Superb Blower Door Test

 

It was a quiet week at the Sumac Grove.  For the most part we watched the insulation dry.  We brought in two large commercial dehumidifying units which have been operating for nearly a week now.  The relative humidity (RH) has gone down from 74% to about 34%, but the insulation is still quite damp.  We will run the equipment through the weekend and see how it is doing.  We have been using a hygrometer with a long probe which measures the RH deep in the insulation.  We are still getting readings in the 70 to 80% range in some areas.  We won't begin drywall until we are satisfied that the moisture levels are low enough.  

Michael Holcomb of the Alliance for Environmental Sustainability came out to perform and inspection of the site before we install the drywall.  This inspection is a prerequisite in LEED for Homes.  While he was there we ran the blower door test to measure the air volume that can be attributed to air leaks in the building envelope.  

The blower door is a canvas frame with an exhaust fan built into it that is fit firmly into a door opening.  All openings in the home are closed as they would be in normal operations.  The exhaust fan is hooked up to a computer.  There is a small flexible hose that goes through the canvas frame that samples the air pressure outside the building, and another one inside to measure the air pressure on the inside of the building.  The fan is turned on to create a negative pressure in the building.  The pressure differential between the two measurements is measured by the computer and calculated against what it knows the volume of air generated by the fan speed to be.  This is an image of a typical blower door testing apparatus.


The new air infiltration guidelines for energy efficient homes that Energy Star has just published established a benchmark of 3 Air Changes per Hour (3 ACH).  Passive House requires a maximum leakage rate of 0.6 ACH.  Michael measured 0.26ACH, less than half of the Passive House requirements.  He has never seen a measurement so low, and we were thrilled to know that all of the design elements we incorporated and the work we invested to obtain the airtight design were vindicated.  



Last week the drywallers installed the drywall in the basement, the garage, and the ceiling of the house.  Judy and I spent the weekend blowing in cellulose insulation over the garage ceiling.  Though we probably will not use it very often, the garage is insulated well enough that a small 1,500 watt electric heater will make it possible to work on projects in the winter.  The garage was designed to include a workshop at one end, and space can be expanded by removing the cars.  The Clopay overhead garage door is insulated with 2" of foam with insulated glass for daylighting and is scheduled to be installed tomorrow.  

As we waited for the insulation to dry we finished up a few details.  The last of the blocking for the barrier free design requirements has been installed.  We put reinforcing members in to accommodate the future installation of grab bars.  We have almost finished up with the exterior insulation and lath.  They were just finishing up this gable this morning, and should finish the east gable next week. 

The turning point

In spite of the short work week we got a lot done.  The heat was turned on with only a few troubleshooting issues with the controls and only a few minor leaks in some of the piping connections.  We have had three sunny days in a row, and the added solar gains have warmed up the home very quickly.

The "wet blown" insulation was installed in the walls on tuesday, and the attic insulation was installed on Wednesday.  Wet blown insulation has a moisture content and a mild adhesive in with a recycled cellulose material.  Chemicals are added to inhibit mold and insect infestation.  With the 10" wall thickness, the weight of the insulation causes it to sag, so they added horizontal baffles to reduce the settling.  There is still a little bit of settling at the top in some areas which will be repaired in the next few days.  

 

To extract the water from the insulation and accelerate the schedule, we rented two industrial dehumidifiers to work over the weekend.  We have set a goal to get the moisture content down to the same residual levels as the wood studs which will be determined with a moisture probe.  We have turned the heat up to about 80 degrees to bake out the moisture from the insulation for a day or two, and then will turn the temperature down.

 

 The attic insulation is blown in dry.  It is slightly over two feet thick providing an "R" value of 90.  We will install a little bit more over the garage ceiling. The space is designed to be used as a workshop, so we have insulated the walls and ceilings in the event we want to use the space for a winter project.   We have a 2" thick insulated overhead door that we expect to have installed next week.

 

The drywall was delivered this morning, and the board hangers finished the basement and started the garage.  Tomorrow they will install the ceiling in the main house.  No board will be installed on the walls until we are confident that the moisture content in the wall is stable.

 

 

The metal roof was completed shortly after this picture was taken.  The metal roofing end up being symmetrical over the front entrance.  No amount of planning could have been as effective as plain good fortune.  

 

The exterior rigid insulation proceeds at a slower pace.  The plaster lath installation is very labor intensive.  Installation of the lath on the north elevation is complete, and work begins now on the south elevation. 

Next week we hope to have the garage door installed, blow in attic insulation over the garage, finish up some wiring connections, continue with installing the plaster lath, and install the track for the large pocket doors.