F.A.Q.
on the Building Envelope
F.A.Q. on Roofing
F.A.Q. in General
F.A.Q. Spray Foam Myths
Building
Envelope
Question: How does SPF reduce energy use
in buildings?
Answer:
* SPF provides a continuous air barrier.
* SPF prevents moisture infiltration through air leakage.
* SPF minimizes dew point problems and condensation.
* SPF avoids thermal bridging.
* SPF resists heat movement in all directions.
* SPF provides reliable performance under varying
conditions.
Q: What is the difference between a vented
and unvented attic
A: Unvented (conditioned) attics use air-impermeable
insulation as a barrier to prevent moisture condensation
on the underside of roof decks. Vented attics minimize
condensation by allowing the escape of moisture to
the exterior by air flow.
Q: If you spray the underside of a roof deck
with SPF insulation, should you vent the attic?
A: No, the application of SPF insulation to the underside
of the roof deck minimizes the potential for condensation.
The SPF insulation develops a thermal and moisture
gradient that avoids the development of dew point
conditions in the attic. Because of this, moisture
won't condense or accumulate and, therefore, does
not need to be vented to the exterior.
Q: Do you need a vapor retarder or a vapor
barrier with SPF insulation?
A: It depends of the use of the building, the climate
and the materials of construction. In normal occupancies
and moderate climates, SPF insulation typically does
require a vapor retarder. Extremes of climate and
building use may require vapor retarders/barriers.
Check with your design professional for specific recommendations
and refer to SPFA technical document, AY 118, Moisture
Vapor Transmission for further information.
Q: Is SPF a good soundproofing material
A: Both low and medium (2lb/cubic/ft) density SPF
effectively reduce noise from outside sources by sealing
cracks and gaps that allow sound to travel through
the walls, floors and ceilings into the building.
They are less effective against noise caused by vibration.
Q: What is the difference between low density,
open cell SPF and medium density closed cell SPF?
A:
* 1/2 lb Spray Polyurethane Foam (SPF)
Low density, open cell SPF refers to a generic spray
polyurethane SPF that weighs between 0.4 to 0.6 lbs
per cubic ft when fully cured. It is spray applied
to a substrate as a liquid and expands about 100-150
times its original volume to form a semi-rigid/flexible,
non-structural SPF insulation. The SPF has an R-value
around 3.5 per inch and typically uses water as the
blowing agent.
* Medium Density, Closed Cell Spray Polyurethane
Foam (SPF)
Medium density, closed cell SPF used in interior applications
typically refers to generic spray polyurethane foam
that weighs between 1.5 to 2 lbs per cubic ft when
fully cured. It is also spray applied as a liquid
to a substrate and expands about 35 to 50 times its
original volume to form a rigid, structural SPF insulation
with a compressive strength between 15 to 25 PSI.
The SPF has an R-value of around 6.0 per inch (aged
R-value) and uses high R-value blowing agents.
* Similarities: Both products are
excellent air barriers in buildings, provide great
insulation, can assist in the control of condensation
within buildings and have great environmental benefits.
Roofing
Q: How long does a spray polyurethane foam
(SPF) roof last?
A: The oldest performing SPF roofs are over 30 years
old. Because the physical properties of the SPF change
little with age, how long the SPF roof system lasts
depends primarily on the original application and
long term maintenance.
Q: How do you maintain a SPF roof system?
A: SPF roof systems should be inspected semi-annually
and after events that could cause physical damage.
Small (less than 3" diameter) dents, cracks,
punctures from dropped tools, wind driven debris can
be repaired with an elastomeric sealant compatible
with the SPF and coating system. More extensive damage
can be repaired by reapplying SPF.
Typically SPF roof systems are re-coated every 10
- 15 years, depending on the type and thickness of
coating used and factors specific to the roof (such
as wind erosion effects, hail, foot traffic, abuse,
etc.) Recoating extends the service life of the SPF
roof system.
Q: Where can I use a SPF roofing system?
A: SPF has excellent adhesion to a variety of substrates
including, BUR, clay and concrete tile, shingles,
metal, wood and concrete. Since they add little weight
and can be applied in varying thickness to add slope
and fill in low areas. SPF roofing systems are often
used as recover system over existing roof coverings.
SPF roofing systems excel where:
* Additional insulation is desired.
* The roof substrate has many penetrations;
* The roof deck is an unusual shape or configuration;
* The roof is in a severe weather environment, (hurricanes,
hail, etc)
* Lightweight materials are required.
* Slope must be added to provide positive drainage
* It is desirable to keep existing roof covering
Q: What are the environmental limitations
of installing SPF roofing systems?
A: As with other roofing systems, SPF can be applied
in a wide variety of climatic conditions. Follow the
manufacturer's recommendation for ambient conditions.
The SPF and protective coating should not be installed
when there is ice, frost, surface moisture or visible
dampness present on the surface to be covered. Barriers
may be necessary if wind conditions can affect the
foam quality or create over-spray problems.
Q: How do SPF roof systems compare in cost
to other roof systems?
A: SPF roofing systems are cost competitive with
other systems. Life Cycle Cost Analysis performed
by Michelsen Technologies demonstrated that over a
30 year life span, SPF roof systems cost between 10%
and 50% less on average than comparably insulated
membrane roof systems. (Averages were based on SPF
roof system recoats of every 6, 10 and 15 years. A
copy of the Life Cycle report is available from SPFA.)
General
Q: Why do you need coatings or coverings over SPF?
A: SPF is water resistant without other coverings,
however, the surface of SPF can deteriorate under
the sun's ultraviolet (UV) rays. Typically, elastomeric
coatings or aggregate coverings are used to protect
the SPF against UV radiation.(note include other coating
benefits.)
Q: How long has SPF been around?
A: Spray polyurethane foam was first used commercially
in the US in the 1960s for cold storage and industrial
insulation projects. SPF roofing systems evolved from
exterior applications to tanks and pipes in the late
60s to early 70s.
Myths
Roofing:
Excerpts from SprayFoam Magazine, June 2007 issue
written by Jim Andersen, BASF Polyurethane Foam Enterprises)
1. SPF roofing systems do not last.
Many research projects have been conducted to document
the performance of SPF roofing systems throughout
the United States. Among them, the National Roofing
Foundation (NRF) conducted a series of surveys relating
to the field performance of SPF roofs. The initial
study was conducted in 1995, and a Phase II study
was conducted several years later to look at unique
SPF roofing details. Another study, which was performed
at Arizona State University, documented the performance
of SPF roofing in all parts of the United States.
Over the course of several years, the customer satisfaction
level was initially — and remained — very
high for the roofing system.
2. SPF roofs can only be installed during
very limited conditions.
SPF and elastomeric roof coatings can be installed
in all geographic areas of the United States. Most
applications occur when the target temperatures are
45°F to a very warm 120°F. Considering that
solar gain on a dark surface will raise the temperature
by as much as 35 degrees during a sunny day, this
provides a wide temperature range for installations.
Although it is true that moisture— such as rain,
frost, dew, and snow— on the substrate will
prohibit the application of foam or coatings; still,
there are ways around this application barrier. The
SPF industry has established guidelines stating that
spray foam is not to be applied when the temperature
is within five degrees of the current dew point. Applicators
typically monitor the weather conditions through weather
data and by using handheld electronic measurement
tools.
3. Birds eat SPF roofs.
Birds on top of roof systems are a common occurrence.
Any slight surface imperfection caused by birds is
very easily identified on SPF roofs, while these same
damaged areas might not be so apparent with conventional
roofing systems. In most cases, the peck will not
cause a leak and can easily be repaired as part of
routine maintenance or roof inspections. If necessary,
a simple reseal of the bird peck with a sealant (compatible
with the roof coating) will repair the spot. In recent
years, the use of roofing granules embedded in the
top layer of elastomeric coatings has brought about
greater resistance to bird damage and even "bird
damage" types of roofing warranties from several
industry suppliers.
4. You can't walk on SPF roofs.
The Spray Polyurethane Foam Alliance (SPFA, www.sprayfoam.org)
and National Roofing Contractors Association (NRCA,
) are two industry trade associations that offer a
great deal of information on SPF roofing. Both organizations
agree that when used as roofing foam, the physical
properties of SPF suggest the use of spray foam with
a minimum compressive strength of 40 pounds per square
inch or higher. This is a general guideline that will
work in all parts of the United States. Less compressive
strength foams are used where less foot traffic is
anticipated or where the geographic area is not as
hard on construction materials.
5. Insurance companies will not insure SPF roofing
systems.
The SPF industry has spent several hundreds of thousands
of dollars testing their roofing systems at independent
laboratories. One such lab is the Factory Mutual Research
Center (FMRC), which is owned by an insurance group.
They do insure — as well as test — SPF
roofing systems.
6. SPF roofs are soft and don't stand up to
high winds, fire, and hail damage.
The FMRC has tested several industry members' SPF
roofing systems for wind, fire, and hail resistance.
The SPF roofing systems continue to provide some of
the best results in this battery of tests for roofing
systems as they relate to performance during extremes.
7. SPF roof systems are not green.
SPF has been in use for more than 35 years. As such,
it was one of the early insulated roofing systems
that promoted the use of insulation and light-reflective
roof coatings to help save energy. The use of seamless
insulation and white or light-reflective coatings
have been in use for longer than most of the cool
roof-type roofing systems that we find in today's
market place. Many of the industry's SPF roof system
components have been charter partners in the Energy
Star Roofing Program to save energy. Several industry
companies are active in the Leadership in Energy and
Environmental Design (LEED) program, among others.
SPF insulation continues to offer some of the highest
insulation value and performance per inch than any
other type of insulation roofing material.
8. People tear off SPF roofs.
Usually tear-off of a SPF roof happens because of
a couple of reasons. One is that the particular roofing
contractor making this statement does not have the
knowledge, equipment, or capability to install or
repair the SPF roofing system. The repair of a SPF
roof is normally a lower-cost solution than the removal
of the SPF roof. If a roof contractor does not have
this capability, he tears the SPF off and installs
one he can do — just as SPF contractors do with
other roofing systems. The second reason for this
tear-off scenario is that the roof in question is
a poorly installed, designed, or maintained SPF roofing
system, and it may be best to tear it off and start
over. Every day, I talk to many people who have very
little knowledge about the SPF roofing systems, yet
the industry has excellent documents on how to inspect,
repair, and install these types of roofing systems.
Most often, this myth occurs due to lack of knowledge
about the roofing system. Most of the applications
that I have seen over the past 35 years have been
good-performing SPF roof applications. They are the
norm rather than the exception.
9. You can't get a good SPF roofing system.
Seeking the lowest priced system or the one with the
longest warranty is most likely not the best way to
buy a roof. Start by contacting either of the two
trade associations and researching the requirements
for the SPF roofing system to be correctly installed.
Check out the SPF contractor, just as you should do
with any roofing contractor or construction professional.
Ask to see past work that can be visited, or ask for
references that you can call. Design professionals
can build up the best specifications with the best
products, and yet the project may not be done by the
best applicators. We have many applicators in our
industry who have proven themselves and their workmanship
for more than three decades or longer. They have a
history of putting down good SPF roofing systems.
Those that do not have knowledge of a product or system
create myths. Those that compete against a particular
system can create them. Those intending to either
install or purchase the material or end product should
understand the facts of any particular construction
material, design, and proper application. Spend a
little time and look into the system, and you will
be very pleased with its performance when properly
installed.
|