Double RoofA green roof has fantastic architecture. It is unique, you feel cooling underneath it, and it is fun to play on top. The heat from the sunlight got converted into food for the plant instead of heat gain to the occupant underneath. If it doesn’t, the soil or the moisture in the soil gives heat-insulating purposes.
The other definition of a double roof is known as one single roof splits into two, one overlaps the other part a little, with an air gap or a window in between the split.
If any condition doesn’t allow a green roof design, a double roof design prevents a building indoors from excessive heat gain in the tropical hot, and humid climate places.
Two kinds of double roof
A double roof can be defined as a roof system with one roof shading another with gaps in between.
The first roof on top shades whatever underneath from the hot sun prevents the second roof below from direct heat gain, the air in between the two roofs serves as a heat insulator or air movement that can draw heat away before the heat can get to the second roof.
Creative solutions suggest a different combination of any two kinds of roof. For example, solar panels as the top roof, concrete roof as the second roof with an air gap in between them.
The other definition of a double roof is known as one single roof splits into two, one overlaps the other part a little, with an air gap or a window in between the split.
Jackroof is one of the second types of double roof that exist a long time ago in the history of human civilization and architecture.
The jackroof seen in the traditional Malay House has deep roof eaves. The jackroof operates perfectly for passive cooling and sun shading with an air gap positioned high up on the roof for air exchange.
The problem with the traditional long roof eaves in the modern context or other use is that when ample daylighting is needed, the middle part of the house hardly gets natural daylighting.
There are a few interventions in the later period to the issue:
Having transparent roofing sheets that bring natural daylight into the spaces, but direct solar and glare would cause heat gain to the indoor.
But some of the Malay Houses were traditionally built in the forest around tall trees. They resemble the best example of what man-made and Mother nature can co-exist with one another - Man builds around trees, they also grow trees, tree shades their house in a certain critical hour of the day from the hot sun.
Sunlight is avoided, daylight is embodied.
A little intervention can turn the traditional solution into a better modern context use: Replacing the top part of the jack roof with light transmittable material, such as glass, polycarbonates, or translucent tile, but control the placement of it to prevent direct solar heat penetration. Minimize it if direct sunlight is unavoidable.
A sawtooth roof works best in this case. A sawtooth with an operable window or an air gap.
The sawtooth window faces only a certain angle of the sun, which in turn, gets sunshine through the window for only a short period of time.
In most of the hours during the day, the window faces the reflected sunlight (daylighting) from the cloud in the sky.
A sawtooth roof brings natural daylight into the indoor in two ways: Direct reflected daylight and reflected ceiling light.