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Masonry Stoves

Clean, green heat from Heavenly Heat Masonry Heaters. Now available in Australia

http://www.heavenlyheat.com.au

Overview of Masonry Stoves

Masonry stoves (or Russian or Finnish stoves) have yet to gain a foothold in Australia. They have been used for generations across the higher latitudes of the entire northern hemisphere where their efficiency of burning fuel and the friendly, even warmth they emit could keep families comfortable even in the harshest of winters. Only the mountain dwellers among us need to combat such a climate but our southern winters still bring a need for warmth.

The qualities of masonry stoves make them ideal for environmentally conscious home owners in places where timber is the fuel of choice. They burn with minimum pollution and with most of the heat generated being used where it is required. This is unlike slow burning fires that create more smoke and deposits and lose much of their heat to the atmosphere.

In principal a refractory core is surrounded by a skin of stone, brick or even elaborate tiling. This is often done very artistically. A short hot fire is lit; the gases being channelled up and down around the core before leaving via the chimney. Much of the heat in the flue gases is absorbed into the masonry and then exudes gently out over the next 12 hours or so. Users relate the feel of the heat to that of warm sunshine, rather than the ‘all or nothing’ output of traditional fires.

Masonry stoves have been traditionally custom built by expert masons, but now there are kits available (see the Tempcast site below) whereby individuals with some bricklaying skills can build their own masonry stoves, which come in a variety of configurations depending on where in the house the stove is positioned.

There are many online sources of further information, those in English are mostly from the USA or Canada. Here are a couple of useful sites:

http://www.tempcast.com/
http://www.vtbrickoven.com/masonry/index.html

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Where can I order strawbales from?

Strawtec has a list of reliable suppliers of strawbales. We recommend that you check out our LINKS to find out more.

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Characteristics of a good building bale

Typical Residential Building Bale

The early Nebraska bale buildings where mostly made from baled meadow grasses, thus hay. Hay is usually baled green; it is leafy and contains seeds. These make it prone to decay and attractive to rodents, hence it is not recommended as building material. It is also more expensive than straw as it is baled for fodder and is not regarded as a waste product. In contrast, straw is baled from the dry stalks remaining after the harvest of grain; it is tough and fibrous, a renewable resource grown annually and, as a by-product of grain production, usually regarded as a waste product. Most commonly the strawbales used for building are from wheat, barley and rice crops.

Good building bales should be uniformly well compressed. To assess tightness of a bale, pick it up by its strings. The strings should not separate from the bale by more than 2 centimetres (your knuckles should touch the bale) and they should not twist or sag when lifted. A well-compressed and tight 2-string bale should weigh 18 kilograms or more (or between 90 and 120 kilograms per cubic metre) in an acceptable dry condition.

Bales are usually tied with polypropylene string, sisal twine or wire. It is best to choose poly-string, as sisal is not as strong and prone to rot and wire may rust if it is not galvanised.

For residential building two string bales are the most commonly used. Their general size is about 350 millimetres high, 900 millimetres long and 450 millimetres wide.

However, these dimensions are not as important as the close uniformity of size, especially the proximal consistency in height and width is.

Dryness of the bales is one of the most important characteristics you need to observe for. Like any organic material, straw will decompose if the right conditions of moisture and temperature exist. The moisture content of a bale suitable for building should be less than 15 percent.

A specialised moisture meter can measure the percentage of moisture content of a bale, the farmer or farmers supply shop may be able to lend you the tool.

However, there are many other simple signs and methods to check for moisture in a strawbale. Open the strings of several bales and have a good look inside the straw. Feel if it is moist to touch and check if it has a damp smell. The bales should have a golden yellow colour; any sign of black mould is a sign of composting. Observe the storage facilities carefully; check that there are no leaks in the roof, that the floor and walls are dry. Always sample a number of bales from different places in the stack to allow for highest accuracy in the assessment of your bales.

Each bale has a cut and a folded side; the folded side is the shaggier one. Look at both sides and make sure they are relatively even as they will require less trimming later on.

Observe that the straw is clean. If too much grain is left mixed in with the straw it may attract pests and activate microbial activity.

The average costing of a strawbale lies between $4.00 and $8.00. The price mainly depends on if you can load and pick them up yourself or if they need to be delivered and how far they come from. You need about 3 bales per square metre when laid flat.

We are happy to help if you have problems sourcing the right bales, please e-mail us at strawbales@bigpond.com for supplier contacts.

If you need to store the bales before use they are best stored in a dry barn or shed. If you build infill walls you may stack the bales under the finished roof construction. If you cannot store them properly have them arrive on the day of your wall raising.

Concluding a few recommendations on safe handling of the bales. Wear gloves when lifting bales by strings to avoid pinching or cutting skin. Long shirt sleeves help to avoid scratching and itching to arms. If the bales are very dusty or you suffer from allergies/asthma use a face mask when handling bales. Remember proper lifting techniques such as bending knees, no twisting of body, and getting help if it is too heavy.

Do not forget to install fastening points where you plan to hang heavy items to walls later on. One method is to hammer wooden pegs into walls where needed, or at regular intervals if no plan for hanging things is as yet in place. For very heavy wall hangings you can secure the pegs with a large plywood square on the outside wall. Mark location of pegs etc. on a diagram to be able to find them after bales are rendered.

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Loadbearing or infill?

Loadbearing, also called “Nebraska Style” because of the historical precedents, describes construction in which the weight of roofs and floors above the ground are supported, partly or entirely, by the strawbale walls. Loadbearing structures are easier to build because the skilled work of framing is replaced by the simpler task of stacking bales.

The easier and quicker system of building loadbearing walls will save costs by reducing timber (or other framing material) needs as well as reducing the need for skilled labour. However, the loadbearing system does have some disadvantages and faces more difficulties from building officials than other systems.

Firstly, the straw bale walls are raised before the roof is completed, leaving the bales unprotected from storm and rain. Loadbearing walls need time to settle under the weight of the roof before they can be rendered. It is best to wait between four and six weeks for the walls to settle; unfortunately this waiting period leaves the straw bales unprotected from rain and storm again and it is not always practical to have to wait before the project can progress. It is possible and recommended to pre-compress the walls however, it is still necessary and important to observe a settling period. The top or roof plate must be a very strong and continuous plate, especially over door and window openings, in order to be able to transfer roof loads to the bale walls without bending or buckling. Because of the loadbearing role of the bale walls, openings in these structures are commonly fewer and/or smaller than in infill structures. It is also more difficult to build very high (more than eight courses) or even two story structures with the loadbearing method and walls cannot be too long or too wide apart without a supporting cross wall structure. Often temporary bracing has to be installed to stabilise not yet rendered bale walls. Last, loadbearing wall systems are not always appropriate, especially in regions that experience heavy snow loads, seasonal rains and high winds.

Wall raising for a loadbearing structure with temporary corner braces in place

Today, most strawbale buildings in Australia are infill structures, mainly because building inspectors, architects and builders are still unfamiliar with the loadbearing concept and retain some resistance to it.

Non-loadbearing, also called post and beam or infill, describes construction in which no weight of roofs or floors above the ground are supported by the strawbale walls. Instead, strawbales are used as infill material between or around a structural frame, which can be timber, steel, concrete, masonry, LVL (structural plywood) or any combination of these. This construction method has become predominant, as most builders, architects, building inspectors, lenders and insurers are familiar and comfortable with its application. Again, this method has advantages and disadvantages over others.

Infill construction has usually a better chance of council approval. The design is very flexible and easily adaptable to conventional systems. Large openings for doors and windows to gain from passive solar energy do not pose a structural problem. There is even compression on all walls even the ones with little or no bales. It is easier to replace sections of a bale wall if moisture or other problems with the bales were experienced. Completion of the roof provides dry storage and protection for the bales while not rendered, as well as for the balers at wall raising time. Last, there is no settling period and work on the building can continue without delay.

Wall raising for a post and beam structure; steel posts are wrapped in Hessian

Disadvantages of the infill building method include the possible greater expenses for framing material and frame construction time, extra footings for posts and increased need of skilled labour.

The potential for volunteer labour and owner-builder involvement may be lower with this more complex construction system.

Combinations of the two building systems are usually called hybrids; they have the potential of taking advantage of the best aspects of both these systems however, it needs to be considered that due to the different structural systems compression of the walls will be different. As all systems have their appealing and flawed points it is left to you to make a decision of what system best meets your needs, budget and skills.

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What about durability & resale value?

The evidence provided by existing and in good condition strawbale structures from as early as the late 1800s should be enough to support the strength and longevity of strawbale building.

If the bale house is appropriately designed, well built, constructed from good quality materials and looked after caringly, the resale value of the structure should be the same (or even better due to the excellent energy ratings and long term savings) as for any conventionally built house.

Remember: “Don’t let a pig build your house…”

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How do strawbales perform in regards to passive solar design?

The physical components of an ideal passive solar design include adequate thermal mass to store and release heat on a 24 hour cycle and an insulating exterior wrap to reduce heat loss to the outside in winter and heat gain to the interior in summer.

Therefore, proper placement of high-mass materials such as clay render, bricks, concrete, tiles, adobe or rammed earth in the interior of the structure provide thermal mass, while the highly insulating strawbale walls greatly reduce the heat transfer by conduction.

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What about moisture?

Moisture is the enemy of all builders, regardless of the materials they are using. Fungus (dry rot) will be able to cultivate and bales will start to decompose if high moisture levels (over 20 percent) are maintained over a long period of time.

Vapour barriers are not recommendable with strawbale construction. With a vapour barrier the render will not be able to attach directly to the straw therefore, eliminating the substantially greater structural benefits gained from the bonding of the two materials and also requiring extra wire mesh or similar for the render to attach to.

Protecting your bale walls with an appropriate foundation, generous roof overhangs, intact & well maintained guttering, porches and verandahs and suitable render materials are the most effective ways to avoid direct rain exposure, splash back, and resulting moisture damage to the walls. Well applied, intact, properly maintained and breathable render will also protect the strawbales from moisture damage.

The ability of clay to absorb and release moisture from/to the surrounding air creates not only a perfect and healthy living environment but also helps to maintain acceptable moisture levels within the strawbale walls. Clay is also well known for its ability to preserve therefore, clay helps to protect your strawbale walls from dry rot and other fungi. These are some of the reasons that clay is our preferred choice for rendering. If external walls need extra protection, a more weather resistant lime render finish can be applied.

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What about fire?

Strawbales suitable for building are dense and difficult to burn.
They contain only very little oxygen to feed a fire.

American test results show strawbale construction to be exceptionally resistant to fire.

A test of a rendered strawbale showed the following:

Material Fire Resistance
Un-rendered strawbale 30 minutes
Rendered strawbale 2 hours
Timber framed and cladded building 8 minutes

Also, the irregularities of a bale wall require a fairly thick coat of render, providing an extra layer of protection to the bales.

Remember: Care needs to be taken with loose straw around the building site, as it is much more vulnerable to fire.

The first official Australian tests assessing the performance of rendered strawbales for their use as wall systems in high-category bushfire prone areas were conducted by the CSIRO in July 2002.

The preparation of the bales to be tested was planned, sponsored and completed by our construction company.

Bales tested Quantity Comments
Clay rendered 3 Complied with current performance criteria
Lime rendered 3 Complied with current performance criteria
Cement rendered 3 Complied with current performance criteria
Un-rendered bales 3 Did not comply with current performance criteria

Everyone present, CSIRO staff, Bush Fire officials, architects, engineers and builders were surprised and impressed by the excellent performance the strawbales displayed during the fire tests.

To help the approval of your project you may provide your local council with a copy of the test report, especially if you build in a Bushfire endangered area. The CSIRO test report can be purchased from Bohdan Dorniak, please contact him at bdco@merlin.net.au.Whilst we are on the subject of bushfire tests, a new window glass has been developed by Pilkington Australia in conjunction with DuPont for use in Australia’s bushfire prone areas.

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What about termites, rodents & insects?

The prime source of food for termites is timber. They much prefer wood to straw. Consequently a strawbale house entails less risk of damage from termites than a timber house does.

However, normal precautions against termite infestation, as used with any other construction technique, should be followed to protect the vulnerable components of your building from termites.

Remember: Because of the high frequency and cost of termite damage, no insurance company in Australia currently provides insurance against damage caused by termites.

Walls built with tightly pressed strawbales provide fewer spaces for pests to live in than conventional timber frame houses do. Also, because clean and dry straw has very little nutritional substance, it is unable to support a pest population for long in itself.

If the render is well applied, contains no or only very fine cracks and is well maintained, the risk of any pest infestation into your walls is very low.

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Comfort, Creativity & Aesthetics

Strawbale buildings have their own unique feel and character. The thickness of the walls provides a feel of calm, safety and comfort. Deep window seats, alcoves, niches, and subtle curves (see Photo Gallery) are creative features, which can easily be integrated with this flexible but durable material. It is a pleasure to look at the thick, soft and flowing walls, they are similar in appearance to old thick stone and adobe walls, reminding of past centuries European country living.

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