Firefighters from Slough, Maidenhead, Bucks and London rushed to the scene shortly before 9.30am.
They were told that there were a number of workmen in the property at the time and two of them were trapped by rubble from the collapse.
Two ambulances, a rapid response vehicle, the Thames Valley Air Ambulance critical care car, a Hazardous Area Response Team, a Tactical Advisor and Incident Commander also attended the incident.
Thamea Valley Police were also present.
One of the trapped patients had sustained serious injuries and has been taken to the major trauma unit at the John Radcliffe Hospital, Oxford.
The second trapped patient sustained less serious injuries and has been taken to Wexham Park Hospital for further treatment. Three other patients were assessed and treated for minor injuries at the scene.
One of the first neighbours on the scene was Priscilla Dupreez, who was outside her house waiting for the removal van coming to help her move to a new home.
She said: “I heard crash and there was a cloud of dust. The whole of the roof had come down.
“A lady came out of the house, someone called an ambulance.
“About 12.35 I saw them carry someone out.
“A paremedic came to my house and asked to use the shower. There was a man so covered in dust they could not examine his injury properly until they had cleaned him up.
“It has been quite a day – I have had to put my move off until tomorrow.”
Once the two trapped people had been rescued, the fire crews made the scene safe before handing over to a structural engineer. They were on the scene for approximately four hours and 40 minutes.
The road reopened shortly before 3pm.