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Spray foam is an excellent innovation and a great alternative to the traditional building envelope’s batt fiberglass insulation.  It creates a sealed envelope that keeps moisture and reduces air leakage. It eliminates compression, voids and gaps normally found with fiberglass batt insulation that can lead to a reduction in thermal performance. Appropriate applied spray foam can even pay for itself through reduced energy cost.
Unfortunately some contractors and spray foam salespeople are selling the air conditioning industry short. Homeowners are being told they can put in half of what is required by designed load calculation. This is a pure sales tactic. Spray foam is more expensive therefore spray foam companies and contractors need to help offset the cost.
A few design concepts that seem to be taken out of consideration are:

1. Home many windows (solar heat gain)
2. Lighting  and plug outlets (heat output)
3.  How many and what type of appliances are in the house (heat output)
4. People  and their activity (moisture and heat output)

These are a few attributes that must be considered when sizing an air conditioner for a home or space. Spray foam is a great way to keep things out, but in turn they also heat and moisture in.
The spray foam space indoor air quality is improved in the area of prevention of nuisance particles entering through air infiltration, but one important life sustaining element is prevented from entering the space.  Oxygen! Since the home is now a sealed envelope you have to find a way to bring in fresh air. Hypothetically peaking (DO NOT DO THIS!), think about placing a bag over your head and tying off the opening around your neck. How long do you think you will be able to breathe? Not long right? Well that’s precisely what you are doing when you encase your home with spray foam. The indoor air can become stale and the levels of CO2 can increase causing individuals occupying the space to feel side effects that include feeling sick and light headed.
The good news is that there is an easy fix. Outside air can be supplied to the home through the air conditioning system. This ensures air is conditioned prior to entering the home. Since fresh air is circulated through the AC system, the unit must also be adequately sized to handle the un-tempered outdoor air. It takes a larger unit to temper 100 plus degree air down to around 75 degrees. That’s bad news for spray foam sells people who claim you can cut the AC size in half. In most regions, especially in the South, that is not a practical trade off.
The concept and application of spray foam insulation is an up and coming technological marvel. Its benefits by far supersede the traditional building model of using batt insulation.  Contractors and home owners must be aware that with these benefits comes a few crucial draw backs and if those issues are properly addressed, then the space occupants will have a very energy efficient and comfortable environment.