After the roof, exterior walls have the next largest impact in the 'greening' of a home. Most homes are built from 2x4 wood framing with sheetrock (gypsum board) interior. 2x4 walls can be more 'green' by using wood saving framing techniques with alternate sheathing and insulation components. New products like no-paper (no mold) gypsum board and spray insulation should be specified. To create still greener walls ECO has worked with locally available wall systems which offer green features like better energy performance, better air quality, and less waste. The following are our favorite 'GREEN WALL' systems for exterior walls. Some have also offer advantages for interior walls (provided the volume or space needed for mechanical, electrical and plumbing systems is properly designed).
#1: GREEN 2X6 WALLS TIGHTLY SEALED WALLS FOR ANY PLAN:
Switch from common 2x4 on 16" spacings to 2x6 on 24" spacings. You will be hard pressed to find a cost difference, but the wood volume will be less (up to 19%), the wall will be stronger, have less thermal bridging, and allow thicker batt insulation. Or consider filling the 5.5" wall cavity instead with 3.5" of spray open cell urethane, or spray cellulose for superior sound insulation with no waste. The walls will be extremely air tight. Add the same spray insulation system for the roof structure. You will loose 2" in each perimeter wall, but when is a slightly smaller conditioned space a bad thing?
#2: SIPs - FOR GREENER WALLS FOR MOST HOME PLAN
SIPs USE FAST GROWTH TREES TO PROVIDE 2.5X STRONGER SUPER-INSULATED TIGHTLY SEALED WALLS It is also easy to switch from common 2x4s to SIP wall panel construction. Several Texas factories make Structural Insulated Panels and local SIP contractors offer many years of experience.
SIPs are very strong and very energy efficient (<50%) and best when SIPs are also used for the roof systems. Any floor plan can be built from SIPs. Additional design details for wiring, plumbing, HVAC locations are best addressed in the design phase. And for real world construction speed, there is no building system that can complete with a SIP home built by an experienced SIP crew. Once the SIP shell is up, brick, Hardie, roofing, and sheetrock are applied in a normal manner. A simple but durable, energy efficient, 'green' home solution is a SIP structure with Hardie siding and a standing seam metal roof!
SIPs offer many features to the homeowner and to the builder (the following are valid points taken from the Structural Insulated Panel Association's "Designing with SIPs" course we completed)
• Higher resale value and appraisal (Appraisal Institute Study) • Reduced callbacks due to nail popping, cracks due to lumber shrinking • Lower labor skill needed, Reduced man hours per home • Two to Three times stronger, no need for steel strapping! • Smaller HVAC required• Happier customers, greater comfort • Less site waste, Greener product & process • Integrates easily with other building systems • Less or no temporary heat required during building in cold climates • Less building material theft during construction • Temporary service savings for owner/builder • Trim labor cost is reduced• Less trade coordination required • Weatherproofing goes faster—moisture exposure for all products reduced • Air sealing is easier, and less complicated resulting in less or no mold • Drywall contractors can hang drywall faster since they don’t have to look for studs • Drywall contractors and can bid lower. Straighter walls. No nail pops • Stone and Stucco contractors can bid lower work faster due to OSB on all sides.
SIPs are also an excellent solution for flood areas that require crawl space foundations. Overly complex hip roof designs can not be easily built using SIPs, but cathedral, sloped and vaulted ceilings make smaller home plans seem larger. Again, you will loose 2", but when is a smaller home a bad thing? Talk to your designer, to ECO, or Google "R-Control".
SIPs are also an excellent solution for flood areas that require crawl space foundations. Overly complex hip roof designs can not be easily built using SIPs, but cathedral, sloped and vaulted ceilings make smaller home plans seem larger. Again, you will loose 2", but when is a smaller home a bad thing? Talk to your designer, to ECO, or Google "R-Control".
#3: AAC BLOCK CONSTRUCTION
AAC WALLS PROVIDE INSULATED CONCRETE WALLS WITH NO STUDS OR SHEETROCK Also consider if AAC Block construction which offers great energy performance (<50%) can fit your needs. Several Texas and NAFTA factories make Autoclaved Aerated Concrete block or Mix Aerated Concrete Block. Local masons see little difference between AAC and CMU construction. AAC uses less wood, no foam, no sheetrock - so no termites, rot, mold, fire, or water damage potential.
Any floor plan can be built using AAC block, but it is better to design from scratch to take full advantage of all that AAC block can offer. Additional design details for wiring, plumbing, HVAC locations need to be addressed in the design phase. AAC home roofs are built using SIPs or 2X wood with spray foam or spray cellulose insulation. AAC is different and you will need to design for it, but these are a lot of positive features provided by one system.
Aerated Concrete Blocks come in different sizes, from this small 5"x5"x10", to medium 8"x8"x24" to jumbo 8"x24"x48". Small/Medium blocks are easily stacked by one person, and in the case of the smallest, by one hand. With the right design, we think 5"x5"x10" blocks will be comparable to 2x4 construction in both cost and energy performance making it a good low income option. The larger 8"x8"x24" AAC block will outperform the best insulated 2x6 home.
Most Aerated Concrete blocks are attached with a thin coating of adhesive mortar and then further reinforced by vertical and horizontal grout and rebar sections. The unique 5"x5"x10" LiteBlok is designed to dry stack like a lego and then be grouted with vertical rebar. All Aerated Concrete blocks work with standard electrical and plumbing systems. But ECO also knows how to detail all the Mechanical, Electrical, Plumbing details on the blueprints. This allows easier coordination with those MEP trades.
The photo on the left is at the start of a 2-story low income AAC block project under construction (Nov 1 2007) in east Houston. This projects used 8"x8"x24" aerated concrete with a high flyash content. To meet the low income target, for the most part the AAC block walls are being installed by this owner-builder and one helper. Eco provided the foundation, design, the framing design, and all AAC block design and all construction details.
The photo at the bottom is an Austin AAC and wood framed project we engineered in 2005. This is one of two projects ECO engineered that are becoming LEED certified by the US Green Building Council in 2007. Design details like the arch shown below are easy to add with AAC block. If your project can take the time to investigate AAC, you should look into this system. Talk to your designer, to ECO, or Google "AAC block construction".
SIPs are very strong and very energy efficient (<50%) and best when SIPs are also used for the roof systems. Any floor plan can be built from SIPs. Additional design details for wiring, plumbing, HVAC locations are best addressed in the design phase. And for real world construction speed, there is no building system that can complete with a SIP home built by an experienced SIP crew. Once the SIP shell is up, brick, Hardie, roofing, and sheetrock are applied in a normal manner. A simple but durable, energy efficient, 'green' home solution is a SIP structure with Hardie siding and a standing seam metal roof! 
SIPs are also an excellent solution for flood areas that require crawl space foundations. Overly complex hip roof designs can not be easily built using SIPs, but cathedral, sloped and vaulted ceilings make smaller home plans seem larger. Again, you will loose 2", but when is a smaller home a bad thing? Talk to your designer, to ECO, or Google "R-Control". 
Any floor plan can be built using AAC block, but it is better to design from scratch to take full advantage of all that AAC block can offer. Additional design details for wiring, plumbing, HVAC locations need to be addressed in the design phase. AAC home roofs are built using SIPs or 2X wood with spray foam or spray cellulose insulation. AAC is different and you will need to design for it, but these are a lot of positive features provided by one system.
Aerated Concrete Blocks come in different sizes, from this small 5"x5"x10", to medium 8"x8"x24" to jumbo 8"x24"x48". Small/Medium blocks are easily stacked by one person, and in the case of the smallest, by one hand. With the right design, we think 5"x5"x10" blocks will be comparable to 2x4 construction in both cost and energy performance making it a good low income option. The larger 8"x8"x24" AAC block will outperform the best insulated 2x6 home. 
Most Aerated Concrete blocks are attached with a thin coating of adhesive mortar and then further reinforced by vertical and horizontal grout and rebar sections. The unique 5"x5"x10" LiteBlok is designed to dry stack like a lego and then be grouted with vertical rebar. All Aerated Concrete blocks work with standard electrical and plumbing systems. But ECO also knows how to detail all the Mechanical, Electrical, Plumbing details on the blueprints. This allows easier coordination with those MEP trades. 
The photo on the left is at the start of a 2-story low income AAC block project under construction (Nov 1 2007) in east Houston. This projects used 8"x8"x24" aerated concrete with a high flyash content. To meet the low income target, for the most part the AAC block walls are being installed by this owner-builder and one helper. Eco provided the foundation, design, the framing design, and all AAC block design and all construction details.
