Floor Values

Building a Passive House means you do things very strangely sometimes. In traditional “stick-built” construction, each floor gets built out to the structure perimeter, and exterior walls sit atop the floor. But this house has a double shell in which only the inner wall sits on the floor. The outer wall sits on the supporting joists; between the two is an insulation cavity.

We’ll eventually fill the entire insulation cavity with dense-packed cellulose. The insulation was delivered all at once shortly after we lifted the timber frame. We’re talking five hundred forty seven 25-pound bags of basically shredded newspaper, which took us three hours to unload from a 60-foot-long tractor trailer. We piled them high and then covered with tarps to keep rain off.


Ben stacks 25-pound bags of cellulose.

The crew used a renter blower to pack the first hundred or so bags of cellulose between the floor joists. They immediately covered it with Mento, which is not a breath mint but a hardy weather barrier. We rely on the Mento to protect the cellulose from moisture… this stuff does NOT want to get wet.


The floor system is filled with cellulose and sheathed in Mento. (Note the first floor footprint is double the size of the original timber frame.)

The floor is a tongue-and-groove material we installed on top of the Mento. First we installed long spacers to create a service cavity. Kelly led our installation of the floor itself – he works for Montpelier Construction and he’s had lots of experience in this vein. Kelly showed Ben and me how to screw diagonally through the tongue into each spacer and how to use a wedge (such as a chisel or cat’s paw) to force every row tight to the previous. As we pieced each 24-foot row together out of two or three lengths of flooring, we tried to keep the seams away from what will be high-traffic parts of the house.

The flooring varies a little in thickness, so we don’t have a very smooth surface right now. And with all the wall construction yet to come, we’re sure to walk all over it and scuff it up even more. Once things are protected, we’ll give the floor a good sanding to make it beautiful. (Also, it’s possible we will put a finish floor on top of the tongue-and-groove… I never asked Cillian his plans.) But right away, the finished floor enables us to lower the timber frame!


Floor is floored and timber frame is ready to come down. In the back there’s a wall under construction.

2 thoughts on “Floor Values

  1. Scott, I thought you would find this interesting. Copy/pasted from the writer’s almanac:

    He went on to build the Eiffel Tower for the World’s Fair in Paris in 1889. At 1,000 feet, it was the tallest structure in the world at the time, and Eiffel decided to leave the metal scaffolding exposed because he thought the tower would be more stable if the wind could blow through it. Many people at the time thought it was ugly, but it still holds up to the wind. In 1999, Paris was hit by a windstorm that knocked down more than 100,000 trees. The Eiffel Tower only swayed nine centimeters. Not only is it stable, but it is also remarkably efficient in terms of materials; if melted down, the metal structure of the tower would only fill its base to a depth of two inches. Eiffel gave his name to the famous landmark, but it was his work on the tower itself that gave him *his* nickname: “the magician of iron.”

  2. Pingback: Two Hundred Fifty | PERCH ENGINEERING PLC

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