Traditional construction roofing system, lack of maintenance, and poor workmanship were some of the causes of roof failure during a windstorm in Bhutan, a study by the works and human settlement ministry has found.
The study under the National Adaptation Programme of Action II project was conducted to develop a windstorm resilient guideline for roofing system in the country.
The guidelines state that in traditional construction, the roofs are usually simply supported and gravity load based. It points out poor workmanship as a major cause for the failure of roof. “Poor workmanship in various truss joinery and connections and improvisation at site without any design basis tend to fail during windstorms,” the guideline states. “Lack of periodic maintenance is also a main cause of roof failure during windstorms. Material strength deteriorates mainly due to exposure to moisture and insect attack in absence of routine maintenance.”
An engineer with department of engineering services, Gita Maya Sunwar, said that in terms of planning aspects, the guidelines recommend better site selection, layout of the building, and orientation of buildings. “Recommendations on better creation of load path for safe delivery of wind loads from roof to foundation through proper connections and securing the connections, ways to secure the CGI sheet, and use of tie downs to hold the truss systems were made.”
In Bhutan, four types of roofing system—jabzhi roof,jamthok roof, drangim roof, chenkhep are commonly observed.
Gita Maya Sunwar said that in recent history, the houses in Bhutan have proven vulnerable to damages due to frequent windstorm.
She added that the damages are particularly to the roofs of rural houses across the country. “The major events of damages due to windstorm in April 2011 and December 2013 where roofs of over thousands of houses were damaged and every year damages to hundreds houses across the country calls for a need to have guidelines.”
Although the guideline has not been implemented, the department has currently trained few dzongkhag engineers and technicians from 20 dzongkhags and trainees from Technical Training Institutes on using the guideline. “As of now, the department has not made it mandatory but it will work on it,” Gita Maya Sunwar said.