The Polyurethane Foam Book

Chapter Three: Foam Roofing

by David B. South

Foam roofing is becoming more and more widely accepted. Coatings are the key; they are getting better. Consequently, earth-covered foam roofs have become extremely competitive. But the cost of the coating is not necessarily a reliable measure of its performance.

Case #1:

Our job: at a shopping center, cover the existing roofs of two buildings - one with 25,000 square feet and the other with 75,000 square feet. A coating supplier had convinced us that the best material available was a new, two-component, super-duper coating. We decided to use it over two inches of urethane foam.

Because we got this project in early fall, we knew that we didn't have much time before the first freeze hit. So, we contacted coating suppliers and found we could get enough of the new, super-duper component material to do the smaller building. That left us with the "ol' standby," acrylic, for the larger building. We informed the owner of the problem. He said he had to have the roof "now."

So we applied the dual-component material over the urethane foam as specified on the small building and the acrylic on the large building. The acrylic was guaranteed for one year; the dual-component was guaranteed for ten. Well, you guessed it. The next summer the dual-component coating failed -- miserably, all over the whole roof.

When a coating fails, it's a real mess and difficult to remedy. To scrub away the failed coating, we affixed steel brushes to blades of an electric-powered, rotary lawn mower. Then we recoated, using the acrylic. It held up extremely well. I believe that in the twenty years that followed, it's been recoated only twice and that's not bad at all.

Case #2:

Our job: A farmer asked us to coat his potato storage with urethane foam. He had a problem with air leaking through the bales of straw insulation and into the building. We told him that if he could get the dirt off the straw, we would do it. So, he removed the dirt, as best he could, and we sprayed two inches of urethane over the straw.

Spraying urethane over straw is a trick in and of itself. First, we sprayed the foam; then we cut away all the little straw hairs that stuck out. Finally, we sprayed the top inch to cover it and to form a total, water-tight seal.

Since the owner was short on money, he wondered what would happen if we just buried the roof with more dirt. We knew from tests and experiments that urethane foam doesn't degrade if it is covered with dirt, and certainly the sun can't get at it. So, we suggested he give it a try. That roof has been one of the most successful roofs we have ever applied. It never failed, even though the building eventually rotted out from under it.

"Gravel Foam" or Earth-Covered Urethane Roofing

A few years ago, some foam companies started talking about "gravel over foam" roofing. It made good sense. Of course, you can't cover a building with a steep pitched roof with gravel. But on a nearly flat roof, gravel stays on, and there is nothing better than covering the foam with gravel or earth. Obviously, the roof structure must be able to handle the weight.

The most successful gravel material is road base. Road base is usually a 3/8" minus crushed rock with all the fines left in it. In other words, it has not been screened like roofing gravel, just crushed. It is heavy dirt. Put 3/4 of an inch of it over the foam and it will protect the foam from the sun. If protected from sunshine, the foam takes care of itself. It will even stand considerable ponding water -- a disaster for most coatings.

For buildings that have the strength, an earth covering of sod usually works well. Four to eight inches of top soil and planted grass over the urethane creates a permanent roof.

Cold Roof Prevents Ice Build-Up

Icicles can be a tremendous hazard. They occur when heat rising through a roof melts the snow, causing it to run off the roof. At the roof's eaves where the air temperature is below freezing, the water freezes into icicles. Those pointy icicles can break off and fall on people and property. Often ice build-up tears off a roof's edges. In many cases, ice dams force water up over ridges and into buildings. A cold roof, as in the description that follows, will eliminate all these problems.

Here is a way of creating an extremely effective roof in cold country: turn 2 x 4s on edge, running vertically up the roof slope over a conventional plywood sheathed roof. Next, spray 2 to 3 inches of urethane between the 2 x 4s and over the 2 x 4s crossing them horizontally.

Place 1" x 6" sheathing 11 inches on center. Then apply hand-split shakes over the top of the sheathing. This leaves a small air space between the hand-split shakes and the urethane foam. The urethane foam is protected from sunshine by the hand-split shakes, and the air moving underneath the hand-split shakes protects them from rotting and ice build up. In mountain country, such a roof is called a cold roof. Rarely will the smallest of icicles form on a building with a cold roof.

Foam Roofing is Still Roofing

A word of caution: Don't buy a foam roof from people who don't know what they are doing. Being a foam applicator does not necessarily qualify the person to be a foam roofer. Exercise great care in selecting a foam roofer. Check references and involve suppliers. Most foam roofing is not warranted by the supplier unless it is inspected by the supplier. Most foam applicators do not have the financial resources to do re-roofs in case of failure. It is extremely important that everybody work together.

Another note of caution: Often, a foam roofer will be called to solve a roof problem after several others already tried to do so. A foam applicator who hears that he's the third, fourth or tenth person called, should take a real close look at the whole situation before getting involved.

Putting roofing on a bad roof deck is tough. If a roof moves or is water laden or has other problems, urethane foam may only be part of the solution. Most of the time, a problem roof requires vents to eliminate moisture, or it may need additional shoring for strength, or it may even require a total rebuilding from the deck up.

Metal Roofs -- Magic Material Answers

Magic material is a good name for urethane foam. If you have an old metal roof that is deteriorating, a couple of inches of urethane can usually make it all better. I suggest two inches because it is so much stronger than one inch. If you spray-in-place two inches of urethane foam on a metal roof with good slope, then apply a good acrylic coating on it, you solve all kinds of problems. You can even put urethane foam on a metal roof that is literally ready to fall in.

In fact, for one roof we sprayed, we had the workers carry a pole, under their arms, attached by a line to their safety harness. If they fell through the roof, the safety rigging would catch them because the pole would straddle several of the purlins. Looking back, that might not have been the most intelligent thing to do, but this customer didn't have the money to re-sheath. We felt very safe with the pole under our arms and, luckily, nobody fell through.

SELLING THE STUFF

Roof Coatings

If there is any drawback to urethane foam, it's that when left exposed, it becomes severely degraded by ultraviolet light. Whenever sunshine is allowed to impinge on the urethane foam, it destroys the bonding of the molecular structure, causing it to literally fall apart. If you spray urethane foam on a roof and leave it exposed to the sun, you can expect to lose about a 1/4" or more per year. A covering is a quick solution.

So, the immediate question is "What kind of covering?" Over the years, coatings to cover foam have evolved. It is readily apparent that urethane foam makes a fantastic roofing. The coatings are the real key to keeping the foam on the roof. In today's world, the urethane foam applicator has an arsenal of coatings that work effectively over urethane foam. Here are a few:

Acrylic and/or Acrylic Latex Coatings

Acrylic and/or acrylic latex coatings are probably the least expensive and the most popular roof coatings. They are water based, readily available and extremely effective when properly applied.

All coatings work best when applied over clean, dry -- and I emphasize dry -- non-degraded urethane foam. What does that mean? It means that the dew that falls in the late afternoon and early evening often causes the coating to debond or not bond as well as it should. It means that if the foam is left exposed for even 48 hours, the sun's UV rays will start to degrade the molecular connection of the urethane, making it less able to hold the roof coating. It also means that a roof that has been left uncoated, or one with a failed coating is extremely difficult to recoat. Dirt and water becomes trapped in the cell structuring, and the cell structure itself becomes sun damaged.

If possible, urethane foam should be applied in the early part of the day. If applied too early or too late in the day, the sun doesn't have time to dry the moisture on the existing roof deck. The roof will have a much better chance of being a good, acceptable finished product if the portion that has been sprayed that day can be coated, even with a light coat.

Since most roof coatings are water based, it is imperative they be applied in warm weather. Generally, 55 degrees Fahrenheit or warmer. Some coatings dry quickly and can take some frost -- most cannot. Most water-born roof coatings, if frozen the first night, will self-destruct. The manufacturer's instructions have to be strictly adhered to in applying a roof coating.

In addition to the acrylics, a large family of other elastomeric coatings is available. The term “elastomeric” means that the coating stays elastic after it is cured. But elasticity means different things to different manufacturers. To some, it means it will have a 10 percent increase of length without breaking; to others, it means it will have a thousand percent increase when stretched. Generally, a 50 to 100 percent elongation is all that is necessary.

Urethane coatings of many types work well for roof coatings. Poly Urea (best known as pickup bed liner) can be used, but it may have a stable color problem. Silicones have had some fabulous successes. All of these are more expensive. But trying to fix a failed roof is really expensive.
Often the “foamer” is called in after other roofing methods have been used and failed. If you receive the call to reroof be sure to ask about what was done in the past. That history will give you a clue as to what you are up against. Often the existing roof is too flat or even has duck ponds -- areas that hold water without draining after a rain. Ponding water is extremely hard to deal with. Most coatings will self-destruct in such conditions.

At times, you may encounter an old roof that is saturated with water. If you run into one of these, be sure to put in roof vents.

Roof vents allow water and condensation out without letting more rain in. If you make the mistake of simply spraying over an existing saturated roof, it will bubble and blister when heat begins evaporating the moisture. In extreme cases, a bubble or blister can be as large as a dog house.

Believe it or not, gravel foam will do better than most coated foams for duck ponds and flat roofs.
One inch of foam is rarely enough for a good job on a roof. I like to use 2 inches. It is not as likely to leak, it has much more strength, and the extra pass or two provides added protection. Three pound density is the best urethane for roofing. Often 2.5 or even 2 pound is used. They work, but foot traffic on the roof is much harder on lighter foams.

At times, the foamer can build in slope to get water out of duck ponds and off the roof. This is always worth considering. Use a board or a string to get the slope indicated. Then spray in a pass to that grade and fill in between the guide passes. You will figure out what is best for you.

Where a roof meets a parapet, the tendency is to “just spray up the corner.” Be careful here. There may and often is movement at these junctions. So, what you need to do is spray in a “hinge.” This is done by covering the junction with a piece of paper or plastic that will keep the foam from sticking to the roof or the parapet.

Fold the paper at a 90-degree angle and lay it so one leg goes up the parapet and the other leg goes onto the roof deck. (I use about 9 to 12 inches on each leg.) Then spray the foam over the paper so that the foam sticks to the paper but not to the roof or parapet wall. That creates your hinge.

Foam has the strength to span the distance, and it will move or hinge if there is movement between the parapet wall and the roof. Obviously, the hinge is very important. A junction that is not hinged but sprayed solid will develop a crack (leak) when movement occurs.

Foam roofing pays for the owner. Often within a short time, the energy savings within the building pays for the new roof.

In the winter, I would often fly my plane over a town after a light snow. It was very easy to spot buildings in need of insulation. The snow would melt off them in a hurry. If you take pictures, then you really have a sales tool when you call on the building's owner.

Leaking roofs account for more than 50% of building complaints. So when you are doing a roof -- foam or otherwise -- be sure to do it right. The cheap job is quickly forgotten if the roof leaks. And then you own the roof. On the other hand, be very careful about money being the measure. Many expensive roof jobs are not any better than a more modest one. But cheap jobs rarely work out. 
Do the job right and charge enough to service the finished roof. You will be getting a chance to do a lot more roofing as the word gets out that you do quality work.

Where do you look for roof jobs? Trailer courts are an excellent place. These jobs are simple and easy if you do your preparation carefully and thoroughly. You might consider having financing in place for the owner by prearranging financing with a finance company. Then you can simply check with the finance company and sign the job up. Small towns are full of commercial buildings with nearly flat roofs. Call on the owners. You will be surprised how many will want theirs done. Point out the energy savings. Many roofs can be sold on insulation alone. 

Remember: big jobs are fun, but the real money is made by doing a job nearly every day. If one of the smaller jobs has problems, it won't sink you. If payments are not on time, you can live for another day. Small jobs are great -- especially if you are able to move nimbly. 

Get yourself a website and an email address. Always pass out business cards that tell what you do. Make and distribute fliers. They do not have to be expensive. Use black and white copies for distribution throughout trailer parks and small towns. Get involved in your community. And always, always return calls.

Always remember: price is a major factor in deciding what is the best value. So don't be the cheapest unless you have to bid the job. Then be extra careful. You may make a mistake and actually get the job.

Download the whole book as a PDF

Table of Contents:

• Introduction: by David B. South
• Chapter One: What Is Polyurethane Foam?
• Chapter Two: Spray-in-place Polyurethane Foam
• Chapter Three: Foam Roofing
• Chapter Four: R-value Fairy Tale
• Chapter Five: Fire and Foam
• Chapter Six: Application -- Substrates, Water and Blisters
• Chapter Seven: Foam and Safety
• Chapter Eight: Foam Equipment
• Chapter Nine: Starting a Urethane Foam Business
• Chapter Ten: Selling Polyurethane Foam for Use in Homes
• Addendum: A History of Polyurethane by Nick Clark

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