| Thatching is a craft that is traditionally handed down | | | | poles that have been chemically treated. The poles |
| from father to son, taking many years to perfect. It | | | | may be spaced up to 900 mm apart. But Building |
| is not normally taught in other ways. So there is | | | | Socie¬ties in South Africa will usually in¬sist |
| relatively little documented information. In South | | | | on a maximum spacing of 700 mm and a minimum |
| Africa there is evidence that many home owners and | | | | pole diameter of 100 mm. |
| potential home owners would welcome such | | | | The grass that is used to form the ridge capping is |
| information. | | | | thinner, softer and more pliable than that used for |
| Because thatching is a labour intensive process, the | | | | the main roof. The lower edges of the ridge capping |
| cost of a thatched roof is normally up to 60% higher | | | | may be trimmed to a decorative pro¬file with |
| than that of a conventional roof. This price difference | | | | chevrons or scallops. |
| can be limited, however, by using the roof space | | | | Alter¬natives to grass ridges are often used, the |
| efficiently, with dormer windows and a mezzanine | | | | most common being preformed fibre¬glass, |
| level for instance where the walling and plastering | | | | sheet metal and cement. The ridge is the most |
| costs will be less. The insulating properties are very | | | | vulnerable part of a thatched roof and particular care |
| good, keeping the home warm in winter and cool in | | | | must be taken to ensure that this feature is |
| summer. Although thatch is one of the oldest building | | | | absolutely watertight. |
| materials, modern, innovative laying techniques ensure | | | | Thatched roofs are con¬structed with dripping |
| that the interior finish is clean, with no loose pieces | | | | eaves; meaning rain¬water gutters and |
| hanging down to harbour insects or encourage spider | | | | downpipes are not provided. Eaves overhangs should |
| webs. | | | | be at least 650mm and provision should be made at |
| Thatch has a natural ability to free-curved shapes to | | | | ground level, around the building, to prevent erosion |
| create a warm, informal finish that blends in well | | | | due to water dripping from the eaves overhang. |
| because of its natural appearance. Thatch, being a | | | | DURABILITY |
| natural material, will mellow in colour from its original | | | | A thatched roof will normally last for about 25 years |
| fresh straw to a dark sheen that tones in | | | | if properly laid. Dekriet will typically last a little longer, |
| wonderfully with the South African outdoors. At the | | | | up to 35 years. A thatch roof ridge require renewal |
| same time, the rustic roughness of textured thatch | | | | every 4-6 years. |
| inside the building lends itself to co-ordination with | | | | CONS & PROS OF THATCHED ROOFING |
| other natural materials such as stone & wood | | | | Advantages |
| etc. | | | | As local materials always tend to harmonize with the |
| The high open ceilings in thatch roofed homes give | | | | land¬scape surrounding their place of origin, |
| the rooms a spacious, airy feeling that can be | | | | thatch, as a natural material, will always blend well |
| followed through with large window openings, and | | | | with a rural environment. |
| perhaps stone or slate floors to add to the rustic | | | | There is an ecological advantage to be gained by |
| ambience. | | | | using thatch in that it is pro¬duced by natural |
| MATERIALS | | | | processes that do not use scarce and expensive |
| Thatching makes use of materials that are naturally | | | | resources of energy. |
| available - grass or reed. In South Africa certain | | | | A thatched roof will ensure that a building will be cool |
| indigenous grasses are normally used. | | | | in summer and warm in winter. |
| There are coarse varieties of this grass, with stalk | | | | Disadvantages |
| thicknesses greater than 4 mm, that are not | | | | Thatched houses are more vulnerable to fire risk |
| considered suitable for thatching. | | | | than those covered with other materials, and it is |
| Natal thatching grass has a finer texture than the | | | | therefore imperative that precautions be taken to |
| Transvaal grass when laid and is often preferred for | | | | reduce the risk. |
| this reason. | | | | Being an organic material, thatch is susceptible to |
| The stalks of thatching grass are normally hollow and | | | | decay and decomposition, and precautions must be |
| about 3 mm thick. Dekriet stalks, however, are solid | | | | taken to minimize the possibility of this process taking |
| and about 3-4 mm thick and considered the best | | | | place |
| quality and therefore the most expensive. | | | | More expensive than conventional roofing. |
| DESIGN | | | | Maintenance intensive. |
| A thatched roof should have a minimum pitch of | | | | FIRE PROTECTION |
| 45° and min 35° over dormer windows. | | | | PREVENTATIVE MEASURES |
| Take advantage of the steep pitch to provide | | | | Lightning protection |
| accommodation in the roof space to make the | | | | Lightning conductors should be installed to protect |
| design more cost effective. | | | | the thatched buildings, in accordance with the SABS |
| Try to keep a thatched roof as simple as possible, | | | | Code of Practice. |
| but the ability of thatch to adapt to free curved | | | | Two avoid an excessive high mast, two masts or a |
| shapes to develop a less formal plan could be | | | | spike on a chimney can be installed if the roof is not |
| implemented. | | | | covered by the protection zone. |
| Consider flashed areas; features that pene¬trate | | | | Chimneys |
| or interrupt the roof should be avoided as far as | | | | Chimney stacks should be con¬structed in such |
| possible. Chimney shafts should be designed to | | | | away that the outer faces in contact with the thatch |
| penetrate the roof plane at the ridge, thus avoiding | | | | do not become hot. A full brick thick¬ness (220 |
| the necessity of back flashing. | | | | mm) is normally sufficient. |
| Soil vent pipes are best located on external walls so | | | | All mortar joints in the stack must be properly filled. |
| that they penetrate the thatch near the eaves line. | | | | The top of the stack must extend to at least 1m |
| Rain water must not be allowed to discharge from a | | | | above the highest point of roof. |
| high level roof onto a thatched roof at a lower level. | | | | Install a spark arrestor, consisting of a piece of |
| Thatch, 150 mm thick, has a mass of about 20-25 kg | | | | stainless steel wire mesh, fitted 700 mm from the |
| m2. The roof framing normally consists of eucalyptus | | | | top, covering the full width of the flue. |