ASSOCIATIONS
A CMA House under construction.
“ It should be generally accepted that for the foreseeable future the concrete masonry block or brick will be the walling material of choice for subsidised housing. Market research shows that South Africans want their houses, even the most humble abode, to be constructed with traditional and dense materials such as concrete masonry, preferring them to the numerous and often lighter alternatives which, as yet, have not penetrated the market to any significant degree.
“ Given that the concrete block is here to stay it goes without saying that it should be deployed in the most productive and durable manner. Quicker construction, minimal wastage and an adherence to documented building standards all form part of the process, and the most effective way to achieve these objectives is through a modular approach.”
Modular construction using concrete blocks / bricks forms the backbone of the CMA House. Fundamental to the whole process are the architectural drawings which not only include walls, door and other dimensions, but unlike traditional plans, detail each and every block used.
“ Building any house, even a small basic structure, is not a simple exercise if it’ s to be done properly,” advises Minnaar.“ And it is attention to detail, especially in the plans and schedules, which make the difference between modular and non-modular construction. Working out precise block layouts is a complicated process, especially at the corners, but the results more than justify the effort.”
Based on a 40m ² unit, the CMA House or, more accurately, two houses, use two different block sizes, one which is largely used inland and the other which is generally found in coastal regions.
Each version includes: a full set of drawings; a normal raft foundation footprint or an alternative Agrémentapproved precast concrete hollow-core option; modular concrete-block walls; and aesthetically-pleasing and thermally-efficient concrete roof-tiles. The plans also include schedules for block-cutting and for matching door and window frames to block sizes, as well as
recommendations for cost-effective waterproofing of external wall surfaces, and some energy-efficiency options.
“ The benefits of the modular approach are obvious. By religiously sticking to a set of modular plans wastage is minimised by reducing the need for odd-sized blocks which is so prevalent in the non-modular approach. In addition, by following a disciplined and identical building procedure time-after- time, the benefits of repetition and mass production come into play. Although it takes longer to produce a set of modular masonry drawings the downstream savings far outweigh any additional investment the preparation of such drawings may incur. Moreover, the modular approach is ideally suited to subsidised housing, given the one-design-fitsmany approach.”
The inland set is based on a solid block which measures 290mm long 140mm wide and 90mm high. The coastal set is based on the 390mm long x 140mm wide by 190mm high hollow block. The 140mm width of both units has sufficient structural integrity based on the SANS 10400-K standard and is more economical than the 230mm width of a standard wall.
When used in a wall with a 10mm layer of mortar the solid block forms a 300 by 100mm module( the old imperial module of one foot). Traditionally window and doorframes are also based on the old imperial system, door frames measuring 900mm and window frames being either 600mm or 900mm.
“ Therefore, the effective way to design with solid blocks and imperial sized frames is first to make all the dimensions multiples of full bricks( 300mm minus the vertical 10mm of mortar lost at the corners),” advises Minnaar.
“ If this design philosophy is followed, half blocks, either cut on site( preferably by diamond cutting discs) or precast will be required at door and window cavities. The result is practically zero wastage, fast construction and full structural integrity, especially where it matters most, around the door and window frames.”
12
MARCH- APRIL 2017
AFFORDABLE
SA HOUSING