Seven homes collapsed. Why?

A row of five unfinished homes collapsed in northeast London Saturday around dinner hour. Another two, several kilometres away, were also taken down by what were reportedly light winds. Why did these homes collapse?

Yes, seven homes were dropped to their knees by winds gusting to 67 km/h as measured at London International Airport. All were only partially built and thus were quite vulnerable, but vulnerable to what? All were two storey homes but after they collapsed it was mighty hard to tell.

One onlooker said, "It wasn't even that windy."

For the complete story and the answer to this puzzle, I have posted more information plus more pictures on Digital Journal.