Building With Straw Bales
In this article, the second of two parts, Barbara Jones, author of the new book, Building With Straw Bales – a practical guide for the UK and Ireland, looks at how to go about the design and layout straw bale constructions.
Building With Straw Bales – a practical guide for the UK and Ireland by Barbara Jones is available from the Green Shopping Catalogue
When designing your own straw bale house, think about what you want it to look like and how you want it to feel inside. Try to forget anything you've been told about building and imagine your ideal space, however wild that might seem! Then work within the practical limitations of the bales to come as close as possible to your dream.
The design of straw bale houses is usually simple and elegant. It is based on a block design and therefore different elements of the structure can be built up easily from the initial shape and dimensions of the foundations. Each section of the house has an obvious relationship to the other sections, and many different houses can be designed quickly and easily from the same basic plan.
For most domestic dwellings, it should be possible for owner builders to design their own houses. The way a straw bale house goes together is simple. It follows common sense principles and it is effective. You should have no difficulty in working out the construction drawings and methods for any type of domestic dwelling.
Once you've decided on what the building is for, what you want it to look like, and what you want it to feel like, read as much as you can about the subject and talk to your friends and anyone else who has experience of self-build and straw bale construction.
Draw the shape of the building you require, as though you were looking at it from above, this is called the PLAN view. Draw in the shape of the bales, their width and length, planning where they lie on the first course of the wall, (as in the drawing below.)
Now imagine you are looking at the finished building, standing on the ground looking north, south, east and west. Draw the face of the building you see from each direction, showing again where each bale is and how they turn corners or curve etc. These drawings are called elevations.
From accurate bale plans you can work out how many bales you need, how many hazel pins (two per bale from the fourth course up), staples (in every bale where it changes direction) and other quantities of materials. Details of foundations, windows, first floor and roof can be worked out. You also now have the basis for drawing your own plans for planning permission.
Principles Of Bale Design & Layout
Before you draw your final plan, and before you finalise the dimensions and lay out the foundations, you need to know the dimensions of the bales you will be using as they can vary a lot!
The bale plan should be made up of a whole number of bales.
Do not have any places in the wall (e.g. beside a window) that are less than half a bale length
Window and door openings must be at least one bale length away from corners.
If at all possible, choose window and door sizes that are multiples of bale dimensions.
In a loadbearing design the walls will settle a bit once the weight of the roof is on, so allow for this by leaving gaps above windows and doors that can be filled in later. With good building bales, settlement in a seven bale high wall should be about 1.2-5cm (-2in). The amount of settlement depends on the density of the bales and the amount of loading applied to them (such as the weight of the roof, if there is more than one floor, etc.).
Having understood the aim of natural and artificial foundations to provide a solid and stable base from which to build your house, we also need to pay attention to the specific requirements of the wall building material we are using, namely straw.
The base of a straw bale needs to be kept dry in the walls of a building. This means:
It must be raised off the ground sufficiently to avoid damage by splashback from rain bouncing off the ground.
There must be no possibility of moisture being trapped at the base of the straw, at the interface between straw and foundation.
Both of these can best be achieved by using self-draining foundations. But there are other reasons for using them too. Why use self-draining foundations?
They have withstood the test of time, and are a tried and tested method. Some of the oldest traditional buildings in the UK and Ireland, many over 400 years old, are made of cob (earth) and use self-draining foundations. There are significant similarities in the properties of straw bale and cob buildings and we can use the knowledge of generations to inform our practice today.
It is sensible in the often wet and windy climate of the UK and Ireland, to use this type of foundation as an important protection against the severity of the weather. If moisture enters the bale walls, it will slowly migrate downwards into the bottom bale, where it will stay and damage the wall if the foundation doesn't drain.
When the foundation is built up above ground level, it not only provides drainage for the wall, but also provides protection against the possibility of damp rising up through the wall from the earth beneath.
Many people are trying to reduce the amount of cement they use in building (for environmental reasons) and a self-draining rubble trench instead of concrete is an option.
Depending on the design, self-draining foundations can be built cheaply and without the need for professional builders.
These examples of foun-dation types have all been used successfully with straw bale buildings in the UK and Ireland. It is also possible to use these ideas in combination. What is important is to follow the basic principles:
Raising the bales off the ground by a minimum 23cm (9in) – preferably 46cm (18in).
Securing the bales to the foundations (preferably with hazel, or alternatively with metal rebar stubs).
Raising the bales at least 2.5cm (1in) higher than the floor level in any room with plumbing, e.g. kitchen and bathroom.
Protecting the bales from moisture from above and from below.
Remembering to incorporate provisions for good insulation.
It is clear that the art of straw bale building has progressed dramatically from its early beginnings on the Nebraskan plains. After seven years of experimentation and adaptation of design to suit our climate, based on common sense and on what works in practice, straw bale building is poised to enter that world of acclaim, the mainstream! Very quickly we will be seeing commercial adaptations of the simple self-build method, and before long, we'll have whole rows of straw bale terraced houses sitting snugly within our urban areas. But I'm sure it will never lose its appeal to those pioneering self-build enthusiasts who just love to experiment and do it themselves.
The Straw Bale House - This book shows you how to build a straw bale house in 4-6 weeks for as little as half the cost of a conventional build.
Serious Straw Bale - A comprehensive book that handles the serious design issues of seasonal moisture, humidity and temperature stresses in more extreme climates.
The Design of Straw Bale Buildings - The State of the Art by Bruce King - A design manual for practising professionals, drawing on the collective experience of the most senior and respected figures in the rapidly-emerging field of straw bale construction.