ProVillage


ECO-BUILDING – PART 8 – Framing

Post and beam systems

Straw bale building are not the same as conventional buildings. This is an advantage and precisely the reason why some people incline to building straw bale houses. The best thing to do is to use framing systems which are adaptable to the bales found for your build. For most non-bearing systems, the framing is a post and beam or a modified post and beam frame.

In a non load-bearing construction the whole strength of the home is in the construction itself. This provides a load path for the roof and floor systems. It also acts with the shear strength for the building. This system holds the house up.

A similar value can also be given to the bales and the sorts, even though the frame is often regarded as the actual structural system.

Special considerations

Mesh used to reinforce the surface renderUsually a conventional frame is to be changed for straw bale purposes in a number of ways. First, there needs to be enough room for the adequate nailing of the lateral shear mesh around the doors and windows. For making this, an additional trimmer may be required depending of the inclusion of the exterior trim. There also has to be enough nailing surfaces along the base of the wall system for a possible mesh to be used.

Framing layout

Unlike conventional construction, the framing does not land on four foot centres and in four foot modules to accommodate plywood sheets. Instead, the layout of framing is designed to fit the size of the bales and support the calculated loads. The more accurate you are with framing to the bales sizes, the less you will have to do during the baling stage. It is also important to pay attention to the header and plate height around the house. The goal is to fit the bales tightly under the top plates to help squeeze the bales and strengthen the wall. The windows and door header heights should be lined up so that numerous layers of stuffing are not required to continue the running bond of the bales.

Roof design

Hip roofRoof designs do not change that much to the conventional roof. When making a gable roof, more custom made bales have to be used, and some designs require more work to be adapted to a straw bale home. As an example: In a gable roof design, more custom-made bales have to be made, as one builds more towards the roof line.

Gable roof

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A roof design can also help diminish the darkness sometimes created by the thick straw bale wall. By making an open roof design or dormers, more natural light can reach the room, thus brightening a room that may otherwise seem dark due to window size and orientation. The roof overhangs are should be quite remarkable in order to protect the construction from rain and/or snow.

Toe ups

The creation of toe ups is a part of the framing process. In a straw bale construction, toe ups are a necessary part of the straw bale construction. They provide adequate nailing surface for the possible wire mesh and separate the bales from the concrete and create a so-called moisture break. Should there occur a water break, the toe ups keep the bales dry and protected. The toe ups can be constructed using pressure treated 4×4 material, gravel and tar paper. They also provide a foundation or base for the bale anchors, which are required by code in various countries. The bales are attached to the toe ups, and the toe ups are attached to the concrete. In this way, the entire system is anchored to the foundation.

Some code books require the use of re-bar impalers for the system, but some nails applied to the toe ups have also been accepted in certain areas. The nails create a much stronger connection for the bales and do not interrupt the separation of the bales from concrete the way a rebar sections buried in the concrete does. Many building departments have easily accepted this kind of change in the construction.

Straw bales stacked on toe ups in a construction

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