If you’ve chosen roll roofing to replace your current roofing system, you may probably want to know if it’s important to install an underlayment as well.
Unlike shingles, roll roofing does not need an underlayment. Still, it’s an inexpensive material that acts as an added layer of protection for your roof, especially in areas that see a lot of extreme weather events. So, while it’s not a necessity, you should add it if you have a more flexible budget.
If you decide to underlay your roll roof and want to give your roof a smooth and flat look, nail down the underlayment properly before rolling it.
Before we can get into the benefits of using underlayment, it is crucial to research the roofing system you want to install.
Roll roofing is a less expensive option for re-roofing different existing roofs, like sheds, shops, garages, and other outbuildings.
While it’s less durable and often used to supplement other roofing materials, it is still one of the easiest roofing materials you can install that doesn’t require advanced DIY skills.
When installing roll roofing, you might want to consider an underlayment because of the several benefits it offers.
Benefits of Underlayment
First things first, what is an underlayment?
A roll roofing underlayment is a water-resistant barrier that is installed directly onto the roof deck. It’s applied under all other types of roofing and serves as an extra layer of protection from wind, rain, snow, and other inclement weather.
Several key benefits come from installing roll roofs over an underlayment. Here are our top four benefits:
Acts as a Moisture Barrier
Why do you need to worry about moisture for your roofs? Because roll roofs are made of organic felt or fiberglass mats saturated with asphalt and faced with granular stone aggregate.
If moisture from the decking or flashing gets to the fiberglass mat, your roofing will absorb the moisture and cause mold problems or age fast.
Underlayment with a built-in ice/water barrier provides the protection you need from moisture.
Provides Added Insulation
When you think of insulation, you might think that they are only added to walls, windows, doors, and floors. However, your roofing can cause fluctuations in your heating and cooling bills too.
Underlayment provides added insulation for roofs, keeping you comfortable by minimizing heat gain in summer and cold in the winter season. As a result, you don’t have to worry about your energy bills skyrocketing, and you’ll enjoy the space even more.
Acts as a Sound Blocker
Your home can be invaded by various sounds, including sounds of traffic, neighbors, pedestrians, construction, rain, and other elements hitting the roof.
Roofing underlayment acts as an extra obstacle that sound waves must travel through, absorbing the roof noises to the point that it’s either inaudible or producing a soothing sound. Also, it will dampen the noise from the outside to such an extent that it is barely audible.
Provides An Even Surface For Roofing
Roof decking doesn’t always adhere well when applied directly to roll roofs. And like most roof components that expand and contract depending on the temperature of the day, putting a rolling roof directly on the roof deck will only make it look uneven.
Underlayment provides a smoother and more predictable surface for the roof covering than roof decking.
You Need Roof Underlayment For Build Code Compliance
Depending on the States you live in or the manufacturer’s guidelines, you want to confirm if an underlayment is necessary for roll roofing.
While most codes might not demand an underlayment, others may require you to underlay your roll roofs and even specify the type of underlayment to use.
The most common types of underlayment are felt and synthetic underlayment. So, make sure you research to comply with the material warranties.
Provides Extra Weather Protection
Most roof materials, including roll roofing, are susceptible to wind uplift damage and ice or snow dams. In such severe weather situations, the use of a specialty roof underlayment can keep the inside of your home from being directly exposed to the elements until the roof can be repaired or replaced.
Types of Underlayment Used for Roll Roofs
Here are some of the main types of underlayment most commonly used with roll roofing and other types of roofing materials. Each has different characteristics and will add a specific benefit to your roofing project.
Asphalt-Saturated Felt
Asphalt-saturated felt paper remains a popular choice, especially for residential, steep-slope applications and other places where a water-resistant surface is desired.
Felt paper consists of asphalt-saturated felt, rubberized asphalt, or non-bitumen synthetic made of cellulose base.
This type of underlayment is applied over the roof before installing the shingles and acts as a secondary barrier to moisture caused by wind-driven rain and ice damming.
Roofing felt comes in two thickness: 15-pound and 30-pound. 15 pound is the lightest of the two and has a perm rating of 5. High humidity can affect this rating.
Thirty-pound felt is much thicker, stiffer, and more water-resistant to damage, protecting your roof longer even after being exposed to inclement weather conditions.
Rubberized Asphalt
Rubberized asphalt (often called SBS modified underlayment) is manufactured by recycling rubber materials from items like worn-out road tires, discarded boots, and tubing and adding slate and sawdust.
They have rubber-like properties and are peel and stick underlayments. They don’t require fasteners but instead form and seal well around staples, nails, roof penetrations, and unusual shapes to aid waterproofing.
Rubberized asphalts are also more heat resistant than asphalt-saturated felt, making them a good choice for large panels bonded together or heat-fused into one seamless membrane.
Additionally, if you don’t have your primary roof covering ready for installation, you can temporarily use rubberized asphalt for up to 180 days.
These underlayments are not typically used in whole-roof applications because they are expensive, heavier, and can be difficult to use and apply.
Non-Bitumen Synthetic
Non-bitumen synthetic underlayment is a more advanced replacement for felt underlayment and is made from weaving or spinning polypropylene or polyethylene.
They are exceptionally lightweight and have superior wind resistance and tear strength to asphalt and rubber underlayments.
Since they’re much lighter and resilient, they are easier to handle, help improve job site productivity for roofing contractors, and resist damage that could occur during installation.
Synthetics are also highly resistant to UV rays and can be left uncovered to the sun during and after installation for periods from six months to a year without drying out.
Some of the problems you’re likely to face with synthetic underlayment include low permeability and not being suitable for low-sloped roofs. They are also more expensive than other types of roofing underlayments.
How to Install Roll Roofing
While installing a rolling roof is no simple task, if you have had experience installing asphalt shingles roofs, taking on a roll roof DIY project should be manageable.
If you have absolutely no experience, a ready attitude, some knowledge on roll roofs, the right tools, a degree of caution, this instructional manual should be all you need to put a roof over your building.
A quick heads up for you as you prepare for the installation, be sure to pick a fairly cool day of about 50 degrees Fahrenheit, so your materials are malleable and easy to work.
Roll Roofing Materials and Tools
- Roll roofing material
- Tape measure
- Roofing cement
- Push broom
- Ladder
- Hammer
- Roofing nails
- Chalk line
- Caulk gun
Step 1: Measurements and Preparation
Before you embark on the actual work of roll roofing, you want to ensure that you are well prepared for the task ahead of you. Your tape measure comes in handy at this point because you need to take the measurements of the length and width of your roof surface.
Your measurements will help determine how many rolls of roll roof you will require to complete your project. Be sure to add an extra 10% on your roll roof purchase to cover for what will go into trims. Ensure all other tools are also available.
A critical step in preparation for roof installation is thoroughly cleaning dirt off the roof with the push broom. Take time to even things out, e.g., by hammering any nails sticking out your sheath and replacing damaged wood.
Step 2:Applying Roof Cement to the Edges of your Deck
Apply cement to the bottom edges of your roof deck before installing your first sheet. This cement has adhesive properties, which enhances grip.
Step 3: Apply the Base Sheet
Unroll your base sheet on the roof deck, making sure to leave a ¼ inch overhang on the drip edges. Ensure to rub on the surface of the material with your feet as you move back to allow it to stretch and attach evenly to the deck. Depending on what underlayment material you choose, nail or apply fasteners as you move backward.
The best way to apply the fasteners is between (20 to 25 centimeters) apart. If you are using nails, ensure to keep them (2-3 centimeters) from the edges.
Step 4: Attach the Roll Roof Sheets
Apply roof cement on the bottom edge of your roof deck to adhere to the roof drip edge. From the edge of the roof deck, measure 35 inches upwards of the roof and the line using chalk, so you have a straight parallel line.
Position your first roll roof sheet along the chalk line, then nail the bottom edge and sides to fasten the sheet to the deck. Position nails at 6 inches apart and 1 inch upwards from the bottom of the rim.
Measure another 34 inches upwards of the roof from the top edge of your first sheet. Apply about 2 inches wide of roof cement on the top edge of your first sheet, then position the second sheet overlapping the first.
Align your sheet with the chalk line. Nail the bottom edges of the second sheet and its sides 6 inches apart as you did with the first sheet.
Repeat this process until your roof is completely covered.
Step 5: Seal the Vents
If you have vents on your roof, seal them with roof cement to fully secure your roof. For best results, cut a hole on the roofing sheet around the vent so the roll roofing overlaps it.
Next, spread the cement around the edges of the hole and lay down the sheet, pressing on top to ensure it holds firmly. Complete this process by nailing around the vent to ascertain a firm grip.
Step 6: Cover Nails, Trim Edges and Clean Up
Now that your roof is complete and you have all your layers, you may complete the job by covering your nails with roof cement to seal them into the roll roof. Finally, trim hanging edges, clean up and enjoy your new roof!
Does Roll Roofing Need Underlayment FAQs
Does Rolled Roofing Require Felt?
Roll roofing can be applied directly to your roof deck without Felt or underlayment. Applying felt, however, will give you the added benefits of an extra layer of insulation that will better protect your roof from rain, snow, and harsh winds. It is, therefore, beneficial to apply felt.
What Is the Best Underlayment for Rolled Roofing?
The best underlayment for rolled roofing is dependent on the specific needs of your roof and your budget. Synthetic underlayment is, however, superior for its water-resistant and lightweight nature. It is also easier to handle, harder to tare, more wind resistant, heat resistant, and less prone to damage compared to others. It is, however, less porous and unsuitable for lower sloped roofs.
Do You Nail Down Roll Roofing?
Yes, roll roofs need to be secured by nailing. The best approach is to nail each layer of roll roofing 6 to 10 inches apart along its sides and edges during installation. An alternative approach to secure roll roofs without nails is by applying a propane torch to heat the layers, so they stick in place.
How Do you Adhere Rolled Roofing?
Rolled roofing is adhered using roof cement which has adhesive properties. Before you install your first sheet of roll roof, apply the roof cement to the edges of your deck, then place your first sheet over it. Next, apply the cement about 4 inches wide on the top edges of your first sheet and layer the second sheet upwards. Follow this process to the end.
How Much Do you Overlap Rolled Roofing?
The overlap between rolled roof sheeting should be about 4 to 6 inches. After placing the first sheet, layer it with cement along its edges, then place the second sheet over the first with an overlap of 4 to 6 inches. Be sure to take your measurements and mark them with a chalk line to get them right.
Can I Put Rolled Roofing Over Rolled Roofing?
Yes, you can put rolled roofing over another rolled roof. If you have any challenge removing an already existing roll roof layer, you may install a new layer of roll roofing over it. However, to achieve a clean install, take time to clean out the old roof of all debris and even out any protrusions.