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In this case, there is no building of new properties involved. The Council are upgrading each home to a certain standard as far as plumbing, central heating, new bathrooms, new kitchen, rewiring etc are concerned. A number of vacated houses already exist on the street. The council have upgraded these void properties first and the tenants are allowed to move to a house that has been upgraded If they desire instead of living in a house while the upgrading is going on at their home. If they do move to an alternative home, they may re-locate to this house permanently.
It's not that uncommon a system apparently and works very effectively.