Flat Roof Repair Round Rock

An Introduction To Flat Roofing Systems

If you own a commercial building here in Round Rock or the surrounding area, chances are you’ve never been on top. In this post I hope to give you a keen insight into the inner workings of your roof to either fix it yourself, or hire a responsible contractor.

Please don’t attempt to fix it yourself without knowing a few of the basics. It could set you up for a more extensive repair than what was originally required.

A flat roof system fills entirely different needs than a steep roof or a pitched roof with shingles. The pitched roof utilizes a shedding system, while the flat roof uses a watertight skin or membrane that is placed over the top of the building.

For example, a steep roof is like an umbrella and the flat roof is a wet suit. Since the two are completely different, each will require its own different approach, materials, installation methods and conditions that need to be considered.

The term flat roof may be a little deceiving, as roofs should never be flat because they have to drain water. So actually this is a very low pitched roofing system. Water will run whichever way the roof is pitched, to be channeled through gutters and downspouts, centrally located roof drains, and/or scuppers (drainage openings through walls, including parapet walls).


Flat roofing will not be as expensive as steep roofs that use clay or slate, but it is less expensive than asphalt, wood or another relatively inexpensive material.

The installation of a flat roof will require a weather-tight skin over the top of the building and is very demanding. All the while a weather-tight condition must also be maintained at chimneys, plumbing stacks, skylights, vents, and around the edges.

The Functions of a Flat Roof

The perfect flat roof would:

  1. Keep water out
  2. Last the lifetime of the building
  3. Not pose any fire threat (during or after installation)
  4. Be strong enough to walk on, move equipment across and be suitable for attaching equipment
  5. Control heat loss and heat gain from the building
  6. Add to the architectural appeal of the building
  7. Be inexpensive


There is no perfect roofing system yet, although all keep the water out, or at least most of the water most of the time. And most flat roofing systems are designed to last 20 to 30 years.

Due to the combustible nature of the materials in flat roofs, they can act as fuel during fires. They are not durable when walked on and foot traffic and equipment traffic has a deleterious effect. Anything attached to roofs such as antennas and satellite dishes creates vulnerable spots. They are expensive, unattractive and are not even designed to protect against heat loss.

The traditional flat roofing material is tar and gravel which is commonly referred to as built-up or nun. Felt paper and either coal tar or asphalt are used during installation. Since coal tar is rarely, if ever, used anymore, we’ll focus on asphalt.




The common built up flat roof is considered to have a minimum 20 year life expectancy, while many last 30 to 35 years. Used extensively on commercial and large buildings, it’s complicated and dangerous. Hot asphalt or tar kettles with 400°F asphalt applied with mops and buckets make for an environment where accidents can happen. And it’s strenuous work hauling heavy materials to the top of the building.

Since leaks are rarely directly below the flaw in the roof above, it’s difficult to inspect. It’s very difficult to track where leaks occur because you can’t get a look at the membrane underneath.

Not until the late 1960s and early 1970s were there more alternatives to the costly built-up roof or the lower quality roll roofing. Since roll roofing was so inferior to the built up, it was often considered a temporary roof. There was an obvious need and plastic (PVC), synthetic rubber (EPDM or elastomeric), and the modified bitumen all started to appear around this same time period. They became referred to as single-ply roofs. Single-ply is not built up in layers like tar and gravel roofs.

These single ply roofs became quite popular because they were cheaper, the materials are easier to install, and leaks are easier to trace. But single-ply was not without problems.

Early on, PVC cracked, EPDM roofs opened at the seams and pulled their flashings loose as they shrunk and modified bitumen often split and opened at its seams.

Over the years these products have been refined and no longer have these deficiencies, and more improvements can be expected.

We have seen divided opinions during the 1990s as these two systems competed with one another: built up or single-ply. The single-ply in some areas at the single-family residential level has taken hold largely based on cost. The homeowner can experience cost savings due to the reduced labor to install single-ply.

The trade-off appears to be the life expectancy for these new roofing alternatives. Having been around for 20 to 30 years, the current systems have undergone many changes. Some manufacturers’ warranties offer a 20 year life expectancy on single-ply systems to make the owner comfortable with the purchase. Since there have been incidences when the roof has not performed as promised, we don’t have truly a good sense of the life expectancy.

We may even see built-up roofing disappear within the next 20 years as single-ply systems are becoming more common and are improved upon.

There are a number of distinctions between residential and commercial roofs. The location of the insulation and amount of insulation used are just a few. Residential has batt-type insulation which is usually applied between roof joists below the wood deck that makes up the roof.

Metal or concrete decks are used in commercial, and insulation is usually installed above the roof deck. While the typical commercial building will have less insulation than residential buildings, that distinction appears to be changing.

Since installing insulation above the roof deck carries some inherent problems, there are some alternatives when it comes to commercial roofing options. The contractor can utilize Roof Membrane Assembly (IRMA), or a Protected Membrane Roof (PMR), which are inverted applications. The insulation is applied on top instead of underneath the roofing membrane.

Wood decking (sheathing) is what you’ll find in most homes. The older homes used plank roofing and the newer homes used plywood. The savvy contractor will use exterior grade plywood that will be thick enough to span between roof joists without sagging.



Built-up roofing dates back to the mid-1800s. Even then, bitumen’s waterproofing and adhesive qualities were well known.

Organic felt, made from by-products of paper, wood and cloth manufacturing, is the base of an asphalt built-up roof. This is basically a fibrous material soaked with asphalt or tar, which are petroleum based products. Asbestos felts, fiberglass felts and polyester fiber felts may be available as well. The felt is layered from two to five times with hot asphalt applied between layers.

The asphalt acts as a waterproofing element, while the felt acts as a stabilizing element, holding the asphalt in place and providing strength while distributing forces. When exposed to the ultraviolet rays of the sun, the roof is susceptible to rapid deterioration. The felt and asphalt layers will not last anywhere near 20 years. To off set this, aggregate (gravel) mixed with tar is applied as a finishing layer.

The gravel reflects the sun’s rays keeping the roof cooler. The gravel also provides a modicum of fire protection and some protection against foot traffic. Walking on flat roofs, except in the case of inspections, is discouraged.

A quick word on recreational roof decks. Do not use a built up roof without providing wood walkways and/or concrete paving units to walk on. You will be asking for trouble later as the roof deteriorates from the wear and tear.

Some gravel alternatives are available: the use of light colored reflective paints to protect the asphalt, or the use of decking. Both will protect the membrane from ultraviolet light and keep the roof cooler.

If the flat roof fails, it’s caused by one or more of thirteen reasons. Over the years I have put together a list that helps me diagnose a situation to better serve my customers. Leakage and damage to the structure can occur and there are many things that can go wrong.

Here is my list I consider at each inspection followed by individual details for each:

  1. Old/worn out
  2. Mechanically damaged
  3. Patched
  4. Multiple layers
  5. No protective surface (e.g., gravel or paint)
  6. Blisters
  7. Alligatoring
  8. Gravel erosion
  9. Ridging and fishmouths
  10. Membrane movement/splitting
  11. Ponding/vegetation
  12. Debris or storage on the roof
  13. Exposed felts

Some, if not all of these conditions can be traced back to poor installation which is why it’s important to pay close attention to which contractor you award the job.

‘An ounce of prevention is worth a pound of cure.’
—Benjamin Franklin


Let’s get into each condition.


Old/Worn Out

Old roofs deteriorate over time and will be affected by weathering, mechanical abrasion like foot traffic and air pollution. We’ll get into flashings later, but it’s worth noting here they provide clues to the age of the roof membrane. But, as always, I believe the remaining life is more important then the age of the roof.

Mechanically Damaged

Any roof system will be susceptible to mechanical damage. We have mentioned foot traffic earlier. The roof may also have been impacted from equipment that is moved across or installed on the roof, wind, sharp gravel, and falling objects such as tree branches and hail. This type of damage is easy to spot and repairs should be quickly made to prevent deterioration of the roof and eventual leakage.


While patched roofs are common, it is not uncommon to find weak areas where these patches were applied. The actual patches are under the gravel, but you can spot these patched areas by newer gravel which may be a different color or texture than the original gravel.


Multiple Layers

It’s common practice for the new membranes to be layered over old membranes. This is not best practice though, for a number of reasons. By doing this, you are adding weight unnecessarily to the structure. And you are most likely trapping water that has leaked in by adding the new membrane. This will lead to rot or cause premature failure down the road.

I find multiple layers more common on residential homes. The unscrupulous contractor underbids his job and saves money by simply adding a new membrane over the old one, and the gravel is removed and later re-used. The multiple layers will result in higher maintenance or shorter life than you would otherwise expect.

You may be able to spot this by looking at the perimeter of the roof. There may be more than one drip edge flashing. This is not fail proof. The drip edge flashings may have been removed prior to the second layer being applied.

No Protective Surface

I have seen in some cases where there wasn’t any gravel applied after the felt was laid. The gravel is needed to protect against sun damage and helps keep the roof cool.

This is another decision based solely on cost. A cost cutting contractor’s quote will include a tar and gravel roof, but will not apply to the gravel, saving both time and money. And since homeowners have no reason to venture up on their roof, the shoddy work is never identified. Until the roof fails.

The upside is that I can have a good look at the membrane and easily spot where the leak is occurring. I’ll add a protective layer and proceed to finish with the tar and gravel as a final layer.


When the roof heats up with the sun, the gases expand and bubble up through the surface, or expand to form bubbles or large blisters. They are caused by air or water being trapped either between the roof sheathing and the membrane or the membrane plies. Air or other gases (such as solvents) can also be trapped in the asphalt.

The smaller blisters, referred to as blueberry blisters, will eventually break over time and leave a crater in the roof. Water then penetrates eventually reaching the felts which ends up weakening the roof.

Larger blisters rarely pop up through the surface and can get quite large. Problems occur if the roof is cold, and the weight of foot traffic, snow, or ice may cause the blisters to rupture. This will cause immediate leakage into the mebrane and eventually beyond.


Suffice it to say, blisters do eventually break without some mechanical action, and the sun will cause the asphalt to crack and split eventually. You can head off potential roof failures by walking the roof to check for sponginess.  You may also be able to see blisters by looking along the roof surface. The cure is to cut open the blister, dry it out, re-seal and finish with gravel.


The sun will make the top surface of the asphalt brittle and the volatiles, which keep the asphalt flexible, are boiled off. The expansion and contraction that occcur due to weather fluctuations will cause the surface to crack. It will look like the characteristic alligator skin pattern. These cracks deepen over time and eventually will allow water to seep through both the upper layer of asphalt and the felts.

Causes of this condition are either asphalt that’s exposed from faulty installation or erosion of the gravel surface.

Gravel Erosion (Wind Scouring)

The elements can wreak havoc and the wind and water will eventually wear the gravel away in exposure prone positions. Inspect the windward corners of a building and don’t forget to locate any downspouts that discharge into a flat roof from a roof above.

Gravel acts as a protective agent and once it’s gone, the sun can dry the asphalt quickly. It’s critical to have a uniform gravel cover. Spots where the gravel is either thin or missing can be recovered without complication with a simple gravel and tar application if the asphalt and membrane haven’t been compromised.

In some cases, wood decking, paint or other protective covers takes the place of gravel. As long as they protect the asphalt from the sun and allow for proper drainage, they are fine.

 Ridging and Fishmouths

Ridges in felts are caused by either installation problems, thermal expansion and contraction of the decking or structure, or expansion from moisture or slippage of the felts.

Fishmouths are ridges that are opened on the edges which may have been caused by the felt being twisted during applicatioin.

This allows for the elements to have direct access into the membrane. Not good. You can spot or feel ridges, wrinkles or fishmouths by walking the roof. The gravel may cover some of these issues and they may not be easily visible. Be careful not to step on these areas during colder weather as you may crack or split the membrane. Prompt repairs are recommended.

Membrane Movement/Splitting

The membrane that’s installed with the felt and asphalt may shrink from thermal expansion and contraction. It’s typically a progressive problem from cycling in and out of cold weather. The membrane eventually does not rebound completely when the temperature warms up. This can continue year after year, making the membrane shorter and shorter.

When moisture escapes from inside the building (usually along a seam), splits may occur.   Also splits can occur when flexing happens under a live load. A good example is when there is an accumulation of snow and ice and it eventually melts off.

Membrane slippage can occur if the roof is too steep as well, and is most likely to occur during hot weather when the asphalt is softer. The contractor will be aware of the various types of asphalts and their maximum slopes. Some flow more easily than others.

The causes include asphalt that is the wrong type, layers that are too thick, high outdoor temperatures, asphalt which was overheated on installation, or the dry-laid base sheet that was not well secured to the roof deck.

Splitting differs from the random splitting that occurs with advanced alligatoring and is a tension failure across the field of the membrane. This is caused by shrinkage of the membrane relative to the roof deck.

Once splitting occurs, flashings can be torn loose, the membrane splits and seams opened up. If severe enough, parapet walls or curbs can be pulled over and plumbing stacks can be dislodged.


There are a few exceptions but roofs should never be dead flat. By design they should slope to allow water to drain to the perimeter or to the interior. Water has an opportunity to then exit the roof through drains. If your roof has water forty-eight hours after a rain, you have ponding. If there hasn’t been any rain for a while, you can determine if you have a ponding issue by locating circles that are particularly dirty on the roof. Algae or vegetation growth are also indications of water ponds on the roof.

Ponding may be caused by poor design with no slope, sagging of the structure which disrupts the slope, no drains or an inadequate number of drains, and drains that are blocked or are at high points on the roof.

Ponding may seem benign but has detrimental consequences and should be addressed. It shortens the life of the membrane and the weight of the ponded water deflects the structure, exacerbating the problem. As water accumulates, the more the structure sags.

If a ponding roof leaks, there is typically a large amount of water involved, which ends up causing a significant amount of damage inside the building. A 20′ X 20′ area one inch deep is equivalent to having four 45 gallon drums of water waiting for an opportunity to penetrate the membrane or even worse, leak down into the structure.

Vegetation growth is typical with ponding and impedes drainage, making ponding worse. Roots penetrate the membrane, making them crack and clogging drains.

Debris or Storage on the Roof

Part of roof maintenance is to keep the roof clear of debris. Problems that arise are usually a result of materials left from some construction activity in most cases. Materials stored on the roof may pierce the membrane, add to the live load on the roof or impede the drainage off the roof.

Materials or any other debris for that matter should not be stored on the surface. You will be served well if you remember to pay attention to drains. They act as magnets for leaves, twigs and other debris.

Exposed Felts

Watch for felts sticking up through the asphalt. This is caused by either an inadequate top pour of asphalt or cracks from broken ridges, blisters, or felts having to make 90 degree bends at perimeters or flashings. Sometimes contractors will fail to adhere the felt at the edges properly or not lay it out flat to relax before installation.

Unless remedied, water will be soaked into the roof. This will lead to premature failure and leakage.



Modified bitumens or polymer modified bitumens or mod bit, are sometimes referred to as rubberized asphalt. It performs on either low-sloped or steep roofing. It was introduced around 1975. An asphalt based product enhanced with additives gives it additional strength and flexibility which reduces asphalt flow at high temperatures.

It comes in both liquid form or in sheets. The sheet form is almost exclusively used in residential applications.


There are two types of mod bit roofing. The APP (Atactic Polypropylene) modified bitumen is a plasticized asphalt product which has been found to perform better in warmer climates. The SBS (Styrene Butadiene Styrene) modified bitumen is often referred to as rubberized asphalt, which has been found to perform better in cold weather, although the two are indistinguishable in the field.

Modified bitumen products can be reinforced with fiberglass or polyester fabric, and are asphalt compatible.

When these new coverings were introduced, there typically was no ultraviolet protection. This may still go on in some areas to this day. Most contractors though will provide ultraviolet protection in the form of either a granular surface similar to asphalt shingles, liquid applied latex coatings, foil surfaces like aluminum or copper, or ballasted, which is more common in commercial properties.

This additional protection helps to extend the life of the membrane and help to protect against high heat and mechanical damage. The unprotected mod bit roof, which is black, can get hot. Real hot. An unprotected surface can easily be 70 degrees warmer than the outside temperature. When the outdoor temperature is only 91 degrees, it would make the roof approximately 160 degrees! Please remember us poor contractors during the summer months.

Modified bitumen products are installed using a torched-on method, sometimes called heat welding, or are mopped-in with hot asphalt. Alternatively there is a peel and stick product as well. While the SBS modified bits may be applied with any of these three methods, the APP mod bit is usually torched in.

There are two camps when it comes to deciding what the best practice is for holding the membrane down. One camp believes that fully adhering means less movement including fluttering caused by the wind. The other camp feels that partial adhering is best because this allows for expansion and contraction and movement possibilities between the roofing material and the substrate. A ballasted system is held down with loose gravel and there is no adhering of the membrane to the substrate.

Its customary modified bits will go down in a single-ply system residentially, although there are higher quality installations that are two-ply. There is the rare occasion when a single-ply mod bit sheet is applied over two or three plies of felt and asphalt.

Thickness ranges from roughly 2mm to 5 mm (40 to 160 mils) and rolls are typically 39 inches (l meter) wide and 25 to 50 feet long. Sheets are cut into lengths of either 15 to 25 feet which should lie flat to rest before they are laid. Seams will be either torched together or mopped together using hot asphalt. The flashing is the mod bit material itself.

When I get called out because a customer’s roof is leaking, I’ll have a list of things I check if it’s a mod bit roof:

  1. Check to see if old and worn out:

Old roofs are prone to have some leakage and will require me to repair or replace the roof membrane. Causes of an old roof are, time, weathering, mechanical abrasion such as foot traffic and air pollution.

  1. Look for openings at seams and flashings:

Poor installation practices and excessive tensile stresses in the membrane are root causes for this condition. Since this is so common, I pay special attention to the seams and flashings.

  1. Check for surface cracking

This may be caused by shrinkage of the material, because of aging or a manufacturing defect like no proper coating that protects against the heat and sun. It’s important to note if the cracking is surface only or goes all the way through.

  1. Is there some loss of granules:

If so, I’ll imbed more granules. Easy fix. If there is some visible loss, it’s usually caused by either erosion from moisture or foot traffic or it’s a manufacturing defect.

  1. Has some slippage of the membrane occurred:

Slippage is very common here in Texas because of the heat. Happens more with SBS mod bit than APP. These other causes will be difficult to pinpoint, but I’ll check for inadequate adhering of the membrane to the deck, or an inadequate protection from heat by lacking the proper coatings or granular surface. It’s also prudent to check if there is an  excessively steep slope that is causing the problem. Also, it may simply be inadequate amount additives in the mod bit to provide sufficient resistance to the asphalt flowing, which would be a manufacturers defect.

  1. Are blisters visible:

While not often seen with mod bit roofs and don’t pose a serious problem, blisters may be your problem. Often caused by moisture below the membrane or trapped within the membrane. And it could only be a manufacturing defect that’s causing it.

  1. Can I see any visible punctures or tears:

Foot traffic, falling branches and shrinkage can be culprit if there are tears. If a membrane is excessively taut it may be improperly adhered to the decking at installation. Undue tension will cause you some problems from any sharp object that may impact the roof. Causing the membrane to puncture or tear.

  1. Has there been any ponding/vegetation:

Typically caused by a poor design, or can occur from settlement of the building. If the roof has some deflection from any unnecessary loads, this will promote ponding. It’s not clear whether and to what extent ponding may shorten the life of the roof, but the consensus is that’s undesirable on any roof. Ponding and vegetation on both built-up roofing and mod bit will have the same issues apply.

  1. Has the roof been patched:

Patches on mod bit roofs are common. Not only does this indicate previous problems, but it points to an increased vulnerability to future leakage.

  1. Check for visible signs that there are installation problems, including:

a. Seams facing up the slope or inadequate overlap of seams at side or ends

b. End seams not staggered

c. Inadequate fastening of the membrane to the roof deck which may be caused by

                         * Incomplete torching or mopping

                        * Excessive torching or mopping

                        * Mopping with asphalt that is too cool poor surface preparation

                        * A wet roof deck 

d. Look for poor sealing at seams and flashings (often owing to under heating or overheating the material)

e. Is there inadequate drainage that is causing ponding

Inspections for modified bit roofs are similar to built-up roofing, but I’ll want to identify what I have on my hands either way. It’s hard to tell by just looking.



I’ll look for an exposed asphalt membrane, to see if there is coating present. Furthermore, I will be assured it’s modified bitumen if the seams are about every 3 feet and I can see bleed-out of asphalt at the seams. I’ll check the flashing material is the same as the roofing material and there are no nails visible.

The majority of my inspection is devoted to seams and flashings. I’ll pay close attention to high traffic areas for wear or physical damage. I’ll recommend concrete roof pads in these areas if I see unwarranted wear.

The mod bit systems have only been around since 1975. Life expectancies have not been well established. Most manufactures offer the 20 year warranty. I will provide this information to the customer and offer to service the roof after installation. Beware the contractor that gives life expectancies for any roof surface. This is against ASHI Standards.



This stretchy rubber is similar to the inner tube on a bike. The synthetic rubber can either contain vulcanized or nonvulcanized elastomers. The most common synthetic is EPDM (Ethylene Propylene Diene Monomer). It was introduced as a roofing material in the early 1970s. Since the mid 1990s, it has gained popularity to be the second most used commercial roofing membrane in the US, after buildup roofing. Its use is mostly limited to commercial buildings, but it does show up from time to time in residential work.

Reinforcing does occur usually with a polyester fabric by embedding in the rubber or laminating to the back for added strength, and no protective coatings for ultraviolet light or heat are needed. Coatings may be used to enhance esthetics or to add a layer of fire resistance. Coatings include either ballast or Hypalon, which is the brand name for CPSPE (chlorosulphonated polyethylene).

Typically, EPDM sheets are 0.8 to 1.6 mm (30-60 mils) thick, and are laid as a single sheet up to 50 feet wide. Some are up to 5,000 square feet. This makes for fewer seams which are points of failure.

There are a few ways to attach the material to the roof deck: Contact cement, tacking it down with bars or buttons or laying it loose and using ballast to hold it down.

Ballast is not used for homes, but is popular commercially because it provides protection from weathering for the membrane. If the slope is significant, contact cement is preferred. Using fasteners is best if the roof can’t stand the weight of ballast. Fasteners are the go-to in re-roofing applications. Hot asphalt may be used, but the EPDM will require a polyester mat laminated onto the bottom so the asphalt adheres properly. The proper asphalt must be chosen because not all asphalts are compatible with EPDM.


EPDM is also vulnerable to oils. Freon from leaky air-conditioning units will deteriorate the rubber over time.

The seams are sealed using either tape or contact cement. Additional protection is offered with the use of caulking along the edges in addition to the tape or cement. EPDM is great material in this instance because the sheets are so big and do not require a lot of seams to be sealed.

Flashings material is typically EPDM membrane itself. Manufacturers offer a 20 years life expectancy, but failures of EPDM roof membranes have occurred inside this period.  For that reason, predicting life expectancies can be inaccurate since the product is relatively new and advances are always being made.

Other synthetic rubber roofing products include two Dupont branded materials: Neoprene which is a DuPont brand name for polychloroprene, which has been around since the late 1950s, and Hypalon which is clorosulfonated polyethylene (CSPE) and has been used for roofing since 1966.

Chlorinated polyethylene (CPE) has been around since 1964, and Polyisobutylene (PIB)  has been around since the mid-1970s. Both are compatible with asphalts.

The savvy contractor will look to find a brand name somewhere when doing a repair, otherwise the materials will be hard to identify as to which synthetic rubber you are working with. If I can’t definitively identify any, I’ll treat the repair using “single-ply” techniques.

My list at inspection is similar to the other flat roofs. Again, I’ll be aware of the following:

  1. If it’s old or worn out.
  2. Look for openings at seams or flashings
  3. Is the surface cracking or splitting
  4. Can I see any patches
  5. Are there punctures or tears
  6. Is there evidence of ponding or vegetation
  7. Is there discoloration due to premature failure
  8. Installation problems, including:
  • Not well adhered,
  • Too taut (tenting), because of;

                        *Shrinkage (usually thermal)

                        *Sheet expansion during hot weather installation

                        *Insufficient allowance for membrane relaxing prior to installation.

  • Fastener problems, including

                        * Too short

                        * Corroded

                        * Exposed/leaking at the top

                        * Too few

                        * Loose

  • Inadequate slope, causing ponding
  • Wrinkles, ridges or fishmouths
  • Poor sealing of seams and/or flashings

Not to put too fine a point on it, but if you’re hiring a contractor without a good record, you are going to have a poor quality roof. EPDM is a high quality product, so when I inspect a roof, a lot of stock goes into determining if the failure is a workmanship issue. And what I find more times than not is the prevalence of workmanship issues are on residences using EPDM than on commercial buildings. This leads me to believe that too many residential contractors without sufficient amount of experience are taking on these projects. Sometimes the higher paying jobs are too hard to turn down I guess.



PVC (Polyvinyl Chloride) known as thermoplastic roofing is expensive and includes additives which make it fire retardant and resilient to UV radiation. It is not common at all in single family homes. It was first introduced in Europe during the early 1960s and wasn’t widely adopted in the US until the mid 1970s.

Unlike PVC pipe that’s ridged, the PVC roofing material is a flexible plastic sheet. Similar to the vinyl used in swimming pool liners or inflatable water toys, it does not stretch like the synthetic rubbers, nor is it compatible with asphalt. It should never be used if it has a chance of coming into contact with asphalt based roofing products either. Asphalt shingles are a good example.

Another caveat regarding the use of PVC: when it comes into contact with polystyrene, a chemical reaction occurs. You’ll see sheets of polystyrene used as roof insulation. If the two are being used, you’ll need to use some kind of barrier between the two materials to avoid this reaction.

Prior to the early 1980s, fiberglass or polyester fabric was not used for reinforcement as it is today. If a roof is failing and it’s an older roof, this is the first thing I’ll check.

Contact cement, fasteners or ballast are used in securing the material to the decking. Again, it’s rare ballast is used in single-family residential applications.

PVC rolls can come as either 5 or 10 feet wide, while the membrane is typically 0.8 mm to 1.5 mm (32 to 60 mils) thick. When the seams are sealed, hot air welding or solvent welding is used.


Prior to reinforcements being used in modern PVC, failures in the flashings were common in the early 1980s. The failures resulted in the shattering of the membrane, and required a complete replacement of the roofing system. The failures more commonly occurred during colder temperatures, and may have been caused by a loss in the plasticizer. The colder temperatures also caused the plastic to become more rigid and brittle; that is why you never walk on PVC roofs when the temperature is below 50 degrees. If you have one of these roofs, be careful who you have out to inspect it.

My list for PVC roof inspections is similar to other roof materials with a slight variation. I’ll have the following list to remind me of where the potential problems are.

Here it is again:

  1. Old/worn out
  2. Openings at seams and flashings,
  3. Surface cracking or orange peeling
  4. Punctures/tears,
  5. Ponding/vegetation
  6. Patched
  7. Discoloration
  8. Wrinkling, ridges and fishmouths
  9. Fastener Problems
  10. Movement of roof projections
  11. Installation Problems, including
  • not well secured or fastened to the roof deck’
  • inadequate slope, causing ponding
  • wrinkles, ridges and fishmouths caused by poor installation technique
  • poor detailing at seams and flashings
  • PVC installed in contact with asphalt or asphalt based products
  • PVC in direct contact with polystyrene insulation

Life expectancies for any single ply roofing system are difficult to pin down, and the PVC membrane is no different. While there are PVC roofs in Europe more than 30 years old, there are still roofs less than 20 years that have failed. The consensus seems to be though about 20 years.

Installation problems do crop up. A contractor either did not understand the material or rushed the job. Sometimes it’s hard to find good help. Either way, I see problems all the time that stem from poor workmanship. When I encounter a PVC roof, the inspection is like other flat roof systems. I will make sure the surface is uniform and there are no irregularities that would compromise a watertight fit.

I will also get a real good sense, by walking on it, if it is going brittle or has become rigid.  If this is the case, it is likely deteriorating. If it appears taut, it is likely due to shrinkage and will need to be replaced by a more supple sheet.

Shrinkage will shift roof penetrations such as plumbing stacks, electrical masts and the like. If I see this occurring, I’ll also see gaps where weather has been seeping in.



Although not very common, metal roofs are very popular in the hill country and I receive more and more requests every day for pricing. I have covered metal roofing extensively on one of my other pages (METAL ROOFS), but will review the information here. If you  want more information on the subject, I would suggest checking it out.

Material Types:

  • Tin
  • Terne
  • Lead
  • Zinc
  • Copper
  • Aluminum
  • Galvanized Steel
  • Stainless Steel
  • Steel
  • Aluminum




Problems I will check when inspecting metal roofing systems:

  1. Leaks; not easy to determine cause.
  2. Rust;
  • Weather and age
  • Air pollution
  • Failure to maintain Painting
  • Dissimilar metals in contact with each other
  • The abrasive effect of tree branches, for example, rubbing the protective coating off the metal

3. Loose or missing fasteners, may be caused by;

  • Poor workmanship at installation
  • Vibrations
  • Corrosion
  • Deteriorated substrate no able to hold fastener in place

4. Bent or damaged metal may be caused by;

  • Physical damage caused by walking on the roof or animal activity
  • Impact damaged from items falling onto roof
  • Wind damage
  • Inadequate allowance for thermal expansion and contraction

In any event, avoid the use of asphalt as a patching agent. I have found it has a tendency to trap water, thereby promoting rust. I prefer the use of paint instead.

In summary, as with the other roofing systems, it’s hard to see everything I would like to. But if I focus my attention during repairs on the perimeter, the intersections of material and all the roof penetrations, I will get the job done.

A more detailed section on metal roofs can be found here: METAL ROOFS



Roll roofing, also know as selvage roofing, is made from the same material as asphalt shingles and is covered in granular material. It is a lower quality option considered if a temporary solution is needed.  I generally will offer this as an option if costs are an issue for roofing garages, sheds or other outbuildings. However, I will not recommend this for single family home re-roofing, for example.

It’s often confused with modified bitumen because of the granular surface. They look the same, so a simple way to distinguish between the two is you will be able to tear off a corner with roll roofing, and with mod bit, you will not.

A waterproof membrane underneath is not required and flashing can either be roll roofing, aluminum or galvanized steel. I sometimes see more, but the maximum number of suggested layers is only one.

Roll roofing is considered a temporary solution because its life expectancy on flat roofs is about five years. You can be the beneficiary of a roll roofing system that last upwards to maybe ten years if the roof has more of a pitch than flat, doesn’t encounter severe weather and the nail heads are not exposed. Good luck.

I encounter the same issues with roll roofing as I do with asphalt shingles. Installation techniques will vary, but I would recommend concealing nail heads and using more than one layer. This will not always be the case from one contractor to another.




The following is my list I developed over the years of inspecting roll roofs:

  1. Cracked; usually the result of shrinkage from aging.
  2. Blistered;  may be a manufacturing defect or from old age, but can be the result of the use of too much cement on the seems at installation.
  3. Buckling or Wrinkling; will be areas to fail early because of wear, result of poor installation techniques by not allowing material to rest properly, or not cut into 12 to 18 foot lengths. I will also check for any contraction of the substrate.
  4. Open Seams; poor installation techniques. Best practice is to make sure seems are cemented in place and do not face up slope where they can trap and collect water.
  5. Loss of Granular Material: check high traffic areas. Causes are age, abrasion or a manufacturer’s defect.
  6. Fastener Problems; improperly installed or age related. Know which fasteners are intended to be exposed and which ones are not.
  7. Cemented Directly to Sheathing; this is poor workmanship. Will cause splitting.
  8. Mechanical or Physical Damage; foot traffic, animal activity, snow and ice removal, or just careless roofing work.
  9. Downspout Discharge; water will erode roofing material when upper gutters discharge directly on to lower roofs.
  10. Multiple Layers; meant to save contractor costs at installation but will promote uneven wear at the points where ridges are formed.
  11. Algae Discoloration; ultimately just an aesthetic issue usually caused by wet and warm conditions. Will not harm roof materials and I suggest do nothing.

While we are not proponents of this approach, I do find where a built up roof has had a roll roof installed over the top, it is used as a top coating of sorts. So a roll roof may be at the end of its life with a three or four ply “built up” roof underneath it. It’s always good to know what you have on your hands.



This is a nice roof option because there are no seams. PUF is applied by spraying and it forms a single ply roofing membrane. It is fairly impervious to physical damage, sun damage and moisture from the durable outer rubber coating.

First used during late 1960s, it had a number of problems that cropped up in the 1970s, giving it a bad reputation. Although some have failed prematurely, it’s generally accepted that these systems last for up to 20 years.

PUF is applied in two applications and will reach a total thickness of about one inch. The edges will not be as thick to allow for flashings and drains. A good contractor will achieve a very smooth surface when installing it to avoid a rough texture which allows moisture to penetrate the pin holes.

A good primer applied to thin plywood decking will help the PUF to bond to the substrate. Avoid wood plank decking as the thinner plywood performs better in this application.

The top coating is then applied in several thin layers. It’s an elastomeric coating, and needs to be applied quickly after the PUF is laid. The foam PUF is vulnerable to ultraviolet rays and will deteriorate unless it has this protective layer.

The coatings can be either modified asphalts, neoprene (Hypalon), butyl rubber, silicone, urethane, acrylic latex or epoxy. Each manufacturer of specific PUF lines will recommend which type of coating to use on their product. Just pay attention. Some may even recommend a primer applied to the PUF before the coatings are applied.

If I’m on a repair job that’s a PUF roof, I’ll most likely only need acrylic or urethane caulking materials to patch up minor repair jobs. You’ll need to match up the materials though; silicone coatings must be repaired with silicone, and so forth. And asphalt for repair is discouraged altogether. If the foam has significant cracking issues, I’ll use a backer rod for support before patching.

After having been on a number of these PUF roofs, here is the list I developed that breaks out all the issues I run into. This will help you as well:

  1. Leaks and wet insulation; occurs when flashings fail, deterioration or physical damage. Such as punctures or if the PUF separates from the substrate.
  2. Deterioration of the PUF; can occur if an improper coating was used, a manufacturers defect or there was a delay applying the coating.
  3. Cracking or splitting; there can be many reasons if this occurs, an uneven membrane from poor installation, roof deflection, not properly adhered to decking or the shrinkage of the material.
  4. Delimitation or blistering; caused by either shrinkage or the separation from the substrate. Delamination typically a result of the two pass application process.
  5. Ponding due to uneven application; poor installtion.
  6. Coating problems; bird pecking, flaking, pin holes, delamination, erosion, crazing, chalking, spalling.

If you need assistance with a polyurethane foam roof, check to see the last time it was recoated. Coatings need to be replaced every eight to fifteen years, depending on the manufacturer and your environment. You will have foam damage if you don’t.

Sometimes it may be pesky birds pecking holes in the material or I may experience slippage while walking the surface as a result of the PUF separating from the substrate. In any event, make sure you check the underside of the roof from below.


** So, my parting reminders would be flat roofs do not shed water like shingles on a pitched roof. They need to be watertight. It’s not a bad idea to have a professional out every so often for inspections; someone that will know what to look for to head off potential problems that lead to more expensive repairs or a total re-roof before it’s time.


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