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How
do I choose a roofing system?
What is
the difference between asphalt and coal tar?
How can
I ensure that my roof will not blow off?
How
long can I expect my roof to last?
Which
roof is best for a school, chemical plant, etc?
What is
built-up, modified bitumen and single ply?
| Q: |
How
do I choose a roofing system? |
| A: |
Although many specifiers and/or
building owners take the viewpoint that the selection of a roofing
system is a simple matter of economics, this is erroneous and often
disastrous logic. Budgetary concerns are certainly a very important
part of the process of choosing a particular system. It should not,
however, be the only criterion.
There are many types of roofing systems
available, including hot built-up, single ply modified bitumen, metal,
cold-applied and sprayed-in-place foam. Within each of these
categories, there are ranges of prices depending on the available
funds. However, a number of other factors must be considered before
dealing with the cost issues. The list of these factors is a long one
and beyond the scope of this format. Sensitivity of operations in the
building, code requirements, climate, installation complexities and
limitations, occupant considerations, long range building use and
ownership, insurance issues - the list goes on and on. The direct
answer to the original question is that if the decision-making party is
not familiar with roofing, good advice should be obtained from a
trustworthy professional who can review all the factors to be
considered. Roofs are expensive in any form and choosing the right one
should be accomplished with as much information as can be obtained.
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| Q: |
What is the
difference between asphalt and coal tar? |
| A: |
Both of these materials are black, sticky and usually
applied after heating in a kettle. Other than these characteristics,
they are totally different materials. Asphalt is derived from
petroleum; coal tar is obtained from coal. The chemistry of these two
“bitumens” is completely different and results in a much different
level of performance on the roof. Coal tar is limited to roof slope
applications of 1/2 foot or less. Asphalt, depending on the grade, can
be used in situations in which the slope is up to 6”/foot. Coal tar,
because of its chemistry, is much more water resistant than asphalt and
is about 25% “denser.” Roof systems are available in which asphalt is
used to construct the membrane and coal tar is used as the surfacing
layer to take advantage of its superior properties.
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| Q: |
How can I ensure
that my roof will not blow off? |
| A: |
The United States is rated by locale,
surface terrain and building proximities for wind uplift (blow-off)
requirements. The first step in assessing needs is to determine the
required wind uplift levels for your facility. The most prominent
rating authority is Factory Mutual (FM) – a consortium of insurers who
have created a testing company to study these types of issues.
FM publishes charts and guidelines to
determine wind uplift factors and requirements. Once the necessary wind
uplift levels are known, roofing systems which meet these requirements
must be chosen to ensure that the severest conditions will be resisted.
Underwriters Laboratories is also heavily involved in this roof
performance area.
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| Q: |
How long can I
expect my roof to last? |
| A: |
This is the “$64,000 Question,” to borrow a term from
the past. The best analogy for this question is: “How long will an
automobile last?” Have you purchased a roof that was suited for the
abuse it receives? Do you perform the necessary maintenance that should
be accomplished on a regular basis? The answers to questions such as
these go a long way in determining the answer to the initial question.
Generally, single ply sheets are rated for between 10 and 15 years of
serviceable life and built-up roofs have an additional 6 years or so of
extra service. These, of course, are very rough estimates for the
reasons cited above.
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| Q: |
Which roof is best for a
school, chemical plant, etc? |
| A: |
Each type of roofing system has its own list of features
and benefits. Certain single ply roofs have excellent chemical
resistance characteristics that make them well suited for buildings
which are subjected to chemical spills, deposits, etc. Built-up roofs
are thick, resistant to puncture and abuse and are great for schools
where students go on roofs to retrieve baseballs, use the roof as a
secret meeting place or play area, etc. The situation must be analyzed
and the best roof chosen for the specific need.
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| Q: |
What is built-up, modified
bitumen and single ply? |
| A: |
This is a straightforward
question which could have a very long answer. However, very briefly,
built-up, as the name implies, is a membrane which is created or built
in several plies by alternating layers of reinforcing felts and
bitumen. Modified bitumen products are coal tar or asphalt products
that are enhanced with polymer modifiers to improve performance. Single
ply materials are produced from polymeric plastics or rubbers and put
down in sheet form.
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