Dealing
With Alternative Construction Methods
Through Performance Based Building Codes
by Claire Benge
Technical
Adviser for the
New Zealand Building Industry Authority
Paper for the
2nd International Conference on Construction Industry Development,
and the 1st Conference of CIB TG29 on Construction in Developing Countries:
CONSTRUCTION INDUSTRY
DEVELOPMENT IN THE NEW MILLENIUM
October 27 — 29, 1999
SINGAPORE
Abstract
In
a world that is becoming more regulated and more aware of liability it is
increasingly difficult to introduce radically new materials or to revive traditional
methods of construction. As third world countries face increasing poverty,
higher costs and demands for conservation of world resources, the use of alternative
(ie non-mainstream) or revived traditional methods of construction to improve
the housing of people in third world countries in the new millenium is becoming
important. Performance based building codes have the facility to accommodate
diversity of construction methods, satisfying the regulators, conservationists
and lawyers alike while providing improved cheaper buildings.
This paper will discuss the New
Zealand experience of processing building consents for alternative methods
of construction such as earth buildings, straw bale construction and log houses.
The performance criteria of NZ Building Code clauses B1 "Structure", B2 "Durability"
and E2 "External moisture" and others are used to measure the adequacy of
systems. The use of performance based building codes to assess materials or
systems that are not current standard construction can be used in any country
taking local considerations into account.
INTRODUCTION
In a magazine called "Appropriate
Technology" an English architect, Robert Barclay, wrote:
"With some notable exceptions,
most building regulations in the Third World are invariably restrictive, tend
to inhibit the development of building materials, and to frustrate improvements
in construction methods, including the important sector of alternative low-cost
building materials"
And:
"Not the least of the problems
is the urgent need for housing or shelter which uses appropriate technology
to achieve the most at the least cost. Invariably, neither existing building
regulations, nor the local building by-laws, are sufficiently receptive to
the use of low-cost materials and technology, or, at best, attempts may be
made to adapt or waive specific clauses as emergency measures to suit particular
circumstances. Building regulations should be framed to facilitate the further
development and use of appropriate materials and methods of construction consistent
with health and safety requirements"
He concluded by saying that national
building regulations based on a narrow concept of enforcement will be of very
limited use. Regulations that are forward-looking and permit reasonable interpretation
in their use are much more likely to achieve the desired result.
That was written in 1987. Has
much changed since?
PERFORMANCE BASED BUILDING
CODES
Traditionally, building regulations
have been prescriptive, saying what must be done and how to do it. By nature
such systems of governance are very restrictive because they cannot cover
every foreseeable circumstance and certainly they cannot cover unforeseeable
circumstance. In recent times, as regulatory authorities search for more flexible,
less time consuming and cheaper methods of regulating building, they have
been leaning towards performance based building codes. Performance based building
codes simply state what must be achieved and are therefore by nature very
broad and versatile.
Performance based building regulations
can encourage the use of local materials and traditional construction methods,
or new technology that results in cheaper construction, to improve the housing
of the poorer people in third-world countries. The performance based New Zealand
Building Code has been in use for over 6 years now. As the New Zealand construction
industry has become used to the system, its ability to be flexible and save
costs is beginning to be demonstrated.
THE NEW ZEALAND STORY
The New Zealand Building Act 1991
set up the Building Regulations 1992 and a 6 months lead in period saw the
full introduction of the New Zealand Building Code in January 1993. The New
Zealand Building Code has 37 clauses covering all aspects of the building
code. These are divided into 8 sections, classified as General Provisions,
Stability, Fire Safety, Access, Moisture, Safety of Users, Services and Facilities
and Energy Efficiency. These are the mandatory clauses and are performance-based.
Each clause has a 5 tiered system of sub-clauses. These tiers are as follows:
1. Objective — states the
purpose of that clause, usually based on health, safety and accessibility
2. Functional Requirement — states what has to be achieved,
3. Performance — states
how to achieve the Objective in either a qualitative or quantitative
form.
The next two tiers are of equal
importance and are collectively called the Approved Documents. These are non-mandatory
clauses and are prescriptive. They are a shortcut to proving compliance with
the mandatory clauses above. They are not the only way to prove compliance,
which can also be done by demonstrating that an alternative solution will
comply with the Performance criteria. The Approved Documents consist of the
following:
4. Verification Method — Calculations or test methods
5. Acceptable Solution — Cookbook method
It is in the alternative solutions
that the flexibility of the performance based code lies. Alternative solutions
need to show that they achieve the relevant requirements of the mandatory
clauses of the code.
Under the New Zealand Building
Act the regulatory authority (city council, district council, regional authority)
administers applications for building consents. Section 34 of the Act requires
that the regulatory authority shall grant the consent if it is satisfied on"reasonable
grounds" that the provisions of the building code would be met if the building
work was properly completed in accordance with the plans and specifications
submitted with the application. Thus the applicant has to show documentary
evidence that will give the Regulatory Authority reasonable grounds to be
satisfied that the building code is met. Compliance with the Approved Documents
obviously constitutes reasonable grounds. When a building material or system
does not comply with relevant Approved Document the applicant must supply
the regulatory authority with documentary evidence that provides reasonable
grounds for being satisfied that the building will comply with the building
code.
Proof of Compliance
A building does not have to be
built in accordance with the Approved Documents, but if it is not, the owner,
designer, builder or manufacturer has to show the regulatory authority that
the design complies with the relevant clauses of the NZBC. One way of demonstrating
compliance is "history-in-use", eg. a building system that has been in use
for some time and proved satisfactory. Tests and standards other than those
named in the Verification Methods and Acceptable Solutions may also be used,
but the regulatory authority will need to know what relevance or standing
they have. In working out what information is needed it helps to ask the following
questions:
"What is required by this clause?" and then
"Does the design satisfy those
requirements?"
When a material has been used
locally for years, has a history-in-use and an established tradition of trade
practice compliance is not difficult to prove. It is alternative systems from
a different location or lapsed traditional local materials that cause difficulties.
This is where the Performance criteria of clauses and the Durability requirements
become very important because they provide the measure by which it can be
shown that the building material or system is satisfactory.
Background to the New Zealand
Building Industry
By world standards New Zealand
does not have a long history of building construction. European settlement
began only 150 years ago. The indigenous people (Maori) who settled in NZ
from Polynesia in the 13th century used a mixture of timber for the structure
of their houses with raupo (reed) infill panels for walls and roofs with the
occasional low earth structure. The country is geologically young and does
not have large resources of building stone or much suitable material for brick
manufacture. It was covered with forest including trees that supply superb
building timbers. The frequency of earthquakes, the ability to grow exotic
timbers (mainly Pinus Radiata) quickly and efficiently, and a small population,
well dispersed, led to light timber construction becoming an obvious choice,
particularly for housing and smaller commercial buildings. None of the examples
used in this paper are traditional in New Zealand although there are links
to materials used by both Maori and the early European settlers.
Alternative Construction
As the technical adviser for the
BIA responsible for clauses E2 "External moisture" and B2 "Durability" the
first uncommon building material that we were asked to deal with in day to
day queries from both building officials and potential owners was earth building.
This may surprise some people in other parts of the world but in New Zealand
this is an unusual type of construction. Some earth buildings were constructed
by the early settlers (a few are still in existence today, the most famous
being Pompalier House, a rammed earth structure that has been restored to
its former glory). Generally however timber structures were used, partly because
of the problems experienced with earthquakes and partly because of its relatively
low cost and ready accessibility.
Log houses were soon to follow
in the day to day queries. The latest material to appear on the scene is straw
bale construction, an influence from the environment conservationist movement
in the USA.
A pattern has emerged in dealing
with the problem of obtaining a building consent. The owner/designer has to
provide the regulatory authority with documentary evidence that the building
would comply with the building code (Section 34 of the Building Act). Clauses
that cover such factors as minimum hygiene are the same no matter what the
materials from which a building is constructed. For alternative construction
methods, the main relevant factors to concentrate on are contained in the
following code clauses:
Structure
External moisture
Internal moisture
Durability
The NZ Building Code
To explain how the performance
based code deals with alternative construction I must first outline in further
detail how the above factors are dealt with by the NZ Building Code.
Structure
The strength of the structure
can be demonstrated by recognisable methods of calculations. The performance
based clause for structure recognises all the likely loads to be imposed upon
a structure. The Functional Requirement of NZBC clause B1 "Structure" requires
buildings to withstand the combination of loads that they are likely to experience
during construction or alteration and throughout their lives. The Performance
criteria are qualitative, consisting of a list of likely loads and other factors
that must be considered when assessing the stability of a building.
Resistance to those loads would
have to allow for the strong horizontal forces experienced in New Zealand
from both high winds (it is after all a couple of large islands in the middle
of an ocean) and earthquake (NZ lies on the edge of the same belt of earthquake
activities around the Pacific Rim that cuts through Japan). Clause B1, like
all clauses within the building code, requires the same performance throughout
NZ. The variation in winds and probability of earthquakes changes from area
to area depending on the forces experienced so it is the means of compliance
that becomes the variable.
External moisture
Keeping the water out of buildings
is dealt with by 3 clauses. Surface water is dealt with by the collection
or prevention of entry of rainwater in clause E1. Penetration of the building
envelope and floor structure is dealt with by clause E2, and internal moisture
by clause E3. E2 "External moisture" is probably the most relevant clause
of these three. E2's Functional Requirement requires that buildings shall
be constructed to provide adequate resistance to penetration by, and the accumulation
of, moisture from the outside. The Performance criteria are again qualitative
and deal with keeping out moisture that would cause undue dampness or damage
to materials and includes moisture brought in from outside by building materials
(such as concrete and timber).
Internal moisture
Internal moisture can be just
as dangerous to health as rain from the outside. The moderate temperatures
and high relative humidity experienced in NZ in conjunction moisture emissions
from the occupants result in condensation and thus growth of fungi and mould
within houses. The Functional Requirement of NZBC clause E3 "Internal moisture" requires that buildings shall be constructed to avoid the likelihood of fungal
growth and damage to building elements being caused by use of water. The Performance
criteria deal with causes of condensation, requiring a combination of ventilation
and thermal insulation, and with overflow and water splash from sanitary facilities,
requiring impervious and easily cleaned surfaces combined with floor wastes
where appropriate.
Durability
The durability provisions of the
building code are to ensure that a building continues to comply with the code
after its date of completion. NZ, in deciding on the minimum period of time
that a building material or total building should last, took into consideration
not only peopleís expectations but also the national cost (a requirement
in the Act under which the code is mandated). Various factors contributed
to the decision that the life of a building should be not less than 50 years,
including common construction methods, the youth of the country, rapidly changing
technology, life styles and demographics. We recognised that structure as
the mainstay of a building must have a durability equal to the life of the
building. Other building elements having less importance could have a shorter
durability period. Ease of access, replacement and detection of failure became
the important factors. Based on concern for health and safety, and taking
into consideration normal maintenance, building elements that are difficult
to access or replace or for which failure would not be detected during normal
use or maintenance must have a durability of the life of the building being
not less than 50 years. Building elements that are moderately difficult to
access or replace, or for which failure would be detected during normal maintenance
require a durability of at least 15 years. Only elements that are easy to
access and replace, and for which failure would be detected during normal
use require a durability of no more than 5 years.
The NZ Building Act, however,
allows for the ability to nominate the intended life of a building. This is
because some buildings (eg. temporary building, semi-permanent marquees etc.)
may not always need to remain for a long period of time or because the life
of experimental construction may not be known.
The durability clause not only
relates to all the other clauses, it is the key clause. Compliance with other
clauses must include the measurement of the durability of building elements
or systems. The adequacy of construction to withstand structural forces such
as wind and earthquakes are measured by the likely return of such events within
the durability requirement. Thus a building must be designed to withstand
the force resulting from an earthquake likely to be experienced within a 50
year period,. Similarly the resistance to wind must be for the maximum likely
strength of wind in 50 years. Structural materials in New Zealand must be
able to withstand likely loads not just for one, two or ten years but for
not less than 50 years. This means that some materials, for example those
that are very flexible, may not be suitable, as they will fail within the
life of the building (being not less than 50 years).
Prevention of surface flooding
is measured in terms of return period of rainfall. NZ has made the decision
that buildings other than housing must bear the cost by insurance or by calculating
the risk, but that housing should be protected by law. Houses must be designed
to prevent surface water from entering the building in the 50-year flood.
This is required as a control of the cost to the country rather than inconvenience
to people or a factor of health and safety.
The majority of failures of building
elements are caused by water (Porteous, 1992). Thus compliance of clauses
for external and internal moisture can be greatly affected by the durability
clause. The necessity of protective coatings or the ability of the construction
to keep water out are vital to the assessment of the performance of those
materials.
To explain further how the performance
based code and in particular the durability clause assist in assessing alternative
types of construction this paper considers earth buildings, log houses and
straw bale construction. Each have their own idiosyncrasies but, as will be
demonstrated, they are mostly dealt with in the same way, as can any other
type of construction that is not commonly used, be it a traditional method
that has lapsed or a new, hopefully cheap and efficient technology.
Case histories
a) Earth buildings
Earth buildings have the advantage
of being able to be built from local materials with local labour. The skills
can be taught quickly. What is more, the material does not consume vast amounts
of energy to bake it in an oven, nor are noxious gasses released in its manufacture.
Usually only a small amount of additional materials are required to stabilize
the earth. Cement, lime or even dung can be used, depending on the type of
soil, and sand may need to be added to clayey soils.
Earth is not a resilient material
so there are structural problems involved in resisting the lateral forces
imposed, particularly earthquakes. These have mainly been resolved by having
steel reinforcing rods vertically and horizontally with a timber or concrete
ring beam around the top of the walls to tie them together. Some experimental
work is being done to find a way of using local fibres such as flax to strengthen
the structures without the necessity for steel reinforcing.
Moisture is the other big problem
with earth building. High rainfall and strong winds experienced in many parts
of NZ mean that care must be taken in designing earth buildings to prevent
dampness. Whatever the type of earth building, adobe or bricks, poured earth,
or rammed earth or pisé, the following points need to be adequately
dealt with in the application for a building consent if compliance is to be
demonstrated to the regulatory authority:
• Careful testing of the soil
to ensure that it will be sufficiently stabilised,
• Foundations and floor that have an efficient means of preventing dampness
from rising,
• Location in a well drained area or on a foundation of appropriate height
to prevent flooding in the 50 year storm,
• Contraction and expansion joints in the plaster to prevent cracking,
• A protective coating that resists moisture but is permeable to vapour
in order to seal the surface,
• Adequate flashings at all openings,
• Sloping window sills,
• Allowance for vertical shrinkage in all joinery,
• A roof that doesn't leak,
• Wide roof overhangs to shelter the walls below.
b) Log houses
Because trees grow well in NZ
a small group of people have been experimenting with log houses. We cannot
go by the history in use in Canada and Russia, the main source of information
about log buildings. The timber damaging insects are different, we do not
have the cold winters to kill them off and the rate of growth of trees is
so much faster that our exotic trees have less hardwood than when grown in
their native land.
Factors critical to the durability
of a log building are:
• Design and detailing of the
building (damp-proofing at floor level, width of overhangs, weatherproofing
at windows and doors),
• Initial handling and drying of the logs,
• Exposure to the weather during construction (length of time under construction),
• Protective coating of logs, particularly cut ends, during and after construction,
• Continued maintenance including recoating of logs.
Because there is not enough information
to be sure that a log house has a durability of not less than 50 years, regulatory
authorities usually require a specified intended life from 15 to 30 years
depending on the species of tree. When the specified intended life has been
reached, those houses will be inspected to see if they should be demolished,
repaired or if in good condition, have their specified intended life extended
further. These will add information to the history of such buildings for future
builders of log houses.
c) Straw Bale Construction
Straw bale construction is fairly
new on the scene in NZ, influenced by an upsurge in California. It is understood
that straw bales were first used by the early North American settlers who
had slowly settled from the east to the west of America, building cob or turf
buildings as they went, using the ample supply of this material on the plains.
When they arrived at the sandhills of Nebraska, however, they found that the
turf crumbled when dry and their shelters disintegrated. With no trees for
timber or stone for solid walls they were obliged to use whatever other material
they could find. At the same time the straw balers became commonplace. The
bales were stacked up like giant bricks and plastered for protection against
fire and the depredations of stray cattle. (Welsch 1972)
More recently, clean air laws
have left farmers in California with waste rice straw, which they had previously
burnt, causing large-scale air pollution. Straw bale construction has several
advantages:
• It is made from a waste
product,
• It is light and easy to handle,
• Its thermal resistance R-value of 6 to 8 is extremely high,
• Once plastered, it is very fire resistant.
Straw bale construction does not
have much structural resilience so like earth buildings it must be tied together
at the top of the walls to resist lateral forces, usually by timber beams
connecting to vertical rods through the straw. Structural difficulties can
be avoided by using the straw bales as infill panels to timber post and beam
construction.
Because straw bales are very vulnerable
to damage by moisture, the methods of keeping the water out must be carefully
checked when assessing the adequacy of a straw bale. The durability requirement
in NZ for straw bales when used as infill panels and not as a structural element
is 15 years. If the straw bales are kept dry, a durability of 15 years is
easily achieved and the straw will continue to act as a very good thermal
insulation for that time. The essential requirement is to keep the straw dry.
An useful analogy is to treat the building like a person who needs to have
a good rainhat, coat and gumboots for protection against a storm.
The list of critical factors to
show compliance is very much like the list for earth buildings with a few
additions:
• Foundations that have an
efficient damp proof membrane (DPM),
• A floor high enough out of the ground to prevent flooding in the 50
year storm,
• Low moisture content in the bales (this can be checked with a moisture
meter using a long probe used by farmers when stacking hay),
• A good plaster system over the straw to protect it from wind blown rain
and normal wear and tear, (NZS 4251:1998 is a good reference for specifying
the proportions, mixing and curing of cement plaster even though it does
not include straw bale construction),
• Contraction joints in the plaster to prevent cracking,
• A protective coating that resists moisture but is permeable to vapour
in order to seal the surface and any small cracks that will occur in spite
of all due care,
• Adequate flashings at all openings,
• Sloping window sills (with a water proof membrane under the plaster
to shed rainwater),
• A roof that doesnít leak,
• Wide overhangs to shelter the walls below,
• A good maintenance programme.
APPLICATION TO 3RD WORLD COUNTRIES
This paper has discussed alternative
materials in terms of their use in NZ. The climate in NZ varies greatly from
dry to wet, from snow and the terrain differs from sea level to mountains,
from plains to rolling hills. There has not been a situation yet where the
flexibility of the code cannot cope with the diversity of the climate or terrain.
Even the diversity of our cultures can be catered for.
Some of the performance criteria
are biased towards problems experienced in our climate and other requirements
of our largely European based society. Third-world countries would need to
be aware of their own situations when writing performance based codes. Because
of the flexible nature of such codes, however, they are not likely to differ
much from country to country. Performance based building regulations are the
appropriate framework for facilitating the further development and use of
appropriate materials and methods of construction consistent with heath and
safety. A durability clause within that framework provides a measure that
can be relied on to ensure that the performance will be met.
In particular the durability period
chosen by NZ will in all likelihood not be appropriate to other countries,
based as it is on our particular types of construction and peopleís
expectations. Local materials and customs may dictate shorter or longer durability
requirements. The UK (building mostly in brick and other durable materials)
has a standard that categorises the design life of buildings into temporary,
10, 30, 60, and even 120 years for civic and other high quality buildings
(BS 7543:1992). Certain types of thatched roofs in Fiji have been shown to
last 10 years if treated. Such factors could dictate the durability requirements.
A third-world country, faced with large numbers of the population housed in
conditions of poor hygiene and inadequate shelter could choose a short period
in order to lower the cost and speed up the construction. A short term durability
period could be decided upon in order to clear up slums, refugee camps or
disaster areas, while giving a breathing space for more lasting solutions
to be designed, built and paid for.
There are existing projects that
would have been more easily carried out in response to a performance-based
regulation. There is also potential for as yet experimental systems to be
used under performance based regulations.
Earth building in Fiji
An example of an existing project
that could have been handled more easily with a performance-based code is
the Rotacottage, commissioned by Rotary International for the Ba district
in Fiji. (Thomson, 1999) Land leased from the Fiji Government designated for ëShelter Housingí for the homeless and destitute families in the
Ba District, a prototype was designed to use compressed earth bricks and to
be made and erected by the local people from local earth.
Testing of soils done by engineers
in NZ experienced in earth buildings showed that the soil, being volcanic
had little clay or fines and so required stabilising with 10% cement and 10%
sand. The cottage was designed to encourage airflow through the building with
cross ventilation and gable end roof ventilation. All engineering calculations
for the specification complied with the NZ Loadings Code NZS 4203, a verification
method for the NZ Building Code structural requirements. Natural ventilation
was provided by cross ventilation through openings in the walls, shuttered
for shelter in storms, and with ventilation in each gable end of the roof,
not only contributing to the ventilation and cooling but also having the effect
of negating the wind pressure differential that is the major cause of damage
in cyclones. This feature is in effect an alternative solution for fixing
down of roofing material. The calculations on fixings used for that roof would
be based on not only the strength of cyclones experienced but also the likelihood
of the return event. (Stuart 1999)
There may be some doubt about
the durability of earth bricks in this area, although it is the dry side of
the island, since the location experiences high humidity and torrential rain
at certain times of the year. The points used in NZ to assess the durability
of earth buildings would have been useful here and maintenance factors such
as the ability to keep lush grow away from the walls become important.
Earth or mud buildings have traditionally
been used in the Indian continent, the Middle East, most parts of Africa and
in South Africa. With the right regulations we should be able to revive traditional
methods where they have lapsed and improved the standards in cases where poor
practices have given them a bad reputation.
Other traditional materials
Underground buildings have been
used in centuries past in countries such as Turkey and China. There are cave
dwellings in the agricultural uplands of Tenerife in the Canary Islands. At
the opal mine fields of Coober Pedy in Australia, underground caves are particularly
pleasant to live in while avoiding the hostile surface environment. Modern
earth shelters are now being used by energy conservationists to take advantage
of the earth massís moderation of climatic extremes of cold winters
and hot summers in both North America and the UK.
New materials
Rice straw and bamboo, materials
that are abundant in some third-world countries and may even be waste products,
could be reliably and quickly assessed for use under performance based building
regulations. Straw has been use in bales as mentioned before, both for infill
and structural buildings. It has also been used for making sheet board materials
(Hammer and Richert, 1999). With appropriate protection in order to achieve
the required durability, such boarding could replace more expensive imported
sheet board materials or could be used instead of less sustainable timbers
that when felled could destroy the environment. Bamboo has similar albeit
lower strength properties to steel. Could those properties not be harnessed
as a quick growing renewable building resource?
Waste products of a different
scale are those modern rejects of an affluent society. Refrigerated containers
are such an example. Already insulated and waterproofed, they could be converted
to modular housing. Stacked and locked together in various patterns to provide
communities, they could have a measurable and cheap durability.
CONCLUSION
Robert Barclay called for building
regulations that can "facilitate the further development and use of appropriate
materials and methods of construction consistent with health and safety requirements" Performance-based building codes when used with a measuring stick such as
the New Zealand durability clause allow for the following:
• Flexibility,
• Encouragement of the development of building materials,
• Aiding improvements in construction methods,
• Using local materials and labour,
• Taking into account local conditions and customs,
• Satisfying urgent demands for shelter.
Performance-based building regulations
measured in terms of durability and combined with lateral thinking could be
the solution. We think that we can tell a success story for performance based
building codes in NZ. As demonstrated in this paper, these controls could
be adapted for use in third-world countries in the new millenium.
REFERENCES
Barclay R, 1987, Building Regulations
and Control in Development. In: Appropriate Technology, Vol 13 No 4 p 14—16
British Standard 7543:1992 Guide to Durability of Buildings and Building Elements,
Products and Components Table 1 p 4
Hammer C and Richert J, 1999 Strawboard Makers Number Three in North America,
GreenClips 12 May 1999
Porteous W A, 1992, Classifying Building Failure by Cause. Unpublished PhD
thesis deposited in library of Victoria University of Wellington, 273 pp.
Thomson S, 1999,RotaCottage, In: Earth Building Association of New Zealand
Earthbuilding, April/May 1999 p 18—20
Welsch R L, 1973, Baled Hay Shelter, Shelter Publications, p 70,
Shaw P, 1991 A history of New Zealand, Hodder Moa Beckett, Auckland p 11
