PHPP and WUFI

Thursday, March 28, 2013

PassivHaus Planning Package (PHPP) and WUFI (Wärme und Feuchte instationär) are not my favorite acronyms, but they are pretty silly when made into verbs ("Let's WUFI this"  or "I'll be WUFI-ing for the next hour or two"). It all seems to be goofily appropriate and sensible, though, when speaking with Indigo.

Indigo Ruth-Davis, our PHPP consultant, is certified by the Passivhaus Institute U.S. (The course was presented at Yestermorrow Build and Design School in Waitsfield, Vermont.)  He is a somewhat shy person, a builder and gifted musician who plays the cello like a dream, I'm told, and alternately arrives by large white truck or motorcycle. Tonight he and his partner, Peg, who is a lovely woman with amazing long wavy hair, arrived for a dinner/work session at 6:30.

I work at the Vermont Center for Crime Victim Services, in the next town "over," and despite my proximity to my workplace (about 8 miles), I rarely get home before 6 p.m., for a variety of reasons, including enthusiasm for my job and poor planning. On this particular day, I had driven to Burlington on extremely short notice to meet with some attorneys who were participating in a cultural/legal exchange with Vermont Legal Aid. They were from the Ukraine and were interested in learning about what Vermont is doing to combat the problem of human trafficking in our state.(I'm the chair of the Vermont Human Trafficking Task Force.) We meet at a cafe on Main Street for about an hour, where we conversed with the assistance of a former U.N. interpreter whom they had brought with them.This was fun, fascinating, and also surprisingly tiring -- so by the time I got home, after getting stuck in the first major highway construction project of the season (there's a joke in Vermont about having six seasons: Spring, Summer, Fall, Winter, Mud Season, and Construction), I was pretty whupped. But Peg and I had an instantly easy rapport, and we gabbed as I cooked and Gerg and Indigo put their heads together over spreadsheets and scratch paper downstairs.

So.. they talked about the window schedule (which is construction lingo for a list of windows and their sizes), window placement, and the impact on the PHPP.  They talked about the foundation, insulation, radon, air and vapor barriers.  And what was the result? 

We're at 3.55 -- we need to stay at 4.75 or under -- thus, we have some important decisions left to make, but we're doing really well. Hanging questions: How to heat it?  How to ventilate it?  (This is harder to do on a small house than a bigger house, by the way.)

We will have 8" of EPS under the foundation.  We will have 16" of EPS around the foundation.  We will have a 12 mil. air and radon barrier wrapping the whole foundation.  We will have 16" dense-packed cellulose in the walls and 22" in the roof.  The roof will be essentially flat, to hold the snow (for further insulation).  It will be a rubber roof, fully adhered EPDM. This is what we have on our current house, and it is marvelous -- the only noticeable drawback being that it is hellishly hot on your feet when you venture out on it in the summertime. 

So...the differences between our house and the "conventional" Passivhaus that you, our readers, know? First of all, we are going to have curtain walls. That means that the outside walls are completely separate from the timberframe.  They are not constrained by the posts or braces.  This mimics the construction of our current house.  What this means, in real life, is that you don't have to run any electrical wiring or heating elements through the walls -- they can be concealed in the space between the posts and the inside sheathing of the wall.  Ours, by the way, are all tongue-and-V-groove cedar, from Goodridge Lumber in Albany, VT.  (Goodridge is another story for another time)

The second major difference is that the roof, which is almost flat, will hold the snow.  This provides additional insulation, and we don't have to worry about snow sliding off, or shoveling it, or where we plant shrubs or flowers that could get clobbered.

The third major difference is the timberframe itself.  I love the elegant simplicity of the timberframe, its flexibility, the way its "bones" are visible, like the skeleton of a big animal. You don't need any interior walls -- and if you want to take out the ones you do have, or move them, it's simple, because they're not supporting anything. 

Most folks think timberframes are expensive, but they don't have to be. The assumption is that you're essentially building two houses...the frame itself, and the walls, which are sufficient to support the house.  What we did here was build the timberframe and then hung walls outside of it, which would NOT support the house, but act as a moisture/weather/air/temperature barrier. So, in effect, we have built only one house. The timberframe appears to "float" within the walls -- it's spaced 2" inside them -- which also provides a space to hide electrical cords and such.  It's a beautiful design element which allows you to view the frame itself from many angles, some of which would normally be obscured by the wall.

In this pic of our guest bedroom, you can see wall "floating" outside
the posts and knee braces  and rafters of the timberframe.

The cottage will have a little more structure in its curtain walls than our current house, because we're moving from EPS foam to dense-packed cellulose -- which is not rigid and doesn't support itself. Therefore, we'll have to build a little more structure into the wall.

What's up next?  We're running away to Canada for three days, to the little town of Magog just across the border, for a last-ditch vacation before the actual construction starts. Next Monday, Chris and Indigo will be here to discuss various certifications and the PHPP.