Proper Insulation in New Home Construction

September 14th, 2009 by Steve Homa

There are many types of insulation options. They range from fiberglass, cellulose, extruded foam, expanded polystyrene foam, closed cell and open cell spray foam. Polyurethane foam can also be used but is not as common and produces off-gassing.

Unfortunately the old stand by “fiberglass” still dominates the new home and remodeling market. Fiberglass has made progress with the loss of formaldehyde as a binder and higher density options now available. But fiberglass does very little if anything to stop air movement through it.
Which brings up the most neglected part of insulating a home, “Air sealing”.

You might think that more insulation equals higher R-value, thus a better performing house. This couldn’t be further from the truth. Cold air or heated warm air can move freely through fiberglass or cellulose if it is not properly air sealed first. In fact, a stacking effect can actually draw warm heated air through voids in the ceiling or plumbing stacks into the attic and draw cold air in through other voids in the house.

So how do you air seal properly? Some insulating materials like EPS (expanded polystyrene) foam, which is common in Structural Insulated Panels (SIPs) are natural air sealers by design, so no additional insulation or air sealing is necessary. But products like fiberglass and cellulose need extra attention when sealing gaps and voids from improper installation. They also need special attention around outlets and exterior penetrations. Using closed cell or open cell products like “Icynene” spray foam go a long way to sealing air gaps. A minimum 2 to 4 inches should be applied to the ceiling of the attic space prior to cellulose being applied to seal any voids. 6 to 8 inches should be applied in the box sills (the space between the foundation and first floor walls; an air sealing weak point in many homes) and low expanding foam should be applied to all outlet and window gaps.

This is not to be confused with a new method called “Flash & Batt” where a thin layer of spray foam, typically 1 to 2 inches, is sprayed to the interior side of exterior sheathing and then covered on the interior cavity with fiberglass insulation. In this method, air can move through voids in outlets and will have a dew point that occurs on the foam surface (fiberglass side). This can deposit water vapor in the wall cavity, trapping it where it can cause mold and mildew to form. It also compresses the fiberglass beyond its designed thickness yielding less R-Value. Similarly, fiberglass batt walls with extruded foam on the exterior can produce the same scenario where dew points can form inside walls.

So the best methods to exterior wall insulation is to use a type of insulation that does not allow air or water vapor to move through any part of the wall. SIPs (Structural Insulated Panels), closed cell or open cell spray foams are really the only products that offer such protection. Open cell foams like “Icynene” and EPS in SIPs are the only truly “Green” products that offer superior air sealing with good R-values per inch and no off-gassing over time. Both are water based and give off no chemicals in application or production.

A typical 2×6 fiberglass batt house with a stated R-value of 19 (actual whole wall R-14.6) will have an ACH (air change per hour) of (1.75). The lower the ACH the better. A tighter “SIP” (Structural Insulated Panel) house with higher R-values (R-24) integrated with a hybrid ceiling system (“Icynene” & Cellulose) (R-50) can save significant amounts of energy with an ACH of (.4) and pay for itself in just 3 to 4 years. And don’t forget to apply at least 2” of EPS foam, which does not degrade like “Extruded” foam, around your foundation and under the foundation slab. 37% of a homes heat can be lost through the foundation. For extra durability, we use exterior foams with On-Guard treatment that resists pests and mold.

This entry was posted on Monday, September 14th, 2009 at 2:30 pm and is filed under Energy Efficiency, Green, Save Money, Structure.