09 Flat Roof Collapse

Question 1

To determine the risks of a flat roof, we need to know three facts about any type of roof construction:

Answer 1

1. What type of support system has been used?
2. What method was used to connect the joists to the supporting wall?
3. Is there a built up structure above the main roof supports, or a rain roof covering the old roof

Question 2

When a building has a steel bar joist system supporting the roof, what is preferred to vertical ventilation (which puts FFs on the roof)?

Answer 2

Horizontal ventilation of windows and doors

Question 3

What is the most common flat roof supporting member used in older ordinary constructed buildings?

Answer 3

Conventional solid wood joists

Question 4

An important feature of a wood joist supporting system is that it does not _____________________ when weakened by fire.

Answer 4

Collapse suddenly (it will generally give some warning)

Question 5

The second roof construction fact that helps us to evaluate roof stability is knowing whether the roof joists are rigidly held in position at both ends in a brick cavity. This is called … ?

Answer 5

Restrained Beam

Question 6

An _________________ has the ends resting on a girder or brick corbel shelf, not rigidly held in position.

Answer 6

Unrestrained beam

Question 7

A beam end that is simply resting on a corbel shelf or a girder, functions as a ______________ beam. That is, it is a _________________ or unrestrained beam.

Answer 7

fire-cut / self-releasing

Question 8

The third fact necessary to determine roof stability is for FFs to know whether the roof deck of the wood beam roof is directly attached to the roof beams, or whether it has an intervening space so that the roof deck is resting on a smaller wood framework that was built up above the main roof support.

Question 9

What are some roof hazards?

Answer 9

1. Repairs (the FFs trap)
2. Scuttle covers
3. Disorientation
4. Shafts