The Pop-up Passive House is essentially all insulation

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front elevation

credit: Multipod Studio

Readers have complained about the use of our slideshow format here, so I have edited and added some of the content from the slides below for those who don't want to advance the slides.

There is a lot to love in the Pop-up Passive house, designed and built by Corentin Thiercelin' Multipod Studio. I have facetiously described the Passive House concept as "a shitload of insulation, careful detailing and controlled amounts of high quality glazing."

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Multipod Studio has taken that definition to the extreme; the house is insulation, built almost entirely of giant foot thick blocks of high density expanded polystyrene foam (EPS) foam. It's grey because it contains graphite:

The graphite absorbs and reflects part of the thermal radiation and offers up to 20% improvement of the insulation capacity compared to the conventional white EPS, at equal density.

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The blocks of foam are separated by 12" wide strips of 3/4" Laminated Veneer Lumber (LVL), a form of engineered wood usually used in lintels and beams. Here it is sliced down to plywood thicknesses, but is stronger. "Sandwiched between the blocks, the wooden boards cannot twist or buckle: this greatly increases their mechanical properties." They are then fastened together with very long screws, creating an envelope with 12 inches of insulation.

Is it Passivhaus?

I do have some major reservations and concerns, and am not certain that they are fully addressed by the architects. I do not believe that there is any way this house can meet passive house standards as built, where it is screwed together; I don't see how it can meet the air tightness standards of 0.6 air changes per hour at 50 Pa. It is going to leak between that LVL and the foam.

However the architect shows an alternative where the LVL is glued with polyurethane to the foam, which would seal it up more tightly. Whether this would create a tight enough seal, and how the intersections of the walls at floor and ceiling are detailed, remain an open question.

Is it healthy?

Then there is the whole question of whether one should be using polystyrene foam at all. It is made from fossil fuels; it is full of fire retardants that are possible endocrine disruptors, but it still burns like mad, releasing toxic chemicals. I am not convinced that that it belongs in green building.

However, here again the architect suggests options, ranging from our beloved cork to dense fiberglass or rock wool panels to cellulose. Whether these have the mechanical or air tightness properties of the EPS foam is another story.

Is it safe?

As constructed, this house would not pass any inspection for fire safety that I know of, with a ceiling of exposed polystyrene and wood slats. However the architect notes that this particular home is on borrowed land, is being completely disassembled and it is obviously a prototype. My concerns could be addressed with a layer of cement board or drywall.

In the end what we have here is a very beautiful design and a very interesting structural concept, essentially building a house out of insulation, and minimizing everything else. It uses the structural properties of insulation in novel and interesting ways.

It is also true that the questions around the use of foam in green building are very controversial; it is such a good insulator that people are willing to forgive its flaws. This design certainly uses it to its best advantage and deserves a lot of praise for that.