There is a lot of conventional wisdom out there about what is “typical” for building construction practices. While the collective experience of available labor and availability of materials tends to drive how things get designed and built, it is important not to get stymied by routine practices. With progressive thinking about sustainable design and new ideas about how to manage construction costs, there are many new as well as old technologies that should be explored for the construction of a wide variety of building types. This post addresses my top 10 list of construction methods that, old or new, are considered by the industry to be “Alternative” (by the way, these are in no particular order):
SIP stands for Structural Insulated Panels. They are rigid foam insulation sandwiched between two OSB panels. They can be used structurally and create a wall or roof system with no thermal bridging. These buildings are extremely airtight and have very high r-value, resulting in superior thermal performance in a relatively thin wall. Multistory buildings can be done, but there are structural limitations to the panels as well as fire rated assemblies that need to be addressed for larger commercial use. SIPs can also be used as infill wall panels on frame structures.
ICF stands for Insulated Concrete Forms. They are continuous rigid foam panels that are used as concrete forms and left in place after the pour to create a wall that has both thermal mass as well as high r-value. Some contractors use these only for foundations, but entire structures can be built from them. These buildings are extremely quiet and thermally outstanding. Roof systems would have to be SIP, truss or rafter, so proper detailing is key. Cons are that local concrete costs can drive price per square foot significantly and these buildings are not easy to modify with conventional tools once built.
3.) Radiant wall systems
These are similar to ICFs, only the rigid insulation is an interior layer, sandwiched by the concrete layers. This places the durable concrete layer on the exterior and a layer of thermal mass inside the insulation layer, which results in a superior assembly. The interior layer of concrete also has hydronic heat tubing in it, so they can serve as the heating distribution for the building. These walls have to be formed by a special crew trained in the system and as a result, will be more costly. Radiant wall systems are even more difficult than ICFs to modify once built due to the embedded hydronic tubing.
These structures are essentially stacked straw bales that are finished with plaster, earth or stucco. Straw has relatively low r-value per inch, and not much thermal mass either, but the walls are very thick, so they make up for it. The walls are also very limited structurally. As a result, for anything other than small single story design, a structural frame would need to be incorporated to carry the loads and the strawbale walls would serve as infill material.
Log walls have been around for centuries and utilize solid wood logs as the structure and the finish. There are a wide variety of log coping techniques that range from very rustic with chinking serving as the thermal barrier between logs, to sophisticated milled logs that are very airtight. While wood has a relatively low R-value per inch, the thermal mass of the wall counteracts the loss in r-value. Detailing openings and interfaces to floor and roof systems are crucial to maintaining the thermal barrier in a log structure. Not commonly used in commercial building, Log structures can qualify for a type 4 construction and be used in certain fire assemblies.
Timberframe structures have also been around for centuries. These are essentially heavy timber post and beam framed structures that require an infill material for the walls (SIPs are a good option). Craftsmanship is key in these structures and the joinery is nothing short of pure art expressed within the structure. Finding qualified labor can be challenging and materials need to be specially sourced. Like log construction, Timberframe can also be used in Type 4 construction.
One of the oldest methods, and probably one of the most misunderstood, Cob has nothing to do with corn cobs. It is actually an earthen wall method of construction made of balls of mud and straw (Old English cobs) that are hand packed. This very labor intensive method of construction uses the cheapest of materials provided the native soils on the site are suitable. Walls can be scuplted in organic forms and need to be finished with a waterproof exterior so the rain won’t melt the structure away. The walls have very high thermal mass, which makes up for their relatively low r-value. There are structural limitations on cob construction, so a frame of some kind may be necessary for multistory or larger buildings.
Similar to Cob, Adobe is a clay brick method of wall construction. With suitable on-site soil, bricks can be made and dried then stacked in a labor intensive approach. Like Cob, you get thick walls, high thermal mass, but low r-value. Exterior finish is required to protect the wall and structural limitations still apply.
9.) Rammed Earth
Of the earthen techniques, Rammed Earth is seeing the strongest resurgence today. Made of a suitable recipe of soil that is compressed into a mold, the resulting walls are strong and durable. Like the other earthen methods, high thermal mass offsets low r-value, and the walls are generally much thicker. The resulting walls are very beautiful as you see the strata of the material as it was compressed into the form. These walls are significantly stronger than Adobe and Cob, and require much less maintenance.
Popularized in the 70′s, these structures are often made with used automobile tires, filled with earth. Infill walls would be recycled materials like glass bottles or aluminum cans and every effort is made to utilize local resources and eliminate waste. Portions of the building may be bermed or buried. The term Earthship really was intended to describe a sustainable approach to building, but over time, has resulted in buildings that have very similar characteristics and materials. With modern approaches to sustainable design, the sustainable design philosophy has outgrown the original structures, however, some are still being constructed today.
It is not uncommon to see hybrids of these techniques used together, or combined with more conventional construction. There are also countless other methods that utilize both new and old technologies (some rather interesting – like corrugated paper construction, sandbag or even stacked carpet squares). There is no end to the inventiveness or innovation out there and every building site and type should explore all of the available techniques that may offer a higher degree of sustainability, reduced construction cost, and offer the owner or users of the building an opportunity for personal expression.
Originally posted 2010-01-15 10:28:29. Republished by Blog Post Promoter