Flat Roofing systems: The purpose of a flat roof or any roof for that matter is to keep your home or building safe and dry. The roof MUST protect your investment from the elements such as rain, snow, and even the sun’s heat.
However, many flat roofing technologies on the market today have some major, inherent drawbacks that have origins in their design. In fact, most flat roofs fail to serve their main purpose just a few years after they are installed.
You are presented with so many choices for a flat roof and every roofing contractor will tell you their product is the best.
But which one do you choose and how do you know that you are getting the best deal? Here we have summarized the most common and ‘popular’ flat roofing choices. You can be the judge and decide which is best for you.
Benefits of flat roof construction:
There is a common misconception among many home-improvement contractors and residential builders / architects that flat roofs = problems.
The truth is that flat roofs are very convenient, easier to build, and cost less than pitched / sloped roofs. In some cases, a flat roof is the only way to go, for example, when you have a large size building.
Building a reliable pitched roof in those cases will require extra engineering to accommodate for additional structural weight.
Flat roofs are also convenient for installing large HVAC equipment that otherwise would have to be installed on the ground. You can also use flat roof as a roof-top deck, patio or penthouse. Green roofs are also gaining popularity with environmentally conscious companies and organizations.
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When you compare all the construction costs and environmental benefits, flat roofs by far surpass any sloped roof, for which the roof products of choice are oil-based asphalt shingles. These asphalt shingles end up in our landfills every 12-15 years, and yet more and more of them are produced.
Limitations and Disadvantages of flat roofing:
Flat roofs also have a number of disadvantages. The main one is the fact that there is no slope and all the water/snow sits on the roof. While water can be taken care of with proper drainage, snow will sit on the roof until it melts. This requires the engineers / architects to implement building components with a higher structural load. Another disadvantage that haunted flat roof installations for over a century is ponding water. Until the invention of single ply membranes such as an IB roof, there was no effective and economical way to eliminate the leaks caused by ponding water. That had to be taken care of in the initial design/construction stage. Creating a slight pitch and multiple drains was required, and still ponding water caused over 75% of all flat roof leaks.
Now the ponding water problem is solved by either implementing a slight pitch to the roof – such as in ‘space metal buildings”, using tapered insulation to direct water flow toward drains and with the creation of IB PVC / CPA roofing with hot-air welded seams, ponding water is no longer a problem in small quantities. It is still necessary to have adequate drainage system, since a lot of ponding water can cause structural damages to your house or building.
Types of flat roof: Modern and Outdated roofing technologies.
Outdated (Multiple-Ply Roofs) – some are over 100 years old:
- Build-Up Roof (BUR)
- Tar & Gravel
- Bitumen (Modified Bitumen)
- Rolled Asphalt (usually a “single-ply” install, sometimes uses tar-paper as base ply)
Modern (Single-Ply Membranes)- created within last 30 years:
- IB Roof (PVC roofing) – IB PVC roofing membrane is one of the best low-slope and completely flat roofing products available, and that is precisely the reason why we only install IB roofs. With over 30 years of spotless reputation and leaks-free performance in many different climates – from Alaska’s frigid north-lands to Hawaii’s tropical paradise, IB roofs are protecting the buildings and everything inside, without a single material failure since 1978.
IB roofs still feature the same chemical formula as its original design, and with hot-air welded seams, will maintain complete water-tightness over your roof. - Epdm Rubber Roof – a widely used flat roofing material, mainly popular among contractors because of its low price and no special equipment needed to install the rubber roof. Still, rubber roofs are very prone to leaks, as the seams are glued together, and adhesive tends to break down within 5-7 years. Also in the residential roofing market (and not so much in commercial) there are too many contractors who will install rubber roofing products without proper knowledge and training. As a result, we often go to rubber roof repair service calls to fix problems caused by poor workmanship, often on fairly new roofs.
- TPO Roofing – a single ply thermoplastic roofing membrane similar to PVC roofs from a first glance. But as you start digging, you’ll find numerous problems with TPO roofs, mainly as a result of manufacturers skipping on adding important ingredients into formulation of the TPO membrane, and as a result, quietly scrapping as many as three major generations of the product.
- SFR – Sprayed Foam Roofing (not a single-ply)
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Part I: Inferior and outdated flat roofing technologies
These are very common on older buildings, although many newer buildings also have these systems installed. They are rarely installed on any commercial building today. However, they continue to be produced, and many roofers still install them on residential and small commercial roofs. This is particularly due to their low cost of material, and roofers’ lack of experience with BETTER solutions. It is sad that there are some decent roofers offering such an inferior product to their customers. I often hear something along the lines of: “I’ve been doing ‘torch-down’ for 20 years, and it is the best” – very sad – so we will briefly describe them, without getting into details.
BUR / Tar & Gravel / Torch-down: Multiple-ply roof where each ‘tar-soaked’ ply is applied with a torch (yes, open flame on your roof!), or hot mopped (preheated tar transported to the roof and applied with a mop). Gravel goes on top of this ‘sandwich’ mainly as a protection layer from foot-traffic and sun’s devastating ultraviolet rays. There are many deviations from the above procedure, but they are all within a close range of similarity.
Modified Bitumen: It is also applied with a torch in a similar manner described above. It is however a different material than tar. Modified bitumen has rubber and elastomers added into the formula, so it is stronger and more flexible.
Rolled Asphalt: Similar to asphalt shingles – tar paper is saturated in asphalt, with crushed stones glued on top of it. Rolls are installed in an overlapping pattern, with cold-mop application and nails to attach it to the roof deck. Overlapping seams are sealed with tar.
Problems associated with flat roofs:
The nature of flat roofs’ problems is just that they are flat. Water does not run off the roof. Proper drainage must be in place to get rid of water accumulating on a roof. Usually older roofs are not leveled, so water puddles will appear here and there after every rain, and just sit there until it dries out. This is called standing or ponding water. Most roofing systems were not designed for ponding water. In fact, most manufacturers of the roofing systems on the market today, will void out the warranty if there is ponding water on the roof (we will get to this issue later). Other major problems for flat roofs, are penetrations such as skylights, vent or exhaust pipes, chimneys, roof hatches, drains, etc. However the biggest problem with flat roofs is the seams, because they are the most common areas where leaks occur.
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Seams:
Seams exist on every flat roof (except tiny ‘6×10 porch-type’ roofs, which can be covered with a single sheet of roofing membrane), and are usually put together with some sort of adhesive. After a few years the adhesive breaks due to severe weather changes (here in New England, temperature can change 25 degrees or more, in a matter of one day). Another major factor affecting seams’ adhesive is condensation, which always occurs underneath the roof covering. Condensation expands both in the winter and summer. The most dramatic expansion of condensation happens in the winter time when water freezes, expands and breaks the seam. The same happens to our roads. Think of all the potholes you drive over. Those too were caused by water freezing. In the summer water heats up and also expands. When you see bubbles on the roof surface, it is the water vapor lifting the membrane. The third major factor is actually quality of workmanship and the adhesive itself. For different roofing systems the process is different, but most of them share the same shortcoming – the need for using adhesives, be it glue, hot tar, liquid resin, etc. Adhesives are also required to flash any roof penetrations listed above, but here the workmanship is actually more of a factor than the adhesive.
Conclusion – let’s get real.
It is a shame that in the 21st century we are still using 19th century technology. Even more so, because nearly 50% of roofers in the on-line construction forums will advise you to choose a clearly inferior roof. These heavy and dirty roofs, heat up to 170 degrees and make your AC run like crazy in the summer. These very roofs start leaking prematurely and are impossible to fix. Why would some one acting in good faith actually recommend these? The answer is obvious – they don’t know any better. Fortunately there is ONE modern, technologically advanced flat roofing solution available on the market today – IB Roof. In fact, this solution has been around for a few decades now, and has a proved track record of 30 years of leak-free service!
Read more: Part II – Single-Ply Roofing Membranes – PVC, TPO & EPDM Rubber Roofing.
My brother recently purchased an older home. He noticed that there was a flat roof installed on that particular home, and thought he would have to get a pitched roof installed. I didn’t realize that flat roofs are often convenient, easy to build, and cost less than sloped roofs because they can accommodate large areas without needing extra engineering. That’s something I’ll definitely have to share with my brother.
sir, we have leaking problem in our roof. how fix and ready and you have any plastic sheets with one side paste type please reply as soon as thank you sir.
leo you are obviously a junior roofer.there is a tool called a graual embedder that is basically a heated roller that embeds the granuals into the to sheet allowing the modified bit to come to the surface crating a 4 inch wide smooth strip on the edge of the sheet that allows for counter flshing curbs and walls ect.if you have never seen or used one of these then you are a fly by nighter and shouldn’t be giving any type of advice when it comes to installing a 2 ply mod bit application.in the future STFU and don’t offer advice or comment on something you know nothing about.
What part of the country are you in Leo? It’s unfortunate that people like you are dishing out information on roofing.
You mentioned coal tar roofing not lasting and “West Virginia looking”
men using a kettle as if it was a bad thing. Those men (despite appearance) are more than likely true craftsmen roofers (something you don’t need to apply PVC or foam roofs – you can go to labor ready for your crews). And, coal tar pitch roofs have the longest lasting performance track record of low slope roofs (the correct terminology – not flat).
As far as IB, I work with a lot of architects over the past 16 years and not one of them specified this system. I believe one ol’ man in a truck tried to substitute IB and the architect mentioned he’s not putting a Home Depot roof on a school that expects to be dry for the next 30 yrs.
There is a place for your systems – on strip malls, dollar stores and for building owners that want to flip their property.
I would urge anyone who wants to find out facts on performance to go to the NRCA Low Slope Material Guide. It lists all manufactures, what they cover under warranty and their exclusions.
Remember contractors go in and out of business; so do your research. Don’t let a $200,000.00 contract (example) to an applicator that has a net worth of $150,000.00. Those guys tend to disappear.
If your legitimate business, talk to an a architect. They will add 6% to the job, but will keep the roofers honest, i.e. keep the roofers honest, bidding apples to apples.
If you haven’t been through the roofing racket before, when you hear recover, TPO, PVC, foam or EPDM run for the hills. Chances are all you’ll hear is “we are cheap, space age material, blah blah blah”
I just had to come up with a new term to describe your outdated idiocy. Architects have been specifying EPDM for over 15 years. Get with it, Labor is the most expensive thing in construction. That shit you do takes several more steps (man hours) that the new stuff. There’s nobody that could attempt to be competitive today using those archaic methods. Why would someone use an old asphalt system when modern EPDM, TPO, PVC etc. manufacturers provide and honor 20-50 year weather tight warranties to certified installers? It doesn’t take THAT much for a reputable company (even small) to get certified in Firestone or better yet Carlisle (the best IMO).
Andrew, I’m not sure how you refer to with outdated idiocy … but 1) I have always said that BUR / 4-ply Modified Bit is junk, and rubber is also junk. 2) Also “Architects have been specifying EPDM for over 40 years” (not 15 years as you say)
3) EPDM does take a lot more man hours to install than PVC, because you need to clean and prime seams, and use extra tapes, and fully adhere membrane, etc… but length of installation has nothing to do with fact that most EPDM roof will leak years before PVC …
In any case, you confuse me with your outburst, because you don’t specify who your comment is aimed at 🙂
But for the most part I do agree with you …
Cheers
We just put on a flat roof new install put the tar paper down, stapled per avice. Now when we rolled on the tar coating the tar paper bubbled everywhere when dried. What’s the answer to this problem or advice.
where can I find out about GAF rolled on roofing material -in four foot roles for flat roofs ? goes on top of 1/2 white aerospace material applied in sections. Home depot installed it but got conflicting info on its longevity ( 10 year warranty )
Any supply house carries GAF. Try Home Depot too; I believe they carry GAF, but it may be TAMKO (not much difference)
Hello, I live in Texas and I put elastomeric roof coating over a old 40 year old rubber roof and three years later after we had record heat here they call me about a leak and when I got there I saw bubbles or blisters in places all over the roof. What caused this? I used roof-guard 700
Hi Dean
I have no idea why your coating has blisters, but my best guess is:
1) the roof was not cleaned properly before application of coating product – this causes delamination of coating from the rubber roof (substrate).
2) the coating thickness was insufficient (I believe it should be 30 mil minimum DRY thickness).
3) Most contractors who install small coating jobs, do so infrequently, thus do not have much experience with it. This might not apply in TX, as your climate is much hotter than here in MA, so coatingins are more popular.
4) Ponding water will damage coatings – break them down, and make coating separate from the substrate. This does not apply to ALL coatings, but to most.
Additional fact is the actual coating material AND the application (installation). There could be so many additional reasons for the coating to go bad.
HEAT wave – I don’t know if the heat was the factor in your coating going bad – in theory it shouldn’t have, but I am not really familiar with your particular material. Keep in mind – there are over 50 coating products on the market (maybe over 100). They are all different, and it’s impossible to know much about all of them.
I am right now dealing with a leaking roof that has a coating on it and coating is also blistering and bubbling, and in ponding areas is coming off the rubber. Additionally, the coating make it difficult to repair this roof, because the adhesive must be applied over coating – not directly to the rubber, and it does not hold up well.
Basically, from what I’ve seen, and in MY PERSONAL OPINION, people should avoid using a coating on membrane roof (i think it’s ok to use on metal roofs). Coatings will create more problems than they solve, as they make it very difficult to repair a roof, if there is a leak. Also most coatings are not water-proofing material, though they are advertised as such.
Leo.
Leo,
You say:
granular surface cap sheet. How do you expect to have proper adhesion / contact / bond between two sheets, when there are granules in between them.
I thought that a cap sheet only had granules on the
top surface. You seem to say that it has granules
on the bottom?
thanks,
bill
Hi Bill,
The granules are only on the top, and when field seams are done, there is a 3-4″ strip on one side of Mod-Bit roll, that has no granules (for better field seams adhesion).
But when it comes to field flashing / detail work / termination at the wall, etc., that strip is usually not present, so granules are between the overlap. This is especially critical for skylight / chimney / curb flashings, as shown in this picture:
Therefore in real roof settings, the seam on a modified bitumen roof, often has granules in it, which reduces the longevity of such seam.
Uhmmmm, have you applied a mod bit roof. They do not have granules on what is referred to as the selve edge or what you are calling the seam. Word of advice to roofers that want repeat business, do more research than reading this site
A properly installed coal tar pitch built-up roof will easily last 30 years or more. It may be old technology but it is by no means outdated.
Properly installed shingles roof can last 30 years – but how often does it happen?
Also, there are many limitations to it. You need a positive slope to the roof, and proper drainage.
I think built-up is definitely outdated – but also we are talking about a few types of flat roof at once – built-up can be tar + gravel roof or modified bitumen. These two are completely different animals. Mod. Bit. can be cold applied or torched, and I have issues with both methods, ans especially with the granular surface cap sheet. How do you expect to have proper adhesion / contact / bond between two sheets, when there are granules in between them. Yes it hold for some time, but not 30 years!
Coal tar pitch – man really? when was the last time you’ve seen a kettle? I last saw one 7 years ago – so two dudes that looked like miners from W. Virginia where doing magic tricks on a roof of a store. 3 month later, a new PVC roof went up on that roof… So much for hot tar roofing 🙂
Properly installed shingles roof can last 30 years – but how often does it happen?
Also, there are many limitations to it. You need a positive slope to the roof, and proper drainage.
I think built-up is definitely outdated – but also we are talking about a few types of flat roof at once – built-up can be tar + gravel roof or modified bitumen. These two are completely different animals. Mod. Bit. can be cold applied or torched, and I have issues with both methods, ans especially with the granular surface cap sheet. How do you expect to have proper adhesion / contact / bond between two sheets, when there are granules in between them. Yes it hold for some time, but not 30 years!
Coal tar pitch – man really? when was the last time you’ve seen a kettle? I last saw one 7 years ago – so two dudes that looked like miners from W. Virginia where doing magic tricks on a roof of a store. 3 month later, a new PVC roof went up on that roof… So much for hot tar roofing 🙂
I live in the San Francisco area. I have what they call an Eichler home with a slightly sloping roof. The slope is so marginal that that is just above code for shingles and I’ve seen shingles on only one or two homes. The original roofs were tar & gravel but most contractors are using peel and stick or foam which is starting to gain popularity.
The weather here is a hot dry summer with a moderately cold wet winter.
What’s your recommendation for a roof in my situation?
Thanks….John
If I’m doing a tear off re-roof of a flat commercial roof, how does the cost compare between replacing with a BUR vs. replacing with a single-ply with higher reflectance?
How do you finish off the sides of a flat roof construction? What materials would finsih off the eave and the roof edge?
Hi Joel,
It depends of the roofing material that you are using. However, it is typically a pre-formed metal drip edge, and the roofing material is sealed to it.
On IB Roof, we flap the roofing membrane over the edge, install IB PVC-coated drip edge, and then weld a cover strip (5″ wide roll of PVC membrane) to the drip edge flange, and to the roof itself. Here are two videos demonstrating this process:
I skipped one video in the middle, which demonstrates installing unreinforced flashing on the joint between two strips of drip edge. It is shown in the beginning of second video.
Leo
@Former Roofer
I started using single ply (granted I used TPO but I will get to that in a bit) after I purchased a property that had a building with a singly ply PVC Durolast roof that I was extremely impressed with. It is over 20 years old and I see what you are talking about with hail welts on them. I am pretty sure that’s where they come from, they look like little spider web circles dotted about. I think once a year maintenance is not too much to ask for a roof, where you just put a blob of M1 on the cracks.
I was able to find a roll of PVC to do my own repairs on this roof. On an adjacent building, I used TPO because at the time I thought it was basically the same thing. After doing the PVC roof repairs with PVC the difference is night and day with the material. PVC is far superior material and as far as I can tell it is much more durable and longer lasting than TPO. I will never use TPO again I’d rather wait to have some PVC rolls shipped from out of state like I had to do with my last one.
Anyway I didn’t mean to go off on that tangent but I am not sure what state you live in that you are having a lot of trouble with your single ply. I live in Texas and I am going to be using PVC for my future roofing projects. Besides I know a lot of “real roofers” that use single ply… You should expand on your discontent with pvc roofing
what does IB stand for?
Where can I buy it? I have the men to do the work.
Hi H Roland,
IB stand for Industry’s Best Roof Systems, and we use IB as synonym for their PVC roofing material.
As far as getting it, and having men to do the work – I feel that your men will really have to be equipped with and learn to use hot air welding equipment first. PVC roofing requires considerable investment in tools and equipment to start installing. If you feel you are ready, then contact your local IB rep – he will decide if you and your crew can install IB, but you all will have to get certified first. Good luck.
You are scam artists. You don’t wonder why real roofers won’t apply your product. I feel sorry for any business or person that uses a shotty single ply people like you. Go visit one of your roofs after it hails. They’ll look great and leak like a dish towel.