The property-services company believes new regulations that are a part of the plan will result in a much greater difference in land values between areas zoned for high-density development and those for low density. Land use will become more concentrated and commercial centres will be clearly distinguishable from residential areas.

"The New Bangkok City Plan is more sophisticated than the old plan and we believe the new rules will have a positive affect on the future development of the city," Aliwassa said.

The new regulations place more restrictions on the size of buildings that can be developed. One of the most significant changes is a restriction on the floor-area ratio (FAR), which limits the total floor area of buildings relative to the size of the site. Previously, in most areas of Bangkok, developers could construct buildings with a floor area 10 times the area of the site, or a FAR of 10:1.

Under the new regulations, this will still be possible in the following areas: Silom, Sathorn, Surawong, Langsuan and Sarasin, a part of Rama IV, Rajdamri, Wireless Road, Phloenchit, Sukhumvit from Soi 1 to Soi 21 (Asoke), Phya Thai and a part of Phetburi.

Other areas will have a reduced FAR between 8:1 and 1:1. For example, the area of Sukhumvit between Soi 23 and Soi 71 used to have an FAR of 10:1, but this has been reduced to 8:1, and on Chaeng Wattana road in the northern suburbs, the FAR has been reduced from 10:1 to 3:1.

With a ratio of 10:1 in the Sukhumvit area, 10,000 square metres of floor space was able to be built on a site of 1,000sqm. The land cost made up between 15 per cent and 25 per cent of the cost of a new condominium.

"Only 8,000sqm of floor space can now be built on a 1,000sqm site with the lower FAR ratio," Aliwassa said. "The land cost will now be apportioned to a smaller built-up area and this will probably increase the cost of new buildings."

It is unlikely that vendors of land in central areas will reduce their prices, so the affect of the new regulations will be to add to development costs.

"There should be a positive affect for existing properties, as restrictions on future supply will add value to existing stock," Aliwassa said.

In areas with more significant reductions in floor area ratio, such as the fall from 10:1 to 3:1, the effect will probably be a cap on any increase in land prices. In some cases land values may fall because of restricted development opportunities.

Another change to the city plan affects the open space ratio, or OSR.

Under the old regulations commercial buildings had to set aside 10 per cent of their land area as open space and residential projects 30 per cent.

The new regulations require commercial buildings to set aside between 3 per cent and 6 per cent of total built-up area which, depending on the FAR, will amount to a greater portion of the site for open space.

For residential buildings, depending on their location, between 4 per cent and 40 per cent of built-up area must be set aside for open space. For example, in the zone between Sukhumvit Soi 23 and Soi 71, the OSR for residential developments was 30 per cent of the site area. Now it is 4 per cent of the built-up area. With a FAR of 8:1, this results in 32 per cent of the site being set aside for open space rather than 30 per cent.

The effect will be even greater for new commercial buildings because, while the old rules specified that 10 per cent of the site had to be open space, the new rules require 4 per cent of total builtup area, increasing the open space on the site from 10 per cent to 32 per cent.

"This means it will be difficult to build large buildings on small plots of land," said Aliwassa.