Porch collapse or balcony collapse is a phenomenon typically associated with older or poorly constructed multi-storey apartment buildings that have wooden porch extensions on the front or rear of the building. The collapses have a number of causes, including overloading due to excessive weight from overoccupancy (too many people). Overoccupancy can result from guests filling a porch at a party, from people seeking cooler breezes during a heat wave, or from people filling a porch while seeking shelter from the rain. It may be from the weight of furniture/appliances, wading pools, or air conditioner compressors. After years of rain and snow, it may be from rotted wood, soil subsidence under the porch foundation, rust of nails and fasteners, and not being built to specifications required by modern-day building codes. Many older porches were built before codes required them to be able to support a legally mandated load of so many pounds per square foot or metre, and porches are often not as sturdily built as interior structures. The phenomenon is associated with older or poorly constructed multistorey apartment buildings with wooden porches. Architect Stanley Tigerman said that in New York City one finds steel fire escapes, but in Chicago, the distance to alleys behind multistorey brick buildings encouraged the construction of wooden multistorey porches.

While not an everyday occurrence, collapses happen often enough in Chicago that city building inspectors make a point of checking porches when making inspections. People have been killed and injured by collapses of wooden porches in other cities as well.

A Chicago porch collapse during a get-together in the Lincoln Park neighborhood in 2003 killed 13 people. The weight of approximately 70 people caused the recently renovated porch of the 1890s vintage building to fail. The disaster inspired a 2005 episode of the ER television show. In June 2008, a third-story balcony collapsed in Ottawa, injuring six persons.