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Architectural Design Technology 3
There are several different forms of construction systems, but typically the most common methods used in modern times for low rise buildings tend to be either masonry block or timber framed construction. These construction techniques have been tried and tested over the years, however, could it be possible that there are other methods of construction that surpass masonry wall and timber frame in terms of their advantages?
This report will look into two different alternative construction systems and review them both in terms of sustainability, technical benefits and occupant health and comfort.
What are they?
'Durisol' is the name of a manufacturer that produces an insulated concrete form wall system that comprises of insulated interlocking blocks that are made from the composite of cement-bonded wood fibre. * Once the blocks have been built up to form a wall, the cavities are filled up with concrete, and if necessary, can be reinforced with steel bars. This system has had wide use throughout the world for over 50 years, so how does it perform?
Building with Durisol blocks is an exceptionally sustainable method of construction. To begin with, the blocks themselves are fully recyclable and also are produced from clean, recycled waste wood mostly from timber pallets. The manufacturing process of the blocks consumes a fairly low amount of energy as they do not require kilns or ovens like standard masonry blocks, and all water used for manufacturing is reclaimed from the rain. These are all very 'green' qualities, however there is one significant contradiction in terms of sustainability, and that is that this system requires a large amount of concrete to fill the cavities, just under 0.1m3 per m2 of wall, which may not seem a lot but if you consider an entire building, it adds up. A couple of small compensations for this drawback are the facts that they are dry stacked so there is no actual requirement for mortar joints to bond these blocks together. Also, a waste product from the smelting industry, pulverised fuel ash, is used to bond the wood chips together and reduce the amount of cement needed in manufacturing. The problem with using concrete is that to be made it uses a lot of aggregate and has high embodied CO2, however, studies have shown that compared to the embodied CO2 of timber and steel construction, concrete would be the best option.
Possibly one of the greatest characteristics of this construction form is its outstanding thermal performance. The cement bonded wood fibre that the blocks are made from is a very poor heat conductor, and therefore there aren't any cold bridges so it takes a longer amount of time for internal heat to escape the building. The standard 365mm thick insulated block (pictured above) is insulated with mineral wool and has a U-value of 0.19w/m2K. This can be instantly brought down to 0.15 simply by replacing the wool with phenolic foam insulation. The result of these low U-values will be that less energy will be consumed to heat the building, directly reducing its carbon footprint and at the same time, saving the occupier a lot of money on bills each year. The image to the left indicates the rate of temperature loss in the walls.
In terms of transportation for this specific project, the distance travelled to deliver the blocks would not be that far as Durisol's UK factory is actually based here in Wales. It is located in Newport, Gwent which is approximately 100 miles away from Haverfordwest.
Health and comfort
The materials used have no toxic elements, and are completely inert and resistant to fungal or bacterial growth. Also, the walls aren't subject to infestation of insects, neither are they subject to gnawing from mice or rats as the materials offer no food for vermin.
This system is very safe in terms of fire safety as it is non-flammable. During manufacturing the wood chips go through a mineralising process, a result of which is the blocks high fire proof qualities. When tested against fire to the criteria of British standard part 20:1987,* requirements for structural integrity are satisfied for 4 hours at a temperature of 1100C. The requirements for insulation are satisfied for 3 hours and 37 minutes.
As was mentioned earlier in the report, these blocks have a reasonably low U-value. What this effectively means is that when the heating is turned on, the building will sustain a lot of the heat for a longer period of time, resulting with a high level of warmth, and a nice comfortable environment for the people inside.
From researching into this system, it seems that there aren't really any disadvantages. The only real major problem with using these Durisol blocks is not a fault of the product itself, but rather the lack of widespread familiarity that contractors have with installing them. However, it is a relatively simple system and there aren't really any huge complications to building with it. Therefore, along with its many advantages and benefits this definitely is a very good example of an alternative construction method.