Choosing an Underlayment for a Metal Roof
The underlayment material for your metal roof should be carefully chosen in order to have a roof system that will perform at its very best for decades. Several things must be taken into consideration for your roofing system design and that includes ensuring the four barriers needed for any building enclosure. The four barriers are water barrier, thermal insulation barrier, vapor retarder, and air barrier and that they are in the right locations for a given climate. Keep in mind, long-term, in-service performance can be affected by different factors including the metal roofing system, its expected lifetime service, the climate at the building's location, the slope of the roof, the mathematics, and the surrounding conditions, such as the temperature and humidity levels, within the building. If poor choices are made for the underlayment, this can lead to roof leaks or could entrap moisture due to vapor distribution or escaping air. These activities can increase deterioration of components and shorten the life of their services. In turn, this will lead to unwanted repairs. This is why the underlayment must match the intended lifetime of the metal roofing system.
Structural metal roof panel systems are designed to stretch over structural supports without needing a structural deck. They usually do not include a roof underlayment because the installation does not have a continuous substrate or deck to the support the underlayment material.
For an architectural metal roof panel system, a roof underlayment is needed to control water leaks through the roofing system during heaving rainstorms or when snow is melting. There are upgraded roof underlayments that are specified for cold climates for additional protection against ice dam leakage while high temperature underlayments are designed for environments that have high-temperatures. High-temperature environments can be up to 240°F.
Standard underlayment materials include:
• Asphalt-saturated felt underlayment
• Synthetic sheet underlayment
• Rubberized asphalt or butyl-based sheet with polyethylene facer
• Self-adhering membrane underlayment
• Felt underlayment
The standard and most common material for roof underlayment used on steeply sloped metal roofs is a non-perforated asphalt-impregnated felt underlayment. There are several kinds of felt underlayment including organic reinforced and inorganic reinforced. In comparison, glass fiber-reinforced felt underlayment lies flatter and holds up better than organic materials. One or two layers of non-perforated asphalt felt will be used depending on the demands of the architect, the local building code, and/or the metal panel manufacturer.
Felt underlayment offers little resistance to air and moisture vapor movement and is not an effective air barrier. Architectural metal roofs with felt underlayment are best for buildings that have a proper slope and low levels of moisture in dry or arid climates. Felt underlayment is good in combination with ice dam protection at eaves and other critical changes in colder climates.
Synthetic Sheet Underlayment:
Synthetic plastic sheet underlayment is usually made of polyethylene, polyolefin, or polypropylene that are between 8 to 30 mils thick. It is less susceptible to wind damage and lies flatter when subjected to wetting after the installation. It is also less sensitive to cold weather installation than felt is and costs less than self-adhering membrane underlayment.
Most synthetic sheet underlayments that are sold are vapor-resistant and generally do not qualify as air barriers.
Self-adhering Membrane Underlayment:
Self-adhering membrane underlayments are manufactured with either butyl-based adhesives or rubberized-asphalt and is very effective. It is a peel and stick product designed to stick to the roof deck. It is effective on standing seam metal roofs for ice dam protection in places such as roof eaves, valleys, dormers, and rising walls. Unlike the manufactured asphalt-based membranes, the manufactured butyl-based self-adhering sheet provides a greater protection for higher temperature surrounding. These higher temperatures can reach up to 240°F.
This is particularly important for architectural metal and roof assemblies because of the elevated roof surface temperatures. This is especially true for desert climates and high elevations that can go beyond the melting point of some asphalt-based sheet membranes which will damage the membrane. The membranes are typically vaporing impenetrable and because they are fully attached to the substrate, adjacent sheets and the side and end laps, they resist air pressure changes and serve as an effective air barrier material.
It is very important to choose the best most effective underlayment for your metal roofing system. You want the best roof performance that will provide longevity to the roof while protecting the building.
MFM Peel And Stick Self-Stick Roofing
This is a patented, original self-stick roll for roofing and is perfect for many other surfaces that can be difficult to waterproof. It can be used for different surfaces including metal roofs, Trailers or RVs, sunroofs, and mobile homes. It is also used as a flashing for ducts, chimneys, air conditioning units, vents, and for gutters. MFM Peel and Seal is manufactured of polymer films, aluminum composite foil, and rubberized-asphalt adhesive. It makes this product very flexible and it will not tear, dry out, or crack thanks to its excellent long lasting properties that will not wear out. This product resists water and exposure to various elements and reflects heat. There is absolutely no other coverage that will be needed. MFM Peel and Seal is very easy to install as long as the surface is smooth, clean, free of any dirt or debris, and is dry.
You will have to apply an asphalt primer to the surface before applying MFM Peel and Seal. This is especially important on surfaces such as OSB, plywood, masonry, and composition board. Once everything has been properly prepared, simply peel the material off the paper on the back and then just roll it onto your surface. Use a hand roller to iron out any creases or marks and then use a knife to cut off any leftover material.
• Sticks to just about any surface
• Great for RVs, sunroofs, and trailer homes
• Excellent for low slope and low pitch roofs
• Stays in place and is waterproof
• No needed tools
• Comes in 4 colors
• There are 5 different widths
• Handles high winds
• Is made in the USA
• Thickness of 45 mills
• Colors are white, gray, almond, and aluminum
• Each roll is 33 feet 6 inches long
• Widths Of Rolls Per Case:
12 rolls of 3 inches,
9 rolls of 4 inches,
6 rolls of 6 inches,
4 rolls of 9 inches,
3 rolls of 12 inches,
2 rolls of 18 inches, and
30 rolls of 36 inches per pallet.