Loft
Conversion Roof Roofing
Roof construction
This article is about the type of roof construction that consists of
beams and an outer weatherproof skin, as found on most domestic
architecture. Such roofs may take a number of different shapes and be
constructed of and covered with a variety of materials.
The loft conversion roof should be checked for any signs
that rainwater is entering the roof space. The appearance of dark
stains on the roof rafters is a strong indication that this problem
exists. Repairs to the roof are usually carried out during the works as
part of the loft conversion process due to the construction of dormers
and fitting roof windows.
A simple ridged roof consists of inclined
rafters that rest on horizontal wall-plates on top of each wall. The
top ends of the rafters meet at the horizontal ridge plate or ridge
beam. Horizontal purlins are fixed to the rafters to support the roof
covering. Heavier under purlin are used to support longer rafter spans.
Tie beams or ceiling joists, are connected between the lower ends of
opposite rafters to prevent them from spreading and forcing the walls
apart. Collar beams or collar ties may be fixed higher up between
opposite rafters for extra strength.[1]
The rafters, tie beams and joists serve to transmit the weight of the
roof to the walls of the building. There are a number of structural
systems employed to facilitate this, including the use of wall-plates
set at the top of the wall, hammer-beams, which spread the weight down
the wall and create an equilibrium between outward and upward thrust,
king posts which transfer the weight of the roof ridge, and various
types of trusses.
In cyclone and hurricane prone areas the main engineering consideration
is to hold the roof down during severe storms. Every component of the
roof (as of course the rest of the structure) has to withstand the
uplift forces of high wind speeds. This is not normally a problem in
areas not prone to high wind.
Modern roofing technologies, apparent in the accompanying photo of a
house under construction in a cyclone-prone region of Northern
Australia, include the purpose-made steel hook bracket which is bolted
to the truss with M16 bolt. The bracket is bolted to an M16 bolt cast
in situ, embedded 300 mm into the reinforced concrete block wall. This
system is typically in place every 900 mm around perimeter.
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conversions roofing regulations
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