Not as much as you might think. Depending on the selections you make during our consultation your spray foam insulation will cost you between 20 and 75% more than traditional insulation. An average 1400 square foot bungalow insulated with spray foam insulation would only cost about $ 1700.00 more than with professionally installed fibreglass. On your mortgage based on a 25 year amortization this is only about $ 9.00/month or $ 108.00/year. Spray foam insulation will save you many times this cost every year so the repayment period is basically the first month you turn on your heater or your air conditioner.