Passive House foam is more expensive than PV

[Martin Holladay]

According to building scientist John Straube, the very thick layers of EPS used under the concrete slabs of American passive house buildings are more expensive than PV. In other words, designers would get more bang for their buck by reducing foam thickness and installing a PV array. Read about it here:
http://www.greenbuildingadvisor.com/blo ... -too-thick

[Kat]

Martin,

We appreciate your continued high interest in Passive House, but please refrain from using our bulletin board to advertise your articles on GBA. If you want to contribute constructively to the discussion on the bulletin board you are more than welcome, but just writing one sentence and then referring to your other writings, which I think, quite frankly, border on populist reporting rather than well informed discussion, is not cool.

Also, while flattering that you like to use my name as much as you do, it does sound more like you are trying to discredit me. You never quote me or make an effort to verify your understanding of Passive House with me.

Instead you prefer to talk to other people, "experts" and smart guys, who I bet have little idea about the PHPP (I wish they did, then we could finally have an educated conversation), as their quotes in your article once again show.

This is a great community and I can see that you value their informed comments.

Thanks for your consideration,

Katrin

[Martin Holladay]

Katrin,
I'd be happy to quote your response. Do you have a substantive response to the technical issue that John Straube raised?

[Mark Siddall]

The guys a Building Sciences are interesting and I've enjoyed reading a good deal of their work (though sometimes it's not always all that it's cracked up to be). I can't comment upon any calculations that they may have done, but it strikes me that focusing upon the elemental approach - a wall, a roof, a floor, or a window - squanders the any ability to engage with whole systems engineering - by taking this elemental approach you can 'pessimise' the whole.

The whole systems approach that is in many ways inherent to PassivHaus has been shown to be cost effective in Europe, and recently there was an interesting study from the USA in the journal "Energy and Buildings" that looks at Net-Zero Energy Homes and Katrin's PassivHaus - with a theoretical PV array to achieve "zero". The study found that PassivHaus was one of the cheapest ways of achieving net-zero energy (though it did recognise that at this time there may be climatic limits to the economy).

Obviously there will be a cost limit to what is affordable but this has to be viewed on a project by project basis over a realistic time frame, say 25-30 years, and you have to choose the correct datum - i.e. say an uninsulated building or the regional/national average stock rather than current regulations (if you don't do this you can't compare really apples with apples). With this in mind I recently tweaked a copy of PHPP so that I can calculate the net present value of the energy saved - and then the cost /kWh saved (as opposed to bought) for that period. As long as the NVP for the whole building remains within acceptable cost boundaries then you have an affordable solution. [ I've not managed to use bolt-on for a project yet but one of the great things about PHPP is that you can make these tweaks and alterations (though I should note that if you want a Certified home you can't use a copy that you've tampered with!) ]

So where does this leave EPS? If you made a whole house, PassivHaus or not, using EPS insulation it may turn out with a NPV that is to high - to me this just suggests that the type of insulation should be refined to address whole life costs (this may be a result of climatic considerations requiring a certain resistance, due to cost/supply issues or some other factor). Here you could optmise sub-components, such as any EPS forming a slab on grade, by improving the U-values elsewhere and/or using cheaper insulation and by reducing that of that used under the slab. To my mind this is just good value engineering practice and has nothing to do with PassivHaus.

Mark

[chadludeman]

Somebody forwarded this to me a few days ago and I got a kick out of it. To me, it's as simple as figuring that you will pay about $7500 - $10K in setting up a PV system in a home before you even buy a single PV panel. I don't think any of us building Passive Homes are spending more than this in extra sub-slab insulation.