Straw Bale House Engineering and Design for Energy Efficiency

Straw Bale Design

Straw bale home design began here in the US with the resourceful Nebraska pioneers of the late 1800s. Having little wood on the plains and facing strong winds, the settlers had to be creative with their home design, using what was at hand. So, they baled their hay and built homes. Finding how well they worked, they later created straw bale houses by plastering over the straw bales.

Previously only appreciated by those Nebraska architects struggling to survive, today, straw bale homes are beautiful, contemporary structures that offer a cache of incentives. Precision Structural Engineering provides residential home engineering, custom home design and more using straw bales in construction. Could there be a straw bale home in your future?

Some Examples of Straw

Bales can be made from materials including:

Wheat
Rice
Rye
Barley
Oat

Because straw is usually locally available it is viewed as a readily available material. Straw bale building is the most popular natural building technique in practice today. When designed for green living, a straw bale home is one of the most comfortable and efficient style of homes available today. Some folks even host old-fashioned bale-raising parties to get their walls up. PSE Consulting Engineers provides straw bale home design so you can so you can take professionally engineered plans to your chosen contractor for construction.

What is a Bale?

A bale is a rectangular compressed block of straw bound by string or wire.

What makes a correct bale?

A bale must meet the following criteria:

Dry density of 7.0 pounds per cubic foot
Rectangular compressed block of straw with a minimum thickness of 14 inches
Moisture content shall not exceed 20 percent.
Bales shall be bound with ties of either polypropylene string or baling wire

Benefits of Straw Bale Design

Renewable Resource

Straw is an abundant, renewable resource perfect for a sustainable home design, which can be engineered to meet your local building department requirements. Have you seen all those cereal boxes on the grocer’s shelf? The making of those cereals produces over 200 million tons of waste straw each year in the US alone! Most of it is burnt, sending up billowing clouds of smoke, polluting our air.

Energy Efficient

Instead of using petroleum-based insulation products to fill walls, the entire wall is built from a natural, energy-efficient insulating product—straw. Because of its energy efficiency—a straw bale home can lower your energy bills by up to 75%—straw bale house construction is promoted by the federal government (http://www.energy.gov/).

Quiet

The naturally thick sheltering walls offer a sense of protection and sanctuary from the outside world that conventional homes often do not. The thick bale walls eliminate almost all unwanted outside noise. Conventional homes do little to block noise.

Healthy

Natural building materials allow you to breathe easy in your home. Straw bale homes offer an alternative to “Sick House Syndrome.” New homes today are polluted with chemicals from building materials that create allergies, asthma, ill health, and fatigue. Using natural materials and sustainable structural design eliminates this problem.

Beautiful

Straw may seem like a simple material, but the strategic design of a straw bale home can result in a beautiful structure. It’s easy to create beautiful, curved, sculptural walls.

Increased Fire Resistance

Conventional construction offers only a 20-minute burn resistance. Because of the density of the bales and the thick plaster, straw bale home construction yields a 60-minute burn resistance.

Myths About Straw Bale Home Design

Myth: Straw Bale Homes Are Not Sturdy

Are you thinking of the big bad wolf? Do not worry! Your straw bale home or building will be engineered for wind, seismic, lateral, and vertical loads—as well as the big bad wolf. There are several ways that a straw bale building can resist lateral forces:

Straw bale wall assembly with reinforced plaster skin
Diagonal bracing system
Engineered frame
Hybrid system (combination of the reinforced plaster skins and the engineered brace frames produces a strong structure)

Myth: Straw Bale Homes Will Rot or Grow Mold

As long as the house is designed and the materials drained correctly, there is no need to worry about mold or rot in the walls of a straw bale home. There are straw bale houses that have been standing for hundreds of years and are doing very well.

Myth: Straw Bale Homes Will Catch Fire Too Quickly

Like a telephone book, condensed and packed straw will not catch fire due to lack of air/oxygen flow through the material. In addition, straw bale homes are covered with fire resistance stucco.

Myth: Straw Bale Home Construction is More Expensive

Straw bale home construction is about 15% more expensive than traditional stick-frame construction. However, it is possible to complete some or all of the work yourself, making it cheaper on labor costs. Additionally, the cost savings over time due to a straw bale home’s energy efficiency will make up for the extra cost.

Types of Straw Bale Design

There are 2 types of straw bale homes—load bearing and non-load bearing (also known as Post and Beam). There are some important differences between the two:

Non-load Bearing:
Non-load bearing straw bale homes (infill design) are constructed so the bales are stacked within a structural framework, such as steel, wood, etc. These buildings can be multi-story. There must be a height to width ratio of 5.6 to 1 and openings shall not exceed 50% of the total wall area.

Load Bearing:
In Load-bearing straw bale homes, the stacked bales support all or part of the roof. These homes are limited to one story.

The thick bale walls eliminate almost all unwanted outside noise. Conventional homes do little to block noise.

Resources and Links

As experienced residential structural engineers, PSE has completed many straw bale home design projects. PSE provides everything you need to expertly design a straw bale home, including comprehensive structural plans and specifications that you can take to qualified contractors for construction. We focus solely on the engineering and design phase—we do not provide construction services or assistance with material procurement. For more information about straw bale home construction, please visit strawbale.com

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