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.
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a steel flat roof contractor
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