With Blow in Insulation, How Much Insulation Is Enough?

Building codes have increased the amount of blow in insulation that is installed in new homes. In the 1970’s, adding insulation to a home was based on economics. As a result, those homes rarely had more than 4 inches of insulation in the attic. By the mid 1980’s, the word started to get out that a warm house wrap provided a more comfortable home and, since heating and cooling costs were going up, insulation was a good thing. It wasn’t until the mid 1990’s that energy codes started to take a real close look at home comfort and energy efficiency and began to provide some real data and direction on home insulation.

Today, the amount of blow in insulation that is expected to be installed in a new home takes the whole house approach. If you place R-40 in the ceiling, perhaps you only need R-19 in the floor. But, if you put R-25 in the ceiling, you need to put more in the floor than the R-19. The whole house approach allows for greater flexibility in-house design. insulation retrofit

Four Important Insulation Facts:

1. Insulation conserves energy and increases comfort by slowing the transmission of heat. Reduces the size of heating and cooling equipment required in direct proportion to R-Value. Insulation decreases both heating and cooling costs.

Measuring Insulation Depth

2. To be effective, the surface supporting the blow in insulation needs to be air-sealed.

Blow in insulation is not a very good air barrier. In other words, air passes right through it. When air is allowed to pass through insulation it looses it’s insulating capacity. If you look at insulation installed in an attic and some of it is almost black, that is the area that has had air passing through it. The insulation filters the air and it turns dark from all the dirt and dust in the air.

3. The first 4 inches is the most important.

It’s a case of diminishing returns. Blow in fiberglass has a rated R-value of about R-3 per inch. So 4 inches would have a R-value of R-12. Double the depth to 8 inches and you would think that you have doubled the R-value also. Unfortunately, that is not the case. The first 4 inches is the most important, the second four inches is important, but not as important as the first four inches. The third 4 inches adds R-value but not as much as the second four inches.



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