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Roofline
Roundup
For roofline installers the issue of roof
ventilation can be complex as there are different requirements
for different roof structures. Getting the ventilation wrong
can lead to long term condensation and damage to the rafters.
Before the 1960’s houses had efficiently ventilated roof voids
due to the nature of slate roof construction. However, when
felt roof linings were introduced “under tile” the ventilation
of the roof void became restricted. In the ‘60s houses with
inefficient insulation created few roof void problems. Soon
after though, technology introduced loft insulation, wall
insulation, double glazing, central heating, laundry white
goods, and more baths and showers. The net result was that the
home became a warmer enclosed environment with much more
humidity. Sealed windows and doors meant that this warm moist
air was forced in to a cold “sealed” loft space where
condensation took place.
Approved Document F (Ventilation) of the Building Regulations
were amended to protect timber roof trusses from rotting from
the extra moisture, and ventilation of the roof space was
introduced.
The regulations require that for roof pitches greater than 15°
an equivalent of 12.5mm continuous air gap is required.
However where roofs are flat or have a roof pitch of less than
15°, this increases to an equivalent air gap of 25mm.
This leaves installers asking “what type of ventilation should
I use?”
The simplest ways to ventilate roofline are over fascia
venting or soffit ventilation. Over fascia vents are more
aesthetically pleasing but leaves can accumulate at the back
of the gutter installation and effectively reduce the air
ventilation level.
Soffit ventilation is by far the most effective. There are
three ways to ventilate soffits:
1. A ventilated strip that fits alongside a conventional plain
soffit. This form of ventilation is recommended by some
roofline manufacturers but it can often come with nylon mesh
which reduced air flow, and over time will get clogged up with
dirt and insects and will require regular maintenance.
2. Disc vents. This option requires accurate calculations to
ensure the correct air flow, depending on the size of the
discs, and the volume of the roof, and they have labour
intensive installation.
3. By far the most effective option is pre-ventilated soffits.
The correct airflow will be achieved by using either standard
ventilated, giving an equivalent 12.5mm air gap, or double
vented, increasing the air gap to an equivalent of 25mm. And,
because they are pre-formed the installation time is
significantly reduced
For further information on installing roofline or if you have
any questions email Ken Davies at kendavies@everwhiteplastics.com
or call 01685 882447.
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