5.1. SR 09-19-1994 - Laserfiche WebLink

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31 . ing the water in gradual increments. As with the tapered in- sulation example, height restrictions at the details are more easily dealt with. The primary advantage of this approach compared to the tapered insulation approach is cost. De. pending on the type of roof system and the complexity of the insulation layout design, the installed insulation cost for the tiered system can be 10 percent to 40 percent less than the tapered system. This cost saving can go a long way to offset any loss in service life of the roof system caused by minor ponding with the tiered system. Scuppers Ind Downspouts Once the surface water gets to the drain, it must be able to flow off the roof. Often the extra materials used to flash in the drain, or scupper, result in a build.up around the drain and some damming of water. This effect can be minimized by placing the drain, or scupper, in the center of a depressed area made by tapering the insulation. The tapered area' should be slightly larger than the largest flashing sheet. In climates where freezing temperatures often occur, ice damming at scupper outlets and ice damage to the down- spout arc often problems. The open.faced down-spout was developed to minimize the potential for plugging while con- tinuing to provide the waIl protection and control of water flow afforded by a totally closed downspout. Using a dark color for the downspout allows solar heating to help keep the downspout as ice-free as possible. Cenain types of buildings, such as school buildings, may have other special considerations. It is amazing how a new downspout can provide children with access to the roof. A W-shaped open-faced downspout securely anchored to the wall is a design that doesn't leave much for children to grab (Figure J). Also, there should be no projections or sharp sheet metal edges that could cause injury. This design has an advantage over the more conventional open-faced down- spout when using factory color-coated sheet metal. The en. tire exposed face will have the colored face showing. The in- side of the more conventional open-faced downspout shows the reverse side of the metal, producing a "racing stripe" on the building unless the inside is painted. This "child-proof" downspout provides a reasonable solution to a couple of typical downspout problems. Contractors that have used it have found it to be fairly easily fabricated and installed, while providing essentially the same function as the more . ~ conventional open-faced downspout. Likewise, building owners are satisfied with the reduced potential for injury and traffic on the roofs. Inside-Outside Drains A beller approach to edge drainage in nonhern climates is to install an inside-outside drain. This is usually more expen- sive than an exterior scupper and downspout. But its ability to remove snow.melt water is much beller, and the risk of damage from ice falling off the wall is eliminated. It is also relatively vandal-proof. This type of roof drain system is simply a roof drain in. stalled at the low point of the roof surface. The drain leader runs down the inside of the exterior wall and discharges out through the waIl a foot or two, above grade (Figure 4). The interior location keeps the drain and leader open during cold weather. Ice build-up at the discharge is minimized because the draining water has warmed slightly. Damage from any ice development is minimal because it forms at grade level, not at roof level. REMARKS There are still many buildings out there with ponded ,,'ater on the roof. With some thought at the time of reroofing, most of these conditions can be reduced or eliminated using some relatively simple methods. The resulting roof system is more likely to reach its maximum serviceable life, at the lowest Iife-cycle cost. 1" insul. 3" insul. -t Area of substantial ponding 1/e"/ft. tapered insul. Scupper-'7 B ROOF PLAN No Scale 1"insul. 1/8"1It. tapered Insul. 3" insul. Root surface slope ~ . Deck slope B TAPERED INSULATION SECTION No Scale FiguTt J .' ',". .0, . 'cI'o". "'.? '0"-;' It Deck Slope Exist. concrete deck showing exaggerated deflection between bearing walls