Questions have been raised about how the ACT Land Development Agency (LDA) has managed recent land releases, with concerns it has led to inflated prices.

As the city rapidly expands outwards, the LDA has rushed to boost supply.

But recent sales have seen blocks in suburbs like Throsby, in Canberra's north, soar well above the original valuation.

In February, Tegan Gaha and Matthew Partridge were among hundreds of people hoping to secure a block of land in Throsby at auction.

"We live in Harrison currently, and we'd been looking at the development across the road for a number of years," Ms Gaha said.

Their prospective 594 square metre block was independently valued at $391,500, but they were prepared to stretch to $450,000 if necessary, however in a flurry of bids, the block sold for $540,000.

"I don't know who can afford to buy those [blocks of land], but it's not the average people anyway," Mr Partridge said.

Even smaller, average-sized blocks of 450sqm do not come cheap.

At Moncrieff two years ago, a block of that size would set you back about $242,000.

A similar size in Throsby today, even by ballot, comes in around $424,000.

Flooding the market is leading to inflation: builders

The Master Builders Association's Michael Hopkins has blamed the inflated prices on the LDA's practice of holding back land, before flooding the market.

"Typically what we see with releases in the ACT is long periods of drought, where there is literally no land available for purchase, followed by a big flood to the market," he said.

"There's a mad scurry from homeowners and builders to try to get their hands on land."

Mr Hopkins said the problem was deeper, with the system unable to keep up with demand for single house blocks, while other approvals for apartment projects languish.

But the LDA's David Dawes said environmental clearances in Gungahlin and Molonglo delayed the program for three years, and was beyond its control.

"We are very conscious about the fact that we do need to get more single dwellings to the market, hence why we're doing Throsby all at once, why we'll do Taylor all at once as well," he said.

But Mr Dawes said despite the demand some builders were worried about the mass of land coming on the market.

"Talking to some of the builders, they were struggling there in Moncrieff and they were concerned that we were bringing too much land on," he said.

Mr Dawes said the Government's release plans were based on demand, Australian Bureau of Statistics data and its own population projections.

Prices forcing families to NSW

After feeling forced out of the Canberra market, Ms Gaha and Mr Partridge have decided to cross the border and buy in Googong.

Matthew Partridge and Tegan Gaha have bought in NSW after being shut out of the ACT. ( C News )

"Everywhere from Yass to Queanbeyan to Bungendore ... People are getting better value away from the ACT at the moment," Mr Partridge said.

Ms Gaha's and Mr Partridge's decision to move to NSW is a trend which is making some in the building industry worried.

"When supply is not meeting demand, it's a natural consequence that demand is going to be met somewhere else," Mr Hopkins said.

"Yet a lot of these people will work in Canberra, so roads and hospitals still provided by ACT Government. We don't think that's a healthy situation, [we] would like to see those benefits captured by the territory."