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Replacing Flat Roof Areas - The Hot or Cold Process Debate...

Posted on 28 July, 2013 at 10:46
I realize its not as popular a debate as say, politics, guns or sports - But for those of you struggling with which materials are right for you to re-roof your patio, porch, garage or other flat surface roof, this is one debate that may affect you personally for a long time. And one not so easy to decide.
The truth is, its also a topic heavily debated even among very experienced professionals. In fact, two of my own installers with over 12 years of experience each, have opposite opinions of which they prefer! Fortunately, my experience trumps theirs, so I (along with the customer) have the final say. As with most debates, each side has their unique benefits and drawbacks. I'll list just a few of the most common processes of each along with some pluses and minuses that will hopefully help you determine which you can best live with.
Opinions vary widely, so please keep in mind that these are just my educated opinions, based on my 35 years of experience.
Also, if you are re-roofing an existing building- with very few exceptions- you should plan on stripping off the existing materials down to the bare wood. No low-slope product is warranted if installed over previous roof layers.
HOT ROOFS: Although there are several types of hot roofs available, I'll focus only on the two most common applications for residential and smaller commercial buildings.
1. Built-up Roof. For many decades, this was THE standard used for new flat roof installations. Its a process still commonly used today, though mostly in larger commercial and multi-unit residential buildings. But many roofers still swear by this as being the best process, even on relatively small areas.
We've all seen the hot tar kettle trailers being pulled down the road or beside some building emitting the smelly, hot tar fumes. This hot tar is used to fuse the base sheet, 3-5 layers of felt and the smooth or mineral-surfaces cap sheets together.
Some of the Benefits of this roof are;
Excellent track record- This process has endured over 150 years with great results;
Durability- Built-ups are designed to last 15-25 yrs and, coated regularly, can last even longer;
Cost Efficiency- Although the initial investment can be high, the cost over time will usually be much lower than most other roof types.
Redundancy-  All this means is that each of the multiple layers underneath provide added protection, should the layer above begin to break down.
There are some Drawbacks to this type roof, some are obvious. Here are a few;
Cost-The initial cost of these are usually higher than the other common processes, especially in smaller areas. But as noted above, if you factor in the years of service, that cost is reduced;
Inconvenience- Obviously, you'll have to put up with the mess, cumbersome nature and smell created by this process.
Maintenance & Breakdown-With these roofs, it's extremely important to inspect the roof periodically! Leaves, bird feces and other debris left to accumulate can break down and form acids which eat away at the asphalt. Low spots or pooling areas also need to be addressed as soon as they're noticed.
Poor Installation-This is one of the most common negative factors in these roofs. As you can imagine, most educated people wouldn't dream of doing this hard, dirty, low-paying work for a living. As a result, many companies are left with a workforce of less than the brightest individuals. Mistakes are routinely found but not always caught. Also, each climate and region requires different grades of asphalt and other materials. That's why its so important to know the history of the company you employ.
2. Torch-Down Roofs. These types of roofs became very popular during the early 90's, especially in our desert regions where where heavy, continuous rain isn't an expected concern. It's a process still commonly preferred by qualified professionals. Different grades are available, from a standard 10 year warranted to the 15 year "Rubber-backed" material offered by some manufacturers. Some of the Benefits of these roofs are;
Short-term Cost Efficiency- While still higher than the cost of cold-process roofing, the cost over time is still a bit lower over its 10-12 year expected lifespan.
Clean Installation- Because the adhesive qualities are built into the backs of these materials, even when heated, fumes are usually barely perceptible from the ground. Edges and corners have a much more consistent & neater appearance than built-ups. roofs.
Maintenance- If the surface on which its installed is fairly true, maintenance of these roofs is usually relatively minor.
A few of the torch-down roof's Drawbacks are;
Inability to withstand heavy, continuous rain- For some reason, most of us have found the overlapping seams' adhesives tend to break down during extended rainstorms. If gutters are used, its also imperative to keep them free of blockages so water doesn't back into the edge seams.
Installation nightmares- Obviously, a blow-torch near any wood or plywood surface can be a hazardous combination. These should be installed only by very qualified and very experienced individuals.
COLD PROCESS ROOFS: As with the hot roofs, there are several types of cold available. Again, I'm only going to focus on the most common.
1. Self-Adhered ("Peel & Stick"). These gained popularity during the mid-90's, with tales of hot roof contractors starting fires and the escalating insurance premiums that followed. The process of a self-stick roofing sounds much easier than it is and can be, if your slope is at least 1/2" per foot and guidelines are carefully followed- The two most important being the underlayment nail pattern and using a min. 18"- 100lb industrial roller to complete the cap sheet application.  Benefits are obvious;
Ease of installation- A properly trained contractor can install these materials fairly quickly so labor costs offset the higher material costs.
Durability- If properly installed, these warranties equal torch-down products.
Maintenance- Also virtually the same as torch-down (see above).
Some of the Drawbacks of this product;
Specific Installation Conditions- Weather conditions need to be just right- moderate to warm- for proper adhesion to occur. Also, substrate surfaces need to be true and free of divots, high or low spots, in order for the roller to function properly.
Inability to withstand sustained rains- As with the torch-down products (see above), these seams can be problematic in areas with high rainfall totals.
2. Cold-Process Rolled Roofing.  I don't want to spend much time on this process as its the most seldom used by professionals. This is the least costly process but also the one with the shortest lifespan of all flat applications. Installation can be performed a couple different ways: One with cold-process liquid used between the #30 underlayment and the cap sheet or the other with just plastic or the better, modified cement on all edges and laps. A few tips for these installations are;
Base sheet (felt) needs to be thoroughly nailed- Not just stapled;
Cap Sheet lengths should not exceed 12', with alternating vertical seams and lap end to end at least 4";
NO NAILS on the cap sheet, to allow for natural contraction and expansion;
All laps and edges need complete adhesion, but not so much cement that it reverses the slope in these areas.
Again, keep in mind that the above are my educated opinions and this is not meant to be a comprehensive study of every or any low-slope roof process. But I hope it does help some to understand the products just a little better while making a better informed decision on what's right for you.
Please feel free to Email me with any specific questions you may have regarding your particular situation.

Categories: Roof Repair Tips

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