Inspections of Texas

The Dangers of Spray Foam Insulation

Current building science is to build it tight, ventilate it right, and manage the indoor air quality for a healthier home.  There are many new products on the market for homes in the last 10 years.  One of those is spray foam insulation.  There are both pros and cons to this product.  It is up to the individual home buyer to decide whether they want a home with spray foam insulation or not.

The Basic Science:  There’s no more of that sticky fiber in the traditional fiber glass insulation that makes you itch for hours if you rub against it.  Spray foam, once installed, does not appear to deteriorate and go flat like the traditional batt-fiberglass insulation that we see in 40 year old attics.   Spray foam insulation helps reduce noise better than traditional insulation.  Part of the noise reduction is in the seal created that is much better than fitting strips of insulation between the ceiling joists.  This tight seal is also more energy efficient. But because it keeps things out, it also keeps heat from escaping which causes the attic in a home to become too hot, causing the insulation to lose effectiveness and leading to energy loss. 

The Problem:  There is one major issue with spray foam insulation in the Houston metropolitan area.  That is the issue of humidity.  Because spray foam insulates the attic at the roof, the attic is then inside what is called the “thermal envelope” of the home.  That means there must be a method for removing the humidity in the attic or moisture will develop on the drywall ceiling between the conditioned space in the home and the unconditioned space in the attic.  Everyone in the Houston knows what happens when drywall receives moisture over time.  The accumulation of humidity grows into that bad 4-letter word no one wants to hear – MOLD!

The Remedy:  Spray foam attics can be fitted with helpful devices.  The first and most effective strategy is to have both a supply and return vent in the attic to condition the air.  Because a cooling system works by evaporating the moisture this removes the humidity.  However, this means the Heating, Ventilation, and Air Conditioner (HVAC) system load needs to have been properly calculated to include cooling/heating the attic.  If this is not correct, the HVAC system may be overworked and its expected lifetime will be reduced.  It also means more energy is spent to cool/heat the attic. 

The Alternative Method:  The other, less expensive method is to install a mechanical vent like in the bathroom that expels the humidity to the outside 24/7.  However, the danger is now in the question, “How long will these mechanical vents last if they run 24/7?”  It may be possible to install an alarm when they quit working properly so it can be replaced.  Otherwise, we’re back to that same bad 4-letter word – MOLD if they quit working and are not replaced immediately!

We have seen several well-known and trusted national home builders miss the conditioning and dehumidifying process of the attic space in new home builds.  The builders either don’t know the problem, or they have decided not to invest in solving the problem.  This is one more reason why it is so important to have a knowledgeable home inspector inspect both new and previously owned homes.  We protect you, your health, and your investment!


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