Once the decision is made to re-roof a building, the building owner or property/facility manager is faced with a dizzying number of options. The starting points for this analysis are the budget for the roofing project, the investment plan for the building, its construction, the climate it is in, the insurance carrier, and the building code jurisdiction. Each type of roofing system, including cool roofing options from Conklin, has pros and cons that make it more or less suitable for a given building. The trick is to find the option that comes closest to the requirements of a particular situation.
The first decision is whether to tear off the existing roof and start from the deck up, or to install a new roofing system over the existing one. There are valid reasons for tearing off the existing roof, and there are equally valid reasons for leaving it in place. Before making this decision, you should have a moisture survey performed on the existing roof — nuclear isotopic, infrared thermography or electrical capacitance — to evaluate the amount of moisture-laden materials in the roof.
When the area of wet roofing exceeds about 25% of the total roof area, the cost of repairing the wet areas begins to approach the cost of tear off. In that case, it makes no financial sense to re-cover the existing roof because the wet materials must be removed before reroofing.
On the other hand, if there is a mission-critical area under the failed roof, it may make more sense to leave the existing roof in place. It will provide some protection from weather and debris during the roofing installation. Mission-critical areas include switching stations, clean rooms, electronic-assembly areas and critical-care areas.
There are also many cases in which a tear off is the best course. If the deck is in marginal condition or if the condition is unknown, it makes more sense to tear off the existing roof to be able to inspect and repair the deck as the roof is replaced. If the construction of the building will not allow extra weight on the structure, a tear off is mandatory. The building code may require a tear off if there are existing layers of roofing on the building.
If the height of the finished roof elevation is already close to existing through-wall flashings or to the tops of equipment curbs, a re-cover will decrease this distance even further. Ponding water and wind-driven rain can overflow low flashings. Drifting snow can pile up against the walls and curbs, and as the snow melts it can also overflow the flashings. Re-covering the roof may bury through-wall flashings behind the new roof flashings, causing water that should be draining to the exterior to drain behind the roof into the building.
If there is any doubt about whether to re-cover or tear off, common sense says tear off the old roof because chances are good that the reason for the re-roofing is the existing roof has been leaking for a long time. A leaky roof is logically not a good foundation on which to build a new roof.
Once you have decided whether re-covering or replacement is the appropriate course, the options become more varied and the choices correspondingly more difficult. There are several types of roof decks and insulation, many types of membrane systems and different ways of installing them. There are multiple options within the options and, to top it off, several surfacing choices. To add to the confusion, there are many roofing manufacturers making or private-labeling many different brands of each of these items. So how do you choose?
First, it’s important to dispel the myth that there is a “best” roofing system. Any type of roofing system can provide an acceptable roof provided two conditions are met: First, it is an appropriate system for the building upon which it is applied and, second, it is installed properly.
Any discussion of roof system options means speaking in generalities. And for every generalization, there are exceptions. So “all” really means “almost all.” If a particular roof system type is not the best one for a certain application, don’t use it. Although any roof system can be forced onto any building, there’s no need to do it when there may be a better one available.
Also, remember to factor the influence of building codes and insurance requirements into the mix. These will often dictate when and where any particular system can be used and how it will be installed. It is important to consult a professional roofing contractor before making this critical decision.
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