Efficient prefab?

[S-F]

In order to get to passivhaus levels you will need 16" - 18" walls (assuming you use cellulose) with no thermal bridging at all. I doubt you will find exactly what you want already set up for you but it wouldn't be too hard to adapt something to meet passive standards.

[AC_Hacker]

Originally Posted by S-F

...it wouldn't be too hard to adapt something to meet passive standards.

I did find out that at least there is a firm in Canada that designs Passive Houses, and they have certified builders, also in Canada, with whom they have co-ordinated working relations who are qualified to properly execute the designs. They are also trying to get Passive House qualified builders in the US.

From what I have been able to find out, there are stringent techniques used to achieve an air-tight house that go way beyond what would be considered normal building practices. And then there are the techniques used to get the required insulation levels. So among areas of focus are:

• superinsulation
• airtight construction
• mechanical heat recovering ventilation
• high performance doors and windows
• window placement to minimize heat loss & benefit from solar gain

High performance doors and windows go considerably beyond what is generally available in the US.

I did find that Certified Passive House Consultant Trainings are taking place...

...and that they are screening for serious qualified people for these trainings...

...at first I thought it was a trade association thing, closing ranks, but then I came across this link to passive house related building practices, and I remembered that what is now known as Passive House actually started with the Super Insulation initiative and also combined the Passive Solar ideas, and was then picked up by the Germans who refined the ideas and devised a way to generalize construction for any building site and climate. (by the way, the listed 'best practices' manuals are not all currently available, but if you make use of archive.org, you can still find them.)

So I think that what is going on is that Passive House organizations world wide are making a very steep claim, namely that energy use will be 10% of 'normal, well-insulated homes'... and they want to make sure that homes that carry the Passive House name actually achieve that goal.

From what I have read, trying to retrofit a house to Passive House standards is simply not possible, but it is possible (not easy) to get to 20% energy use of 'normal, well-insulated homes'.

I know that I would be quite pleased to get even close to that.

So, "...wouldn't be hard...", wouldn't be too right. Meeting Passive House standards is a very high bar.

-AC_Hacker

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[RobertSmalls]

Originally Posted by S-F

In order to get to passivhaus levels you will need 16" - 18" walls (assuming you use cellulose) with no thermal bridging at all. I doubt you will find exactly what you want already set up for you but it wouldn't be too hard to adapt something to meet passive standards.

With some spray foam insulations claiming twice the stabilized R-value of cellulose, it might be doable with 8-9" walls with no thermal bridging, e.g. with steel studs. I wonder, would the increased cost of spray foam insulation be made up for by the savings in lumber, framing labor, window and door trim, and per-square-foot taxes?

Vacuum insulated triple glazing and 18" walls would be nice, but I view them as very expensive toys. I'm inclined to go with a very efficient, 2x6-framed, well sealed house with ventilation heat recovery and good, south-facing double-pane windows. Who knows; it might be passive nine months out of the year, and pretty close in August, January, and February.

[MN Renovator]

Originally Posted by RobertSmalls

With some spray foam insulations claiming twice the stabilized R-value of cellulose, it might be doable with 8-9" walls with no thermal bridging, e.g. with steel studs. I wonder, would the increased cost of spray foam insulation be made up for by the savings in lumber, framing labor, window and door trim, and per-square-foot taxes?

Vacuum insulated triple glazing and 18" walls would be nice, but I view them as very expensive toys. I'm inclined to go with a very efficient, 2x6-framed, well sealed house with ventilation heat recovery and good, south-facing double-pane windows. Who knows; it might be passive nine months out of the year, and pretty close in August, January, and February.

There may be an increased cost in spray foam insulation if you use it but if you go with Structural Insulated Panels with new construction, you avoid the framing labor, get a thinner wall than using fiberglass or cellulose. Since it is rigid foam inside, you have a built-in vapor barrier and air sealing that is hard to mess up too. Doing a little reading to see if these can be bought thick and it seems Wikipedia mentions that they can be 12" thick. If the stuff is polystyrene, which I think is R-5 per inch, it would be about R-60, right? Since there is no framing members, no thermal bridge, you would just need to worry about the air sealing and thermal bridging of penetrations like doors and windows.

It was my impression after watching a television show on prefab houses about 5 years ago, Build one place, ship somewhere else and assemble. The show I was watching explained how instead of using nails and screws, attaching components with adhesives were used instead to speed up the process. I thought it was fascinating. I thought they used SIPs in the construction.