283757893275

218 Barry’s Advanced Construction of Buildings
150 girth ridge cap
Galvanised or plastisol corrugated steel
sheeting hook bolted to purlins
Ventilated air space between
sheets and insulation
150
Gutter bolted
to wall sheets
Wall sheeting
and insulation
over sheeting
rails
Angle purlin fixed
to angle cleat
Line of top of
lattice roof truss
Over purlin insulation boards
with timber spacers to provide
air space
8 , 10 ,11 and 12
corrugations, 610
762 , 838 and 914
cover width
19
Standard 3
corrugated steel
cladding sheet
Figure 4.52 Corrugated steel cladding sheets.
Over purlin insulation with inner lining
Where mineral fibre mat insulation is used and where more rigid forms of insulation will
not be self-supporting between widely spaced purlins, it is necessary to use profiled inner
lining sheets (or trays) to provide support for the insulation. The lining sheets also help to
provide a more attractive finish to the interior.
Linings are cold, roll-formed, steel strips with shallow depth profiles adequate to support
the weight of the insulation. The sheets are hot dip galvanised and coated with a protective
and decorative organic plastic coating. To prevent compression of the loose mat or quilt,
its thickness is maintained by Zed section spacers fixed between cladding and lining panels
as illustrated in Figure 4.53 and Figure 4.54. The space between the top of the sheeting and
the insulation is passively ventilated to minimise condensation, and a breather paper is
usually spread over the top of the insulation. The breather paper protects the insulation
from any rain or water condensate, yet allows moisture vapour to penetrate it. Some manufacturers
also manufacture ‘structural’ trays, which provide a stronger internal lining and
thus help to improve security to the roof.
Over purlin composite (site assembled)
This system comprises a core of rigid preformed lightweight insulation (or mineral
wool and spacer), shaped to match the profile of the sheet and the inner lining tray. The
separate components are assembled on site and fixed directly to purlins and lining sheets
with self-tapping screws (Photograph 4.6). Side and end laps are sealed against the penetration
of moisture vapour. Factory-formed composite panels have largely replaced this system.