- Green Technology
Straw Bale House Construction - Part 3
Straw Bale Structure
There are two different methods to build a straw bale house, which are load bearing and timber frame or infill.
Load Bearing Structure
In load bearing construction, the bales are utilized as a structural element for the house, as they carry the load of the roof assembly. The bale walls are fastened to the roof plate and foundation, which spreads roof and floor loads to the width of the wall. The principles of load bearing structure are similar. Once the stacking of bales are interlocked, the corner from one direction to another will stabilize the entire structure firmly. To enhance the wall stability more, the pre-welded mesh (net) is utilized on the internal and external face of the wall.
Load bearing structure reduces the quantity of building material, such as it reduce the quantity of timber or steel in a house as bales are utilises to support roof assembly so that very few amount of timber will be required.
The bale walls will be exposed to climate until the roof has been installed.
Due to load bearing construction settling of structure is very quick as the roof loads compress the bales.
Construction of house is very straightforward because of less structural element to bale around.
Timber Frame/ Infill Structure
In a timber frame and infill construction, straw bale house needs a wooden or steel frame. The roof is being erected after the construction of a frame and then bales are being installed into the frame as insulation. In this method, bales don't have any structural role in carrying roof or floor load, which all are being carried out by wooden or steel frame. However, the lateral stability of the house will be given by straw bales only.
It gives covered area to store bales, as roof assembled before installation of bales inside the walls.
The bale walls have to compress manually before rendering.
The roof gives good protection to walls from the climate.
It is expensive in a material.
It has a high ecological footprint.
In the construction of straw bale house, a designer should take moisture (water) consideration first, as it is a curse of a building. Moisture is the reason for most structure problems. Its presence in the building could create lots of difficulties. The structural damage will be at greater risk because of wood decay and steel corrosion. Additionally, it can damage interior surface and finishes by fungal growth.
To eliminate moisture related problems, a designer should identify a moisture source, its traveling pattern inside the structure, plumbing leakage, air leakage, roof leakage and groundwater. Besides that, rain is the biggest enemy of straw. It could penetrate inside the building easily and deteriorate interior finish and furniture. Rain could also cause problems such as discoloring, staining, efflorescence and human health problems. Approaches such as wall design, building shape, and site design choice should be taken into consideration to prevent rain-related problems. The best moisture control strategy should always design during the planning stage, but not solving them after the structure got affected.
Followings are the various approaches to protect straw bale walls from rain:
Climate condition plays an essential role in evaluating rain exposure of building. The climate zone is valuable for determining the drying potential and moisture potential since hot and dry weather accelerates the drying process. The houses in numerous parts of the UK are exposed to serious wind-driven rain, which is very dangerous for building’s walls. Selecting an appropriate site could assist in minimizing the amount of rain that could affect the walls of a building.
The site assists in controlling the rain by various protections, such as plantings, berms, and buildings, which will minimize the rain load. The driving rain load can be minimized in one or two stories building by landscaping, planting and constructing next to another building. Surrounding buildings and topography of same height situated within the two building heights will give a good amount of protection.
Building Shape and Mass
The mass and shape of a building influence the wind driven rain which could hit the wall. The shapes of roof and overhang also have an essential impact on the building. Research has shown that overhangs and peaked roofs could minimize the rain deposition by roughly 50%. The overhangs and peaked roofs guard a wall against rain by redirecting air flow and shadowing. In addition, hipped roofs can give protection to all four walls of the building from rain.
Ground and Surface Water
Every structure should be saved from flowing groundwater. The building needs to be raised above the grade to prevent it from surface water and the site should be graded to direct the surface drainage. House needs berms and swales to direct the both ground and surface water around the building. During snowfall, the accumulation of snow on the walls is always inevitable. When the snow starts melting, the water penetrates inside the walls, and it will start to weaken the walls. The grade separation and cladding over the drainage space are the best way to control snow accumulation and melting.
Plumbing failure and problems could cause numerous serious damages inside the straw bale house. Water lines should never run inside the straw bale walls, if any leakage occurs then it would be impossible to detect its actual root cause. If the owner has a desire to penetrate the plumbing lines inside the walls, then it should be placed in a watertight plastic pipe and which should be sloped outward to control any leakage.
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© 2017 Ashish Dadgaa