Chapter 14
BUILDING REGULATIONS
It would be very unusual for your strawbale house, extension, studio, etc. not to meet current Building Regulation requirements in relation to the strawbale element. We have worked on so many now we have lost count, and have never experienced any problems that couldn’t be overcome by discussion! It’s important to understand that buildings are ‘regulated’ in order to make sure that they do not pose a threat to anyone or anything in terms of health and safety, so regulations are very useful when thinking about good practice. They include requirements to make sure that fuel and power is conserved and that people with disabilities can use buildings too. The procedures for dealing with the Building Regulations are different in Ireland and in the UK.
In Ireland the plans, which may or may not include all relevant Building Regulation information, are submitted for approval to the local planning authority, and everything is dealt with by them. The responsibility for ensuring compliance with the Regulations lies with the person who has overall responsibility for the design and its practical implementation, and who oversees the quality of work. It is expected that this will be an architect, but it doesn’t have to be. You may have submitted your own plans, for instance, or your building firm may have designated its own person.The local authority may come to inspect your building at any time, but may not.
In the UK, the planning department and the Building Regulations department are separate and require different information, although it is usual for all information to be contained on one set of drawings, submitted to both departments. Ultimate responsibility for ensuring compliance lies with an Approved Inspector, who may work for the local authority but may instead work for one of the independent Approved Inspector companies, set up under new laws a few years ago. These inspectors will insist on visually making sure that certain aspects of the construction are built as agreed: for instance, they will want to see that any low-impact foundation designs that have no cement or plastic in them are built according to plan, or that specified damp-proof courses are actually in place before concrete is poured, and so on. You are required to pay a fee for this service, and it can be very helpful to have the inspector on site if you want to ask any questions.
The Building Regulations for both Ireland and the UK are contained in a number of documents, called Technical Guidance Documents in Ireland and Approved Documents in the UK. In Ireland they can be obtained from the Government Publications Sale Office in Dublin, and in the UK from NBS Building Regulations (www.thenbs.com/BuildingRegs). There are some differences between them (for instance the Irish Regulations make reference to European Standards as well as British Standards on materials), but one of the most notable (as of July 2007) is that the Irish ones are printed on recycled paper and the UK ones are not!
Both sets of documents are labelled from A to P, including Part L covering the same subjects. They clearly state:
“The adoption of an approach other than that outlined in the guidance is not precluded provided that the relevant requirements of the Regulations are complied with.”
Irish Technical Guidance Document
“The detailed provisions contained in the Approved Documents are intended to provide guidance for some of the more common building situations.”
and:
“There is no obligation to adopt any particular solution contained in an Approved Document if you prefer to meet the relevant requirement in some other way.”
UK Approved Document
‘Document A’, for instance, refers to the structure of a building and will advise you on the minimum thickness your walls should be and the thickness of concrete you should have in your foundations. This example highlights a major issue around sustainable and strawbale building and the Building Regulations: the Regulations are written to cover the most common types of twentieth-century building materials, that is, concrete, brick and timber. If you are choosing to use other types of materials, or to use the same ones in different ways, then you will have to discuss this with your builder/architect in Ireland and your Approved Inspector in the UK, because there will be no written guidelines. The documents do not mention straw walls 450mm thick, or lime mortar and stone foundations, for instance, or limecrete and leca floor slabs – but this does not mean you cannot use them. On the whole, we would expect the builder/architect and Approved Inspector to be sensible, wellinformed people who are up to date with current developments in building practice. These people have lots of useful knowledge that can be helpful to you in designing your building, and can access their colleagues or other advisors if they need to inform themselves further about any subject.
However, there are many people in the construction industry who are not aware that there are other ways of building apart from conventional methods, or who are nervous of stepping away from what they know and what is written in the documents.
This does not mean it cannot be done, and in the UK your Approved Inspector is often the best person to help you with this (together with your strawbale and sustainability consultant, of course!). When contemplating building anything new or unusual, it is necessary to go back to first principles and look at what the aims of the Regulations are. They are there to ensure that whatever is built does not pose a health-and-safety risk in any way and, more recently, that the building is energy-efficient. All new buildings, extensions and alterations must comply with Part L of current Building Regulations. This covers many aspects of the building, including design to reduce heat loss, provide airtightness and conserve fuel and power. The usual way we do this is by designing for solar thermal efficiency, to utilise the natural energy of the sun to provide heat that can be stored in some materials (thermal mass) and prevented from leaving the building by insulation and good design details. Additional heat could be provided by an energy-efficient heating system, such as an air-source heat pump with under-floor heating.
The Regulations cover all aspects of building, but for our purposes, although the whole building is built predominantly of sustainable, natural materials, the only areas that are substantially different from other building techniques are the walls and foundation design. So the areas of concern for Building Regulations are:
• thermal efficiency (insulation)
• acoustic efficiency (sound insulation)
• fire resistance
• structural performance
• durability (including degradation due to moisture)
• airtightness
• log book, energy ratings etc.
Thermal efficiency
In brick or block walls, this often takes the form of expanded polystyrene or foam (high in embodied energy, and using pollutionintensive production methods) stuck to the back of the blocks inside the cavity of the wall. Other types of eco-construction may use timber and sheepswool or Warmcel as insulation. With strawbale walls, the insulation (straw) can also be the building block – and the surface for plaster – so reducing the need for extra materials. The amount of insulation of a material is measured by its U-value.
The U-value, or thermal transmittance, of a material is the amount of heat transmitted per unit area of the material per unit temperature difference between inside and outside environments.
It is measured in units of Watts per square metre per degree of temperature difference (usually measured in Kelvin): W/m2K. Put simply, the U-value is a measure of how much heat a material allows to pass through it.
The lower the U-value, the greater the insulation of the material.
Part L of the Regulations (2006) states that the following elements of a new extension or new build must have a U-value no greater than those shown in the table opposite (top).
Element | U-value (W/m2K) |
Walls | 0.30 |
Floors | 0.22 |
Flat roof with integral insulation | 0.20 |
Pitched roof with insulation at ceiling level | 0.16 |
Pitched roof with insulation between rafters | 0.20 |
Windows, roof windows and roof lights | 1.80 |
Doors with more than 50% of internal surface area glazed | 2.20 |
Other doors | 3.00 |
Straw bales have a U-value of between 0.13 and 0.20, depending on the quality of the bales used and the degree of skill used in installing them. This doesn’t include the render or plaster on either side, which would lower the U-value beyond this.
The high insulation value of straw is achieved because of the width of the bales. Compare the U-values of other common wall building materials, shown in the table below.
Materi | U-value (W/m2K) |
105mm brickwork, 75mm mineral fibre, 100mm light concrete block 13mm lightweight plaster | 0.33 |
100mm heavyweight concrete block, 75mm mineral fibre 100mm heavyweight concrete block, 13mm lightweight plaster | 0.40 |
100mm lightweight concrete block, 75mm mineral fibre, 100mm lightweight concrete block, 13mm lightweight plaster | 0.29 |
Source: Chartered Institute of Building Services Engineers (2002) ‘Thermal Properties of Building Structures’ in Guide A: Environmental design.
There is no doubt that strawbale walls exceed the requirements of Building Regulations for thermal insulation. Further information on the thermal tests conducted so far on straw bales is available in Appendix 1, and on the website of The Last Straw magazine,zwww.thelaststraw.org/resources.
Sound insulation
In The Netherlands research has been done into the sound insulation provided by straw bales (see The Last Straw no. 53), and we have overwhelming experiential evidence that straw walls offer far more sound insulation than do walls built with conventional twentieth-century techniques. People who live in, use or visit strawbale buildings remark on the quality of atmosphere found inside them. They are cosy, calm and quiet. They offer a feeling of peace. There are at least two sound studios in the USA built of straw because of its acoustic properties, one in Wales (www.pindropclub.co.uk/strawdio/index.htm), and several more meditation centres. Strawbale walls are increasingly being used in airports and motorway systems as sound barriers to reduce traffic noise. Recently, plastered strawbale walls have achieved Building Regulations approval as thermal and acoustic walls in semidetached houses.
Fire resistance
There is no question that strawbale walls fulfil all the requirements for fire safety as contained in the Documents.
In 2004 amazonails conducted fire-resistance tests with the Building Research Establishment (BRE), which showed that lime-plastered strawbale walls will withstand fire for a minimum of 2 hours 40 minutes. Compare this with a conventional plasterboard and scrim finish on a timber stud wall, which withstands fire for 30 minutes.
The same tests also showed that it took an hour before there was any temperature difference at all on the side of the wall away from the fire, which is an indication of its insulation value. The fire side of the wall was fired with the same furnace that all building materials are tested with – subjecting the wall to naked flames and temperatures of over 1,000ºC.
Unfortunately there was not enough money available to extend these tests up to British Standard (the only difference being that the wall system would have to be larger, at 3m2, rather than the 1.5m2 walls tested), but the results are the same as have been demonstrated in many other countries: seewww.thelaststraw.org/resources.
It is a popular misconception that strawbale buildings are a fire risk. This misconception seems to come partly from the confusion of straw with hay, and the collective memory of (relatively rare) spontaneous combustion in hay barns (from large haystacks baled too wet and green). Straw is a very different material from hay, and there are no known cases of spontaneous combustion with straw, even when stored in poor conditions.
There is a risk of fire with straw, however, during the storage and construction process. It is loose straw that is the risk, since it combusts readily. If you were to cut the strings on a bale and make a loose pile of the straw, it would burn very easily as it contains lots of air. Therefore it is essential to clear loose straw from the site daily, store straw bales safely, have a no-smoking policy on site, and protect the site from vandalism. If a wall is to be unplastered for a while, be sure to trim it, getting rid of the ‘fluffy bits’ that would encourage the spread of flames.
Once the straw is built up into a single bale wall it tends to behave as though it were solid timber, particularly when it is loadbearing and therefore under compression, but also when used as infill. In a fire, it chars on the outside and then the charring itself protects the straw from further burning. It’s like trying to burn a telephone directory – if you tear loose pages from it, they will burn easily, but if you try to set fire to the whole book, it’s very difficult.
When the wall is plastered both sides, the risk of fire is reduced even further, as the plaster itself provides fire protection.
For the purposes of Building Regulations, a wall built of any material that is covered with half an inch of plaster has a half-hour fire protection rating, which is the requirement for domestic buildings. All the firetesting research done on strawbale walls concludes that this type of wall-building system is not a fire risk. A list of research documents can be found in Appendix 3 and on The Last Straw website.
Research in the USA and Canada reached the following conclusions.
“The straw bales/mortar structure wall has proven to be exceptionally resistant to fire.
The straw bales hold enough air to provide good insulation value but because they are compacted firmly they don’t hold enough air to permit combustion.”
Report to the Canada Mortgage and Housing Corporation by Bob Platts, 1997
“ASTM tests for fire-resistance have been completed. The results of these tests have proven that a straw bale infill wall assembly is a far greater fire resistive assembly than a wood frame wall assembly using the same finishes.”
Report to the Construction Industries Division by Manuel A. Fernandez, State Architect and head of Permitting and Plan Approval, CID, State of New Mexico, USA, 1997
Structural performance
The requirements laid down in ‘Document A: Structure’ are for brick, concrete or timber walls. You will find no guidance here for building strawbale walls. This does not mean it cannot be done! Research in the USA has shown that structural loadbearing strawbale walls can withstand loads of more than 10,000 lbs/sq ft, equivalent to 48,826 kg/m2.*
There is no doubt that loadbearing straw walls can withstand greater loads than will be imposed on them by floors, roofs and possible snow loading. It is the design of associated timber work, the even spread of loads around the walls, and the quality of building that is crucial here, not whether the straw can do it.
With infill walls, in timber-frame structures, the straw does not take weight anyway and there are conventional calculations available for the structural strength of other types of framing.
Durability
This is the area of most concern when designing strawbale houses in order to comply with Building Regulations.
Will the strawbale walls retain their structural integrity over time, or will they suffer material degradation caused by moisture, from either condensation, rain or ground water? While this is a consideration for all house builders, in fact all that Building Regulations require is that the walls pose no threat to health and safety.There has been no research to date on the durability of strawbale houses in the weather conditions we experience in the UK and Ireland, but we are conducting research, in partnership with Lincoln University, on loadbearing strawbale council houses built for North Kesteven Council. What little research has been done in the USA and Canada shows that there should be no need to be concerned that strawbale walls will not withstand the test of time and the rigours of our climate.The key to durability lies in good design, good-quality work and maintenance. Past experience is an allowable and viable method of establishing the fitness of a material, as it says in the Documents, provided:
“The material can be shown by experience, such as its use in a substantially similar way in an existing building, to be capable of enabling the building to satisfy the relevant functional requirements of the Building Regulations.”
Irish Technical Guidance Document
“The material can be shown by experience, such as in a building in use, to be capable of performing the function for which it is intended.”
UK Approved Document
There is also a specific reference to the use of short-lived materials in the UK Documents:
“A short-lived material which is readily accessible for inspection, maintenance and replacement may meet the requirements of the Regulations provided that the conse-quences of failure are not likely to be serious to the health or safety of persons in and around the building.”
Not that straw is a short-lived material, but this clause should reassure anyone who is still not fully convinced of the capabilities of straw. In any case, a building that is designed well and built well should not experience any long-term effects of degradation due to moisture. There are plenty of examples in the USA of strawbale houses enduring for over 50 years with no signs of deterioration. The oldest known ones still inhabited today were built in 1903 in Nebraska, and the oldest in Europe is near Paris, built in 1921. In the UK and Ireland we have only fifteen years’ experience of building with straw bales, so it cannot yet be said that strawbale buildings will survive for long time periods in our climate. We do, however, know that even if there is degradation of the straw it is easily repaired, and that it degrades slowly and therefore poses no risk to safety.
Airtightness
The airtightness test is used to determine a building’s air leakage, and basically determines whether your building has been designed well, and then built well. Obviously, heat will escape from anywhere that air does. For the test you have to close all the windows and doors and use a machine that sucks air out of the building. The rate at which air moves, and is therefore being sucked into the building through unintended gaps, is then measured. Most problems in standard designs occur at the junction between the roof and walls, around windows and doors, and around electrical boxes. Buildings larger than 15m3 need to be tested and their air leakage proven to be no worse than 10m3/hr/m2 at 50Pa. As far as we are aware, only one UK strawbale building has been tested to date, and the tester said it was the most airtight building he had ever tested, at 1.56m3/hr/m2! We are not at all surprised, and would expect the same results from all our strawbale buildings. We have some very good design details for straw that are now being used in mainstream construction.
Most problems with airtightness occur because of poor-quality work and lack of understanding of the reasons for following designs accurately, coupled with using outdated designs that can’t really be improved, such as the cavity wall system. It’s common for electricians installing electrical back boxes to break through the internal concrete block skin into the cavity of the exterior wall, thus exposing the building to air leakage via the cavity. Monolithic wall systems such as strawbale ones can never suffer from this defect and are therefore inherently better, reducing the potential for poor-quality work. Not only that, but strawbale builders are usually very conscientious people who have chosen this type of construction for very sensible reasons, and when we run courses to help them build, we use a process that involves each person in a thoughtful and responsible way. Building with this sort of awareness can create much better-quality buildings. We pay attention to the process of building as well as the function, and it produces amazing results!
Log book and energy ratings
New buildings are now required to have a log book. This details lots of information about the building, including the type of construction. It also shows the calculations based on type of insulation, floor-to-window area ratios, U-values of different components, etc., which combine to produce a figure showing how energy-efficient the building is – the SAP (Standard Assessment Procedure) rating (or similar). The log book for a strawbale building would also include details of how to maintain the walls and plaster/render, what to do in case of accident, e.g. water penetrating the bales due to storm damage on the roof, etc., how to fix things to the walls, and how to make extensions or alterations.
And finally . . .
Lastly, a word of caution about Building Codes, Building Regulations and building practice in general.
You need to be careful about what you read in books and on the internet about strawbale building and how it must be done. Much of the information available is based on US Building Codes and methods of building, which are not necessarily appropriate for Ireland and the UK. There is an increasing body of knowledge available about practice in Europe, but we would not necessarily agree with all of it. We would encourage you to inform yourself as fully as possible of the principles of good strawbale design, and then make up your own mind.
There is a fundamental difference between Codes of Practice in the USA and some other European countries, and our Building Regulations. Other codes may be prescriptive: that is, they tell you that you MUST do it a certain way. In Ireland and the UK, Building Regulations are guidelines. They advise you on best practice, but you can do it another way if you can show it’s effective.
Prescriptive codes can mean that as new and simpler techniques are developed and the nature of straw is understood more fully, new practices cannot be used officially until the Building Codes have been altered. For instance, the Codes in some US States require that stucco wire must be used on straw buildings that are cement-rendered. This means that even if you are sure it is not necessary you still have to do it. Very quickly it becomes ‘fact’ that strawbale buildings must be wrapped in stucco wire, when the reason for the ‘must’ has become lost. In Germany it is still not permitted to build loadbearing strawbale buildings, even though we have been doing it here with full legal approval for fifteen years! So it is healthy to practise common sense, coupled with an enquiring mind.
When faced with a choice about whether or not to try a new or different construction technique, always ask yourself first: Does it work? But don’t stop there. Ask the most important question next: Is it necessary, or does it just over-complicate the building? And finally, ask yourself: Do I have the knowledge, skills and support required to carry out my dreams? The best strawbale homes are straightforward, beautifully simple (often simply beautiful!), and created as the result of many people’s efforts.
* Ghailene Bou-Ali (1993) Results of a Structural Straw Bale Testing Program. MSc thesis published as a summary by the Community Information Resource Centre, Tucson, Arizona.