Frequently Asked Questions
- We are developing daylighting system specifications
for one of our national retail clients.
How can we know for sure how much light transmission we will get from the various
skylights we are reviewing?
- Do I need FM Approved or UL Listed smoke vents?
- Is prismatic a proprietary product?
- What’s the most important decision to be made when
specifying skylights for daylighting systems?
- How can I verify that a manufacturer’s smoke vent
is UL Listed?
- Are diffusion and haze the same thing?
- Is 100% diffusion difficult to obtain?
- Has any skylight manufacturer patented prismatic
glazing?
- How important is the frame and frame cap in skylight
design, install-ability, and longevity of a skylight?
- We are concerned about safety for occasional workers
on our roofs.
What is the strongest glazing available in the industry?
- I’ve heard fiberglass turns yellow and brown after
a few years?
- What is prismatic? Is it a new skylight glazing
material?
- How long can I expect skylights to last?
- What is a thermal break?
- How do the various glazing materials compare in
cost?
- We plan to put skylights in our manufacturing plant
to save on our electric light bill. How do we determine the best size, how many
we need and how to space them?
- What should be our goals in daylighting our warehouse
operations?
- What skylight performance properties are most important
in reducing energy cost?
- What is Shading Coefficient (SC)?
- What is Solar Heat Gain Coefficient (SHGC)?
- What is U-Factor?
- What is R-Value?
- What is Visible Light Transmission (VLT)?
- What is Luminous Light Transmission (LLT)?
- What are the CC designations?
- I was in a retail store recently and noticed the
skylights overhead had light and dark stripes alternating across their width. Is
this intentional? And, if so what is the purpose….to be decorative?
- What is light harvesting?
- Are there skylights that provide good light but
less heat than traditional skylights?
- I’m chairing a school board committee on the remodel
of several schools in our district. We’ve seen reports that indicate natural light
enhances learning.What information do you have on this subject?
- We are in the precious gem and jewelry business
and would like to daylight our warehouse. What should we do to keep our warehouse
secure?
- We are on the east coast of the US and plan to daylight
two warehouses that have been hit by hurricane force winds twice in the last ten
years. What type of skylights should we consider?
- If we make the decision to start daylighting our
new facilities how much can we realistically expect to save in energy costs?
- Are there skylights that provide good light but
have greater insulating value than traditional skylights? We are considering daylighting
a refrigerated warehouse.
- Can we increase sales by daylighting our stores?
- I’ve heard a little about silica aerogel as an insulator
in skylights how does this work?
- Are there any unique skylight designs that are truly
leakproof?
- Has anyone proved productivity gains by daylighting?
- What exactly is the OSHA fall protection standard?
And, how do skylights comply with this standard?
- Most of our facilities are in “tornado alley”. Are
there any skylights that are really hail proof?
Q: We are developing daylighting system specifications for one of our national retail
clients. How can we know for sure how much light transmission we will get from the
various skylights we are reviewing? Back To Top
A: If you want the real light transmission (LT) of
the skylights you are reviewing you’ll have to do some work. There are two key issues.
First, ask for and look at the various manufacturers’ detailed drawings. Why? For
example not all 5’ x 6’ skylights actually have an inside curb dimension of 60”
x 72” for a true 30 square feet of light transmitting area per roof penetration.
Some skylights that are casually identified as 5’ x 6’ only have 28 square feet
of inside curb area. Why does this matter? In comparison, if everything else were
equal the true 30’ square foot 5’ x 6’ skylight has 7.1% more light than the undersized
28 square foot 5’ x 6’ skylight. If you were daylighting an 80,000 square foot store
with 4.5% of the roof area in skylights (3,600 square feet) you would need 9 more
of the undersized skylights than you would with the true 5’ x 6’ skylights to achieve
the 3,600 square feet. Multiply this times the number of new stores you build a
year, or 5 years, or 10 years and this is very significant.
Secondly, you need to see a NFRC laboratory or an IES laboratory, light transmission
or photometric light transmission test report obtained by testing a complete skylight
configured just like the one you are reviewing. Most skylight manufacturers send
small (4” x 4”) unformed samples of their glazing to a laboratory for LT testing.
The result from this test is then reported as the LT for the skylight. While this
is common practice and accurate information for the small unformed glazing tested,
it doesn’t necessarily reflect the LT you will get from the skylight. A skylight’s
dome shape can have a significant effect on light transmission.
Q: Do I need FM Approved or UL Listed smoke vents?
Back To Top
A: It depends on your local code and fire authority.
However, since 2006 only UL 793 Listed smoke vents meet the International Building
Code (IBC). FM Approved smoke vents do not meet the building code.
Q: Is prismatic a proprietary product? Back To
Top
A: No not at all. Prismatic has been around for a
long time. It can be purchased from a number of plastic sheet companies and from
numerous skylight manufacturers.
Q: What’s the most important decision to be made when specifying skylights for daylighting
systems? Back To Top
A: Glazing. Of the various components of a skylight,
glazing has the most significant affect on the optical, thermal and mechanical properties
of the unit.
Q: How can I verify that a manufacturer’s smoke vent is UL Listed?
Back To Top
A: Go to UL’s web site www.ul.com
go the bottom of the home page, look under useful links, click on “online
certification directory”, enter the manufacturer’s name under begin a basic search.
If the manufacturer has UL certified products their certification page will appear
and the model(s) that they have certified will be listed. If the manufacturer doesn’t
come up they do not have UL certified products. Also, be advised only the model(s)
listed on the manufacturer’s certification page are UL Listed.
Q: Are diffusion and haze the same thing? Back
To Top
A: Not really, but they are used synonomously in
the skylight industry. They are used interchangeably to refer to the breaking up
of concentrated light and scattering the light in all directions. Good diffusion
spreads the natural light evenly at the task level and reduces or eliminates glare.
Q: Is 100% diffusion difficult to obtain? Back
To Top
A: No. Most medium white tinted acrylics, whether
smooth finish or prismatic imprinted finish have very good diffusion properties.
However, due to its prism pattern clear prismatic can have a diffusion percentage
in the 90’s whereas clear smooth acrylic will generally have less than 3% diffusion.
Q: Has any skylight manufacturer patented prismatic glazing? Back To Top
A: No. It is not a proprietary glazing material.
However, like any other material there are differences in the quality and performance
of various prismatic materials.
Q:How important is the frame and frame cap in skylight design, install-ability,
and longevity of a skylight? Back To Top
A: Very important. The frame and frame cap are the
foundation of the skylight. When specifying aluminum frame skylights it is not enough
to only specify architectural grade 6063-T5 aluminum. You should compare various
skylight manufacturers’ frame dimensions and thicknesses and then specify minimum
dimensions and thickness.
Q: We are concerned about safety for occasional workers on our roofs. What is the
strongest glazing available in the industry? Back
To Top
A: If you want maximum safety for the entire service
life of your skylights you should install safety screens or security grills under
the skylights. Most skylight manufacturers do load testing on the glazings they
use in their skylights when the glazing is new, but we are not aware of much load
testing of aged glazings after 10, 15 or 20 years of service. All plastics age over
time with exposure to the elements of sun, rain, wind and pollution. As the plastic
ages its optical and mechanical properties begin to degrade. Therefore, you can
expect the strength and impact resistance of the glazing to decline over time.
To answer your specific question, in terms of ranking our glazings by strength and
impact resistance we would rank Tufflite Polycarbonate first, Energy Star Fiberlite
second and Trituff Coployester third.
Q: I’ve heard fiberglass turns yellow and brown after a few years?
Back To Top
A: Yes it does, however all plastics whether PMMA
based smooth acrylics or prismatic imprinted acrylics discolor with age due to the
elements of rain, wind, pollution and continuous UV exposure. Fiberglass glazing
has a significantly different appearance than acrylic, copolyesters and polycarbonates.
Initially fiberglass glazing has a soft white brownish color, much like a farm fresh
hen egg in color. As the fiberglass begins to age it tends to transition through
various stages of yellow. Light yellow at first and later darker yellow until the
color begins to become brownish again. The color changes with age are most noticeable
from the outside of the skylight (on the roof). From below, in the building interior,
the view is much more consistent over the life of the skylight and it is a view
of white diffused natural light. Color in skylight glazing is more a matter of perception
than reality in terms of light transmission. Color does not affect light transmission
as significantly as it does the perception of light transmission. Of all colors,
yellow is the color that most negatively affects the perception of any plastic’s
clarity or light transmission.
Fiberglass has been used as a glazing material in skylights for nearly forty years
and has demonstrated several superior performance qualities in comparison to other
common glazing materials. Fiberglass glazing has similar light transmission with
100% diffusion, lower solar heat gain coefficient, greater UV blocking and similar
insulating (U-Factor) properties in comparison to acrylics, copolyesters and polycarbonates.
The most impressive attribute of fiberglass glazing is its strength and longevity.
Thousands of 25 year old plus fiberglass glazed skylights and smoke vents can still
be found in service today predominately in the high UV southwestern US. Recently
load and light transmission tests were performed on numerous 5’ x 6’ Energy Star
Fiberlite skylights that had been in service for a range of 13 years to 20 years
in the southwestern US. All of the skylights tested held 5,000 lb loads without
catastrophic failure (only small tears developed which a person could not fall through)
and none lost more than a fraction of their original light transmission.
Q: What is prismatic? Is it a new skylight glazing material? Back To Top
A: No it’s not new. Prismatic is simply acrylic which
is imprinted with a pattern during the plastic sheet manufacturing process. The
most typical imprint used for skylight prismatic glazing is a prism pattern which
gives it better diffusion characteristics than smooth finish acrylic.
Q: How long can I expect skylights to last? Back
To Top
A: It varies widely. It depends primarily on the
quality of materials used in the design and construction of the skylights. If longevity
of service life is a key criterion in your buying decision then you need to look
at the details of design and materials of construction when evaluating skylights.
Items you should compare are frame and frame cap dimensions and thickness, glazing
technical data sheets and sealant technical data sheets. Sealant is one of the mostly
commonly overlooked but critical components of a skylight. For example; which do
you think would provide the better long life seal? A UL Listed, 25 year, engineered
thermoplastic molded seal or a bead of silicone?
Q: What is a thermal break? Back To Top
A: A thermal break is an element of low thermal conductivity
placed between any two materials in an effort to stop or reduce the transfer of
heat from one to the other. Thermal breaks are common in both windows and skylights
and serve the purpose of reducing or eliminating condensation. An AAMA compliant
thermal break utilizes the “poured and debridged” design. In this design the frame
extrusion has an open cavity in the mid section of the frame that runs the entire
length of the frame. This open cavity is filled (poured) with a high strength, long
lasting, non-thermally conductive epoxy. After the epoxy cures the aluminum is milled
away on both the top and bottom of the frame just above and below the epoxy (debridged).
When the process is complete there is a complete separation of the exterior aluminum
frame exposed to temperatures on the outside of the building and the interior frame
exposed to interior temperatures and humidity. Poured and debridged thermal breaks
have proven to be the most effective design, in minimizing exterior temperature
transfer to interior building space and in the elimination of condensation. Some
skylight manufacturers without true thermal breaks in their skylight design utilize
insulation on the interior of the skylight frame. This insulation technique is sometimes
promoted incorrectly as a thermal break with the marketing terms “insulated thermal
break” and “thermalized thermal break”. These insulation designs may not be as effective
in preventing condensation as an AAMA compliant “poured and debridged” thermal break.
Q: How do the various glazing materials compare in cost? Back To Top
A: From lowest to highest in terms of material cost
the ranking is as follows. Quasar prismatic imprinted
acrylic, Bristol smooth finish acrylic,
Trituff copolyester, Energy Star fiberglass,
Tufflite polycarbonate,
Coollite solar heat blocker (meets the Nat’l Energy Code),
Nano Insulgel super insulator, Quasar Low-E
solar heat blocker & super insulator (meets the Nat’l Energy Code).
Q: We plan to put skylights in our manufacturing plant to save on our electric light
bill. How do we determine the best size, how many we need and how to space them? Back To Top
A: You need a professional energy analysis and daylighting
plan. With some consultation and about 12 to 15 inputs from you about your building,
what type of manufacturing you do, your cost of electricity, etc. we can provide
you with a daylighting plan that will answer your questions and provide you with
estimated annual energy savings and return on investment (ROI).
Q: What should be our goals in daylighting our warehouse operations?
Back To Top
A: Turning off the electric lights. Reducing your
electric lighting cost by 35% to 65% and increasing productivity.
Q: What skylight performance properties are most important in reducing energy cost? Back To Top
A: Light transmission. The three most common measurements
used in defining skylight performance are light transmission (LT), solar heat gain
coefficient (SHGC) and U Factor. Light transmission has by far the greatest impact
on energy savings of the three measurements. As an example: Using
Skycalc, a commonly used energy and daylighting analysis software program,
we theoretically daylighted a 100,000 square foot retail store with 30 foot ceilings
and an electric rate of $0.12 kwh. In both analyses the daylighting system utilized
a qty of 160 – 5’ x 6’ skylights. In analysis A – the skylights had LT of 47%, SHGC
.42 and U Factor .74 the estimated annual energy savings with these skylights was
$46,600.00. In analysis B – the skylights had LT of 70%, SHGC .50 and U Factor .70
the estimated energy savings with these skylights was $59,881.00. Even though the
skylights in analysis A had a much lower solar heat gain than the skylights in analysis
B the sacrifice in LT to achieve the lower solar heat gain proved to be a poor economic
tradeoff for the building owner. SHGC and U Factor performance do not affect total
energy savings as much as Light Transmission. For maximum energy savings you want
maximize light transmission.
Q: What is Shading Coefficient (SC)? Back To Top
A: A measure of the solar heat transmission of a
fenestration in comparison to the solar heat transmission of 1/8” clear glass. Shading
coefficient is being phased out in favor of the newer solar heat gain coefficient
(SHGC) measurement, and is approximately equal to the SHGC multiplied by 1.15. The
shading coefficient is expressed as a number from 0 to 1. The lower a skylight’s
shading coefficient, the less solar heat it transmits, and the greater its shading
ability. A low shading coefficient in combination with a high LT% and high diffusion
is the key to optimal skylight performance.
Q: What is Solar Heat Gain Coefficient (SHGC)?
Back To Top
A: A measure of the solar heat transmission of a
fenestration in comparison to the solar heat transmission of 1/8” clear glass. Solar
Heat Gain Coefficient is now favored over Shading Coefficient. SHGC measurements
include both the radiant solar heat as well as a calculation of the conductive heat
from the fenestration. SHGC is expressed as a number between 0 and 0.87. The relationship
between SHGC and SC is SHGC = SC x 0.87. The lower the SHGC the less solar heat
the skylight transmits, and the greater it’s shading ability. A low solar heat gain
coefficient in combination with a high LT% and high diffusion is the key to optimal
skylight performance.
Q: What is U-Factor? Back To Top
A: A measure of the rate of heat loss of a fenestration.
U Factor ratings are expressed as a number between .20 and 1.20. In the US this
number represents Btu/h ft² F. The metric equivalent is W/m²K. Insulating
value is indicated by the R Value, which is the inverse of the U Factor. The lower
a skylight’s U Factor the greater its resistance to heat flow and the greater its
insulating value.
Q: What is R-Value? Back To Top
A: An expression of insulating value. R Value is
the reciprocal of U Factor a measure of the rate of heat loss of a fenestration.
The higher the R Value the greater the skylight’s resistance to heat flow and the
greater its insulating value.
Q: What is Visible Light Transmission (VLT)? Back
To Top
A: The measure of how much visible light passes
through a fenestration. Visible light transmission or simply visible transmission
(VT) measures the segment of the light spectrum from 380 to 740 nanometers. This
is the portion of the light spectrum that can be seen by the human eye. The higher
the VLT or VT a skylight has, the greater its light transmission. VLT is expressed
as a number from 0 to 1.
Q: What is Luminous Light Transmission (LLT)? Back
To Top
A: The measure of how much total light passes
through a fenestration. Luminous light transmission (LLT) measures a broader segment
of the light spectrum than VLT. This includes portions of the light spectrum that
cannot be seen by the human eye. The higher the LLT a skylight has, the greater
its light transmission. LLT is expressed as a number from 0 to 1.
Q: What are the CC designations? Back To Top
A: A classification of light transmitting plastics
under the Uniform Building Code Standard 26-7. Under this standard, light transmitting
plastics are tested to ASTM D625-74 standard and are rated either CC1 or CC2. Plastics
rated CC1 have a burning extent of 1 inch (25mm) or less when tested in nominal
0.060 inch (1.5mm) thickness (or in the thickness intended for use) by this test.
Plastics rated CC2 have a burning rate of 2.5 inches per minute (64nn/min) or less
when tested in nominal 0.060 inch (1.5mm) thickness (or in the thickness intended
for use) by this test. Our Trituff Copolyester, Energy Star Fiberlite and Tufflite
Polycarbonate glazings all have CC1 ratings.
Q: I was in a retail store recently and noticed the skylights overhead had light
and dark stripes alternating across their width. Is this intentional? And, if so
what is the purpose….to be decorative? Back To
Top
A: No it is not intentional. What you saw was most
likely a specific competitor’s skylight that has an unusual, and in our opinion,
a radical, steep ribbed, dome shape that blocks light transmission. The dark stripes
you saw are not transmitting as much light as the light stripes.
Q: What is light harvesting? Back To Top
A: A marketing term for daylighting or skylighting.
Q: Are there skylights that provide good light but less heat than traditional skylights? Back To Top
A: Yes. We have several new “green building technology”
skylights. Our proprietary Coollite and
Quasar Low-E are two that have exceptional solar heat blocking performance.
Q: I’m chairing a school board committee on the remodel of several schools in our
district. We’ve seen reports that indicate natural light enhances learning. What
information do you have on this subject? Back To
Top
A: There are a number of daylighting education studies
that show greater rates of progress in math and reading test by students in well
daylit classrooms than students in non-daylit classrooms.
Q: We are in the precious gem and jewelry business and would like to daylight our
warehouse. What should we do to keep our warehouse secure? Back To Top
A: You’ll have no problem with building security
if you install polycarbonate glazed skylights and security grills.
Q: We are on the east coast of the US and plan to daylight two warehouses that have
been hit by hurricane force winds twice in the last ten years. What type of skylights
should we consider? Back To Top
A: You should use Miami Dade County Hurricane Approved
skylights. To obtain this hurricane approval, skylights must be tested to and pass
a series of test that resemble hurricane conditions.
Q: If we make the decision to start daylighting our new facilities how much can
we realistically expect to save in energy costs?
Back To Top
A: It varies. As you would expect it depends on a
numbers of factors, including the dimensions of your building, the climate they
are located in, your local energy rates, the use of the buildings, etc. However,
having said this there are numerous studies that show 35% to 65% electric lighting
savings and with a comprehensive energy management system the savings could be even
greater. You should consult with a Daylighting expert and you’ll have a very good
idea of your potential annual energy savings in no time.
Q: Are there skylights that provide good light but have greater insulating value
than traditional skylights? We are considering daylighting a refrigerated warehouse. Back To Top
A: Yes. We have a number of new “green building technology”
skylights. Our proprietary Nano Insulgel and Quasar Low-E are two skylights that have about 6
times the insulating value of a traditional skylight.
Q: Can we increase sales by daylighting our stores?
Back To Top
A: Very likely. There are numerous daylighting retail
studies that show sales increases of up to 40% in daylit stores versus non-daylit
stores.
Q: I’ve heard a little about silica aerogel as an insulator in skylights how does
this work? Back To Top
A: Silica aerogel is an extremely low density solid
manufactured by supercritical drying of silica gel. The resulting 3% solid 97% gas,
highly porous material nearly eliminates heat transfer by convection, conduction
and radiation. We utilize silica aerogel in two of our new proprietary green building
technology skylights. In addition to its super insulating properties it is highly
translucent, has excellent sound dampening characteristics and is non-toxic.
Q: Are there any unique skylight designs that are truly leakproof?
Back To Top
A: Yes. There are skylights with design and materials
of construction features that make them much less likely to leak than traditional
skylights.
Q: Has anyone proved productivity gains by daylighting? Back To Top
A: Yes. There are a number of daylighting productivity
studies that show productivity gains of up to 40% attributable to daylighting.
Q: What exactly is the OSHA fall protection standard? And, how do skylights comply
with this standard? Back To Top
A: The Federal OSHA standard for Walking-Working
Surfaces; Guarding Floor and Wall Openings and Holes follows:
CFR#
1910.23(e)(8)
“Skylight screens shall be of such construction and mounting
that they are capable of withstanding a load of at least 200 pounds applied perpendicularly
at any one area on the screen. They shall also be of such construction and mounting
that under ordinary loads or impacts, they will not deflect downward sufficiently
to break the glass below them. The construction shall be of grillwork with openings
not more than 4 inches long or of slatwork with openings not more than 2 inches
wide with length unrestricted.”
Q: Most of our facilities are in “tornado alley”. Are there any skylights that are
really hail proof? Back To Top
A: Yes. The hail resistance of a skylight is dependent
on its glazing material. The standard we consider to be most effective in determining
the hail resistance of a glazing is Factory Mutual’s FM 4431 Section 4.2 Severe
Hail Test. Under this standard and test procedure glazing material, maintained at
a temperature of 40 degrees F, is tested by pneumatically firing 2.0 inch diameter
freezer ice balls from a distance of 5 feet and at a velocity of 76 mph against
the glazing. Glazing materials that pass this test would be considered hail proof.
Our Energy Star Fiberlite and
Tufflite Polycarbonate both pass the FM Severe Hail Test.
