Roofs

Question 1

definition of a roof

Answer 1

a structure, which
surmounts a building to keep out the weather and
may be flat, pitched or curved”

Question 2

Roofing panels of PTFE-based material are commonly
welded together. It is current good practice
to design what regarding a fire

Answer 2

1. welds to fail and vent the fire at low
   temperatures
2. the panels in tension-supported structures should be designed such that they cannot become
   detached at one end and hang down into the f

Question 3

label a diagram of important features
of the form of roof construction often used in domestic
dwellings

Answer 3

ridge 
purlin
rafter
joists
battens
tiles
close boarding
coping

Question 4

define and describe a trussed roof

Answer 4

This type of roof is used to spread the load and
direct it to the walls and the ground. Construction
varies widely both in its use and design. The older
styles of timber rafters, either tensioned by iron
rods or timber, and the cast-iron trussing found in
large old mills and warehouses etc

Question 5

describe a portal or rigid framed roof

Answer 5

The Portal frame consists of, essentially, a continuous
member conforming to the outline of the roof
and connected to vertical columns. This continuous
frame has the effect of passing the roof loading
to the rest of the structure (Figure 5.28). They
are especially suitable for single storey industrial
or storage buildings giving long, wide open areas

Question 6

describe a monitor roof

Answer 6

A type of roof found in factories or stores is
illustrated in Figure 5.29. It is of a relatively
light weight and is designed to give the maximum
amount of light by the use of “upstands” of glass
or polycarbonate. The nonglazed portions are
usually light decking and the walls are generally of
a lightweight “sandwich” cladding, the whole
I supported by precast concrete frames

Question 7

what are the general points to remember re roofs in a fire

Answer 7

1. generally not readily combustible
2. Except thatch
3. pitched roof has voids that can extend
4. rising heat and smoke
5. lack of access
6. nail plates failing
7. hard conditions
8. slates and tiles falling

Question 8

how does cast iron compare to steel

Answer 8

Cast-iron is of greater cross-section and density
than steel and such trusses can still be found in
place after a fire providing there has not been a
sharp change in temperature i.e., a heated truss
struck by a jet of water

Question 9

consideration re reinforced concrete roof

Answer 9

Concrete is usually reinforced in some way and
providing the steelworks is not exposed quickly to
the fire e.g. by spalling of the concrete cover, it can
still maintain its support

Question 10

Some rooflights are intended to form a vent when
destroyed by heat i.e., roof ventilators in the form
of haystack lantern lights installed above the stage
area of theatres. Hazardous conditions can arise

Answer 10

1. if a rooflight is recessed above a soffit or
   a suspended ceiling where a fire can develop undetected.
   2.heat and flame escaping from
   a rooflight may reach an adjacent building or
   flammable materials
2. It is important to remember however that most
   rooflights will fail in heat. ( may help vent fire and improve conditions )