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How Much Roofing Felt Do I Need

Do You Even Need Roofing Felt

How to Felt a Shed Roof – Fit long life Roofing Felt

Is roofing felt absolutely necessary? Wouldnt it be so much easier if you could just skip it altogether and avoid the trouble of wet or exposed felt?

Modern roofs and roofing companies emphasize the importance of quality roofing felt installation. If youre wondering why, here are some of the main benefits of roofing felt.

How To Felt A Flat Roof With Self

  • Prepare the Roof

When applying roof felt, the underlying deck should be constructed from moisture tolerant materials such as 18mm WBP plywood or suitable chipboard on a foundation of treated timber. The roof should be clean, dry and any nail heads should be flush with the deck rather than protruding. Any existing felt, excess fixings and adhesive should be removed completely.

Before laying any felt you should also consider the arrangement you will require when fitting roofing felt around edges and install edging timber as appropriate. For example, a triangular fillet for upstands and a wooden batten for gutter drips. Also consider whether or not you will need to remove the guttering. In the long run this may make the installation easier but can also cause problems if the guttering is difficult to reaffix.

  • Lay the First Layer of Underlay Felt

The first layer of felt should be nailed to the wooden decking to prevent any rips or tears when the wood expands and contracts in changing temperatures. Start at the lowest edge of the roof and roll out the felt at right angles to the direction of the roofs fall. Align, measure and trim the felt to size as required by placing a cutting board underneath, scoring with a straight edge and cutting with a hooked Stanley knife.

  • Lay the Second Layer of Underlay Felt
  • Install Any Necessary Gutter Drips
  • Lay the Top Layer of Felt

Selvedge: the edge of the top sheet which is mineral free

  • Finishing Touches

What Is The Difference Between Number 15 And Number 30 Roof Felt

The main difference between the two is thickness. Number 30 felt has a thicker layer of underlayment than number 15 felt, providing you with better protection but also adding extra weight to the roof. In general, number 15 is better for steeper roofs since rainwater will run off the surface quickly.

On the other hand, number 30 is better for flat roofs and less steep roofs where water will tend to linger longer and seep in.

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Felt Roofs Have Three Main Weak Points These Are:

Nail holes – The manufacturers recommend that the felt is secured to the roof with clout nails. The system relies on the bitumen ‘self-sealing’ around the nail sothat water doesn’t get in. Over time the shed felt becomes brittle and the self-sealing is less effective. Also the nails are relatively short and so you frequentlysee nails that have ‘popped’, leaving a lovely hole for water to get in.

Lap joints – The roof is waterproofed by a series of strips of material. The joints between these strips, even when installed with the correct 75mm overlap, are a weakness.

Nailing the felt to the roof creates holes and the joints between sheets both create potential leakage points

Brittle material damaged by uv rays – The waterproofing element of shed felt is bitumen. The parts of this material that make it waterproof disappearwith prolonged exposure to sunlight. The felt becomes brittle and starts to let in water.

When Should Roof Felt Be Replaced

Why Do I Need Roofing Felt?

With a typical lifespan of between 10 and 30 years, it can be hard to know exactly when you should replace your shed roofing felt. If youre confident that the felt roof covering was fitted well, has been maintained and is promptly repaired when necessary, the chances are your roof will last closer to the 30-year mark.

However, nearing the end of its lifespan is not the only reason a felt roof needs replacing. Weather damage and organic growth can signify replacement is imminent.

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How To Install Roof Felt

Installing a felt roof is an easy and cost effective way to protect a shed, garage, or flat roof. Roof felt is pliable and can be fitted nicely against pitched and curved roofs, its applied in layers and covered with a waterproof material which should give you upwards of 20 years protection.

In terms of cost, a small shed should cost in the region of £50 – much cheaper than alternatives such as rubber or fibreglass. A small shed should take just a couple of hours, so even a garage or shed can be done in a day.

This job can be undertaken with no specialist tools, and no naked flames. We recommend you select a professional grade roofing felt no matter the size of the job, its far more durable and will withstand weathering – cheaper alternatives can easily become weakened and tear, leaving you repeating the job inside 20 years.

What Size Does Roofing Felt Come In

Roofing felts are used to seal flat roofs, gable roofs, and pitched roofs. It lies under the roof tiles of residential buildings and consists of a mixture of cardboard and tar or bitumen.

Coarse material is to increase abrasion resistance and UV resistance. You may know roofing felt products by their durability, resilience, and compatibility with health and the environment.

Commercially, roofing felt is usually sold in a roll and comes in sizes one meter wide and ten meters long. In addition, rolls of felt are 36 wide x 144 long for #15 and 72 long for #30.

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How Long Does Roof Felt Last

There are many factors to consider when determining the lifespan of a flat felt roof. It largely depends on how well its been maintained over the years. While its true this type of roofing requires minimal maintenance, extreme weather can cause issues that need to be rectified.

However, the best roof felt, felt is extremely durable. The guarantee you get will depend on the manufacturer, but they usually offer at least 10 years of cover on a felt roof. This is not necessarily indicative of the products lifespan as well-maintained torch-on heavy duty roofing felt can last beyond 30 years.

How Do I Calculate Roof Felt Paper

How to Easily Felt a Shed Roof The Right Way- DIY

Estimating Felt Underlayment Find the square footage of the roof. Measure the length and width of each portion of the roof, multiply length by width for each plane, and add the planes together for the total square footage.

How many sheets of OSB do I need for my roof?

Divide the total roof area by 32 to get the number of sheets you will need to cover the roof. A typical 4 foot by 8 foot sheet of plywood covers 32 square feet. If your roof area is 1,600 square feet, 1,600 divided by 32 will mean you need about 50 sheets to cover the roof. Add 10 percent to allow for waste.

How much is a roll of felt paper for roofing?

Cost of Roofing Felt Paper

Roofing Felt Paper costs
$455.00 $490.00

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Plywood For Roofing: Everything You Need To Know

If you want a strong, durable roof, you have to ensure you have installed the correct roof decking.

This is made up of sheet materials that produce a flat surface so that shingles can be nailed onto it securely, and decking is usually made out of plywood.

What is plywood, exactly?

Plywood is a wood-based material thats constructed from thin layers of wood. These are glued crosswise along the grain to prevent shrinkage and swelling from occurring.

With this in mind, lets explore what plywood is used for in roofing, and why its a good choice. Well also explore what you need to know about the different types of plywood.

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Tips For Calculating Roof Area So Youll Know How Many Bundles Per Square Youll Need For Roof Area Coverage

So you need a new roof, whether its to adorn your newly built home or to replace your existing roof. Like most North Americans, youve wisely decided to go with asphalt shingles due, in large part, to their vast range of styles and color blends. Like most of your neighbors, you plan to have the shingles installed by a professional roof contractor who will handle all the material calculations however, the information below will help you understand how to estimate the amount of shingles and accessory materials you need for your roof.

Calculating how many shingles you need for your roof is very similar to calculating how much carpet you need for your floors or how much wallpaper you need for your walls simply determine the area of the roof and divide by the area covered by each package of shingles.

Sounds simple, right? The only hard part is getting the actual measurements, and there are various ways to do this. Most likely, the roofer will physically get on the roof and, using a good old-fashioned tape measure, measure the areas of all the various roof sections and total them together. Of course, if the house is a new construction, these values will be readily available from the architectural drawings.

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How To Estimate The Size Of A Roof

If youre replacing a roof, the first consideration needs to be the roofs size so you can accurately estimate project materials.

In the U.S., roofs are measured in square footage, and roofing contractors typically quote projects based on the size of the roof in squares. Consequently, gathering the size of the roof in squares and square footage is the first step.

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How Much Felt Do I Need For An 86 Shed

Best Rated in Roofing Tiles &  Helpful Customer Reviews

Most garden sheds indeed are 6×4 in size, which if converted is 1.83m×1.22m. Now, the logic is the same.

An 8×6 shed is 2.43m×1.83m. A roll of felt is 8m×1m which means it is advisable to use a roll for this size of the shed.

A roll of felt is big enough to cover most sizes of sheds. This is because sheds arent as big as residential houses, companies, factories, or churches.

As we earlier said, their small structures hence, using a roll of felt is enough.

You should also know that no matter the size of a shed, a roll or a roll and half would do. If a roll isnt enough, you shouldnt call that structure a shed because its bigger and would require more than necessary.

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Rolled Roofing: Basics Costs & Self

If you are unhappy with the cost and complexity of re-roofing one of your structures with conventional shingle-type roofing materials, there may a solution. Rolled roofing is one of the easiest and cheapest roofing materials you can purchase. Plus, it is one of few types of roofs that most homeowners can install on a do-it-yourself basis, although in a limited fashion.

Should I Use 15 Or 30 Pound Felt

If your roof does not have a steep pitch, you can use #15. This weight of felt is a good economic choice if you have a standard roof. But if your roof has a steep pitch, #30 is a better option because it is thicker and tears less during installation. With #30 you get a thicker layer of underlayment and protection.

Read Also: How To Repair Rotted Roof Plywood

How To Repair Rotted Roof Felt

If you felt has begun to rot, repairing can be as simple as cutting away the affiliated area and replacing with more felt as you would with any patch job. However, if the afflicted area is large you should consider replacing the whole roof. Especially as, this issue may have resulted in damage to the decking or timer of your roof.

How Much Roof Felt Do I Need

Metal Roof Underlayment- Synthetic Felt paper vs. High temp Ice and water shield

Roof felt is available in weights of 15 or 30-pounds per 100sqft. A typical roll of 15-pound felt is 36 wide and 144 long and covers 432sqft. The 30-pound roll is 36 wide by 72 long and covers 216sqft.

To determine how much felt is required for a roof, find the area of the roof deck to be covered. Measure the length from edge to edge and the eave to ridge, and multiply the values for the area of half the roof. Double that value and you have the full roof area. For irregularly shaped roofs, break it down into smaller rectangles or triangles to calculate the areas.

For roof slopes greater than 4/12, multiply the area by 1.10 to account for the 2 overlap and potential waste. If there are hips, valleys, or dormers, increase the total by 10 to 25%. Divide the resulting area value by the area one roll of 15 or 30-pound felt will cover, and round up as its sold in full rolls. For slopes between 2/12 and 4/12, double the resulting area value and then divide by the area a roll of felt covers.

For example:

-A 5/12 roof deck 4x 8 is 32sqft x 1.10 = 35.2sqft. Divided by 432 for 15-pound felt or 216 for 30-pound felt and round up for full rolls for this roof theyll be lots of leftover from one roll for the next project.

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Vs 30 Felt Paper: Which One Should You Choose

The difference between 15 and 30 lb felt is thickness, strength, and durability. #30 lb is thicker, stronger, and less likely to tear than 15 lb, making it ideal for steeper sloping roofs. #15 lb is lighter, less resistant to tear, and is often used on standard roofs with gentle slopes.

There you go! Now you understand the need for roofing underlayment, the different types of underlayment, what felt numbers mean, and most importantly, the main differences between #15 felt and #30 felt.

Why Use Roofing Felt Paper

Roofing experts have discovered that adding a layer of protection between your structural roof decking and your roof shingles helps create a better-looking and longer-lasting roof. In fact, there are a number of important ways roofing felt not only protects your roof, but also your residence. For example:

  • It repels waterWind-driven rain or snow can trap water under your shingles, putting your roof deck and inner residence at risk of moisture damage, leaks, rot and mold. Roofing felt helps ensure the water drains off the roof and doesnt leak into your home.
  • It provides backup protection in the event of ice or water damageIn northern climates, ice or snow dams are another common cause of residential water damage. When the heat from your home melts snow or ice on your roof, the water can then seep into your roofs nooks and crannies and ultimately into your residence, causing damage to ceilings, walls, or insulation. Your best protection against an ice dam is an ice and water protection membrane which can seal around the shanks of the roof fasteners for a leak-resistant fit. However, roofing felt offers additional protection against leakage, providing an extra layer of water resistance.
  • It protects your roof deck while you work on itRoofing felt prevents the deck from being exposed to the elements before, or while, the shingles are being applied.
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    What If You Have A Steep Roof

    To measure a steep roof, use one of the following alternate methods:

    Method 1

    Calculate the roof length by measuring the exterior walls plus the overhang for the length of the house parallel to the ridge.

    Next, throw a rope over the ridge and mark it where it meets each eave. This will give the width dimension to use in figuring your area. This should be done on each roof section containing a horizontal ridge.

    Method 2

    Determine the roof area by using a mathematical formula that accounts for the roof length, total span, and roof pitch:

  • Determine your roof pitch by using a pitch gauge or a smartphone app .
  • Measure the length of the roof surface, including overhangs.
  • Measure the span of the roof, including overhangs.
  • Multiply the length x the span. The result will be the plane area. Use the chart below to calculate the total area of the roof.
  • Calculate the total roof area Plane Area x Correction Factor = Roof Area
  • How Do You Calculate Roofing Felt

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    Calculating roofing felt is no different from calculating the shed roof. You calculate the roofing felt because you want it to fit nicely on your roof.

    Therefore, to estimate the roofing felt, it all depends on your shed roof.

    The steps involved are still the same as earlier discussed. However, theres a little twist at the end when youre calculating roofing felt.

    When rounding up your answer to convert it from square feet to squares, this is done because of the roofing felt. This is because roofing materials are specified in squares.

    At this point, you can calculate the roofing felt since youve converted it to squares. Note that one hundred square feet are equal to one square.

    It will interest you to know that roofing felts are sold in rolls, and one roll of it is one square which covers 100 square feet. This is simple and interesting if you follow the logic.

    You can use the roofing square measurement to calculate the roofing felt. Instead of using tape to take the lengths and width of your roofing felt, you should measure your roof and use it to measure your felt as one roll is even one square already.

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