Breaking new ground
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Copyright© AAAMSA 2009
Ever-increasing building costs, shortages of traditional materials, the need for rapid building techniques, soaring energy prices and greater awareness of energy conservation have cast a spotlight on expanded polystyrene (EPS), which is increasingly used on modern construction projects.
In South Africa, alternatives to the traditional brick and mortar have to be found if our building demand and energy requirements are to be met.
Known as “the fourth-generation building material” after wood, iron, and concrete, EPS has proven itself as a construction material in upmarket and mass housing, warehouses, factories, cold storage facilities and even soccer stadiums across South Africa and the world.
Polystyrene is “polymerised styrene”. The expandable form (known as EPS) is initially produced as small beads containing a pentane blowing agent. The beads expand when treated with steam, forming a lightweight “prefoam”. These prefoamed beads can be processed in a mould to form large blocks of various densities which are then cut into sheets or other shapes.
The question is – why aren’t we using it in low cost housing where demand is highest and EPS is high in performance and low on energy consumption.
EPS is an environmentally sound, fire-resistant material with superior insulation properties, keeping out the heat in summer and retaining indoor warmth in winter.
With this in mind the Expanded Polystyrene Association of South Africa (EPSASA) has built a prototype house on the Council for Scientific and Industrial Research (CSIR) campus in Pretoria, where scientists from the CSIR will conduct tests on the house over a period of time. The investigations will look at the typical performance values of current, more traditional low-cost housing units and compare them to the EPS house. The Automapolyblock building system used for the walls is certified by Agrement, certificate no. 2007/336.
The research seeks to determine whether technology interventions can be developed and introduced to improve the performance of low-cost houses without substantially increasing construction cost. The research will also look at the durability – and increasingly important – the energy-saving capabilities of the materials used in the construction.
EPS house under construction on CSIR campus
Legislation is being introduced in South Africa, which will require strict energy efficiency standards for buildings, and EPS is at the forefront of easy to implement technologies to help meet these requirements. Expanded Polystyrene consists of 98% air and has long being used as a thermal insulator. It has an R value (thermal resistance) of about 4 K·m2/W per 25 mm thickness. EPSASA is confident that the superior thermal insulation properties of the EPS house will ensure that it outperforms more conventional houses – significantly reducing internal energy demand. Research has been done on more upmarket houses using EPS for insulation. Energy savings on the EPS improved house (floor, wall and roof insulated with EPS) – compared to an unimproved house of the same design – has been impressive. For example, the reduction in overall energy load over one year was estimated at 31.4 kilowatt hours per metre square, per annum. That’s a massive saving. Although the saving is likely to be less on the EPS low cost house, as it has less electrical appliances and a lower energy demand, indications are that a substantial saving of kilowatt hours per meter square will be achieved.
Building plan of house
The EPS prototype house is a standard 40m2, low-cost unit with four rooms (two bedrooms) and is equipped
with plumbing, electricity, a geyser and all the comforts that make a house a home. It stands alongside several
other prototype houses of similar design on the CSIR site.
Advantages of building a low-cost house with EPS:
• It’s “green”
superior thermal properties cut energy wastage
material consists of organic materials, is environmentally sound, CFC & HCFC-free and recyclable.
• Speed and simplicity
construction time is 14 days for a trained team (weather permitting)
materials light, easy to handle and assemble
suited to remote locations, components delivered as lightweight, portable packs, which do not require
any mechanical handling
even hand tools are limited to basic items.
• Cost competitive
when comparing material cost only vs. traditional concrete systems, but becomes increasingly
competitive when the cost of labour, equipment requirements and time are included.
• Energy saver
– EPS used as thermal insulation for buildings will save 400 times the energy required to manufacture
the base product
– fewer drafts and a decrease in operating costs for maintaining a comfortable interior environment for
– fire resistant grade of EPS called styFRene TM is being used in this application
– the SANS 428 fire performance classification has been done on this material and it performed well, proving that EPS does not feed flames
– since EPS foam is a non-toxic hydrocarbon, burning it produces water vapour, carbon dioxide and trace levels of ash, similar to paper.
– the structure of the house is reinforced concrete which is 2-3 times stronger than brick
– polystyrene is rot proof, termite and moisture resistant and dimensionally stable, retaining its thermal insulating and moisture barrier properties for the life of the building.
• Low cost housing in urban and rural settings, especially where demand outstrips supply and where high quality, affordable homes need to be erected in a short period of time.
• Opportunity for builders and entrepreneurs. If a builder has a bakkie and a vision, he can get out there with small teams and start erecting these homes with minimal capital investment required.
• Rural women, once trained will be able to build these houses themselves, as the materials are mostly lightweight and manageable.
• Holiday cottages (EPS is rust resistant and well insulated).
• Granny flats.
• With minor adaptations, can be used to build patios or extend the living area of an existing home.
People from all walks of life are concerned about the environment, and measures are being taken to reduce the impact that activities have on our surroundings. EPS actively contributes to a better environment and makes this positive contribution at all stages of its life cycle, from manufacture, to application, to recycling or disposal. EPS is a good example of an efficient use of natural resources.
The building envelope which comprises the roof, walls, windows and floors of a building controls heat gain in summer and heat loss in winter. Building materials and designs that maximise the exclusion of heat in summer and trap and store warmth in winter increase the effectiveness of the building envelope, creating much more comfortable and less expensive to maintain living environments.
The introduction of Energy Efficiency Standards for Buildings – through legislation which has been promulgated in South Africa – will intervene to reduce peak electricity demand usage and slow the growth in overall power demand. Ultimately energy efficiency standards will be part of the building code of South Africa and thermal insulation will become a prerequisite in future building design. Expanded polystyrene buildings have been meeting these standards for decades now, way ahead of their time!
So here’s how it’s done The foundations and floor As with any building, strength and durability depend on well laid foundations. This is even more so with a modular polystyrene system, as the building block dimensions and the way they connect do not allow for corrections to levels at a later stage. All the principles of laying conventional foundations apply, but keep the substructure as level as possible. Where the ground is uneven or slopes, and a step in the foundation is necessary, implement in 300mm sections to compensate for the dimensions of the blocks used to build the house.
Foundation laid, insulation sheet glued down and spacers placed
Under floor insulation
Once the foundation is laid and the fill has been compacted, the down over the surface and glued together. In this instance, the fou EPS sheets to create a thermal and moisture barrier below the fl accurate.
Lay the EPS sheets and glue together. Next, insert the spacers, sheets. This ensures that when the concrete is poured for the fl the EPS sheets.
Place the reinforcing mesh over the spacers.
Pour the concrete, level off and float the floor.
The walls are built with hollow EPS building blocks which act as a permanent formwork for a reinforced concrete infill. They are simple to build with as they just click together. Unlike the 6-9 months required to become a competent brick layer, operators can be trained to build with the EPS wall block system in a couple of days.
The hollow, moulded building blocks fit together like a ‘Lego’ set. Where shorter blocks are needed, one can simply cut them to size using a hand saw and minimal physical effort. The blocks are supplied in different thicknesses, from 120mm, to 150mm and 180mm. They come in either open ended or closed ended versions. Vertical and horizontal reinforcing bars (rebars) are placed inside the blocks throughout the wall building process. This is done before each round of wall filler concrete is poured into the blocks. Each block is 1200mm long and 300mm high, equivalent in size to 36 bricks!
Chalk in the wall and door positions, as well as other relevant detail from the building plan. Once this is done, start by laying down the first row of blocks for the outer walls as well as the inner walls of the house.
Chalk markings and first layer of blocks positioned to floor plan.
Set up the profile lines on all corners and place doorframes in their correct positions. Ensure that the doorframes
When shorter blocks are required, simply take a
measurement and cut blocks to fit using a hand saw.
Holes being drilled for starter bars
Once you are certain everything is laid out correctly, drill holes, approximately 10mm deep, into the foundation for the starter reinforcing bars. It is recommended that you place the starter bars at regular intervals, approximately 600mm apart inside the blocks. Starter bars must be placed at comers, wall joints, and on either side of windows and doors. Cut starter bars and hammer them into the foundation. Ensure that you cut them to a size that will allow for easy lifting and placement of blocks on upper lines (a length of about 1.5m is recommended).
Hammer the starter bars into foundations
A double, vertical YB reinforcing bar (rebar) is placed
either side of all doorframes
At this stage, before any concrete work is done, make provision for piping by inserting false pieces of drain and water pipes into the correct places in the walls.
Using a hand saw, cut out the holes for the placement
Remember to angle the sewerage drain (left) slightly
downwards as it exits the house.
The false sewerage and water pipes can be removed at a later stage, once the concrete has set. The permanent piping can be easily inserted once required.
Concrete fills and reinforcing
Place the first YB horizontal rebars inside the block, on top of the guides. Insert the rebar continuously above first block bending it around corners.
The second line of blocks placed on top of the first
will further secure the lines. Reinforcing must be
continuous, especially around corners and t-joints
As you place the second row of interlocking blocks
onto the first, ensure that the blocks are staggered,
but that the castellations are perfectly lined up and
then carefully slot the one into the other. The
castellations are the star-shaped protrusions along
the upper side of the block.
They should slot neatly into the receiving block above. There should be no gaps between the rows, as this makes it easier to place the blocks on the ensuing lines, as the wall gets higher. Note how the blocks are staggered along the vertical joints. It is important to keep the tops of the blocks clean by dusting with a dry
paintbrush. Once three lines have been placed, all rebars secured and piping holes prepared, fill blocks with 15MPa concrete. The concrete can be poured into the cavity by spade or by bucket.
Filling the building blocks with concrete.
The concrete fills the system through gravity flow.
Compact the wall infill using a short piece of timber.
When concrete sets place the next three rows, fit windows or formwork for windows and continue to fill with concrete, placing additional 1 m lengths of rebar vertically, in line with the starter bars. Remember to tie the bars to each other as the wall rises.
Remember to always tie the rebars together.
Secure window frames.
Walls can be built up to 5 times as fast as brick, with building rates of 50m2 per day per building team readily achievable. Once you reach window height, insert the window frames and secure them, making sure of your levels. Use timber or fibre cement formwork above window openings to hold concrete in place above window openings. Above windows and doors insert two Y8 rebar lengths continuously on top of first block above openings to create ring beam and lintel. Attach hoop iron or wire to the ring beam to secure roof sub structure and fill with concrete to wall top. Pace the basic shape of the gable and find the top of the pitch by measuring according to plan. Secure a builders’ line from the wall to the apex.
Taken on the morning of day four of construction,
the rebars are being secured to create a lintel.
Place top blocks to fit gable shape.
Use the profile line to mark out the shape of the gable. Remember to include the vertical rebars all the way up and into the gable walls, as these assist in supporting the roof structure. Cut the top surface of the blocks, as well as the rebars, along the line. Fill the gable wall with concrete.
Gable wall as seen from the apex.
Finished walls and gable.
Notice how the internal walls are also built up to the shape of the gable, as these will assist in securing and supporting the roof panels. Once the walls are built, the fittings and fixtures can be prepared and the plaster applied. The first step in preparing for the roof is to build the beam ties into the top of the wall. The top ring beam is situated just below the final block. Tie the beam ties to the reinforcing before filling the final block.
Alternative walling systems
EPS panels with a light-gauge steel core and a spray-on fibre cement plaster. Factory manufactured ready to build panels with preassembled door and window frames are easily erected on site using the tongue-and groove method.
Fittings and plaster
Prepare chasing for water lines and wall conduits, as well as plug and switch housings for electrical fittings, simply by cutting into the polystyrene walls. Ensure sufficient space is cut away, as this is closed up again in the plaster stage.