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.

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.

If you have 12 inches of blow in insulation in the attic and you are thinking about adding 4 more inches, it might not be a very cost-effective measure.

4. Cellulose is superior as a blow in insulation.

Insulation Blowers

Today, the two main types of insulation is fiberglass and cellulose. Cellulose may be the best product for blow in applications because it is inexpensive, easy to install to correct density, and resists air penetration.

In the colder climates, like upper North Dakota, current code has attic insulation at R-49 and wall insulation at R-21. In warmer climates like parts of Texas, attic insulation should be rated at R-30 and walls at R-13.

In the colder climates, like upper North Dakota, current code has attic insulation at R-49 and wall insulation at R-21. In warmer climates like parts of Texas, the attic should be rated at R-30 and walls at R-13.

So, How much insulation is enough?

1. Consider cost-effect measures.

The payback period for retrofitting insulation varies greatly, but studies show that added insulation usually pays for itself in saved energy costs within five to 10 years.

2. Dense pack the walls.

When filling walls with blow in insulation, fill the wall cavity full using dense pack installation methods. Follow the instructions written on the bag of insulation to determine how many cubic feet of wall space one bag of insulation should cover.

3. Double attic insulation.

When adding blow in insulation to an attic, at least double the depth of the coverage that is already there, up to 20 inches. If your attic already has 10 inches of good cover, than add 10 more inches. If your attic has 11 inches of insulation, look somewhere else in your home to save energy, adding insulation to the attic that already has 11 inches, would not effectively decrease heat transfer.

Remember, to get the most benefit out of blow in insulation, you need to air seal the supporting and adjacent surface.

Most of your building stores will have insulation blowers that you can use to blow in insulation in your own attic and walls. It’s a process that can be a do-it-yourself project and one that can make your home more comfortable and a home that uses less energy to heat and cool.

Thank you for stopping by, hope to see you soon, but I won’t leave the light on for you…