Flat Roofing Technology BUYER'S GUIDE

Excuses for Poor Design

Many roofing manufacturers advocate re-roofing over existing roofs to enhance sales, knowing a competing manufacturer will do the same. Landfill disposal problems, equipment, manpower and hauling costs also encourage many roofing contractors to install new flat roofs directly over old flat roofs. Many contractor and manufacturer warranties run out or are useless when the damages accompanying the flat roof failure include insulation, fasteners, sheathing, roof joists and drywall. These components are yours and are not considered part of the roofing itself.

Remove the Old Roof

It is strongly recommended that the existing roof be torn off. Moisture and water vapor trapped in the old roofing system, should it be left in place, can attack the underside of the new roof presaging the roofing components including the recovery board, insulation, metal fasteners and the roofing membrane. If a minor puncture occurs in a new roof that has an existing roof membrane underneath, many gallons of water can enter the puncture before it is detectable by the occupants. The water that is trapped in between the two roof systems stays there long after a repair is done and will begin to degrade or render useless new insulation and again attack the fasteners and new roof from underneath. Roof sheathing and structural components can suffer from severe deterioration from the effects of long moisture saturation.

Drainage of Flat Roofs

Attempts to achieve good drainage on roofing systems is an extremely important goal. Great amounts of standing water cause several dangers. In the event of a roof puncture, the building would be forced to accept all accumulated water which could include several hundreds to thousands of gallons. Common punctures may be caused by animals, tree limbs and human traffic. Temporary or permanent repair of an underwater puncture may be impossible in winter months and in extended rainy periods during the summer. Standing water can also cause nesting sights for micro organisms that can attack roof systems, laps and flashings causing premature deterioration.

Two systems are available for providing roof drainage on existing buildings. The least expensive is to use tapered expanded polystyrene (plastic foam) sheets designed and cut to be installed thicker to thinner resulting in a constant uninterrupted slope. A second method required complete removal of the roof deck, building new rafters to slope and redecking prior to roofing. This system is generally used when and if new insulation is added to a vented ceiling system.

Drainage of roof systems should be a major design consideration. ""More is better"" is a safe way to design drainage because almost all structures have deflected surfaces caused by settling of the building and structural roof components that are not truly level. 100% drainage is almost always unachievable, however, several gallons that will dry up within 48 hours is by far superior than the hundreds often occurring on a poorly designed system.

Insulation and/or Ventilating a Flat Roof

Addressing the improvement of insulation in an existing flat roof structure is often overlooked during re-roof design and for a very good reason. Often the roofing contractor is putting his ability to "sell a job" on the line when detailing of proposed insulation is questioned.

Most flat roofing contractors have minimal knowledge of ""performance based"" insulating systems. They also may know that by properly addressing insulation, the re-roofing procedure may double in cost. The contractor may be tempted to promote an inexpensive insulation product underlying the new roofing as a primary addition to your energy package, when in effect you may receive next to nothing in energy savings in return. It makes the roofer look as if he is addressing energy savings without actually doing it, therefore enhancing his ability to sell a job. There are three insulating systems discussed here; vented type flat roofs, Corbond insulated roofs and sandwich type deck roofs.

Vented Systems

Most homes that have flat roofs have an insulation system that consists of 4"" to 6"" of fiberglass or mineral wool batts inserted between the rafters, and a minimum of 1 1/8"" air space between the batt and roof deck. The bottom of the perimeter ventilation is then provided through penetrations in the roof overhang.

These systems, correctly implemented, have performed reasonable well in addressing removal from the building of harmful water and water vapor; however, in almost all cases they are very energy inefficient. This inefficiency occurs because of 2 phenomena.

Wind Effecting Batts

First, fiberglass or mineral wool batts are rated for their efficiency by measuring the "R" factor (calorific unit of heat loss per hour). The "R" factor is measured through the center of the batt without wind loads. When we consider the space or crack occurring between the rafter and the batt and the space between the butt ends of the batt, performance may substantially drop. Introduction of wind in the course of necessary ventilation also substantially reduces batt performance.

Frost Effecting Batts

The second phenomenon that often occurs is the breakdown of the batt insulation due to the occurrence of occasional condensation and/or frost. A vented flat roof system, unlike a steep roof vented system (heat rises), depends on wind to ventilate and blow out moisture occurring above the fiber insulation. In due course there may be occasional frost cycles occurring in the batts on windless days. These frost cycles break down the binders that make mineral and fiberglass insulations perform. The ongoing cycles may continue to reduce performance for the life of the insulation system.

Add New Batts?

This procedure requires removal of the old roof and roof deck. Remove the old deteriorated batts leaving the wrapper backing. Install a new roof deck and re-roof using the "re-roofing guide". Remember that we need a 1 1/8" air space above the new batt and below the decking. This may limit new insulation thickness unless increasing the rafter depth is accomplished. The cost is substantial and efficiency is increased but the payback may be very disappointing. Remember the cracks in the batt insulation and wind affecting those new batts will be installed under adverse conditions. An additional disadvantage occurs with and air space between the old insulation paper remaining between rafters and the new batt. Wind often can travel between the old paper and the new batt rendering it useless at times.

Sandwich Roof Systems

Sandwich type systems include a roof deck that has no insulation below. In residential construction they generally include 2 5/8" of cedar decking supported by interior beams having a surface finished to the interior. They were generally insulated with 1" to 2" Perlite board type insulation nailed to the top surface of the cedar decking and covered with an asphalt built up roof. Little if any consideration was given to energy efficiency; however, they performed quite well in addressing water protection and water vapor in that the heat loss was so great that no water vapor had time to accumulate in the house.

Addressing Sandwich Roofs

To properly address insulation on these roofs they must be removed, both the roofing and sometimes the Perlite, down to the roof deck. A vapor retarder must be installed and a suggested minimum of 3" of plastic foam board nailed down. Performance factors must be taken into consideration that are not common knowledge. Plastic foam insulations are rated by "R" factors just like fiberglass; however, they outperform fiberglass at colder temperatures. Plastic foam is not appreciably affected with wind loads. They are much more energy efficient and less "R" factors are necessary.

Sandwich Roof Insulation Standard

3" of plastic foam installed in 1 ½" layers with all horizontal and vertical joints staggered should be today's minimum standard. 3" equals the dimension of standard wood blocking required at the perimeter of the roof. Increments of 1 ½" are used to increase insulation thickness in conjunction with this wood blocking. Beyond 3" becomes payback vs. investment cost or an environmental concern issue which may exceed a 3" performance standard.

State of the Art Insulation - Corbond

A third insulation system new to this market must occur as a team effort between the re-roofing contractor and a certified Corbond Insulation contractor. This is the most effective system known. The procedure includes removal of roofing, roof decking, batts and paper backing. The Corbond Insulation contractor then sprays 3" to 4" of Corbond insulation between the rafters, bonding the ceiling and rafters into a solid unit. New sheathing is installed and re-roofing occurs using the "re-roofing guide".

Heating costs through the ceiling may be reduced up to 90% using Corbond. No cracks exist because it bonds to the rafters and drywall creating a perfect air-tight system not subject to wind or frost deterioration. Venting requirements are minimal because water vapor does not substantially penetrate Corbond. This is by far the most long-term comprehensive system to correct the woes normally associated with flat roofs.

Avoid systems that try to eliminate ventilation or systems that combine fiber type insulations with above deck plastic foam roof insulations. Success with these type composite systems is usually unachievable because of air leakage and the inherent nature of water vapor.

Summary

Insulation types, standards, performance and venting requirements continue to be misrepresented and misunderstood in flat roofing and specifically flat roofs on housing. Properly addressing an insulation upgrade in conjunction with your new roof requires a supportable standard, one that addresses the performance you expect protected by correct ventilation, vapor barriers or the inherent characteristics of a Corbond Insulation system.

Re-roofing is not a casual maintenance item. Materials must be selected, manufacturers must be appraised and procedures planned and evaluate to create a roof system that performs to the expectations of roofing material life, and that protects all related building components.

The goal is to develop an individual re-roofing specification for each job. This is achieved through a design process supported by knowledge of roof problems, their courses, effects and what materials properly address those problems. Our process also addresses performance of the overall system and each of its components to successfully control energy usage and moisture movement as well as achieving a water tight roof. Choose carefully.

Shingle Roofing Today BUYER'S GUIDE

Shingle Design Features

Shingle roofing has "come of age" so to speak. Traditional styles of shingles, or the 3 in 1 sealdown shingle once 100% of many roofing companies business, is now only 60%. Architectural shingles or designer shingles have taken over 40% of the market. Even though the expense of these shingles is greater, the effect on your home may develop a greater ascetic investment value. Your roofing contractor should have design capabilities as well as be able to show you homes where these products are installed. Steepness of the roof will also require possible selection alternatives.

Shingle Roofing Materials

Roof covering selection can be difficult. Changes in technology and raw material availability often cause unknown changes in what we would normally consider standard type products. The weights, thickness, internal components and wind seal material widely vary. The roofer should know some history of organic asphalt shingles and fiberglass asphalt shingles. They should know what worked, what was marginal and what our ""best bet"" is for today. The selection is vast.

Warranty

Depending on the manufacturer, warranty is not the answer. Manufacturer reputation must ""pass today's tests"" as to not only the quality of the material but their short and long term profit goals and warranty enforcement practices.

Having a warranty is nice, but collection on a warranty problem may be another matter. A good relationship between the contractor and manufacturer is necessary, for warranty implementation can also quickly negate a manufacturer's warranty, reducing it to a technical nightmare not worth the energy of legal costs to enforce.

Consider Accessories Carefully

The quality, gauges, weathering finish, type and implementation of roof accessories must be reviewed. Consideration of metal edging, valley type and quality, vent (both exhaust and intake), chimney flashing and counterflashing, roof to wall flashings, skylight flashings, kitchen, bath and dryer vents, vent pipe flashings and ice dam protection play an all important role in a valuable roof covering. Each component and procedure should be able to perform to the expected life of the shingles.

Unusual and Nonstandard Construction

Unusual and nonstandard construction requires extensive technical design and execution standards not available or known to many roofers. Technical documentation and other ""same type"" projects should be explored. Care in contractor selection and experience is critical.

Details Make a Roof

Few homeowners realize the full ramifications of poor detailing of a new roof covering, specifically roof to wall, chimney and skylight flashing. Seepage between roof coverings, unseen inside their home, may cause total saturation of the underlying roof. Further saturation of the underlying decking and structural lumber follows. Decay of these underlying wood components may go unseen for years, often inviting further destruction from carpenter ant infestation. Repair of roof deck problems and structural components can often double or triple the cost of successive roof covering. Manufacturer warranties mean next to nothing when borderline design, workmanship and accessory selection occurs.

Underlying Specifications

Specifications relating to insulation, ventilation and ice dam protection often go unnoticed by homeowners. Many owners assume that because they have no evident leakage or damage inside their home, they will be protected for the future. By merely recovering the roof and adding a few extra roof vents, they believe the roof deck and structural performance will continue. This may be a very poor assumption.

Ventilation

Good ventilation requires consideration of insulation quality, air intake, exhaust, vapor barriers, and humidity conditions. Roof vents are only 1/3 the answer. Air entry must be consistent so the attic temperature and humidity in the air mix consistently and evenly. Soffit ventilation for air entry or other air entry systems must be evaluated or improved. Your roof deck and insulation quality depends on it. Kitchen and bath fans must also vent outside of the attic to eliminate frost cycles.

Roof decking, specifically plywood, may withstand borderline attic ventilation and frost cycles for the duration or life of a first roof. Additional stress of re-roof nailing and loading activity can cause partial failure on the plywood deck during re-roofing. Continued attic frost may cause complete failure of the deck during the life of the second roof. Proper ventilation can stop this cycling of frost.

Insulation

Insulation also breaks down with attic frost. Moisture effect the glue binder of fiberglass much like the glue in plywood. As time goes by, its effectiveness grows less, increasing the ventilation requirements. If venting stays the same, the attic frost cycle may escalate causing faster insulation decline along with plywood delamination.

Tear Off or Recover

The factors that determine whether an old roof covering should be torn off or recovered are weight, roughness, shingle design and shingle exposure on the existing roof.

One rule of thumb regarding weight commonly followed is that 2 roof coverings are almost always acceptable and 3 is rarely acceptable. There are exceptions to these rules based on roof steepness and initial construction practices. Even if weight is not the problem, roughness and existing shingle design may require tearing the old roof off.

Roughness of an old roof can cause these problems. First, a new shingle roof may not lay smooth over the old roof. This can be unsightly. Second, a new shingle roof without a smooth surface under it is subject to hail damage. Third, shingles laid over a rough substrate may not wear evenly. Exceptions to laying shingles over a rough roof may include using heavier architectural type shingles and/or a ""nesting method"" procedure. This procedure consists of laying shingles so both the old roof and new roof have equal thickness throughout. Using very heavy textured type shingles, 360 to 400 lb. per square, may eliminate the need for old roof removal. A good contractor should be able to pre-judge the final appearance. If you still have questions regarding the contractor's judgment, ask the contractor for a ""same type"" application you can verify.

Summary

Re-roofing is not a casual maintenance item. Materials must be selected, manufacturers must be appraised and procedures planned and evaluated to all become part of a roof system that performs to the expected shingle life and protects all related building components.

Our goal is to develop an individual re-roofing specification achieved through a process supported by knowledge and on that addresses performance, not just one that limits loss. Choose carefully.