Comments on: A Really Cool Net Zero Energy Home in the North Carolina Mountains

By: Jeff Carroll

Jeff Carroll — Fri, 28 Feb 2014 23:06:29 +0000

Allison,

Allison,

Now that you've gone through this cold of a winter, I'm curious how the passive solar performed.

We're building a passive solar house in Missouri of only 1650 sq ft, and I don't believe radiant will be worth the cost in such a small space. We're curious about your opinion as to comfort level with the slab when the radiant heat is off, if you can say. We'll likely install mini-split ductless over a R10 insulated slab-on-grade.

Thanks for any information.

By: Art Smith

Art Smith — Wed, 27 Nov 2013 23:53:02 +0000

Alsion-

Alsion-
One of the more practical net-zero homes recently in the press. However, the SIP story, like politics tends to be nor fully told accurately. They simply are the best building product we should be utilizing…and I will be covering why in my next book “SIMPLE SIP HOMES” … as you visited in certifying my recent Energystar rated R40 SIP & Timber Truss project.

By: Brian Knight

Brian Knight — Tue, 20 Aug 2013 22:40:58 +0000
Having been in this house
Having been in this house several times I can attest that it is just as cool in person as it reads in this article. I do have to question the claims made about the SIPS being a builder that has long preferred them.

It can be tough to compare costs between SIPS and stick built mainly due to labor costs. SIP material costs tend to be more but labor costs are almost always reduced with the proper planning and execution. As with everything high performance, the details are what matter most.

I know that their excellent builder has experience with SIPS but have also heard rumor that they prefer not to use them. Iam pretty sure that the builder does not usually do foam sheathing which makes it tough to get comparable labor costs especially never having done the same plan both ways. Iam sure Matt and Amy relied heavily on their input to calculate the labor portion of the savings.

Walls are one thing but doing the roof differently could have changed the entire look from the inside with its impressive vaults. Its tough to compete with SIPS on full vault situations from a performance and labor cost standpoint.

I am of the opinion that when you add up the additional labor and material costs to properly seal the structural sheathing, foam sheathing, Airtight drywall and detail needed to properly secure the siding and trim that SIPS will be cost competitive with much fewer joints to air seal and give more continuous insulation overall. As others have noted, ORNL has had favorable cost effective results as well.

There is also the issue of square footage. SIPS (especially urethane) offer the most R per inch of any common building assembly. If you were to use a 2x6 with 1" foam to get roughly the same R value as a 4.5" urethane panel you lose 2.5" of interior floor space to increased wall thickness. On this house with its daylight basement wall and upper story wall panels, this could add up to around 40 sqft. 40sqft x 150$ per sqft = 6000$ of wasted space.

I also have to question using energy modeling software to look at the simple payback of any single detail involved in building an energy efficient home. I think following the 2012 IECC prescriptive minimums is good practice but when you look into the details with the performance software, it seems like you should cut corners everywhere probably to avoid overpromising on savings among other issues.

Other than the wild payback calculations and outright claim of SIPs not being cost effective, this was a great article on a great home. I hope more folks follow their example!

By: Chaz

Chaz — Wed, 08 May 2013 20:33:43 +0000
Allison, you state that the
Allison, you state that the Superior walls have a continuous R-value of 12.5. I recently toured a superior walls plant and the XP board in the wall is not continuous. It does not go behind the 2 3/8 inch concrete stud. The stud is wrapped in 1 inch of EPS foam. I am not sure what difference that would make in a HERS rating.

By: Curt Kinder

Curt Kinder — Thu, 02 May 2013 06:45:24 +0000
What's nifty about the SIP
What's nifty about the SIP debate is that we can garner a similar result (air tight + well insulated wall) at least 4 different ways, to wit: SIP, ICF, continuous exterior insulation, or sprayfoam. In other words, there is more than one way to skin the cat, whether cooked, (contact made with hot stovetop) or raw (cold stovetop)

I'm pleased to read that a heat pump water heater was planned. It took a mile high pile of subsidies to make solar thermal surpass the HPWH. When the subsidy community smartens up and quits delivering solar thermal nearly free of charge, HPWH will be there to take up the slack and we can move on to better strategies such as neighborhood PV.

I'd like to see more done with refrigerant desuperheaters and grey water heat recovery, though neither is cost effective for all but the biggest single family households.

I'm all about craft beer and Asheville is centered in pretty country, so perhaps a road trip is in order.

By: Kent

Kent — Wed, 01 May 2013 16:32:46 +0000
Matt or Amy I know you chose
Matt or Amy I know you chose to use SIPS in your personal house because had been impressed with their performance from your experience with them as HERS Rater. Yet, you emphatically claim different results in your own house. Is there something unique about your house that affects the energy savings or how you are callulating the energy savings that causes it to have such a poor payback. Your numbers are just to extreme to be believable. You certainly have had enough experience with SIPs to know what kind of performance to expect and you chose to build with SIPS. The way you have presented it, it comes acrosss as though you have an issue with your SIP supplier and are trying to discredit SIPS.

By: Charles

Charles — Wed, 01 May 2013 16:01:38 +0000

Mark Twain once said
Mark Twain once said something like “A cat who touches a hot stovetop will never touch that stovetop again. And he will never touch a cold one again either….” We must be careful what lessons we choose to learn from an experience. To say that the SIPs would take THOUSANDS of years for a positive return on investment is misguided at best. A basic tennent of good building science is to START with the building envelope – and they have done that. Then they seem to ascribe all of the energy savings to something else and only allow the building envelope the last of their savings. Even according to Allison’s own “sizing rules of thumb” for a super-insulated home their system appears to be oversized at 3 tons, and this appears to be substantiated by other key points and comments.

Everyone from the US Dept of Energy (on a national basis) to local building groups all over the country have studied SIP homes and saw – WITH ALL ELSE CONSTANT – energy savings of 50% or more while saving on things like labor and insurance costs.

By: Greg Ferris

Greg Ferris — Wed, 01 May 2013 00:19:38 +0000
Please explain why the SIP
Please explain why the SIP construction was not cost affective. You should have saved framing labor and did you consider the infiltration reduction not to mention the consistant R value? Perhaps if you would not have used polyurethane foam SIPs you would have saved some money. I do not work for a SIP manufacturer but I have built with SIPs. Can you tell me what you paid for your SIPs per sqaure foot? Did you consider the cost savings of insulation materials & Labor added to your ,would be stick construction framing materials and labor cost?

By: Amy Musser

Amy Musser — Tue, 30 Apr 2013 18:29:08 +0000

Allison, consider yourself
Allison, consider yourself invited! You may have heard that Asheville is “beer city USA”, so come on up!

I think one of the most important points you’ve made is that the HERS is just a “miles per gallon” sticker – your mileage probably will vary. And why shouldn’t a person who lives in a net-zero house also use less energy for appliances and the stuff they plug in? It should be emphasized that this doesn’t mean there’s anything wrong with the HERS index.

I’ll try to give a few short answers to the many excellent questions. If you don’t mind me promoting a blog where I talk about the house all the time – http://www.wncgreenblogcollective.wordpress.com – there’s more there.

ERV vs. HRV: In climate zone 4, energy use works out about the same. The HRV has a better sensible (winter) efficiency, ERV has a better latent (summer) efficiency. The house is so tight that we stay a little more humid than I’d like in the winter, so an HRV would have been a better choice. The model of ERV that we have has a twin-model HRV, so we just got an HRV core for it that we’re planning to swap out seasonally. I would add that the humidity impacts of ventilation strategy are very climate specific, and that in the end ventilation is not a dehumidifier. It’s just another thing that contributes to the overall humidity picture.

SIPS payback – the obvious question is “compared to what?” We think we could have gotten similar performance (thus the $5 per year) from a frame wall with 2-3″ of rigid exterior insulation. But we also like our SIP walls and think they’re really high quality. It’s really just a question of payback.

Water heating – our original plan was for a heat pump water heater, and this would have freed up some space in the mechanical room. We happened to get a deal on a pilot program with our utility for solar thermal that changed the financial situation.

Geothermal – ditto here. I probably need to write a whole blog about this decision myself. With state and federal tax credits, the install cost for geothermal was about the same as we could have done air-source. And given the nature of our house, our heat doesn’t even come on until it’s so cold outside that a traditional air-source would be using strip heat. The particular model we used starts at 3 tons and is dual-stage. The lower stage is about 2 tons, and this matches our cooling load pretty well. The 3 ton size matches our heating load, and we get good runtimes in both seasons. We’re pretty happy with the match we were able to achieve between the system and our loads. Passive solar homes are weird – especially on heating they tend to spend more time running near peak load, because if the sun was out, it wouldn’t be on at all.

By: Debbie

Debbie — Tue, 30 Apr 2013 01:49:59 +0000
"using an HRV instead of
"using an HRV instead of an ERV"

can you explain why HRV would have provided more savings than ERV?

I'm a fan of SIPS over ICF..even given the added costs of both as compared to regular stick build.
over the years, I've come to the conclusion that the SIPS/ICF choice is one area where the homeowner spends extra $$ more for peace of mind than savings. (I'm in a hurricane zone btw)

beautiful home, congrats to owner/builder/designers!

Debbie, who is
also a fan of hippy energy.

tia,
Debbie