A kettuvallam is about 67 feet in length and has a width of around 13 feet in the middle. The materials that go into the making are local and ecofriendly; bamboo poles, coconut fibre, ropes, bamboo mats, carpets etc. The main wood used is "Anjili" (Artocarpus hirsuta). There are houseboats with fully furnished single room, double room and triple rooms.
The hull is a series of wooden planks, long cut and carved, tied together using coir with coconut fibers stuffed in between.The hull which is made of hundreds of fine but heavy-duty planks of jack-wood is held together absolutely by coir knots (not a single nail is used). This framework is then coated with a caustic black resin extracted from boiled cashew kernels. And it lasts for generations.The kettuvallam is motorised and is steered in deep waters by means of oars. Long bamboo poles or 'punts' are used to propel in shadow areas. Bamboo beams sprouting off on the sides are used as foot holds for the same. Bamboo is used for the framework of the roof and splits of bamboo are used for weaving mat for roofing.
Basically the kettuvallam was designed to transport cargo and as such many design changes had to be made to make it a tourist vehicle. The height of the roof was increased to get sufficient headroom. A plank was laid all through the length to reduce the disadvantages of the curved shape of the hull for walking and comfortable seating. Windows and other openings were provided for light, airflow and view. The entrance is provided in the centre of the linear axis with a top hung panel.
Most of the latest designs have incorporated 3 bedrooms with toilets, a living space and kitchen. There, of course, are variations. Some have a lesser number of bedrooms but with a large living space and maybe a deck balcony at the roof level. Normally, the platforms that cantilever from the hull are used as balconies. Innovative changes have been made to accommodate modern fittings. For fixing the toilet seats, shower tray and ceramic floor finish a concrete slab is laid at the floor level. The soil outlets of the toilet seats are taken through the hull and let out to the flowing water beneath. The water for use is stored in a plastic tank kept at the top portion of the main body connecting to the kitchen and toilets. The pipes, tank and other synthetic materials are covered with coir or panambu to maintain the aesthetic quality of the eco-friendly materials.
Modern house boats have been designed to meet the Green Palm/Gold Star Certifications by the Department of Tourism, Government of Kerala, which has recently enacted regulations, stipulating the standards of Kerala houseboats or Kettuvallams.