Grain Bin Roofs over Straw Walls

My frequent driving throughout Alberta and Saskatchewan provided me plenty of opportunity to see two of the most common icons of the Prairies: straw bales and grain bins. As an ecodesigner and house builder, I began to study the conical grain bin roof as a potential roof for a straw bale yurt.

Thus was the beginning of a design adventure. And soon opportunities presented themselves, leading to the construction of seven houses that use the conical grain bin roof. They range from 1 to 3 floors, and from 500 to 1,600 square feet in size. With a round roof and a three-foot overhang, they have an Asian flavor to them.

Why consider a grain bin roof for a house? They are long-lasting, easy to assemble, and readily available throughout the Prairies and other parts of the country. A key advantage is rapid roof assembly. The roof sheets usually go up in one day to create quick protection for the rest of construction, including bale work. Several different sizes are available.

The grain bin roof system is free spanning and needs support only on the outside perimeter over the straw walls. Walls can be post and beam style or load-bearing (a circular load-bearing straw bale wall has added structural strength over a straight wall). So rather than concerning ourselves with a post in the middle of the building, the top center of the roof can become a four-foot diameter skylight.

In addition the roof is truss-free, so we can skip that construction step. More importantly we can use the vaulted interior space created by this modular conical roof system. The roofs are sloped at 30 degrees, resulting in a wonderful large teepeelike interior. We have finished the ceilings with plywood or canvas on half-round wood poles. The interior volume of this roof means we can build four-foot high straw walls for the second level of a house and still have a spacious second floor. ^

impregnated stones wear off and petrochemicals can be transferred to your water.

Ceramic Tile

Tile roofs are often associated with Spanish and Latin-American architectural styles. Originally made from local clays, modern tiles are mass-produced, fired, and weatherproofed. More expensive than some options, tiles still use natural materials in their manufacture, look good with the plaster finishes common to bale homes, and provide excellent protection. Installation is slower than with some sheathing, and cutting for angles is likewise slow work. High winds have been known to

9.8a damage tile roofs, so if you live in an area prone to severe wind conditions, check with your building official or other roofers before using tile.

Slate Roofs

Slate is a sedimentary stone, quarried in thin, strong tiles that can be nailed to the roof as shingles. The stone is heavy and the work slow. Slate roofs were once very popular, especially in areas that were close to a quarry. Ranging in color from black to green or red, a slate roof can be stunning when completed. Its natural colors and texture blend well with plaster finishes. Very durable, a slate roof will last indefinitely with some regular attention and timely replacement of loose or broken slate.

9.8a

9.8b

9.8a - b: The conical grain bin lid roof can be used on post and beam or load bearing bale buildings, octagonal or round.

These conical roofs offer incredible wind resistance. A 350 km/h hurricane would not affect such a structure.

The octagon was first used as the design shape, and fit well under the round roof. The wall system has 14-inch-thick posts and beams with infill straw bales. Last year we built our first round straw bale wall to fit under the conical roof. For this we created a simple post wall with 34 2-by-8s equally spaced to create a 1000-square-foot cottage using a 42-foot grain bin roof system painted green.

Off the shelf, the grain bin roof is not rated for Canadian residential snow loads. Therefore we have designed and engineered 12-inch-deep rafters that attach to the underside of the ribs of the roof sheets.

In addition to the strength improvement these rafters create the depth needed for R-50 cellulose insulation. Installing these rafters actually takes more time than the roof sheets themselves. With this level of insulation, the roof is very quiet. You cannot hear rain or hail through it. Sound studio quality acoustics are achieved if the interior ceiling is finished with canvas.

Challenges and disadvantages. Off-the-shelf roof sheets are galvanized, a long-lasting finish which is visually all right in a rural site. But when a colored roof is desired, the galvanized finish is costly to paint over. ^

Thatch Roofs

Thatch is made from bundles of grasses or reeds that are carefully arranged in thick layers and attached to the roof frame to provide protection against water. Thatch has been in use for centuries and, despite its antiquity, is still a reasonable roofing method. Appropriate natural materials are available in most regions of the world.

Although any style of roofing requires special skills,good thatching is particularly dependent on knowledgeable hands. You may find it difficult^ not impossible, to find a good thatcher in North America. A thatch roof is a perfect match for straw bale walls and is long-lasting (40 to 50 years) when regularly maintained.

Living Roofs

A living roof is an intriguing option. A waterproof membrane is laid down over wooden roof sheathing to prevent leakage, and a layer of drainage medium and then soil — which is appropriately planted — is laid over the membrane. A living roof

9.9: Bundles of reed are spread and fastened to the wooden roof strapping.

Another issue we had to face early on was permit problems. The roof system required complete engineering to get a building permit. Separate engineering per roof building is costly. Consequently we designed a generic roof sheet/rafter combination with a standard 50-pound snow load (suitable for most places in Canada). We then spread out this engineering cost over six buildings. After four years of R&D (and fooling around) we now sell the roof system along with the post and beam package with the engineering included.

A construction disadvantage is the fact that the roof assembly requires skills that, typically, framers or carpenters cannot offer. This means that a different trade needs to be hired to build the roof. You could do it yourself if you are the adventurous type and good at following instructions.

The smaller roofs are cost effective especially when combined with designs that reduce the wall height to create a second level. The largest grain bin roof available — the 48-footer — is more costly per square foot than the smaller roofs, but is still cheaper than high-end conventional roof systems.

Future frontiers. We have decided to turn some of the grain bin roof sheets into solar collectors and have begun testing this on one building in sunny Alberta. We simply added another layer of tin to the underside of the south quadrant of the roof to create a one-inch air space. With some ductwork and a fan we have a large amount of free hot air that is then circulated through a concrete floor. Another version of this produces hot water instead.

Overall, the grain bin roof system, in combination with simple post and beam design, has created lower-cost straw bale housing than any other method of construction I know.

— Paul Belanger, ecological designer, Living Design Systems <www.sunandstraw.com>

9.10: The living roof on this bale building is offering up a crop of poppies, and could be used to grow any type of garden.

can be very heavy and requires substantial roof framing to handle the load; you will need to do some research and design carefully if you use this option. While it makes a strong environmental statement and creates an unusual visual effect, a living roof may necessitate the use of significantly more structural and sheathing materials than conventional roofs.

Roll Roofing

A very inexpensive but unattractive and short-term way to sheath a roof, roll roofing is an asphalt impregnated paper that is stapled to the roof in wide swaths. It is quick to install but not nearly as durable as other options. Like asphalt shingles, roll roofing is made from petrochemicals and is not recyclable when its short life is over. Best used when you cannot afford other options, roll roofing can be overlaid with other sheathing materials at a later date.

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