Post And Beams Plan With A Round Cross-section

2007-12-15 Word Count: 451 Category: Home Improvement

Looking for information on post and beam house plans or barn plans?

Many old post and beam barns and houses make use of floor joists and rafters that were made from locally grown straight tree trunks.

Sometimes the builder would flatten one edge of the timber with an adz, so that roofing or flooring could be more easily nailed to it. In Mexico and the Southwest, exposed vigas (beams of round cross-section) are a common and attractive architectural feature.

Owner-builders today sometimes make use of their own home-grown timbers. They can be taken to a sawmill for squaring, they can be milled in the forest with a portable sawmill, or they can be barked and used in their natural round cross-sectional shape.

While this book is mostly concerned with the use of timbers milled on four sides, the author is in no way opposed to the use of viga-type beams, which can be quite beautiful.

Here are some tips with regard to their use.

1. Choose sound straight trees for making vigas.

2. Remove the bark. The easiest time to do this is in the spring, when sap is rising. The greasy sap actually makes barking the wood very much easier, as it forms a slippery layer between the bark and the cambium wood layers. Good tools for barking include a pointed mason's trowel, a straight hoe, or a peeling spud made from any piece of flat stock metal that has an edge sharpened. Barking at the wrong time of the year, such as autumn, may necessitate the use of a drawknife, which is a lot like hard work.

3. For the purpose of judging the strength of a viga, consider its small end as the sectional dimension.

Remember the old saying that a chain is only as strong as its weakest link? This
principle is often appropriate with timber framing, where a mortise and tenon joint can
actually reduce the shear strength of beams where they join a post.

4, For maximum strength with rectilinear structures, alternate large and small ends on
parallel rafters or joists. This is different from the weakest link analogy, as the entire floor or roof is distributed over several parallel rafters and alternating weak and strong members lends greater strength to the entire structure. Stronger members assist
weaker members.

5. With a radial rafter system, there all the rafters or joists head towards the center, as in our round Earthwood house, put all the smaller ends towards the middle, where they are supported by a large post or a post-and-capital. The frequency (space between members) greater towards the center, so the strength there is naturally enhanced.