Basalt Technology (Pty) Ltd.

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Dome Housing


Most recent figures, (Aug 2016), put the housing shortage in South Africa at over 2.5 million dwellings. This equates to about 12 million people (Source Dome homes are an option that could be considered as a partial solution. Whilst the dome homes that are described in this section are not mansions, they can provide safe, fireproof, storm-proof, dry accomodation at a very competitive price. And, there is an opportunity to get small builders to construct them.


Shack image


Basalt Technology (Pty) Ltd is not in the business of building homes. However, our rebar and our basalt rope are precisely the right materials for the Ecoshell construction method. In fact, the developers of the Ecoshells in Texas, USA have refined the process to a fine art. They specify the use of basalt reinforcing for their dome houses. We, at Basalt Technology (Pty) Ltd, are proud to advise on the methods to construct these starter homes. The use of dry interior walling is acceptable due to the fact that the roof is integral and self supporting.


We have the blessing of David South, owner of Monolithic Dome Construction in Texas, USA, and their information is freely available from Why are we giving away this information? Because we know the need that must be filled, we have developed the relationship with the reinforcement supplier, and with David South. We won't get rich on the construction of these dwellings, but we will grow our business, and at the same time, meet a desperate need.


It is admitted that a development of domed structures will have the "NIMBY" factor, but if concerned citizens will get together and overcome the "Not In My Back Yard" reaction, gradual replacement of the horrific squatter camps could be achieved. In addition, whilst tiny, 6.1 m shack replacement homes can be constructed, larger 7.6 m dome shell structures, which fit with the National RDP homes could be fitted into the program. The domes are earthquake and cyclone proof, too!



The Ecoshell dome



6 metre dome photo 7 metre dome photo


First of all we have to decide what size Ecoshell we want. If we are planning a small shack replacement dome, we would look at the 6 metre Ecoshell dome. This dome has a floor area of 29 square metres and a height 3.2 metres. The U.N. recommendation, for a family of 8, is 28 square metres, which we concede is tiny, but it will meet the UN minimum recommendation. The structure is a thin wall unit with a thickness of 35 - 50 mm. It is a unitary dome of reinforced cement mortar on a 6.2 metre diameter, reinforced raft floor.


The 6 metre sized Ecoshell dome is only 72.5% of the size of the 40 m2 RDP home. However, for shack replacement, this would be the lowest cost dome to build. The dome is not constructed with integral interior walls but these could be constructed to the owner's requirements using maxi-brick, concrete blocks, concrete bricks, or insulated dry walling.


The next sized dome that is available is 7.62 metres in diameter and 3.66 metres high. This sized Ecoshell dome would have a floor area of 45.61 m2. This dome is constructed on a 7.8 metre diameter, reinforced raft floor. It has a 14% larger floor area than the RDP homes and is 57% larger than a 6 metre diameter home. A 7.62 metre diameter dome will naturally be a bit more costly to build that a 6 metre diameter dome. The bigger dome has the same exterior wall thickness, so the shell material costs are not vastly affected.



6 metre floor image 7 metre floor image


floor image



The two floor plans are just indications of how the layout inside the domes can be arranged. Walls can be constructed with conventional or maxi bricks, or dry walling used. Since the roof is self supporting, if required a deck type floor could be erected over the ablution section, or even over the section where bedrooms are sited. IF the deck is constructed, it may be necesssary to slightly raise the vertical height of the side walls. In India, 3 storey structures have been built with the Ecoshell system. The third floorplan shows a possible layout for an internal shower and toilet cubicle.


When approached by Basalt Technology, David South gave valid reasons for not going too high with the dome structures. He said, "The wall heights can be raised, but a wooden floor is then introduced into the structure. This becaomes a factor in fire concerns. Rather consider two domes, blended together to gain the extra floor space. If your property size allows it, this would be a far more suitable option."


Often, South African RDP homes, concrete floors are often laid at 150 mm thick. This does not comprise of the normal foundation which is laid in excavated trenches and a brick outer skin is built onto the foundation. The separate concrete floor is then cast inside the retaining brick skin wall, which is rasised to floor height. These floors are not raft type flooring. In the monolithic Ecoshell dome, the floor system consists of a totally reinforced floor slab and ring beam system.


With Dome houses, a reinforced ring beam is cast as part of the integral reinforced concrete floor. The excavation for the ringbeam is dug around the periphery and rebar installed. The rebar for the floor of the dome is laid on spacers above the compacted base. Concrete is poured in the peripheral trench and the reinforced concrete floor section as a raft unit. The raft will absorb any ground movement or heaving. The floor level in a dome home is approximately 100 mm higher than the surrounding earth.


Please note that the following mix designs are not hard and fast rules. The materials that will be used on site should be tested for suitability and economy. This information is given as an illustration!


Mix design for floor concrete - per m3


Cement CEM II 42.5 400 kg 8 x 50 kg bags
Sand Building sand 950 kg 0.7 M3
Stone 13.5 - 19 mm 980 kg 0.73 m2
Water Potable 210 l w/c 0.525


Mix design for sprayed or plaster applied walls and roof - per m3


Cement CEM II 42.5 450 kg 9 x 50 kg bags
Sand Building sand 1100 kg 0.7 M3
Water Potable 180 l w/c 0.46 -0.48


PLease note, AGAIN, that the following mix designs are not hard and fast rules. The materials that will be used on site should be tested for suitability and economy. This information is given ONLY as an illustration!


Reinforcement - 6.2 m dome


The 6 mm StoneRod rebar required for a 6.2 metre reinforced raft floor with ring beam is 220 metres. Actually, an extra two perimeter bars of 20 metres each may be prudent. Monolithic Domes design does not request them, but an extra R550 - R600 @ current exchange rates (Mid Aug 2016) may prove a good investment!


Three(3)reels of 6 mm StoneRod basalt fibre rope are suggested for the 3.2 x 6.2 metre dome. At current exchange rates of 1 US$/R13.75, each reel costs R710.00 including VAT of 14%. Although the design calls for 2 reels an extra reel has been added. This does raise the estimated costs but it appears prudent to add an extra reel to the bill of quantities. The total cost would be R2130 Incl.


For 260 metres of 6 mm StoneRod rebar the cost would be R3582.80 Incl VAT. An additional 3 reels of 6 mm StoneRod rope would cost R2130.00. Therefore the estimated reinforcement costs, including extras is R5712.80.


Reinforcement - 7.8 m dome


The length of 6 mm StoneRod rebar required for a 7.8 metre reinforced raft floor with ring beam is 310 metres. As suggested earlier,the use of two extra perimeter bars of 30 metres each, may be prudent. The cost of the rebar for the floor would be R5098.60 Incl VAT.


Four(4)reels of 6 mm StoneRod basalt fibre rope are suggested for the 3.66 x 7.6 metre dome. Although only 3 may be required and each reel is costing R710.00 including 14% VAT, the extra R710 is not significant. The total cost of rope reinforcement would be R2840.00. Adding the cost of the rebar adds a further R5098.60 to the cost making a total of R7938.69


Concrete requirements


The 6.2 metre diameter dome floor and foundation is estimated to require approximately 3.85 m3 of concrete for the floor and 3.5 m3 of sprayed, or plastered, mortar for the walls. Door openings and windows have not been factored out, but wastage is a factor.


The concrete floor has a 6.2 m reinforced concrete slab with a 200 x 200 mm ring beam and a 100 mm integral thick floor slab. 6 mm rebar is used in the concrete floor at 350 mm centres. The structures are not insulated but a layer of vermiculite, or poly-bead mortar could be applied over the structural core, and then finished with a thin mortar seal.


Concrete cost for the 6.2 metre floor of 3.85 m3, if priced at R1400 per m3, would be approximately R5390. The cost of the mortar for the walls adds an an additional R5250, @ R1500 /m3, or R10640.00, excluding reinforcing. The material cost including the addition of the cost of reinforcing will raise the shell cost to approximately R16352.80 including VAT.


The 7.62 metre diameter floor and foundation will require approximately 5.5 m3 of concrete. In addition, 4.85 m3 of sprayed, or plastered mortar will be required for a 50mm thick wall. Once again apertures for door openings and windows have not been subtracted from the material required, but wastage is a factor.


The concrete floor, of 6.8 metres diaameter, has a 200 x 200 mm ring beam and a 100 mm integral thick floor slab. 6 mm rebar is used in the concrete floor at 350 mm centres. 4 rings of 6 mm rebar reinforce the ringbeam.


Concrete cost for the 7.62 metre floor would be approximatrely R7700 @ R1400/m3. Adding the mortar for the walls will raise the costs by R7275, @ R1500/m3. This raises the cementitious costs to R14975.00 excluding reinforcing. The addition of reinforcing will bring the shell cost to approximately R22913.60 including VAT.


The Ecoshell Airform


There is one more cost that has to be factored in to the actual dome construction. This is the cost of the "Airform". Of course, the erection, services and door and window fittings are not included. But, for the sake of factoring in "some" equipment costs, the blower and hold down brackets have been incorporated into the airform costs.


6 metre airform drawing 7 metre airform drawing


According to the manufacturers, an Airform should be able to produce 100 structures. For sake of safety, let's estimate the production of 90 homes per airform. The cost of a 220v inflator fan and the required number of tie-town strips are also included in the base price.


The 6.1 metre purchase price (excluding shipping costs, duties and the other costs such as insurance, etc) would be $4355.37, or about R59886.00. This equates to an extra R665.40 per structure.


Labour and ancillary costs, such as fittings, doors, windows, interior walls, and ablution items. No cost of plumbing or electrical options such as conduits, piping and plugs, lighting or swithches are included.


Also, if spray applications are used as the better option for construction, the inclusion of an small shotcrete type air compressor, concrete mixer, concrete pump, and spraying head need to be amortised into the cost.


Without the ancilliary and other costs, a dome would be approximately R170010 for a 6.1 metre Ecoshell dome structure.

The 7.8 metre purchase price (excluding shipping costs, duties and the other costs such as insurance, etc.) would be $5827.98, or about R80135. This equates to an extra R890.40 per structure.


Once again, labour and ancillary costs, are NOT factored in.


Without the ancilliary and other costs, a shell would be approximately R23804.00 for a 7.8 metre Ecoshell dome structure.


If labour and profit are added at 1:1:1, the 7.8 metre shell could cost R71412.00 and the 6.1 metre shell would cost R51003.00


Finishing and waterproofing. The method used for finishing and decorating domes in warm climates is to paint the domes with lime based whitewash. The domes, if correctly constructed are weatherproof.No expensive coatings are required. However, owners can have fun decorating dome houses..,


Fun dome


According to, the current subsidy amount for a ‘starter house’ of 40m² consisting of two bedrooms, a toilet and kitchen with sink, is set at R55 706 for top structure and R22 162 for infrastructure. An additional 15% is available for coastal areas (SCCCA) and the geo-technical variance brings the total subsidy amount to approximately R100 000 per beneficiary.


Pricing is conservative, and has allowed for extra materials in the reinforcing, and has increased delivered ready-mix concrete products by approximately R100 per cubic metre, for both the fireproof, tornado proof, 7.8 metre dome and the 6.1 metre dome. In addition, in comparison to the 40 metre RDP homes, which are only 87% of the interior size of the 7.8 metre dome, more living space is available. The original Airform price has been amortised into the cost of ninety domes, and the total costs have been tripled, to allow for labour and profit. However, in Mexico, a small crew of University students built their first dome in 3,5 days. Labour costs, consequentially, in these examples, are therefore estimated at a very high rate.

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