Rehabilitation and Expansion of the Existing Wastewater ... - UNDP

Rehabilitation and Expansion of the Existing WWTP in Jenin City
Technical Specifications
END OF SECTION
SECTION 5
ROOFING
1-1 Corrugated Steel Roofs
All corrugated galvanised steel sheeting (whether fixed to wood or steel framing) shall be of 23 or 24
gauge fixed with a minimum of 50mm end laps and with a minimum of one corrugation side lap.
When instructed to have a one-corrugation side lap, the sheets shall have a cover of not less than 20
mm and all the lapped sides shall be turned downwards. Where practicable the exposed lapped sides
shall be arranged to face away from the prevailing wind. When instructed to have a one and a half
corrugations side lap the sheets shall be arranged alternatively with a cover of not less than 90mm, the
first sheet being fixed with the lapped sides turned upwards away from the bearer and the cover sheet
with the lapped sides turned downwards.
Sheets shall be secured to purlins at centres not exceeding 300mm by galvanised self-parking screws
(minimum 75mm long) with galvanised diamond shaped washers and lead sealing washers.
All holes for bolts, self-parking screws etc. shall be punched from the underside of the sheets and shall
be on the crown of the corrugations.
Galvanised steel ridge capping shall be supplied and fixed to purlins as described above.
1-2 Screeds
Hook bolts; self-parking screws and washers shall generally comply with BS 1494.
The provisions of Concrete Work section shall apply to the construction of solid reinforced concrete
slab roofs and to hollow slab roofs. The actual finish will be specifically shown on the Drawings or in
the Particular Specification.
Lightweight concrete screeds for obtaining falls or as an insulation layer shall be of approved type of
foamed concrete. The materials shall be measured, applied and cured in accordance with the
manufacturer's instructions and to the satisfaction of the Engineer.
In all cases the finished screed shall be of an approved proprietary type with a density of not less than
400kg/ m2 to receive the applied roofing. Mixing shall take place using approved mechanical mixers.
Concrete screeds for obtaining falls shall be (1:3:6) mix.
All screeds shall be laid in bays not exceeding 10 square metres and formed between stop boards of
the correct height and cut on each side to indicate the slope required in the roofing. The screed shall
then be trowelled with a wooden float to true and accurate falls or cross falls up to the stop boards. A
10mm side gap shall be left between each screed bay for the full depth of the screed. The screeds shall
Arabtech Jardaneh/Palestine
34
Civil Works