Insulation – It’s HOW You Use It

Insulation is an important component of comfortable, efficient buildings. While many people remember hearing about it quite a bit after the 1970s energy crisis’s, it’s history goes back a little farther than you might think.

Waaay back, because in Ancient times the Egyptians used thick brick walls to protect their homes from the heat of the sun and asbestos was used to insulate their clothing. (yes, the same asbestos we wear respirators while working around nowadays)

The Ancient Greeks and Romans used cavity walls, a technique now used in double pane windows. The idea was and still is that a “dead space” of still air will slow down transfer of heat between the two sides of the wall.

The Northern Europeans used a mud and straw mixture to press between the cracks of their log walls, called chinking. In addition to separating the heat and cold, it was also a good way to stop air infiltration. In the middle ages, walls were lined with cloth or ornate tapestries to keep the room warmer as well as absorb moisture from their damp stone walls.

In the industrial age, asbestos was used again to insulate steam and hot water lines, and in clothing to protect people working near intense heat in steel mills. Now that we know that asbestos fibers can get into our lungs and cause cancer, other forms of insulation such as fiberglass have taken asbestos’ place in those same applications.

When homes were built 100 or more years ago, insulation was not commonly used, and the solution to a cold home was to install more or larger fireplaces, and central heating (such as boilers and furnaces) were available to easily heat a whole house no matter how cold it was outside. In the summer, insulation wasn’t needed because large porches and overhangs combined with transom windows, high ceilings and large windows ventilated the house for cooling effect.

Only after central air and heating began to make an appearance along with increased energy costs did we realize that keeping the heated or cooled air inside our buildings was important. Rockwool and perlite were common in the middle of the century as people first started to fill up the cavities in their walls and cover attic floors. These were both forms of “loose fill” insulation – they were poured into the walls and spread on the attic. Over time, cellulose insulation made from newspaper has become the dominant loose fill insulation.

Batt insulation, first of Rockwool then Fiberglass, became popular due to the batt’s ability to stay in place in walls and ceilings during construction without the walls or ceilings being complete, and both types of batts were able to incorporate a basic vapor barrier in the form of tar-coated paper facing, helping provide moisture control.

More recent forms of insulation have included wet-applied cellulose insulation – which is sprayed onto a surface and it “sticks” as it dries due to starches in the cellulose, and spray foam insulation, which works by spraying a liquid onto a surface which then foams up and expands to fill gaps and cracks. Space exploration has also brought us reflective insulation – which is typically a metallic coating applied to a plastic film. While not separating heat and cold in the same manner as “bulk” insulation like the types described above, it nonetheless does stop heat transfer due to radiant heating, which bulk insulation cannot do without considerable thickness.

Installation of insulation has as much to do with it’s performance as what type is used. Batt insulation, while inexpensive and easy to install, must be placed into the wall cavities with surgical precision to be at it’s most effective. Spray foam insulation is easy to apply if you know how and have the proper equipment, but also suffers if cracks between framing members are not caulked first – the hot or cold air will just go right around the expensive and high performing foam and reduce it’s effectiveness.

So in summary, insulation plays an important part in how our building performs, but must work in tandem with the air seal to be most effective. Here is a comparison with some of the most common types of insulation used today.

Insulation ProductR ValueCostAdvantages / Disadvantages
Fiberglass BattR-13 – R-30 (R-3.25 per inch)$Low cost and quality quality product but a total fill installation is difficult. Craftsmanship is critical. No air barrier.
Recycled Denim BattR-13 – R-30 (R-3,4 per inch)$$A recycled product with no chemical irritants and less energy used in manufacturing. But any batt insulation is difficult to install properly. No air barrier.
Damp or Dry Blown CelluloseR-3.2 – R-4 per inch$A total fill application is not difficult and the fill is typically made with recycled newspaper treated with borate. It is safe for air quality. No air barrier.
Open Cell Spray FoamR-3.8 per inch$$$A quality installation is not complicated and total fill is complete because the foam expands into all crevices. An air barrier inherent however it is more expensive that other types of insulation.
Closed Cell Spray FoamR-7 per inch$$$$$A quality installation for total fill is not complicated. Because of the extra dense quality, roof leaks may not be immediately apparent. Much more expensive than other types.

The most common insulation specified in Green homes in Central Texas today is open cell spray foam applied to the underside of the roof decking in the attic, creating a sealed attic. In the walls, open cell spray foam is common as is blown cellulose because of cost and the fact that heat gain on the walls is not as great as on the roof. Blown cellulose can also be used at the underside of the roof decking, but the appeal of the foam is that the air seal is an inherent quality of the product. The combination of the air seal and a quality total fill installation of insulation is exponentially a greater advantage.