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Energy Efficient Home Design and Remodeling in Southern Maine and New Hampshire
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Green Cellulose Insulation
Perhaps the Greenest, most effective Insulation
What is Cellulose Insulation, what is it made from, and what makes it so Green?
These are all good questions.  Here are the answers:
  • Cellulose insulation is basically recycled ground up newspaper.
  • Generally, it is treated with borates as both a fire retardant, and as an pest repellent.


Cellulose is a very effective insulation for a number of reasons.


  1. It has a slightly Higher R-value than fiberglass.
  2. It fills every nook and cranny in spaces it is blown into.
  3. It acts as a much better air barrier than fiberglass.
  4. Because it is blown into spaces, it does not matter what size space you have.  See Double 2x4 Walls below.


Higher R-Value:  Cellulose has an R-value of about R-3.8 when dense packed into walls.  This is slightly better than fiberglass insulation. 


Nooks and Crannys:  Because it fills all of the spaces, it is much more effective as an insulator than is fiberglass.  Fiberglass does not perform nearly as well as cellulose, because fitting it around any obstructions is very difficult, and so is not often done properly, sometimes even when done by professional installers.


Air Barrier:  Cellulose is a much better air barrier than fiberglass.  This in turn means that there is significantly less air infiltration, or drafts. 


This was illustrated some years ago by a manufacturer of cellulose insulation in Springfield, Vermont.  I was able to observe this test as it progressed. 


They did a test in this way:  They built 3 identical shed style buildings. 

  • The first one was just built with no insulation in the walls or roof. 
  • The second one was built with fiberglass insulation in the walls and roof.
  • The third one was built with cellulose insulation in the walls and roof.


Simultaneously, they set each building on fire. 

  • Of course, the uninsulated building burned to the ground very quickly.
  • The fiberglass insulated building also soon burned to the ground.
  • The cellulose insulated building was never actually completely consumed.


The conclusion was that while the first two buildings had nothing to prevent the buildings from quickly burning to the ground, the cellulose acted so well as an air barrier that it was much more effective at slowing the spread of the fire.  In addition, because of the fire retardant, the cellulose itself was not consumed.


Size of Spaces:  When most homes are being built, the size of the spaces between framing members vary a great deal.  Standard spacing is usually 16" or 24" on center.  However, there are many exceptions to this, because of the placement of openings and so on.  Therefore the size of insulation does not always match the size of the spaces it needs to fit into.  So fiberglass often has to be cut to fit.  This often is a trial and error process, with error often taking precedence.


However, there is another aspect where the size of spaces gives cellulose a decided advantage over fiberglass, or even over spray foam insulation.  When Designing, Remodeling, or Building High Performance Homes with very high energy performance, Cellulose insulation really comes into its own. 


When we Design these types of homes, we can Design what are known as Double 2x4 walls.  This type of Design has several advantages for you.


  1. The First advantage is lower building cost.  This is because of the familiar systems and the lower cost of the materials used.
  2. A Second advantage is that this type of construction is easy for any builder to do, as it uses systems that all workers are familiar with.  All builders are familiar with framed construction, and this Design uses ordinary framing like all builders use.
  3. A Third advantage is we can Design whatever thickness wall we want to make a Very High Performance Wall.  We just space the two framed walls where we need them, and fill the space with dense packed cellulose.  For example, if we want to make to make an R-40 insulated wall, we just space the two 2x4 walls with a 3 1/2" space between them.  We just frame a second 2x4 wall, use a cut off piece of 2x4 to space it away from the first one, nail it in place, and we're done!  Then we just attach plywood gussets to the two walls to stiffen them at the third points.
  4. A Fourth advantage is that we remove any thermal bridges from the walls.  Why is this important?  In a typical 2x6 wall, we can install R-19 fiberglass insulation, but that does not mean that the wall is an R-19 wall.  The framing of the wall which is only about R-6, typically occupies about 20% of the wall.  Therefore, the thermal bridging in the framing significantly reduces the effective R-value of the entire wall.  With a Double Wall Design, there is virtually no thermal bridging in the wall.  Therefore, the effective R-value of the wall is virtually unchanged.
  5. And a Fifth Advantage is that we have a Very High R-Value Wall with a Very Good Air Barrier at a Very Low Cost.  Because we are using Dense Packed Cellulose in the wall, not only is the R-value higher than fiberglass, but because Dense Packed Cellulose acts as a very good air barrier, the wall is much more effectively insulated than one with fiberglass.  Not as good an as Spray Foam Insulation, but the performance is very high at a significantly less cost than if we used spray foam. and we are using no petroleum products.



Copyright 2012 Ronald Sauve All Rights Reserved

This page was last modified on April 06, 2012

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