Tory former ministers have hit out at the government's "weak" planning reforms and called for "bold" action to solve the housing shortage.
John Penrose, Nick Boles and Mark Prisk have warned the country is facing a "slow-motion crisis" that will leave a generation locked out of home ownership.
Communities Secretary Sajid Javid said on Monday the government will consult on changes that will make it easier to build upwards.
But the MPs raised concerns about the scale of the plans.
In a letter to Mr Javid, they said: "You are absolutely right that overhauling our slow, expensive, uncertain and conflict-ridden planning laws is the place to start.
"But given the size of our housing crisis, we'd like to encourage you to be even bolder.
"Unless these proposals allow for building up not out in all towns and cities, and without red tape, they will be too weak to make a difference on the scale that's going to be needed."
Mr Boles, a former planning minster, accused Theresa May of timidity and a lack of ambition as he raised concerns about a string of issues, including housing, last month.
Under proposals put forward by the three MPs, the need for planning permission would be removed for urban property owners who want to build up to the height of the tallest building in the same block or to the fifth storey, whichever is greater.
That would mean the creation of mansion blocks, terraces or mews housing rather than sky-high tower blocks, they said.
The former ministers said the government's plans may simply lead to a change in planning guidance rather than a full-scale extension to permitted development rights.
Mr Penrose, a former architecture and heritage minister and chair of the All-Party Parliamentary Group on housing and planning, said: "We've simply got to build more homes, whether they're to rent or to buy, so they're cheap enough for everyone to afford.
"Housing is a huge, slow-motion crisis, so we've got to be bold. Otherwise a generation will stay locked out of the dream of home ownership and house prices will keep spiralling upwards."