The quest for better sleep is said to be behind the trend

A survey by the National Association of Home Builders has predicted that by 2015, 60% of custom-built homes will have two master bedroom suites.

The quest for better rest is behind the trend as experts say the lack of decent sleep can cause marital tension.

The option of having separate rooms has often improved marriages, they say.

Gopal Ahluwalia, of the National Association of Home Builders, said the trend was a "market-driven demand that's going to continue".

'Flex suite'

Separate bedrooms have often been taken as a sign of a failing relationship, but for many people they appear to be becoming a practical necessity.

Snoring, night-time visits to the bathroom, child-care requirements and shift-working can deprive couples of the recommended seven to eight hours of sleep per night.

The situation has reportedly become more acute as gender roles have changed - with both men and women juggling work and childcare duties.

Families expert, Stephanie Coontz, told the New York Times there were many couples "confident enough that they have a nice marriage, but they don't particularly like sleeping in the same room".

"I don't think it says anything about their sex lives," she said.

Nevertheless, some builders call the extra room a "flex suite" to avoid any embarrassment.

The trend is not restricted to the upper end of the market, the newspaper says.

Lana Pepper of St Louis said she had switched things around in her new apartment to cope with a restless husband.

"My husband is still alive. I would have killed him," she said.