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Building Envelope
Q: How does SPF reduce energy use in buildings?
A:
- 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.
For
more detailed information on both SPF insulation products refer to the
Modern Materials article Learning the Difference between ½ lb and 2lb
SPF, August 2005, page 11 or Spray Foam Magazine, Ask the Expert, Which
SPF Insulation is Right for Me? August, 2005 page 11.
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.
Q: How do I select a contractor?
A:
As with any construction trade, a quality contractor will be
financially stable, have highly trained crews and a good reputation
with their customers and suppliers. So check out all of these elements.
Ask if they are fully accredited through SPFA's Accreditation program.
SPFA's membership directory can help by listing contractors according
to region and type of business.
Myths
Roofing:
(Excerpts from SprayFoam Magazine, June 2007 issue written by Jim Andersen, BASF Polyurethane Foam Enterprises)
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
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