Reality Check: How does migration affect housing?
The claim: Migration to the UK puts a heavy burden on housing stock - we would need to build 240 houses a day for 20 years to cope.
Reality Check verdict: The sums add up. Note that the figures include migration from outside the EU and are a projection based on the past.
Iain Duncan Smith has been talking about the impact of migration on the availability of housing.
"We need to build around 240 houses every day for the next 20 years just to be able to cope with increased demand from future migration," he said.
That works out at a total of 1.75 million houses.
The Office for National Statistics (ONS) makes assumptions about future levels of migration in its population forecasts. In the latest release, published last October, the suggested figure for population increase due to net migration over a 25 year period is five million. Over the 20-year period from 2014 to 2034, the figure is approximately four million.
The average UK household size is 2.3 people so four million people does indeed equate to about 1.75 million homes, or 240 a day.
There are a couple of caveats. One is that the ONS figure is for immigration from both inside and outside the EU. At the moment, the EU accounts for just under half of total net migration.
And second, the ONS numbers are not a forecast of what they expect to happen. They are an assumption made on the basis of what has happened in the past.