The window

The window
The principle of the opening rebate
The opening rebate is a peripheral step or shoulder in the structural
opening and thus forms the contact face between outer frame and
structural opening. The window is fitted up against this step, fixed with
screws and sealed.
To avoid stresses caused by temperature-related movements, the frame
must be built in with minimum tolerance.
All fixings must be protected against corrosion.

The principle of the frame rebate

The biggest problem with the window is keeping out water and wind.
The rebate in the structural opening and the rebates in the frame
members are therefore the most important elements in this battle. Special
attention must be paid to the tightness of the joints between outer frame
and opening, and outer frame and sash frames.
The weatherstripping between outer frame and sash frames remains in
the same position around the entire periphery and is sealed at the
corners. There are two different sealing positions in a window element:
Outer frame–opening
– water and wind
– accommodation of climate-related movements in the masonry
Outer frame–sash frames
The rebate is intrinsic to the design of windows with opening lights, i.e.,
opening windows:
– joint permeability for controlled air change rate between sash frames
and outer frame
– protection against driving rain, water and wind
The window Opening package

Window opening inwards

Such windows are usually fitted from inside. The entire
width of the outer frame is visible internally, whereas from
outside it might be that only the sash frames can be seen.
The window can be fitted flush with the inside face of the
wall. As the window is always fitted back from the face of
the facade by a distance equal to at least the depth of the
step or shoulder, it is relatively well protected against the
weather. The connections do not present any problems
because they are essentially covered and protected by
this step or shoulder. inside outside

outside inside

Window opening outwards

The entire width of the outer frame is visible externally.
The window can be fitted flush with the outside face of the
wall; however, that does mean that the glazing and the
frames are fully exposed to the weather. The connections
must satisfy enhanced aesthetics and quality
requirements because they are readily visible and very
exposed, especially when the window is fitted flush with
the outside face.

inside outside

outside inside
The window Position of window, opening rebate forms
Materials for outer and sash frames

Untreated wood
The following measures must be taken to ensure the durability of wooden windows:
Choose suitable, resistant species of wood such as pine, spruce, fir and larch.
Ensure that water can drain away from all sections and surfaces.
Ensure protection by providing an appropriate surface treatment: priming is a
preventive measure protecting against discolouring mould growth. Impregnation
prevents rotting caused by moisture.

Painted wood
Wood can be painted many different colours. Opaque paints have a lower water
permeability than mere impregnation and they protect against rot.
Problems: resistance to ultraviolet radiation, vapour pressure from inside (in the
case of thick coats of paint on the outside of the window).

Wood/metal
This is the combination of a loadbearing construction of wood on the inside and an
aluminium facing on the outside.
The latter protects the wood, but the architectural expression of the window varies
from inside to outside.

Window sample
Frame: untreated wood; insulating glazing

The window as a component – frame sections

Plastics
PVC is the most common material for the production of plastic windows. The material
of the frame sections is initially white; it can be dyed or coated, but not painted.
The frame sections are hollow (single- or multi-chamber systems), with various forms
readily available. Despite the inclusion of metal stiffeners to strengthen the
chambers, plastic windows are known for their relatively low structural strength.

Aluminium and steel

Metal windows have a high thermal conductivity and so the frame sections must
include a thermal break.

Aluminium windows: Stability is relatively good and so aluminium is suitable for large
elements. As a rule, the surface is treated because otherwise the irregular oxidation
of the material leads to blemishes.
We distinguish between mechanical surface treatments, e.g. grinding, brushing and
polishing, and the electrochemical anodising process, which produces a consistent
oxide layer. Stove-enamelling involves bonding a coat of paint to the metal surface
by firing.

Steel windows: Mainly used for industrial buildings.

Much more stable than aluminium windows. Large window assemblies, especially
together with the glazing, are very heavy (installation problems).
The biggest disadvantage is the risk of corrosion, which can be reduced by painting
or galvanising. Like aluminium windows, steel windows can be given a
stove enamelled finish.

The window as a component – frame sections

Types of glass

Various types of glass are available, distinguished by the

method of manufacture:

– Float glass is today the most common form of glass and

has a flat surface.

– Window glass was the forerunner of float glass and is

characterised by a slightly undulating surface
(cf. window panes in old buildings).

– Rolled or patterned glass has a textured surface and is

therefore translucent, not transparent.

– Wired glass includes a wire mesh inlay, which enhances

the fire resistance and binds together the fragments of a
broken pane.

The window as a component – glass

In addition to these basic types, diverse coatings and Current thermal insulation and comfort requirements have made
surface treatments are possible. The choice of glass and insulating glazing the number one choice for almost all windows.
its coating or treatment influences the architectural Insulating glazing consists of at least two panes of glass bonded
expression and the quality of light entering the interior to an aluminium or plastic spacer. The adhesive also seals the
(direct, diffuse, coloured) plus building performance and cavity between the panes.
security aspects. We distinguish glazing primarily
The thermal insulation properties of insulating glazing
according to mechanical and thermal treatments:
essentially depend on the cavity and the quality of its filling
(various gases), also any coatings that have been applied.
– standard glass
– toughened glass Important parameters
– toughened safety glass U-value: Thermal transmittance is the rate of transfer of heat
– laminated glass through matter. The thermal transmittance of a material (such
– laminated safety glass as insulation or concrete) or an assembly (such as a wall or
– fire-resistant glass window) is expressed as a U-value. The lower the value, the
– heat-treated glass better the insulation. Customary values are 1.0–1.1 W/m2K, but
values as low as 0.4 W/m2K are possible
– insulating glazing
(HIT glass, glass with special interlayer).
– heat-absorbing glass
– solar-control glass
g-value: . The g-value specifies how much energy from the
....
incident solar radiation passes through the glazing into the
interior Or how much heat is transmitted through the glazing
from the sun's rays.. It is made up of two components: the direct
radiation transmission and the secondary heat emissions.
- The G-value is a scale between 0-1: A high G-value of 1
represents the full transmittance of solar energy.
- A low G-value of 0 means that all solar energy is blocked by
the glass.

The window as a component – glass

The window horizontal section

The window vertical section

The opening as a hole

The opening as a hole

The opening as a hole

The opening as a horizontal strip

The opening as a a joint

View of one of the large entrance portals on the northern facade

Hans Kollhoff and Christian Rapp: residential development,
KNSM-Eiland, Amsterdam (NL), 1991–94

About the door by Cordula Seger