Preservation Note 44

Natural Light in Historic Buildings

Doors and Windows

August-99

Windows-08500

Natural daylight can enhance the interior of a building, contribute to a
comfortable work environment, and conserve energy. Historic buildings
are often fortunate to have large windows, which provide generous
amounts of natural light. While original windows are critical design
elements and should be retained as defining features of the building\'s
historic character, they should also be recognized as an excellent
source of natural light.

The sun is a powerful source of light. One square foot of sunlight can
light 100-200 square feet of space. Incorporating natural light into
building design is known as \"day lighting.\" It is a type of passive
solar design, which uses elements of the building itself to capture
sunlight and use it for heat and light. Day lighting is not a new
concept, but has generated renewed interest recently due to the energy
crisis, increased interest in conservation, the trend towards
\"greening\" in architecture, and recent research showing the positive
effects of natural light. This increased use of natural light integrates
energy conservation and the use of renewable resources while it offers
lower energy costs, reduces impact on the environment, and provides a
source of occupant happiness and productivity.

Passive Solar Design and Windows

Windows make buildings attractive and pleasant places to work,
especially in older buildings where the windows are often large with
decorated trim to enhance the room\'s design. These large windows allow
natural light to come in and can easily be part of a day lighting plan
for the building.

The amount of light depends on:

Location of opening

Width and height of opening

Design

Glazing material

Control elements, such as blinds and louvers

The amount of light penetrating a room is limited to a distance of about
2.5 times the height of the opening. Therefore, it is important that
windows are not partially blocked. Sometimes dropped ceilings are
extended up to the windows, limiting light and affecting the appearance
of the opening. Dropped ceilings need to be recessed from window
openings. See Preservation Note 33, Detailing Suspended Ceilings to
Maintain Window View, for more information.

To make windows work more efficiently there are ways to enhance and
control natural light. To bring in more light, elements such as light
shelves (reflective surfaces which spread light) and sun pipes (aluminum
pipe with reflective lining and translucent dome to diffuse light) can
be used. Be careful that installation does not adversely affect historic
material or character of the structure.

To minimize concern about heat gain and glare, control systems can be
used, such as treated glazing, insulation, photosensor dimmers, and
adjustable blinds or drapes. There are new optical materials being
developed that can change thermal conductivity and optical properties
and direction and appearance of light. Again, be careful that
installation of any new element does not adversely affect historic
material or character of the structure.

The practice of day lighting often combines elements in an integrated
system controlled by computers.

Energy Savings

Artificial light consumes about 25% of a building\'s energy use. A room
lit with natural sunlight needs less electrical lighting, thus providing
energy and money saving benefits. Use of natural light reduces energy
consumption during peak electrical use, when daylight is available.
There is, of course, a need for supplemental lighting at night and when
natural light is low. Occupancy and light sensors can be installed to
adjust electrical lighting according to the need for light or the amount
of available natural light and then dim or turn lights off as needed.

Benefits of Natural Light

People need and like daylight. Research into the psychological aspects
of daylight and its effects has determined that daylight is important
for employees\' health, well being, and productivity. Lighting is
considered one of the three most critical things affecting worker
morale; temperature and noise are the other two. With productivity tied
to morale, it is easy to make the link between additional light and
improved performance.

Environment and design of the workplace can affect how employees
function. Studies have found that workers prefer bright offices. Workers
exposed to daylight tend to have fewer health complaints, reduced
absenteeism, are more resistant to fatigue and stress, and are more
satisfied with their jobs. Loss of daylight causes the human body to
slow down and lose energy.

Besides its link to productivity and employee satisfaction, natural
light also provides the benefits of varying light levels, opportunity
for the eye to change focus for short and long range views, and contact
with the outside world.

Federal Support for Day lighting

The concept of day lighting fits well the federal government\'s
initiatives to build \"green\" and promote energy conservation.

The General Services Administration\'s Public Building Service
Commissioner, Mr. Robert Peck, issued a letter to employees on August
20, 1999 announcing major steps GSA will take in the design,
construction, and repair and alterations of federal buildings to support
a building green program. The goals of this program are to incorporate
and address sustainable design principles, energy efficiency and
renewable energy, resource conservation and recycling, and indoor
environmental quality in all projects.

In July 1998, President Clinton directed Federal agencies to retrofit
federal buildings with energy-saving technologies and to reduce energy
use from 1985 levels by 35% by 2010. To make it easier to obtain
equipment and services to reduce energy consumption, Super Energy
Savings Performance contracts were implemented in 1999. This helps
agencies contract with private energy service companies to retrofit
facilities with energy-saving and environmentally beneficial
improvements. Companies on contract can provide Federal buildings with
energy efficient lighting, more efficient boilers and chillers, building
automation and energy management control systems, heating, ventilating
and air conditioning systems, building envelope modifications, chilled
water piping and hot water and steam distribution systems, electric
motors, refrigeration, electrical or cogeneration systems, renewable
energy systems, and electrical distribution systems.