In this section we will discuss new steel / tin / metal roof replacement
in relation to flat roofs.
Steel roofs 101
Let's briefly discuss the materials.
Steel
roof sheets come in a few thicknesses and flavours.
These are the common ones:
0,40
mm - Wafer thin ( not recommended )
0,50 mm - Standard thickness ( acceptable )
0,58 mm - Above standard ( choice )
0,80 mm - Industrial ( industrial enviroments )
All
steel is galvanized to protect the steel from rusting.
There is either 275 grams or 600 grams of galavanising
per square meter on the steel.
Chromadek
Sheets.
A further coating can be applied to the galvanized
steel sheet.
This coating is called Chromadek** and comes in a
few colors.
Chromadek sheets and galvanized sheets carry the same
guarantee as normal galvanized sheets.
In our opinion there is no difference to quality.
Where
do roof sheets come from?
Most commercial steel for roof sheets comes from Mittel
in Gauteng and is sold through various distributors
around the country.
The steel is transported in huge coils weighing between
5 - 25 tonne.
The steel coil is loaded onto a spindle and rolled
out and pressed into a particular profile.
The two most common profiles are IBR
and Corrugated profile.
It is important to note that IBR and Corrugated are
standard profiles and not inherent to steel only.
Fibreglass** sheets and polycarbonate** sheets also
come in IBR and corruated profiles.
The sheet is cut to lengths up to 21.00m This is the
longest transportable length that can be provided.
Some steel distributors such as global roofing supplies
have a mobile factory that can cut longer sheets on
site if neccessary
Why
such long sheets?
It is always a good idea to use full length sheets
and not join sheets head to tail. Allot of waterproofing
contractors don't do this. Instead they will try to
waterproof the joints with waterproofing membrane
or even torch-on products but the reality is that
even the finest quality products won't stop the leak
for good. When the rain comes next winter the leak
starts all over again and the contractor is long gone.
This is a much cheaper method but the best is to replace
the roof sheets .
The steel sheet should extend from the top of the
ridge down to the gutter in one full length. This
is considered standard practice especially on a low
pitched roof.
The reason behind is this that water does not run
off low pitch roofs very well. It may run back under
a head-to-tail over lap. If it does not run back into
the roof it will rust on the overlap and eventualy
water will start dripping into your kitchen.
We also recommend using IBR profile on roofs with
low pitch. The reason is that IBR has deeper profiles
and therefore the chance of water overflowing the
overlaps of the sheets placed side by side is minimised.
Roof fixtures
The preferred method of securing roof sheets are using
self drilling screws which have self sealing washers
Avoid roof nails that require to be hammered in. These
damage the sheets and are hellishly difficult
to remove at a later stage should the steel roof sheet
need to be lifted for whatever reason.
Roof screws can be sealed with a bitumen mastic if
they are leaky.
Very
important is that the roof fixtures are always fixed
through the ridge of a sheet and not on the trough
of the sheet. The water flows in the trough of the
sheet.
Flat roof replacements / sheets
home extensions : Braai rooms, room extensions etc
Metal
flat roofs are commonly found on building extensions
to existing homes.
Building contractors and home owners usually choose
to tie the metal roof installation into a tiled roof
of an existing house.
This type of roof design is fine if there is enough
roof pitch on the steel flat roof section.
A major problem on a steel flat roof is low pitch
when sheets extend longer than 6m. The problem is
that over time the support structure starts to bow
slightly under the weight of the roof.
This causes the ends of the roof sheets nearest the
gutter to lift lightly. The result is that small amounts
water which are supposed to fall into the gutter now
travels back under the sheet and drips off inside
the roof.
We
call this run-back and there are only two ways to
fix this flat roof problem.
)
crimp the ends of the sheets to form a pouring lip
2) raise the pitch of the roof
If
crimping does not work you will most likely have to
raise the pitch of the roof and even possibly put
new steel sheets on.
Some roof contractors try to put rubber closures or
expansion foam or even worse try to seal the ends
of the sheets at the gutter side. This roof fix usually
aggravates the problem. Click
here for a steel flat roof contractor
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