Building your wooden prefab house in an arid area needs some special attention.
ln the hot and dry zone (arid zones) the most significant problems are those caused by solar radiation and UV rays etc. These can destroy surface finishes, above all coated surfaces of metal sections, metal sheeting, plastic panels and wood surfaces. In hot arid zones, in which diurnal and annual temperature variations are large, it is desirable for walls to absorb heat during the 9 - 12 hours of solar radiation and then to emit the heat to the interior until the cold pre-dawn hours, thus maintaining thermal comfort inside the building at all times (time-lag design theory). Small openings, located at higher levels should permit hot air to escape, and exclude solar radiation and glare.
In hot climates, the long axes of buildings should be orientated in East-West direction, with openings in the walls facing east and west being avoided or kept small, as it is difficult to shade them from the low morning and evening sun. Openings in walls facing South and North are easy to shade from the high noon sun by means of wide roof overhangs.
While the east-west orientation of buildings is important, in hot regions priority must be given to orientation for air movement; in hot arid zones, importance must be given to exclusion of hot air, sand and dust.
Solid walls with high thermal capacities are common in hot arid climates, as they transfer the absorbed heat to the interior with a time lag, thus restraining the heat when external temperatures are high, and releasing it when temperatures are low. Typical solid walls are made of stone, earth, burnt clay bricks and concrete. Insulation on the outside of a solid wall gives a four times greater time lag than if it were placed on the inside, but it also hinders heat dissipation during the night. A disadvantage of solid wooden walls is their vulnerability to cracking, even when properly kiln dried, mainly due to its mass. We advise that solid wooden walls in arid areas to be kiln dried to at least 7% to 8% moisture content (MC). If such is not possible due ot the capacity of the kiln a higher moisture content can be applied, howeb , one needs to take into account that the wood will take its time to dry out to the lowest Equilibrium Moisture Content (EMC) in an arid country and will cause the wood to shrink based on the difference between the EMC and the MC of the wood when istalled. Shrinkages of 3 to 6 mm have been reporrted. The tongue and groove connections of our exterior siding boards are designed such that these shrinkages can be taken uo easily withut damaging the wood.
Double walled construction has many advantages, both in warm humid and hot arid regions such as:
- the outer layer protects the inner layer from direct solar radiation, which first heats up the outer layer. With a reflective outer surface, this heat absorption is greatly reduced;
- only a part of the heat that passes through the outer layers reaches the inner layer by radiation or convection, and if provided with a reflective surface, it will not absorb all the heat;
- The insulation materials used for cavity walls can be of various types, depending on several factors, such as temperature range, intensity and duration of solar radiation, humidity, building usage, nature of immediate surroundings and can be nsulated wth either glasswool, rockwool or polystyrene foam boards will double act as an insulator, which is an be advantage
- openings at the top and bottom of the cavities allow the hot air, which will have accumulated within, to escape at the top, while fresh air is drawn in at the lower side. During the day, when the fresh air is also hot, air circulation will have no cooling effect, so that it would be ideal (but not practical) to be able to close the openings during the day and open them at night;
- sound transmission is reduced by the air space.
- In warm humid and hot and dry climates, double walled constructions have the additional advantage of protecting the inner layer from rain and moisture penetration. Any moisture that passes through the outer layer is removed be ventilation, and condensation water can trickle down and out through the opening below.
- In warm humid conditions, the inner skin should not be impermeable, as moisture movement is required, while the outer skin (usually thin panels or tiles on lathing) can be either impermeable or not, but care must be taken to avoid moisture bridging from the outer to the inner skin.
The maximum moisture content of double wooden walls in arid areas shall be around 5% for exterior walls and 10% for interior walls, flooring, beasm and columnsl
Roofs are always in the first line of attack by sunlight and easily and fast heated up and is one of the most crucial building elements and is a source of considerable radiant heat. The roofing system, which may include a plenum concept, needs to be designed so as to be self-ventilating or cooling and to be constructed of materials that have a higher thermal value.
Based on the above we strongly advise the following for building in arid areas:
To have a double wall system installed fitted with proper insulation material
The thickness of the exterior siding board to be at least 25 mm
The thickness of the interior siding board to be at least 16 mm and fitted with an aluminum sheet radient barrier
To have all exterior siding boards be kiln dried to 7% to 8% moisture content
To provide openings in the top and boottm of the walls as to create air ventilation
To have all interior siding boards, flooring, beams and columns be kiln dried to at least 10% moisture content
To have the roof insulated following the air gap system with furring strips
To install exterior siding boards which can take up shrinkages of up to 5 mm without damaging the wood
AlLL OF THE ABOVE WILL BE TAKEN CARE OF BY OUR COMPANY.