Hue has long been Vietnam's centre of wooden architecture and many of the buildings here, royal palaces included, are Ruong style.

A typical Ruong house is noble vet cosy, hinting of the imperial finesse that once dominated this city. Each one is made up of compartments (which are separated by rows of columns) and side-wings (which are separated from the compartments using wooden dividers). When Hue was home to Vietnam's emperors, all aspects of life here were dictated by royal decree and while those decrees might sometimes have been taken lightly elsewhere, the royal city never strayed. Thus house building, one of the most important endeavours in life, was undertaken with strict rules in mind.

A decree issued in 1822 prohibited all homes outside the royal compound from having more than three compartments and two side-wings. To guard against the storms that regularly engulf Hue, people built their houses low to the ground. These two factors combined to make Ruong houses in Hue rather small. So to make up for their homes' humble size ancient Hue residents had beams, rafters and other woodwork carved and inlaid generously.

Ruong houses were made from indigenous timbers such as sedonic wood, peck wood and wild jack-fruit wood. It usually took a team of four car- penters and four carvers two years to complete a single house and although such houses are now built only rarely, there remain many Ruong experts who can carve and inlay exquisite patterns in houses today.

When all the separate parts of the house were ready for construction, the owner referred to an astrological calendar to find a good date for the Thuong Luong, or Ridgepole Initiation, ceremony. During this ceremony a pole, on which hung a tantric flag, was placed on an altar. The date of the ceremony and the owner's personal zodiac were written on the flag, which was designed to bless the new house. Two cycas branches were tied to the top of the flag to attract longevity and two, four or six ancient coins were sewn into the hem of the flag to ensure prosperity.

Then, on a plate with flowers, fruits, tea and incense, the owner placed rice, salt, flour and mock money on the altar. On separate plates, each carpenter placed similar offerings on the altar. A red turban was placed on the master builder's plate, which he would later wear as he helped lift the ridgepole into position. At the end of the ceremony, the owner was the first person to touch the ridgepole. The Thuong Luong flag remained on the pole until the house was complete and a house warming celebration held.

According to ancient beliefs, the owner must treat his carpenters well during construction, for if he didn't they might hex the house with a tantric spell. The spell was written on a piece of paper, which was then hidden in a crack of wood. The carpenter need only draw the tantric hex in the air with his left hand, then tap that hand on a beam of the house, for the hex to take effect.

The most important part of Ruong house building was the calculation of the front door's width. For this, ancient Hue builders used the Luban carpentry ruler, which was originally designed by an 8th Century Chinese engineer. There are many versions of this ruler in use today: Chinese, Japanese, Laotian and Vietnamese. Builders in Hue speculate that Emperor Minh Mang (1820 to 1840) added around two centimetres to the original Chinese Luban ruler to ensure that   palaces   built   by his Nguyen dynasty would differ from those of previous dynasties and of other countries.

Two kinds of rulers were used in Ruong construction. The first, a 42.7cm Bat Moc Xich, measured the wooden