Spray polyurethane foam (SPF), a building material with notably high performance, is widely used as a roofing solution. With benefits including versatility, thermal insulation, resistance to inclement weather cycling and storms, strengthening of the building envelope, durability and long life, spray foam has risen in popularity among builders and roofing contractors alike.
The main purpose of a roof is to protect the structure underneath it. As a roofing material, closed-cell SPF is both a thermal insulator and a protective one. The lightweight roofing material is the best choice when:
the substrate of the roof has many penetrations.
the roof deck is unusually shaped or configured.
the roof is being installed on a structure located in an environment that is prone to severe weather.
you need a lightweight option.
an application with an inclined slope provides more drainage capabilities.
keeping the existing roofing is preferred.
Our process for reroofing with spray polyurethane foam is detailed below. Norris Spray Foam is a leader in foam reroofing technology in Texas and we invite you to inquire about the most economical and long lasting reroofing choice for your building.
Dallas Flat Roofing
Spray foam has become increasingly popular in the past few years with builders across Texas as a preferred insulation method. The spray polyurethane foam is also used as a roofing material, but that is not widely known.
For more than a quarter of a century, spray foam roofing has mostly been used to reroof existing flat roofs on commercial and residential buildings.
Norris Spray Foam sprays foam roofing in Texas for both residential and commercial projects. Commercial buildings with flat or low-slope roofs are common in our area, and many of them have old, leaky built-up roofing, so re-roofing commercial buildings is a significant portion of our business.
When you reroof with spray foam, you can:
- Save up to 50% of the cost of a tear-off and conventional reroof installation
- Permanently seal leaks that have increased in number over time
- Save on energy costs as spray foam provides superior insulating properties which TPO and EPDM roofing don’t have
- Minimize weight load on your roof compared with reroofing alternatives
- Extend the life of your existing roof 20-30 years
The following explains the process of reroofing a commercial low-sloped or flat roof with spray polyurethane foam starting with the material and finishing with the gravel application.
Polyurethane Material FAQs
The plastic polyurethane material was developed prior to World War II. In the 1970s, U.S. military officials recognized its value as a lightweight, waterproof, durable, all-in-one insulation and all-purpose covering. Its use has expanded to the private sector since that time.
Polyurethane foam is made by mixing two liquid components at a ratio of one-to-one inside the tip of the spray gun specifically made for these components. As the mixture exits the gun, tiny bubbles form as a result of isocyanates, polyols, catalysts, and a non-ozone-depleting blowing agent. Bubbles form until the material has inflated to 30 to 50 times its original mass.
Denseness of the Closed Cell Roofing Foam
Roof foam has a density and permeability that makes it different from polyurethane foam which is used to insulate walls.
Open-cell spray foam structure is extremely porous and soft. Closed-cell foam is impermeable to moisture, and has a dense central core. Roof foam is more dense than regular foam, and it is strong enough to walk on without damaging it. Because the system is closed-cell, neither air nor water pass through, and it also acts as a vapor retarder.
Foam as Roofing
Foam roofs have their pros and cons, as do any roofing system. One of its most notable features is its ability to adjust to contours that are difficult to flash and waterproof with conventional materials.
A list of the other features the product offers, as well as its limitations can be found below.
Despite the rigid insulation above the sheathing or the batt or blown insulation in the cavity below, many roofs permit significant heat gain.
In addition to this, most built-up roofs act as giant solar heat collectors.
On the other hand, SPF roofing resists solar heat gain. It can be both Cool Roof- and Energy Star-rated with the right coating. The R-value of roofing foam is about R 6.5 per inch of thickness, so a typical application is around 1 1/2 inches thick (though certain parts of the roof get more foam than others).
Reroofing With Spray Foam – Elevation Measurement Across the Roof
Our laser level measures elevation at various points on the roof and records the data. The technician uses the map to identify low spots so he can build up those areas with a thicker layer of foam and prevent ponding.
Long Service Life
Foam that has been cured can maintain its flexibility over time and is chemically quite stable. UV light is the only thing that can damage it — besides being punctured by a sharp object.
Properly applied and maintained SPF roofs should last for generations. UV-resistant top coatings need to be recoated every 10 to 15 years. Upgraded systems can extend the recoating cycle to 20 years.
Unlikely to Leak
Roof leaks occur most often when water enters through an open seam or joint in the roofing material. Water can get into the roof from one place, migrate horizontally between the plies, then come through the ceiling at another location if the roof has several plies, such as the case with BUR. Leaks of this nature can be difficult to find and to fix. An SPF roof is a solid, one-piece system with no joints, seams, or plies. Nothing will leak through it unless it has a hole all the way through it.
SPF is a great option for sloped roofs, but since it’s not as aesthetic as shingles, people mostly install it in low-slope areas where it won’t be noticed.
Additionally, foam isn’t suited for installation year-round in all climates. The roof needs to be absolutely dry and within a range of 50°F at the time of application. Also, there must be little or no wind at the time of application.
Initially, installing a spray-foam roof is not the cheapest option, but after it has been installed it is more energy efficient and has a longer, more trouble-free service life.
The Complete Process
1. Inspecting the Existing Roof
The first thing we determine when we inspect an existing roof is whether it should be stripped or swept. It’s surprising how many multiple-overlay built-up roofs we find — even though they impose an excessive load on the structure and in some areas aren’t allowed by code. In cases where there are multiple roof layers, it’s best to strip back to the sheathing. This lightens the load and provides a smoother substrate for the foam. If there is only a single layer of roofing, it’s often possible to sweep off the gravel, prep the surface, and apply a layer of foam. This allows the building owner to avoid the mess and expense of a tear-off, yet still end up with a lighter roof.
When we inspected the roof of the home shown on these pages, we found leaks, ponding, and an area with rotted sheathing. But since the roof was just one layer, we decided to repair the rot and install SPF over the existing membrane.
Older buildings tend to sag and settle, resulting in ponding. With many roofing applications, this problem is hard to fix — but with SPF, low areas can be filled with foam.
To find low spots, we use a laser level to map the “topography” of the existing roof. We measure the elevation at various locations and draw maps so that the applicator knows where the high and low spots are so that he can adjust the amount of foam.
On the other hand, scuppers and drains should be replaced so the foam will have a clean surface to attach to. Our roofer will cut away the membrane around the existing drainage system. The old fitting will be replaced by a new one that leads to the downspout below. After the new fitting is nailed to the deck and primed, the foam will be applied.
If we merely applied the same thickness everywhere, water would still pond in low spots.
3. Prep Work
Especially when foam is being applied over an existing roof, the prep work is extremely important. Roofing contractors have been known to show up, spray foam on the roof, coat it, and leave it. Such an installation may provide relief from leaks for a short period of time, but the building owner will experience problems over time.
In order to do a good job, the roofer must prepare the surface, repair damaged sheathing, replace sheet metal and flashings when necessary, deal with drainage problems, and apply protective coatings and foam correctly.
4. Surface Prep
To establish a solid bond, all loose material must be removed from the existing roof. The loose gravel must be removed by sweeping and hauling it away. There may be built-up areas with asphalt and gravel. If that material is coming loose, we use a tool to scrape it off.
We clean the membrane by sweeping up any accumulated silt, then blow the residual dust off with a gas-powered blower. We power-wash the roof if it doesn’t leak.
Even though sprayed foam is highly adhering, it is still a good idea to prime the existing surface. We spray a special primer on the surface of the roof using an airless sprayer.
5. Sheathing Repairs
We will replace or strip the framing and sheathing if necessary if we find rot on a roof.
If the building code does not require a Class A fire rating, we prime the sheathing and then apply foam.
We normally nail a fiber-impregnated gypsum board over the patched area before priming and applying foam to achieve a Class A rating.
6. Metal Work
We may reuse the existing sheet-metal vents, but we always install new foam stops along the roof edge.
7. Edge Metal
The edge of a roof is normally one of the weakest points. For reinforcement on the roof edges, we use a metal foam stop that’s hemmed and kicked out at the lower edge.
8. Vents and Fans
If we strip the roof, we may need to replace the existing roof jacks. If we are simply doing a sweep and the jacks are still in good shape, we leave them in place and cover them with foam.
All unsatisfactory vents are replaced.
Existing roof-mounted vent fans can present a challenge because the foam could elevate the surface of the roof sufficiently for water to run into them. We install a custom-made vented cap over the top of each fan and build a curb around it. The old fan will remain in place and may be serviced or replaced in the future.
Don’t allow a roofer install foam in the roof fan without considering the likelihood of a leak or the potential for a need to replace the fan someday.
9. Drains and scuppers
Most of the structures we work on have scuppers or metal dropout drains that connect through the overhang to a downspout below. When we replace the edge metal, we also replace the scupper linings. Also, we cut out and replace the dropout drains. It is possible that they are rusting through, so we need a new, clean surface for the foam to adhere to.
Under certain circumstances, foam can self-flash when lapped up against adjoining vertical walls. Most of the time, though, a counterflash is needed at the roof-to-wall junction to ensure water located behind the wall cladding is redirected onto the roof.
Skylights are a known source of leaks. Frequently, we raise the curbs so the skylight is protected above the foam. Never allow a roofer to foam on the skylight flange. The skylight should be easily removable from the roof so that it sits above any water or rain splash. During the reroofing process, we remove the skylights, build up the curb (if necessary), foam up to tops, and then install the skylights over foam weatherstripping. The roof foam does not require curb flashing or cant strips since it is self-adhesive and self-canting.
12. Equipment Curbs
Heating and air conditioning systems are often installed on flat or low-slope roofs. Using sleepers applied directly to the roof is asking for trouble and should be avoided at all costs.
Equipment should be put on boxed curbs with sheet metal caps. The equipment is separate from the roofing system so it can be replaced without damaging the roof, and the roof can then be maintained without moving or removing the equipment.
13. Spraying Foam
When the preparation work is completed and the weather is right, the foam can be sprayed. The deck must remain dry, and the air should be warm. There should not be much wind. Moisture could disrupt the chemical reaction that forms the foam, resulting in a degraded product.
Wind can increase the amount of overspray and affect the texture of the foam. The surface must be warm (above 50 °F).
Our technicians are willing to stop operations when the conditions are not favorable.
We mask skylights, shingles, sidewalls, etc., to prevent overspraying. When we mask the edge metal, we can apply foam up and onto the edge. We spray the details first, like the edges and the roof jacks, and then we spray the field. We can walk on the foam in a few minutes since it cures quickly.
14. Grinding and detailing
The foam is then brought flush to the edge metal with a grinder, so it slopes smoothly into drains and scuppers. We grind down the foam where it looks too high or is awkward. Detailing involves the use of polyurethane caulking at critical points where the foam meets another material.
15. Coating and Granules
An elastomeric coating is then applied to the foam to protect it from UV degradation. If the foam didn’t have this coating, it would eventually wear out.
To achieve the specified 24-mil to 28-mil coating, two coats are necessary and it takes about 3.0 to 4.0 gallons per square. Due to grinding, we precoat any areas that have been ground.
16. Base Coat
This type of coating is applied like a heavy paint; we brush in the details with a brush or roller, and spray the field with an airless sprayer. The base coat is tinted, so we can tell if we miss some spots with the top coat. The tint also shows through when the top coat wears out, so it functions as a recoat indicator.
17. Top Coat and Granules
After the base coat has cured (usually overnight), we spray on a top coat; before the top coat dries we embed a layer of mineral granules.
Besides creating a more uniform appearance, granules offer several functional advantages.
they speed up evaporation of rooftop water
they resist abrasive wear
they stop birds from pecking at the foam
A superior-quality granule provides additional resistance to UV rays. A typical SPF roof lasts about 12 to 15 years without recoating.
A recoating process involves power-washing the roof, applying primer, and applying a top coat. The cost of re-coating a 2,500 square foot roof will be $3 to $5 per square foot per inch.
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