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Is roofing felt waterproof?

Updated: Jul 20, 2023

Is roofing felt waterproof

Have you ever driven by a home that was being built from scratch or one that was having a new roof put on? While you were passing by, the storm clouds broke open, and the rain fell in torrents upon these open roofs.

Your first thought was probably something along the lines of, "How is that roofing not going to experience mold growth since it is getting soaked? Is the roofing felt waterproof? Is the Shed roof felt waterproof or not? Is there no felt under the roof tiles?" but you did not give it much more thought than that.

Now, let us just cross our fingers and hope the roofing felt was installed correctly to shield the roofing flooring (plywood) against the rain. Is the shed roof felt waterproof? Indeed, roofing felt is designed to resist water and prevent snow and ice from reaching the roof decking. This is one of the felt's primary functions.

The components that make up a roof felt, as well as the functions it serves, will be discussed in the following paragraphs.

What Is Roofing Felt

Roofing felt is a material that is simply put over the roof decking and underneath the roof shingles. It acts as a barrier between the two layers of the roof. Roofing felt is synthetic underlayment, roll roofing material, and roofing tar paper.

Another name for roofing handled is roofing tar paper. It is protected by a layer of asphalt that is put on top to provide a barrier against the elements, and it is made out of a synthetic composite that combines fiberglass and polyester and a wood cellulose composition.

Because of this protective layer, the felt can breathe and repel water.

The different types of roofing felt.

Roofing felt comes in a variety of forms, each of which is subdivided into a specific classification and section. These many forms have varying quality, and their prices vary accordingly.

It differs a bit from flat felt roofing since it has a robust, woven base, although it may grow brittle over time and rot into the guttering if exposed to sunlight. Traditional bitumen sarking was the most readily accessible and least expensive alternative for roofing underlay.

More contemporary options can be purchased; however, despite the fact that they are less heavy and more long-lasting than conventional sheeting, they tend to be a little bit more expensive.

Under the British Standard BS 5250 guidelines, pitched roof underlays can be categorized into one of two distinct groups. These two different groups also decide how long can roofing felt stay exposed. The following are the two categories:

Underlays referred to as HR (High Water Vapor Resistance) are membranes with a significant amount of water resistance (thus the name). Still, they require some kind of ventilation to function properly.

Ventilation will be needed in the loft space for cold roofs and in the area that includes the insulation and underlay for warm roofs; the loft space will need to be ventilated for hard tops.

LR (Low Water Vapour Resistance) Underlays These membranes are more widely known as "Vapour Permeable," which can be shortened down to VPU or "Vapour Open" underlays. LR stands for "Low Water Vapour Resistance." These types offer an additional mechanism for the movement of vapor; this can be utilized in conjunction with ventilation for both warm and cold roofs.

Low Water Resistance Underlays also fall into two different categories or sections:

These airtight membranes have between three and four layers that allow vapor to pass through them. The vapor-permeable membrane that facilitates vapor transfer and possesses strong water hold-out capabilities is located in the middle layer that makes up the sheeting or sarking felt. This layer is also known as the sarking felt.

Air Permeable - In contrast to AirTight membranes, these membranes have only three layers, resulting in a membrane that is both vapor and air permeable. Because these membranes lack the vapor-permeable film layer, they often have a more excellent vapor permeability but poorer water hold-out qualities. This is because vapor may pass through them more easily. 

Why Is Roofing Felt Used

Many different levels are involved in the process of building a roof. These layers are assembled in a highly particular order to provide your house with the most excellent possible level of defense. Let us have a look at the rationale behind why roofers use roofing felt.

Water Repellent

Water can quickly become trapped under your shingles if there is wind or snow. The roof decking (plywood) beneath stays dry because of the roofing felts ability to absorb moisture.

Mold growth and additional damage to your roof decking that could lead to leaks can be avoided using roofing felt. That is why when roofs get damaged early, it makes us wonder: Is there no felt under roof tiles? Is roofing felt waterproof? Is the Shed roof felt waterproof or not?

Backup Protection

When snow and ice accumulate on your roof, the heat from your home will eventually melt the snow and ice, preventing dams from forming. When this happens, water can enter your home through cracks in the shingles. Having roofing felt put is a failsafe measure against water damage.

Weather Protection

Damage to or cracking of shingles can occur over time. You might miss this unless you get up on the roof and take a closer look. Until you can get new shingles installed, the roofing felt acts as an extra defense against the elements.

Fire Rating

The fire resistance of shingles is evaluated with roofing felt as the underlayment. The shingles will not be able to achieve the highest possible fire rating without the underlayment.

Roofing felt, and shingles must match up properly for compliance with building codes. The roofing contractor you hire should be familiar with these regulations.

Roof Decking Protection

Roofing felt is installed as a barrier between the roof and the weather. The roofing decking (plywood) should not be left out in the elements.

Uniform Look

Roof decking typically is not precisely flat or straight. Wood can distort and alter form slightly. Throughout the setup. Shingles can be installed on a more even surface with the help of roofing felt underlayment.

This will also help eliminate the "picture framing" look that can occur when the pattern of the wood decking is visible through the shingles.

Stain Prevention

Any resin which seeps through the wood decking will not make it onto the shingles if you use roof felt. Staining and a weakened shingle are the results of resin penetrating your roof. This can drastically alter your roof's overall appearance.

Other Recommended Maintenance

You should probably learn more about roof decking now that you know what roofing felt is. And is roofing felt waterproof or not? How long can roofing felt stay exposed? And can you think of a roof from the inside? If you can handle these two factors, you will better understand what it takes to replace your roof.

You, the homeowner, can also converse with your roofing contractor, provided that the contractor is appropriately licensed. In this way, you can rest assured that you are not being taken advantage of and that your interests are protected.

Next, you should learn more about the intervals between roof replacements. You can accomplish this by requesting a roof assessment checklist or having one performed by a local home inspection firm.

Finally, be sure you can tell whether leaks in your basement are coming from the roof. If your roof is damaged, the gutters may also be compromised, leading to water damage in the basement. Because of this, your basement will always remain damp as water seeps into the earth. If this happens, mold will spread from the basement to the rest of your home.

When Do I Call A Professional

Installing a brand-new roof may be a somewhat nerve-wracking experience. You will want to make sure you choose a licensed roofing contractor with the highest possible reputation in the industry. The majority of the costs connected with installing a fresh roof are attributable to the cost of the roofing materials itself.

As you solicit bids from various area roofing contractors, you should find that their prices are roughly comparable. Contact the people who provide home inspections in your area if you are unsure who to call about your roofing project.

They can determine whether you require an entirely new roof or minor repairs. In addition, they can recommend a reliable roofing contractor that is also licensed and highly trained.


Having all the information at your disposal before installing an entirely fresh roof or undergoing repairs on an existing one is essential. It is your advantage as a homeowner to communicate in the same language as the contractor. You will be able to comprehend the rationale behind the distinct price ranges and the amount of time that should be required for the qualified roofing contractor to finish the project.


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