ISO/TR 5863:2025

Technical
Report
ISO/TR 5863
First edition
Integrative design of the building
2025-01
envelope — General principles
Conception intégrée de l'enveloppe du bâtiment — Principes
généraux
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Design philosophy and principles for the building envelope . 3
4.1 General .3
4.2 One thing increases, another decreases .4
4.3 One structure variable relates to several function and behaviour variables.5
4.4 Appropriate balance among the behaviours of environmental elements .5
5 Functions of the building envelope . 5
5.1 General .5
5.2 Flexibility.5
5.3 Adaptability .6
5.4 Reusability . .6
6 Structure of the building envelope . 6
6.1 General .6
6.2 Roof system .7
6.3 Wall system above the ground .8
6.4 Wall system underground .9
6.5 Base floor system .10
7 Behaviour of the building envelope . 10
7.1 General .10
7.2 Thermal performance .10
7.3 Daylight and visual information .11
7.4 Ventilation . 12
7.5 Sound proofing . 13
7.6 Airtightness . . 13
7.7 Moisture protection . 13
7.8 Sustainability and integration with technical building systems .14
8 Relationship, synergies and trade-offs . 14
9 Adaptive building envelope .15
10 Integrative design process for the building envelope .16
11 Building envelope commissioning (BECx) .16
Bibliography .18

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 205, Building environment design.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
The building envelope is either a boundary or a space, or both, separating the indoor and outdoor
environments of a building. It is comprised of roofs, walls (above grade and under grade), windows, doors
and foundation. Windows and other openings for daylighting and ventilation are deemed to be an interface
between the indoor and outdoor environments. They transfer physical environment elements such as air,
heat and cold, light, sound and water. A good building envelope secures high environmental performance in
the building with low energy use as well as structural soundness and an aesthetically pleasing appearance.
The building envelope bears a direct relationship to the design and construction of the building. Designing
the building envelope requires a wide range of considerations covering structural, environmental and
aesthetic functions. A comprehensive approach is essential and achieved through an integrated design
process for buildings. This document focuses on the environmental factors and provides design principles
for the quality and energy-efficient building envelope.
The building envelope can also meet structural and safety requirements including earthquake protection,
wind resistance, flood resistance, fire resistance, durability, maintainability and security. However, those
requirements are out of the scope of this document, and can be found in other international standards,
guides and reports.
v
Technical Report ISO/TR 5863:2025(en)
Integrative design of the building envelope — General
principles
1 Scope
This document provides an overview of the design principles for the building envelope in order to achieve a
high quality and energy efficient built environment. The design principles include:
— thermal performance;
— daylight and visual environment;
— air quality;
— provisions of natural and mechanical ventilation;
— air barrier (airtightness);
— watertightness;
— moisture proof;
— soundproofing;
— sustainability and integration with technical building systems and controls.
This document is applicable to new buildings and the retrofit of existing buildings.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
building envelope
elements of a building as a boundary or barrier separating the interior volume of a building from the outside
environment
[SOURCE: ISO 12569:2017, 3.5, modified — The words “elements of a building as a” have been added to the
beginning of the definition.]
3.2
building envelope commissioning
BECx
process of enhancing the delivery of the design and construction of a building envelope by verifying and
documenting the building envelope concepts, designs, materials, components, assemblies and systems that
have been designed, installed and performance tested, and are maintainable, in accordance with the owner’s
project requirements
[SOURCE: ISO 21105-1:2019, 3.5, modified — The words “enclosure” and “OPR” have been replaced by
“envelope” and “owner’s project requirements” respectively.]
3.3
daylight sensing control
device that automatically regulates the power input to electric lighting near the fenestration to maintain the
desired workplace illumination, thus taking advantage of direct or indirect sunlight
[SOURCE: ISO 16818:2008, 3.54]
3.4
design team
group of people who are responsible for building design
Note 1 to entry: The design team can consist of an architect, an interior designer, a lighting designer, a landscape
designer, engineers in electrical engineering, illuminating engineering, HVAC systems, structural engineering and
construction management and other specialists.
[SOURCE: ISO 19454:2019, 3.5]
3.5
heat island effect
phenomenon of elevated temperatures in urban and suburban areas compared to their outlying rural
surroundings
Note 1 to entry: The temperatures can be influenced by various aspects, including the presence of denuded landscaping,
impermeable surfaces, massive buildings, heat-generating vehicles and machines and pollutants.
[SOURCE: ISO 21929-1:2011, 3.14]
3.6
heat transfer coefficient
U-value
heat flow rate divided by the temperature difference between two environments
–2 –1
Note 1 to entry: Expressed in W·m ·K
.
3.7
HVAC system
system that provides heating, ventilation or air conditioning for buildings
[SOURCE: ISO 16814:2008, 3.18]
3.8
rooflight
daylight opening on the roof or on a horizontal or near horizontal area of a building
[SOURCE: ISO 16817:2017, 3.19, modified — The words “or near horizontal” have been added.]

3.9
solar heat gain coefficient
SHGC
ratio of the solar heat gain entering the space through the fenestration area to the incident solar radiation
Note 1 to entry: Solar heat gain includes directly transmitted solar heat and absorbed solar radiation, which is then
reradiated, conducted or convected into the space.
[SOURCE: ISO 16818:2008, 3.216]
3.10
technical building system
technical component for heating, cooling, mechanical ventilation (filtration and exhaust), humidification,
dehumidification, domestic hot water, water supply, drainage and sanitary equipment, lighting, building
automation and control, and electricity production on site
Note 1 to entry: A technical building system can refer to one or to several building services (e.g., heating, cooling,
lighting and domestic hot water).
Note 2 to entry: Lifts and fire extinguishing systems can be included in technical building systems.
Note 3 to entry: A technical building system is composed of different sub-systems.
Note 4 to entry: Electricity production can include cogeneration, wind power and photovoltaic systems.
[SOURCE: ISO 16813:2024, modified — The words “on site” have been added.]
3.11
thermal mass
materials with mass heat capacity storing or releasing heat as the interior or exterior temperature, or both,
convective and radiant conditions fluctuate, and affecting building thermal load
–1
Note 1 to entry: Expressed in J·K .
3.12
thermal resistance
R-value
ratio of the temperature difference between the two faces of a material to the rate of flow of heat unit area
normal to the faces
2 –1
Note 1 to entry: Expressed in m ·K·W .
3.13
ventilation rate
magnitude of air flow to a room or building through the ventilation system, device or building elements
–1
Note 1 to entry: Expressed in h .
3.14
window-to-wall ratio
WWR
ratio of the net glazing area to the gross exterior wall area above the ground
[SOURCE: ISO 16818:2008, 3.249, modified — The word “fenestration” has been replaced with “net glazing”
and the words “above the ground” have been added.]
4 Design philosophy and principles for the building envelope
4.1 General
Both the client and the designer can have a philosophy and set ethics concerning building environment in
general terms. They can also rely on ideas related to architectural and environmental design. Philosophy

and ethics are a base on which the target level of each environmental element is determined and the
design strategies are planned. A building is evaluated from different aspects. Clients and designers can
wish to decide which aspect is crucial or less critical on the basis of their own philosophy and ethics. This
consideration is possible, provided it does not violate the environment design criteria. Philosophy and ethics
relate to the aspects which are determined on more than the others. The theories also encourage a designer
to employ a particular design strategy and work as the rationale on which the behaviours and functions of a
building from its structure are based.
[9]
This document introduces Gero’s theory in design and expands it. Four classes of variables can be defined
to describe different aspects in designing buildings as follows:
— function (F) variables that describe the teleology of the object, i.e. for what it is;
— behaviour (B) variables that describe the attributes that are derived or expected to be derived from the
structure (S) variables of the object, i.e. what it does;
— structure (S) variables that describe the components of the object and their relationships, i.e. what it is;
— experience (E) variables that describe the interaction between the object and users, i.e. how it is utilized.
The notion of function (F) refers to the teleological characteristics of an artefact. The purpose of designing
is to transform function (F; where is a set) into a design description of structure (S) in a such a way that
the artefact being described is capable of producing the functions. The design description is expressed and
documented in the form of drawings and notes.
The notion of behaviour (B) refers to the characteristics of an artefact or mechanisms of an artefact that are
deterministically derived or expected to be derived from the structure (S) of the artefact and that articulate
the functions (F) of the artefact. The physical properties of an artefact are classified into behaviour (B).
The notion of structure (S) refers to the substantial characteristics of an artefact that can be determined
directly in designing. The structure (S) represents an artefact's elements and their relationships, and
determines the behaviours of the artefact.
The notion of experience (E) refers to the interactive characteristics between an artefact and users. Humans
build connections between the function (F), behaviour (B) and structure (S) through experience (E) and
development of causal models based on interactions with an artefact.
For example, consider designing a library. One of the objectives of a library is to provide a built environment
where occupants can read books comfortably. This objective can be expressed in terms of functions of the
library, that is, visual performance, visual comfort and visual safety. The functions are articulated in terms
of values of behavioural variables such as luminance, illuminance and colour temperature of light. The
structural variables – form and materials – are determined to meet the requirements of the above variables.
Since the structure of a building envelope can enhance the behaviour of a certain environmental element
and detract from the behaviour of another environmental element, to design a building envelope is to solve
a multi-objective optimization problem. However, the problem definition is not so easy in the sense that
the formulation of its evaluation function depends on the requirements for the building envelope. The
requirements are co-defined by the clients, architects, engineers and other specialists involved in the design.
Each of the diverse functions of a building can be articulated as a combination of the behaviours of certain
environmental elements. The behaviour of each environmental element is affected by the structure of
the building environment. Therefore, the relationship between the structure and the behaviour of each
environmental element is meant to be clarified prior to designing the building envelope.
4.2 One thing increases, another decreases
Philosophy 1: There are trade-offs between function variables in a project definition, and more than one
optimum solution exist. There is no logical method to select an optimum solution.
Principle 1: A design team determines what is crucial and what is less crucial among the function variables.

4.3 One structure variable relates to several function and behaviour variables
Philosophy 2: A structure variable determines behaviour variables. For example, the dimensions of a window
determine how deeply daylight enters a room and how much heat transfers through the window.
Principle 2: Experts in different fields are involved in designing a component of the building envelope.
4.4 Appropriate balance among the behaviours of environmental elements
Philosophy 3: An appropriate balance among the behaviours of the environmental elements is maintained
during a lifetime of a building, especially post-occupancy.
Principle 3: A plan of operations of the building envelope is taken into consideration in order to maintain the
balance among the behaviours of the environmental elements.
5 Functions of the building envelope
5.1 General
The building envelope physically separates conditioned indoor spaces from the unconditioned outdoor
environment. However, it concurrently introduces useful elements of the outdoor environment into the
indoor environment selectively. The fundamental role of the building envelope is to make enclosed spaces
that are safe, comfortable and healthy. Functions of the building envelope can be classified into the following
three categories:
— structural robustness and safety;
— environmental quality and energy efficiency;
— aesthetically pleasing property.
The building envelope provides structural support against external and internal loads and forces. It controls
the exchange of physical environment elements such as water, air, heat, light, sound and electronic waves
between the indoor and outdoor environments. Systems of the building envelope can enhance energy
efficiency of the building and reduce environmental burdens. Since the design of the building envelope has a
big impact on the external appearance of the building, the building envelope has symbolic and social value.
Building envelopes contribute to town and street landscapes. The building envelope design reflects the
period. A good building envelope enhances the economic value of the building. A building envelope with an
[10]
impression of character or dignity or class can be a reflection of higher status of the occupants.
Daylight openings in the building envelope have an important function of providing views out and
information on the outdoor environment including the weather and time changes. Openable windows and
rooflights also serve as ventilation. In addition, daylight openings practically function as emergency egress
or aid in identifying one’s location in the building in case of emergency.
Façade systems with photovoltaic (PV) modules, often called building integrated photovoltaics (BIPV), can
generate electricity. There are a variety of PV façade systems, e.g. PV cladding, curtain walls, spandrels, PV
tiles, PV glazing, exterior PV blinds or PV louvers.
A part of the building envelope can function as a sensor for outdoor environmental conditions. Outdoor
sensing or monitoring is utilized to control technical building systems such as daylight-responsive lighting
controls.
5.2 Flexibility
In designing a sustainable building, an important consideration is to secure the functional flexibility of the
building, i.e. the ability to adapt to individual user requirements, changes in user requirements, technical
[7]
changes or changes in use of some areas . The design team is expected to consider the asset value over time.
It includes maintainability, flexibility and adaptability of the building to keep its economic performance high
in changing market conditions or in response to changes in user requirements. It also includes minimizing

obsolescence of the design and technical building systems. A well-designed building envelope guarantees
adaptability.
However, replacement of envelope components is extremely difficult for some types of building when
attaching importance to the strength and durability. A long-term perspective is essential for design. The
design team needs to consider the design on the premise that a major part of the building envelope is
unalterable.
5.3 Adaptability
Adaptability for different uses is an important factor of the sustainable building. Buildings are subject
to changes in use during their long service life. It is desirable to consider a certain range of versatility,
convertibility and expandability in designing the building envelope as well as the building. Some parts are
removed or upgraded without adverse effects on the performance of the other parts. ISO 20887 provides
an overview of design for disassembly and adaptability principles and potential strategies for integrating
those principles into the design process for all types of building. ISO 20887 includes requirements that are
mandatory for implementation of specific principles.
Another perspective, i.e. adaptability to climate change, is also an important consideration.
5.4 Reusability
Reusability of building elements and materials is an important factor of the sustainable building. The
notion of reusability is defined in ISO 20887 as ability of a material, product, component, or system to be
used in its original form more than once and maintain its value and functional qualities during recovery
to accommodate reapplication for the same or any purpose. Some building elements and materials are
replaced to meet the new requirements for buildings. It is preferable for the sustainable building to reuse
both removed ones and replacing ones.
6 Structure of the building envelope
6.1 General
The performance of the indoor environment depends on the construction, materials and assembly of the
building envelope. Major components of the building envelope are as follows:
— roof system;
— wall system above the ground (above grade);
— windows, rooflights, doors and other openings;
— wall system underground (below grade);
— base floor system.
Figure 1 shows basic components of the building envelope.
Masonry construction is available with different materials such as stone, brick and concrete. The thermal
performance of masonry walls differs depending on the materials and composition. The dimensions of
openings are determined by masonry units and, in general, the opening area is comparatively small. Box-
frame construction with concrete also limits the opening area in the walls but can have wide openings on
non-bearing sides.
Framed construction is available with different materials and methods such as wood, steel, reinforced
concrete, steel reinforced concrete and concrete filled steel tube. It allows a large opening within a frame
making up the roof and façades. The thermal performance depends on materials infilling the frames.
However, the framed construction can separate the outer envelope from the load-bearing structure.

The structure of a building is selected according to, for example, conditions of the site and ground, the
building scale and form, the construction period, or the budget. Prerequisites, constraints and requirements
for a project define the building design and influence the structure of the building.
Key
1 roof system
2 windows, doors, other openings
3 wall system above the ground
4 base floor system
5 wall system underground
Figure 1 — Basic components of the building envelope
6.2 Roof system
Roof systems are roughly classified into three types, i.e. flat roofing, low-slope roofing and steep-slope
roofing. The slope or pitch of a roof is a critical factor in making decisions on the roof system. Typical styles
of roof are as follows:
— A-frame roof;
— butterfly roof;
— flat roof or deck roof;
— gable roof;
— gambrel roof;
— hip roof;
— mansard roof;
— M-shaped roof or double pitched roof;
— parapet roof;
— pyramid hip roof;
— saltbox roof;
— shed roof;
— winged gable roof.
Roof materials include asphalt shingles, slate shingles, wood shake, metal, tile, membrane and thatched
roofing materials. Protection against rain and snow is the most fundamental requirement for the building
envelope. Flat roofs contain a slope. Moisture proofing is also essential.
Since roofs receive solar radiation directly, thermal insulation is important to prevent rooms at the top
from being heated up, especially in hot climates. Cool roofs (sometimes called reflective roofs) are a roof
system that reflects more sunlight and absorbs less heat than standard designed roofs. They are made of
a highly reflective paint, a sheet covering, or highly reflective tiles or shingles. They function to decrease
roof temperatures, reduce cooling loads and improve indoor comfort for spaces that are not air conditioned.
Green roofs (also known as “vegetated roofs”) are a roof system that is partially or completely covered with
vegetation and a growing medium, planted over a waterproofing membrane. They function as absorbing
rainwater, providing insulation, creating a habitat for wildlife, providing a more aesthetically pleasing
landscape and helping to lower urban air temperatures and to mitigate the heat island effect.
The roof can have rooflights. Rooflights can illuminate interiors as top lighting such as luminaires on the
ceiling. Depending on the number and arrangement of rooflights, rooflights can illuminate a room relatively
uniformly. A luminous ceiling system can be constructed in combination with rooflights. It gives diffused
daylight evenly within a room.
6.3 Wall system above the ground
The wall system consists of components that fulfil the support, control and finish function of the building
envelope. Typical components of the walls above the ground (above grade) are:
— exterior cladding;
— exterior sheathing membrane;
— exterior sheathing;
— insulation;
— structural components;
— vapour retarder;
— interior sheathing.
Daylight openings and other openings are an interface between the indoor and outdoor environments.
They bring information on the external world into a building by the medium of environmental elements
such as heat, light and sound. People perceive changes in time, weather and surrounding circumstances
through daylight openings. Walls often have architectural shading or attachments such as eaves, awnings,
fins, overhangs, balconies or recesses. Ventilation openings provide fresh air inside and remove pollutants
outside.
Providing daylight openings in the building envelope means creating holes for the masonry construction in
building design, whereas it means saving openings for the framed construction. Maximum dimensions of the
windows are structurally limited for the masonry construction, but, by contrast, a minimum requirement
for the dimensions is considered for the framed construction.
Windows are a key component of the building envelope. Their dimensions, positions and structure have a
direct impact on the façade impression and attractiveness as well as the indoor environmental conditions.
Exterior doors are comparatively large openings in the building envelope. Windbreak rooms are often
provided as means to buffer the wind, rain, and heat or cold. Common types of exterior doors are:
— swing doors;
— revolving doors;
— sliding doors;
— industrial doors or overhead doors.
Glazing is a major component in the wall system. It is used in windows and doors, and even makes up walls.
Pre-glazed windows, doors and wall components have advantages of maintaining quality control, faster
installation, and simplified fabrication.
Curtain walls are an exterior wall system that does not support loads other than its own weight. Curtain
walls are attached to the building structure. Seismic and wind forces on a curtain wall are transferred to the
supporting structure of the building. A curtain wall usually consists of aluminium-framed wall and infills of
glass, metal panels or thin stone. Extruded aluminium is typically used for the framing members. They are
effective in daylighting. However, control of solar heat gain is difficult when using a large amount of glass
infill. ISO 12631 specifies a method for calculating the thermal transmittance of curtain walls consisting of
either glazed or opaque panels, or both, fitted in, or connected to, frames.
Double-skin façades are a system of building consisting of two skins placed in such a way that air flows in the
intermediate cavity. The distance of the intermediate cavity ranges from 0,2 m up to 2 m in many instances.
It is typically about 0,6 m. Some façades have a shallow cavity less than 0,2 m. However, shallow double skins
must have special control of airflow in the intermediate cavity to achieve the expected performance.
A variation of the double-skin façade is a double envelope system that consists of an outer glazed enclosure
and an inner semi-enclosed wall. The inner wall can exhibit the building framework to the outside.
Atria enclosed by glazed walls act as either a thermal buffer space or a light well, or both.
Reflectance of glass is no small matter. Since the amount of sunlight is enormous, even reflected sunlight
from a glass façade is intense. Reflected sunlight often causes glare or visual annoyance to people walking
or driving a car on neighbouring streets. Its direction changes with time. A concave glass façade focuses the
reflected sunlight and will possibly cause melting or ignition of objects in focus.
6.4 Wall system underground
The wall system underground (below grade) is subjected to different forces and loads. The underground
walls support the following functional requirements:
— structural stability;
— water protection;
— moisture protection;
— durability;
— insulation.
The underground walls can be a cast-in-place concrete or reinforced masonry. Durability of design and
materials is mandatory for the underground enclosure systems. The underground walls are subjected to

high pressure from the ground. They must resist lateral loads to maintain the stability of the wall. The
underground walls are braced or constructed robustly enough to cope with the stresses involved.
Moisture influences durability of the underground walls. Underground walls are waterproofed and
moisture-proofed. In order to exclude moisture, the following can be considered:
— use materials with low porosity;
— provide water proofing membranes or moisture proofing;
— provide proper water drainage systems.
Porous materials absorb moisture from the ground and expand on freezing, causing spalling and friability
of the material. Non-porous materials do not transfer moisture through capillarity. Insulation to the
underground walls helps to reduce the expansion and contraction that occur in the wall membranes. It also
reduces the potential for cracking and helps in terms of durability of the wall membranes.
6.5 Base floor system
Base floors are subjected to under-surface loads from ground and water table pressure. Environmentally,
they are subjected to thermal and moisture problems, insects and soil gas from the outside. The base floor
can be a cast-in-place concrete slab with considerations for structural support and environmental control.
Underground slabs are often a source of water leakage with slab cracking of concrete materials. In order to
prevent it, a layer of gravel is provided beneath the slab covered by a vapour retarder.
7 Behaviour of the building envelope
7.1 General
The building envelope can be either tight or loose. A tight envelope restricts air flow between the indoor
and outdoor environments. A loose envelope allows it. Traditional buildings are vernacular and follow the
local climate, culture and materials available. For example, well-insulated buildings have been made in cold
regions. In contrast, well-ventilated airy buildings have been made in humid regions. Modern technology
offers more options of construction with technical buildings systems.
Passive building design maximizes the use of natural energy sources for heating, cooling, lighting and
ventilation to make interiors comfortable without mechanical or electrical building systems. It includes
considerations of the location, surrounding environment, orientation, massing, form of the building, room
layout, material selection, shading, insulation, thermal mass and positioning of openings.
Active building design means use of technical building systems. Use of PV panels is included. Buildings
generally take both passive and active measures. The building envelope is a crucial component for successful
passive design.
7.2 Thermal performance
Heat transfer through a building envelope is a combination of heat conduction, heat radiation, heat convection,
and moisture movement and its phase change. The U-value referred to as heat transfer coefficients measures
how effective elements of a building envelope are as insulators, i.e. how effectively they prevent heat from
transmitting between the inside and the outside of a building. The R-value measures thermal resistance and
is often expressed as the reciprocal of the U-value.
The lower the U-value of an element of a building envelope, the less heat transmits through it. Lower U-values
mean better thermal insulation performance. Countries can have recommendations or regulations on the
U-value for specific building types. Thermal insulation means separating the indoor temperature from
the outdoor temperature. This leads to reduced heating loads in cold climates and, in many cases, reduced
cooling loads in hot climates.

Thermal capacity describes the ability of a material to store heat. Thermal mass that has higher heat capacity
can be used to store heat gains by solar radiation and then release it when external conditions are cooler.
For example, concrete floor slabs can be used to absorb heat gains during the day and to release them during
the night. Types of thermal mass include water, rock, earth, brick, concrete, fibrous cement and ceramic tile.
Masonry and concrete have a high heat capacity, a high density and moderate thermal conductivity. Heat
moves between the surface of the material and its interior at a rate that roughly matches the building’s
daily heating and cooling cycle. The thermal capacity of wood is relatively low, even though its thermal
conductivity is relatively low. Therefore, it is unsuitable for thermal mass.
Factors of the exterior environment that influence heat transfer through the building envelope are:
— temperature of the ground, air or snow with which the building is in contact;
— direct and indirect solar radiation incident on the building;
— cloud amount;
— direction and speed of winds blowing on the building which affect convective heat transfer from the
surface of the building envelope, ventilation, and infiltration;
— rain, snow, and other forms of precipitation;
— relative humidity levels in the air.
Building shape influences heat loss and gain of a building. Surface area to volume (S/V) ratio is an important
factor for the environmental performance of a building. The larger the surface area, the greater the potential
heat gain or loss through it. In order to minimize heat transfer through the building envelope, a compact
shape is desirable.
Solar heat gain coefficient (SHGC) is the fraction of solar radiation admitted through a window, door or
rooflight. The SHGC is expressed as a number between 0 and 1. The lower the SHGC of a window, the less
solar heat it transmits and the greater its shading ability. A product with a high SHGC is more effective at
collecting solar heat during the winter. A product with a low SHGC is more effective at reducing cooling loads
during the summer. How to best balance solar heat gain with an appropriate SHGC depends on, for example
the climate, orientation, shading conditions.
The SHGC is rated for the whole window including effects of the frame or alternatively, for the centre of
glazing. The centre-of-glazing SHGC shows the effect of the glazing alone. ISO 19467 specifies a method to
measure the SHGC of complete windows and doors. ISO 19467-2 specifies a method to measure the SHGC for
the centre of glazing in fenestration systems, i.e. windows, doors or curtain walls with or without shading
devices.
7.3 Daylight and visual information
Daylight performance for illumination first depends on how much skylight enters the interior through
daylight openings. Sunlight also affects the indoor environment depending on the window orientation.
Although sunlight can cause an unwanted glare for visual tasks and excessive heat, it is fundamental to
health in terms of the biological effects of light. Bright daylight in the morning is essential for resetting
human circadian rhythms. Exposure to bright daylight during winter months helps in maintaining a positive
mood. To ensure a comfortable visual environment, control of glare from direct sunlight is a consideration
in window design.
The amount of indoor daylight depends on the dimensions and the position of the daylight opening. The
potential of windows can be first assessed with the window-to-wall ratio (WWR). A 0,3 WWR to 0,4 WWR is
[15]
considered good. As an estimation, a moderately strip-glazed building has a 0,35 WWR. It is 0,5 WWR for
larger windows or curtain walls, and
...