Greenstar Blox -- A New Energy Efficient Wall Block

Greenstar Blox are a new wall building block product that has been under  development for several years.  The Greenstar Blox offer the promise of high strength, durability, high R values, reasonable cost, and a relatively straight forward build process.  It looks to me like they might make a good material for owner built homes.

GreenstarBlox home


The standard Greenstar Block is 10 by 14 by 4 inches and is made from roughly 65% selected recycled paper, 25% Portland cement, and various additives.  This is similar to papercrete, but the difference is that Greenstar Blox are commercially made to a standardized recipe  using  a standardized process to produce a consistently high quality block.  The Greenstar Bloxs are currently going through an extensive testing program at Texas Tech University.  The results of the testing program are being used to seek building code approval, which is anticipated in early 2012.

One of the most appealing features of the material is the relatively high R value -- as high as R3.2 per inch.   This makes for a wall that is about R25 with little thermal bridging.

To make walls, the blocks are laid in courses  -- a little like building with very large Legos.  The blocks are much lighter than concrete blocks, which makes them easier to stage and lay. 

The Mason Greenstar website provides some information on the Greenstar Blox including pictures of some of the projects that have been built using the blox.

The following notes are from a phone conversation with Matt at Greenstar Blox.  Some of this information is tentative, and I would give Greenstar Blox a call if you are interested in building with their product to get the latest from them.

The blocks are being made in limited quantities now with plans to go to a more automated and higher production system in February of 2012.  While production rate is limited, you can order blocks from them now.  A number of actual projects have been built with the blocks.

The rough cost is about $1.50 per block. 

The blocks are 10 inches by 14 inches by 4 inches thick and weigh just over 8 lbs -- about a third the weight of regular concrete blocks.  The blocks are light enough to float in water. 

The recipe used to make the blocks can be varied according to the application the blocks are being put to, and one of the current activities is exploring alternative formulations.

The blocks have a maximum R value of 3.2 per inch.   The R value varies according to the formulation, and will be less than 3.2 per inch for some formulations.   R values anywhere in this range are quite impressive and should allow a good high R value wall.  The fact that the mortar is the same material should maintain the high R value in an actual wall.   While the blocks are normally used with the 10 inch dimension forming the thickness of the wall, it is possible to build with the  14 inch thickness for the wall for a very high R value wall.

Wall construction:

Wall section

A variety of wall constructions can be used, but this is one typical stackup.



The homes can have the same nice look as an adobe home, but with the added advantage of the high R value walls.

The Geeenstar Blox are essentially an enhanced and standardized form of papercrete.  The blocks are made from 65% selected recycled paper, 25% portland cement, and 10% water and additives.   Their specific  formulation is patented.  The advantages of the Greenstar Blox include relative to papercrete are:  A consistent formulation and production process that results in a block with consistent high strength, high R value, mold resistance, and fire resistance.   You might well learn to make equally high quality papercrete blocks yourself, but there would certainly be a learning curve and the making a sufficient quantity of blocks for a home will be a time consuming job in itself.  The disadvantages of the GreenBlox compared to papercrete probably lie in the areas of cost and in the need to transport the block to the building site.

An extensive set of tests are being run by Texas Tech and the results of these tests will be used to seek building code approval.   This would, of course, be a major advantage for people wanting to build in areas in which getting approval for a conventional papercrete house might be quite difficult.

The current Greenstar Blox website does offer some information and quite a few pictures showing some of the construction projects the blocks are being used for.  An update of the website is planned for January that will probably provide more "how to" information. 

Several owner built homes have been done with Greenstar Blox, and they appear to be interested in this area as a market for their product.

More detail on the results of the testing program done by Texas Tech should become available in 2012.

As things are developing and changing rapidly at Greenstar Blox, I'd suggest getting in touch with them directly if you think you might want to go this way.

Gary November 30, 2011