Improving a home's airtightness includes the following key steps:

• Install insulation properly with no voids or gaps
• Use the right insulation for the right job
  • Exterior vs interior
  • Above grade vs below grade
• Exterior rigid insulation acts as a thermal break for the wall, and improves airtightness if installed properly
• Properly attach the vapour retarder and air barrier, and seal properly

Things to keep in mind:

• When insulating, make sure there are no gaps in the insulation that are more than 3/4". This can allow a convection current and air to circulate in the gap. This increases heat transfer through the wall cavity
• Compressing batt insulation will reduce the effective R-value of the insulation
• Taking the proper time and care to cut and insert batts, and apply spray-foam properly can make a difference in the air tightness and heat transfer of a wall, header, or ceiling/attic
• When installing the air barrier make sure anything that penetrates it is properly sealed with acoustical, approved tape, gaskets, foam sealants or expanding spray foam
• When sealing windows and doors, remember that the attic hatch should be treated in the same manner. Unsealed attic hatches and frames are a common source of air leakage