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All new housing, replacement doors and windows must comply with Document L (Document
J in Scotland), unless specifically excluded. Your national local or preferred
installer will be able to offer you helpful guidance and assistance.
If you are planning any new building or renovation work, it is always advisable
to contact your local planning office for advice on how the building regulations
affect you and your project.
A 'U' value is a measure of the rate of non-solar
heat loss or gain through a material or assembly.
The value is calculated as heat lost per hour
per square metre (W/m2K) and may
be expressed for the glass alone or the entire
window. This includes the effect of the frame
and the spacer materials. The lower the 'U'-value,
the greater a window’s resistance to
heat flow and the better its insulating value.
Document L (Document J in Scotland) is part
of the Government’s Building Regulations.
It was revised in April 2002, following the
Regulatory Impact Assessment, and controls
the acceptable 'U' value of your home –
in general terms :-
- Timber doors or windows should not have
a 'U'-value higher than 2.0 W/m2K
- Aluminium doors or windows should not
have a 'U'-value higher than 2.2 W/m2K
Low-e glass
Low-e glass stands for low emissivity glass. This
glass varies from normal clear glass, in that
one side of the glass has a special metal
coating, technically known as a low emissitivity,
or Low-e. coating. Low-e glass is a type of
insulating glass, which increases the energy
efficiency of windows by reducing the transfer
of heat or cold through glass. That means
in the winter your house stays warmer, and
in the summer it stays cooler.
There are two types of Low-e (low emissivity)
glass available - Pyrolytic (hard coat) considered
to be a medium performer, and sputtered (vacuum
deposition or soft coat) considered to be
the highest performer.
Low-e glass, how does it work?
The radiation coming from your heating system
and your furniture and furnishings is long wave
radiation. This type of radiation should be contained
in your room as best as possible, while the radiation
from the sun should be shielded and reflected
back outside.
Typical system overall 'U' values (approx*)
| System
type |
Folding
|
| SF45 |
SF55 |
SF70 |
SF65 |
SF80 |
SVG99/
155 |
Aluminium |
Timber |
Ali |
| Soft-
Wood |
Hard-
Wood |
| Hard Coat -
centre pane @ 'U' value 1.7 W/m2K
|
N/A |
1.99 |
1.97 |
1.76 |
1.51 |
2.05 |
| Soft Coat -
centre pane @ 'U' value 1.1 W/m2K
|
**2.19 |
1.58 |
1.52 |
1.33 |
1.08 |
1.78 |
*Based on a 3 panel door folding door & 2
panel sliding door system 3000mm wide x 2100mm
high
**Not recommended as an external door
Safety glass
The Building Regulations Document N requires
that a safety glass complying to BS6206 is used
in any full-height moveable glass panel. This
is usually toughened or laminated glass.
Toughened glass
Glass that has been heat hardened (tempered),
increases its strength over ordinary annealed
glass by up five times. There is also an added
advantage that, should it break, it would shatter
into hundreds of tiny non-sharp fragments.
Laminated glass
Laminated glass consists of two pieces of glass
bonded together with an invisible polyvinyl butyral
interlayer membrane forming a sandwich (similar
to a car windscreen), making it very strong.
The main benefit of laminated glass is that,
if broken, the glass cracks while still remaining
attached to the plastic interlayer rather than
falling and possibly causing injury; it also
provides secure protection from unwanted visitors.
In addition, laminated glass reduces bleaching
of carpets, curtains and furniture by reducing
the amount of ultra-violet rays that penetrate
the glass.
Other considerations
In addition to complying with Building regulations,
generally depicted by the type of project other
personal preferences such as the level of solar
heat gain (i.e. solar control glass), privacy
(tinted or integrated Venetian blind units),
or acoustic requirements should also be considered. |
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