Wall opening

Influences on the building envelope

1. Rain

Wall

Erosion of outer leaf, risk of saturation of outer leaf, frost risk a) Masonry (monolithic, two leaves or with external insulation): render/paint b) Fair-face masonry: clay/hard-fired bricks are water-repellent and frost-resistant, special moilar required (seal joints), possibly a ventilation cavity.

c) Lightweight construction (steel, timber): cladding, shingles, planks, boards; if the loadbearing construction is positioned externally, it must be protected (paint, cladding, canopy).

d) Exposed concrete facades: concrete is essentially waterproof, but the problem of carbonation must be considered: carbon dioxide and moisture in the air react with the alkaline components in the cement, which leads to corrosion of the reinforcement and subsequent spalling of the concrete surface.

Window

Rain striking the window is drained via a weather bar on to the window sill. Rebates in the window frame must always be formed to prevent water collecting. The joints with the spandrel panels at the sides are particularly vulnerable.

2. Sunshine

Wall

Measures to combat ultraviolet radiation and temperature rise. Untreated timber facade elements exposed to direct sunlight are particularly vulnerable to deformation, cracking and sometimes "scorching" as well. Nevertheless timber is regarded these days as a building material presenting few problems. Paints, glazes and impregnation are additional measures that can be taken to prevent water entering porous building materials. Dark finishes are a problem because they heat up too much and so are unsuitable for facades with external insulation.

Window/opening

Measures to combat glare and heat gains, and to provide privacy

- Flexible sunshading systems, external:

a) Louvres (aluminium, position of louvres variable) integrated into window head or housed in surface-mounted box on facade b) Roller shutters (wood, aluminium, fabric) integrated into window head or housed in surface-mounted box on facade c) Hinged, folding or sliding shutters of wood or sheet metal (folding against reveals, hinged or sliding in front of facade)

- Fixed measures, external (brise-soleil, canopies, fixed louvres)

3. Noise

Wall

Owing to their lack of mass, lightweight buildings (timber or steel systems) are more vulnerable to noise. Discuss with a specialist if necessary, but not a problem in normal cases.

Window

Thickness of individual panes, total thickness of glazing and airtightness of joints depend heavily on the level of noise to be expected. Opening the windows for ventilation is hardly possible when noise levels are high, so mechanical ventilation will be required.

4. Wind

Wall

Generally, all facade constructions made from small-format, jointed elements, and primarily timber wall constructions, will require the inclusion of an airtight membrane in order to overcome the problem of any gaps that occur in the joints due to swelling/shrinkage.

Window

The rebates in the window frame must be windproof; window frames and glass can be subject to severe wind loads.

5. Soiling of the facade, water entering horizontal joints

Wall, window

Rain in conjunction with upward air currents can force water into horizontal joints. Therefore, horizontal components such as lintels, window sills and cornices must be provided with rainwater drips.

6. Temperature

(The thermal transmittance, and hence the minimum thickness of various constructions, is specified in standards.) Wall

Thermal i nsulation materials guarantee protection against high temperatures in summer and low temperatures in winter. Depending on the system, the layer of i nsulation is separate, the material provides both loadbearing and insulating functions (single-leaf masonry), or the i nsulation requirement is integrated into the building component (timber platform frame construction).

Window a) Insulating glazing b) Double window possibly with insulated frames

7. Vapour diffusion from inside outside

Avoiding saturation of the construction by condensation water Wall

Possible measures:

a) Ventilation cavities (drying out and dissipation of moisture in an air gap outside the layer of I nsulation with the help of natural convection)

b) Vapour barrier/check on the warm side (inside) of the insulation for components vulnerable to moisture c) Vapour-proof internal loadbearing layer, e.g. in situ concrete d) Moisture-resistant insulation, e.g. cellular glass e) Whole construction open to vapour diffusion, e.g. single-leaf masonry

8. Mechanical damage

Wall, window

Soft surfaces (paint, some types of wood) are vulnerable to mechanical damage. Rendered external I nsulation is particularly susceptible (principally at base of wall, i.e., from ground level up to a height of about 2.00 m)

internai sunshade

(does not cut out heat radiation)

a) curtains b) louvres integrated into the glazing s----7

internai sunshade

(does not cut out heat radiation)

a) curtains b) louvres integrated into the glazing s----7

Fig. 73: Schematic section, scale 1:20

Protective layer Ventilation cavity Insulating layer Loadbearing layer

Fig. 73: Schematic section, scale 1:20

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