Roof

So I researched EDPM (ethylene propylene diene terpolymer), a rubber sheet roofing that has been used for over 40 years. In the picture, 1 is the rubber membrane, 2 is the fastener for the underlying insulation, 3 is contact adhesive, 4 is the insulation, and 5 the roof deck.EPDM can be either vulcanized, which means it can be dried out and cured into sheets, or it can be non-vulcanized, which leaves the material in a semi-solid state. The vulcanized EPDM is what is used as a roofing membrane. The non-vulcanized EPDM is usually used for detail work or flashing of the cured roofing material.

EPDM is a synthetic rubber, and it is fair to say that its main characteristic is that it is black. White-on-black EPDM (WB EPDM) is a laminate material, where the standard, black EPDM makes up the bulk of the membrane. The “white” in WB EPDM is laminated on top of a standard black sheet. WB EPDM is white because titanium oxide is added to the laminated piece. This produces the white color. But it also causes the surface to be very unstable. It chalks badly, which can make it very difficult to seam correctly.

A properly seamed and installed black EPDM roof is very good at handling rain, snow, UV rays, abrasions, ozone, and low-temperature flexibility. EPDM comes in wide sheets, reducing the number of seams, which are the weakest areas.

The SKZ Group in Germany conducted a study on EPDM and found that its expected life is between 50 and 75 years. EPDM is being actively recycled.

Installation is simple and fast. It comes in large sheets with fewer seams to leak and take labor. It does not require a cant strip around the edges - less labor. Rubber roofs will flap in the wind if not held down. They can be secured by covering with river rock (ballasted) nailed (not used much) or glued down. An EPDM rubber roof is designed in a way that flashing material needs to be glued around the corners and around roof penetrations with a special adhesive. This presents a problem from the outset, because this adhesive will eventually fail and the seams will start coming apart. To prevent this issue from happening or to repair it, an EPDM rubber roof needs repair at the seams, process known as “reseaming”.

The EPDM can be walked on with no protection and does not appear to be damaged by hail. A ballasted roof is hard to walk on, though traffic will not damage the membrane. But the ballast (stones or gravel) will catch leaves, which rot and plug up the drains and pollute my irrigation water.

Why do EPDM rubber roofs have these installation problems? The reason is simple: while proper installation does not require any special equipment, it does require specific technical knowledge and skills. However, despite the fact that an EPDM roof is a specialized type of roofing and therefore should be installed by expert flat roofing installers. EPDM rubber typically fails at roof penetrations, flashing and seams, allowing moisture to penetrate.

One hidden problem with highly insulated roof structures is that when the waterproofing membrane leaks the water does not appear on your floor or ceiling, but soaks into the insulation. This may go on for years before it is discovered. Meanwhile mold grows in the insulation and the structure rots. Both these problems are very expensive to correct.

Should I consider TPO (Thermoplastic Polyolefin)? TPO is actually in a broad family of rubber roofing materials. TPO is a blend of polypropylene and ethylene-propylene rubber. TPO – as it is currently formulated – does not have a long track record. That track record is also not very compelling. TPO is known to shrink and pull away from seams and curbs. That was one of many reasons for the constant reformulations of the product in the first place. Unfortunately, that problem hasn’t completely gone away yet. The primary advantage is that TPO is cheap.

What about PVC (PolyVinly Chloride)? PVC is naturally white. PVC is heat-welded into a continuous sheet (or comes that way from the factory). Unlike EPDM rubber roofing, PVC roofs are typically installed by professional contractors who have knowledge and experience with PVC roofing membranes. This difference is due to the fact that installation and repair of PVC roofs requires specialized equipment, which is very expensive. Only specialty contractors who are in the business of installing PVC roofs are willing to invest money into all the necessary equipment. Consequently, these contractors are also trained to have all the technical skills required for installation and repair of PVC membranes.

PVC may require protection from puncture in high traffic areas. Older PVC roofs in cold weather are prone to shattering and puncture. As a result, the National Roofing Contractors Association recommends no foot traffic on PVC when the outside air temperature is below 50 degrees. PVC membranes owe their flexibility to the addition of plasticizers. Yet in both warm and cold regions, these plasticizers may migrate or evaporate out of the sheet causing it to embrittle and shrink.

The sudden and catastrophic shattering of a PVC roof membrane is a story being repeated with saddening frequency. The number of roofs that have been shattered has not been well documented. However, the frequency has been high enough for the National Roofing Contractors Association and the Single Ply Roofing Institute to jointly issue an alert. The communique describes the potential for roof failure, which generic types of PVC membranes are affected, and some precautionary measures that should be taken with specific PVC roofs.

Not all PVC roofs have these problems. In fact, there are some reinforced PVC roofs on the market that have performed very well for over 20 years, and are often considered to be the most appropriate single-ply membrane for many applications. Glass or polyester reinforced PVCs do not experience the same shattering tendencies.

In testing several membranes seven to 10 years old, we found the cold temperature flexibility to be greatly decreased. In the case of a membrane taken from a recently shattered roof, the membrane failed the cold bend test at 22 degrees Fahrenheit, while "as new" the membrane passed at -40 degrees Fahrenheit. This would explain why the failures have occurred in cold weather. The membranes are under tension from membrane shrinkage, and have poor low temperature flexibility. Roofs most often afflicted are non-reinforced PVC gravel ballasted membranes.

The addition of reinforcement material to PVC membrane sheets has clearly assisted in preventing the wall-to-wall catastrophic-type shattering. Improved chemical formulations may also be assisting in extending the life of PVC membranes. (1999)

I’d rather spend more on the roof initially and be comforted that it will last many decades with little maintenance and no replacement.

Flashing

Roof flashing is an integral part of a roof system in that it helps weatherproof the different joints and connections of a roof system. This includes locations such as where the roof meets the perimeter or building wall and where designed roof penetrations for vents and mechanical equipment come through the roof. Roof edges and penetrations account for most roof failures.

When flashing failures occur, it can create serious issues, as flashing is usually used at locations where the roofing system terminates. This creates a serious water intrusion problems as water not only penetrates the surface,but gets down to the structure and interior of the building. Flashing failure is almost always caused by a construction flaw or lack of long term maintenance. My roof will have very few penetrations (pipes and vents projecting through the roof).

Another way is to use flashing (waterproof material that protects the edges of the roof) that will last. Sheet metal has its problems: steel will rust. Aluminum can blow off during strong winds. The bond between metal and roofing will fail. Metal and roofing materials expand and contract at different rates - and temperature extremes are daily in Taos, especially on the roof.

Pre-molded flashings are available for round (pipe) penetrations, made of EPDM, and can easily be securely bonded to the roof membrane. Curbs and parapet walls are handled with EPDM membrane glued to the wall or with EPDM peel-and-stick membrane, which is stretchy and can be formed around and into corners. The flashing will extend up and over the top of the parapet, then hidden by the stucco. Since stucco is porous, the flashing ensures that the tops of the parapet walls do not get wet.

Scuppers