Corporation, helped with the work, which was part of the Building America program. You can download the full report (pdf) from the National Renewable Energy Lab (NREL) website.

One part of the work done to support the adaptation was modeling a test house in different climate zones to see what parameters they needed to reach the targets for primary energy and peak and annual loads. The table below summarizes the insulation levels for IECC climate zones 1 through 8.

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As you might expect, the colder the climate, the more insulation you need. A large part of the US and Canadian populations are in climate zones 2 through 5. In climate zones 1 through 3, you could build a Passive House with 2x6 walls. In Fairbanks, Alaska, on the other hand, you'd need some serious thickness in your walls to get R-89. But it takes a special kind of person to live in Fairbanks, so you should have special walls, too, right?

The 10th anniversary (11th annual) North American Passive House Conference is coming up in September. The Early Bird deadline for registering is this coming Monday, 18 July. Get yourself registered and come learn more about what Dr. Joe says is "the only place where real innovation is happening."

 

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Passive House — The Only Place Where Real Innovation Is Happening?

Dr. Joe Lstiburek Surprises Passive House Conference Attendees

 

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Comments

David Eakin
Jul 15 2016 - 12:22pm

The thing that I have always admired about the Passive House program is that the requirements are solely based on meeting a specific energy usage regardless of geographic location, solar exposure, air tightness, and insulation against expected outside temperatures. Most other programs are based on current energy costs (e.g., Energy Star, Pretty Good House), especially alternative costs in using solar PV vs investing in the building shell or that using energy (at present costs) is more cost efficient than investing more in construction. The thing I do not like about all of today's programs (Passive House included) are there are no real-time measurements of indoor air quality (and hence no real guarantee of success; it is assumed that ventilation will solve all ills); there is no regulation of indoor relative humidity (other than conventional AC) which has worked against building in high-humidity areas; it is assumed that residents know best how to mechanically regulate indoor comfort and so the requirement for expensive openable windows is inviolate - regardless of the extensive/expensive HVAC design/controls, whether the occupants are home, any security concerns, or if the occupants are opening the correct windows for optimal airflow (there are much, much better ways to provide daylighting, indoor comfort, and outdoor views without emulating Western European manor homes).

Bill Swanson
Jul 15 2016 - 1:45pm

I've been trying to think of a low labor roof with a high R-value. I like the idea of SIP's but they peak out at R-50 with a 12" thickness. Then I found insulated standing seam roof panels that are finished surfaces on 2 sides. A 6" thick panel is R-48.

Has anyone ever combined the two? SIP panel on the bottom, maybe cedar breather between, and an insulated standing seam panel on top?

Or I could just stick with the affordable option of very thick cellulose.

John Nicholas
Jul 15 2016 - 11:31pm

David, Energy Star is not about costs. It is about doing things right, following the checklists. It is about checking your work, the checklists. Checking someone elses work, the Blower Door and Duct testing.

It is about durability, with the water management details. I am in CZ 4 and find that 5 ACH at 50, R-13 walls, R-38 attic more about end use energy in BTU's. I've seen the same house built on our local investor owned utility and a mile down the road on the REC. Totally different costs, but 1 HERS point lower because of the Blower Door on the house with the higher $$.

David Eakin
Jul 16 2016 - 11:25am

John - the recommendations (prescribed R value, etc.) in the Energy Star program are driven by a balance of current energy prices vs building prices. That is why they have changed over time as energy costs have gradually risen and building costs (at least for framing and insulation) have flat-lined. Is it better than code? Absolutely! Is it best industry practice? No (what's that Passive House air infiltration and insulation requirement at your climate zone again?). Can it change over time due to energy/building cost fluctuation or political pressure? You bet. Passive House standards will need to change to accommodate climates other than Germany, but not the costs nor political whims.

John Nicholas
Jul 16 2016 - 4:05pm

David, Just like a code, which is the poorest house you can legally build; Energy Star is a voluntary program that has a minimum. A builder can build to the minimum or build to exceed the minimum. Our local Habitat for Humanity builds a 3 bedroom Energy Star home. This home has to have a HERS Index of 78 or less and meet all the water management and durability requirements of ES. Typically these home score 72 - 69 depended on how much they exceed the blower door test, which effects duct leakage. Until last Wednesday when I presented the Certificate to their newest homeowner with a HERS Index of 61. Still Energy Star certified.

Want to build to the voluntary program of Zero Energy Ready, you have to build to Energy Star first.

Want to build to the voluntary program of Passive House, certified by PHIUS +, you have to build to Energy Star first.

Is a builder, that builds to meet and exceed the local market with a minimal Energy Star Home, a bad builder because there is no Energy Code that requires insulation in any house? Is the same builder in this market that only insulates attics to R-25 and then says it is the level all builders build to a good or bad builder.

No they are doing the best they can. The one is pushing the bar in his market.

David Eakin
Jul 17 2016 - 3:12pm

John - I mostly agree (except about that "They are doing the best they can." bit.) Even "built to code" is better today than in the past. The main frustration I have is that the prevailing attitude (exclusive to residences - doesn't apply to commercial buildings, cars/trucks or any other manufactured goods) is that houses should last forever, that "old is good because it has 'character'", and that real estate increases in value over time. If we (as a society) buy into this, then these "forever" houses should be constructed with the best industry practices of the day instead of the "Meh, it's good enough." practices most builders adopt. It is how we have our current dilemma in existing housing stock. Conversely, if we do not buy into that - then every 50 years each residence needs to either be re-constructed to meet the "code" of that day or be deconstructed and recycled.

Stan Rusek, PE
Jul 19 2016 - 7:49am

Hi. Great article. What is your opinion of using vip, vacuum insulation panels, for these homes? My opinions follow. Current SOA of vips to me is poor in that they will always leak out to R/in of 4 to 8. The vacuum enclosure bags are permeable and air will slowly leak in. They remind me of potato chip bags! They are fragile and they are expensive go figure. But thermal resistivity though fleeting can be very high, 50 R/in for current fumed silica vip. Now for the plug. I have a better idea. I am the inventor of the AURA stainless steel foil vip superinsulation panel that OC produced in the mid-1990's for about 5 years, and no longer available. AURA products were sold to Whirlpool and others for super efficient refrig appliances at around $4 per square foot at 0.75" thick. The life expectancy of AURA is incredible since they are hermetic in nature with R/in performance of 75 to 100. Net effective R values at 1 inch range between 45 and 60 including the thermal bridging of the thin 304L stainless foil. I have recent test data for panels over 15 years old that supports the fact that center R values are as good as the day they were made. I am thinking of building a plant to make them again. Prototypes are available for thermal testing and the like if one so desires. My current focus is that I work with clients in the very high and very low (cryogenic) temperature ranges where my rugged new hermetic Century panel makes the most sense. But building applications would benefit greatly, especially these special homes, my opinion. The new Century panel would not be cheap yet but could come down to around $4 per square foot at R 60 effective resistance. So there I put my plug in for Century as an insulation candidate! My architect daughter Samantha (PH qualified) in Austin can't wait until Century is available for her designs there. I have been working on improvements to the old AURA design for the last 10 years and I am ready to rock and roll. Just need an angel investor, some ground, some good labor, and it would be ready to produce in 18 months... I am also getting some interest from OC (Achilles) on same subject so maybe they are ready to rock and roll on this too! I am currently the R&D Director at Quietflex Daikin here in Houston as well as consultant for my company Century Super Insulation, LLC.

Kris
Jul 19 2016 - 10:08am

With the amount of mobility in the workforce I suspect average homeowner views the single-family dwelling as an intermediate-term investment that is expected to deliver a modest return when they move in 5-7 years. I suspect a majority of code-built tract houses will make it that far without a problem.

Thor Skov
Aug 17 2016 - 1:37pm

David,

I am building a home in Seattle and I have a couple of questions. How would you take real time measurements of indoor air quality and what would you measure? Also, is there another way to control humidity besides A/C? Thanks.

John Nicholas
Aug 17 2016 - 2:11pm

CZ 4, My location, has a summer design condition of 97°F and 72% RH; Seattle CZ 4 Marine, is 86° F and 66% RH. I would look at a whole house dehumidifier of some type, if you don't want to use a forced air AC. Your area does need dehumidification.

David Eakin
Aug 17 2016 - 6:34pm

Thor - I would recommend going to John's blog space as he has the recommended items (from a University of Pittsburgh study) to measure. The difficulty is that there are no inexpensive, accurate, integrated measuring devices presently for most of those items. Even commonly-available CO meters fall short of recommended safety rules. As far as reducing humidity w/o AC, Matt Risinger (Austin, TX; YouTube channel) often uses ventilating dehumidifiers - and sometimes stand-alone dehumidifiers - in addition to any heating/cooling systems in his location. I believe that a well-known commenter from Ohio is also recommending them for his clients too.