Well, it seems that the houses have always been three-quarter size because of a lack of space when the set was built in the 60's. Even when it was rebuilt in the 80's the same smaller scale was used.
Now the houses on the street are to be built life-size for the first time. Camera tricks and even acting techniques are employed to make the current houses look bigger, apparently the actors are trained to walk down the street to make the house fronts appear full size.
Corrie director Tony Prescott told the Sun: "We use camera tricks - you can do anything with a wide lens - to get it to look normal. But the new set will be scaled up."
ITV boss John Whiston promised, thought, that the look of the street will not change: "We will be using the same factory that made the old bricks and I will be making sure that each one is exactly the same as all the others."