Monthly Archives: August 2013

air barrier

2013 08 07: the picture shows the roof’s air barrier. passive houses have an air barrier on all sides, including the roof, that prevents air exchange with the outside. the black tape keeps air from passing between the sheets of oriented strand board (osb). in the case of the old hopkins road house, the roof’s air barrier is the layer shown. over this will go 2 x 10s that will form cavities for seven inches of mineral wool. under the air barrier is 16 inches of blown in high density fiberglass insulation.

tape sealing the spaces between osb

tape sealing the spaces between osb

nails

the pictures show the spacing of nails in the plywood that is over the wall studs. the maximum spacing of the nails is controlled by code. this is done to be sure that the house can withstand the loads from wind.

west wall

west wall

 

 

 

 

 

 

 

 

close up of the west wall under a window

close up of the west wall under a window

 

 

 

 

 

 

 

a closer close up showing nail spacing

a closer close up showing nail spacing

 

 

 

 

looking nice

2013 08 07 the west side is looking complete, even though it’s not. the wall shown will eventually have 12″ insulation to its outside and 5.5″ of insulation to its inside. the outside of the wall that is shown in the photograph forms an air barrier or at least it will after all the seams between the plywood are taped. this along with the air barrier for the roof and the air barrier for the slab and tight windows or doors, will largely prevent air from entering or leaving the house. as a passive house, this air sealing will be tested with a blower door apparatus in which a fan will be sealed in one of the doors. it will pressurize and then de-pressurize the house. at a pressure of 50 pascal, the house may not leak more than 0.6 air changes per hour (ACH). just a few years ago, this was thought to be an impractical standard; but passive houses regularly achieve better than this.┬ámany houses will leak at a rate more than 10 times 0.6 ACH.

pascal is a metric unit of pressure that has somehow made it into the world of english units that are used almost exclusively in residential construction. 50 pascal is 0.00725 pounds per square inch. .

the west wall looking complete

the west wall looking complete