Air infiltration can account for a lot of energy costs by devaluing the insulation as it moves through as well as allowing frequent air changes per hour (ACH) in a home.
The house we are building now we are using engineered precast, Ideal walls ( https://bit.ly/1izmoex ) which gives us great R value (R30 )and air tightness for our exterior wall system. We caulked on our window flanges and then zip taped over the flange before adding our trim. We used casement windows that are typically tighter. The doors were set in their openings that were sealed with zip tape and caulked and sill seal was put down under the thresholds.
Other air infiltration happens through the sheetrock ceiling at the intersection with interior walls. A surprising amount of air movement happens through interior walls. The first blower door test that we had done on a house in 2003, showed air moving from the attic space down the inside of the sheetrock and exiting at the bottom of the baseboard. A smoke pencil told the tale. For that house my only option was to caulk the baseboad before I added the shoe mold. The sheetrock does not make an airtight seal at the top plate of the walls and air gets through loose fill attic insulation and travels behind the sheetrock. After learning that I started caulking in the attic space before insulation was installed along all of the interior walls as well as the light and fan boxes in the ceiling and bath vens and the kitchen vent. This worked pretty well with most of our blower door tests coming in at around 2 ACH 50 which is less than the 3 ACH required for Energy Star. A couple of houses ago I started installing a gasket at the top plate of the interior walls so when the sheetrock is screwed on it compresses that and forms an air seal without me having to crawl in the attic space as much. It seemed to work as well or better.
Our sheetrock hanger works by himself which means a slower process but with time to work with him on some details. The first house I put the gasket up before he hung the ceiling and that was a lot of hassle for him. He was constantly messing up the gasket in tight spots. On this house I came in after he had hung the ceiling and stapled the gasket up. He appreciated it and I had to replace a lot less of the gasket. For the gasket material I used a 6 inch sill seal cut in half with a hand saw while it was rolled up, so it was less than 3 inches wide which is plenty and goes twice as far.
I caulked around all the ceiling fixture electrical boxes as well as the stove vent duct and dryer vent duct. I will weather strip the attic access and insulate with rigid foam. The weak link is the can lights in the kitchen. I lobbied for track lights that have fewer penetrations and don’t protrude into the ceiling insulation but was outvoted. We are blowing in R-60 in the ceiling so the loss at the cans should be minimal.
The blower door test will tell the tale. It would be nice to get down near 1ACH 50.