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Felt vs. Synthetic - Roofing underlayment


Felt vs. Synthetic - Roofing Underlayment

There are many factors to consider about roofing: from shingles, leak barriers, pipe boots, ventilation, fixture accessories and underlayment, each play a critical role in providing an environmental barrier for the premises. The barrier is laid to prevent the penetration of water, heat and wind from entering the premises even at significant volumes or velocities for each of the weather elements.

Roofing underlayment is laid between the roofing shingles and the roof decking. This is done for Three reasons:

1.    As a water barrier; preventing external water vapor or precipitation from percolating onto the roofing deck

2.    Prevents parts of the shingles chemical mixture from leaking onto the roofing deck, causing expensive repairs

3.    Acts as a secondary ambient barrier, reinforcing the purpose of heat and sound insulation

When laying your roofing underlayment, you may want to compare the differences and distinctions between Felt and synthetic underlayment. It is the subject of a lot of debate for roofing solutions in the determination of efficiency, cost and durability.


These are artificially manufactured materials from polypropylene, fiberglass, polyethylene and polyester. They are light materials that are placed under the roofing shingles, offering a lighter, water and radiation resistant barrier for the roof deck. The materials make for a more efficient water barrier without the factoring of mass, meaning that the sheets are significantly thinner and lighter compared to felt paper roofing underlayment


This is essentially made from asphalt saturated paper that is used to increase the density of the underlayment, and increase the water resistance property with increasing weight. It is usually packed in 15 to 30lbs blocks, with 30lbs with the greatest water resistant property. They are however quite heavy, and challenging to install.

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Making the Choice

Both solutions have viability and preference based on your needs and constraints.

·         Considering Price, synthetic solutions cost generally more than felt roofing underlayment. This goes back to the cost of manufacturing and refinement process, they are however more efficient in preventing water and seepage.

·         Felt roofing underlayment is effective as the weight increases, it is challenging to install but reliable in preventing seepage.

·         Synthetic underlayment is safe to install, it allows room to move around due to the comparatively low volume per installation area. It is also strong, hence durable, giving you a significant duration between the installation and the next roof repair.

·         Felt is sticky to work with and slippery to walk on due to the asphalt and petroleum parts that make it up, it is therefore harder to install and presents an element of risk.

·         Synthetic underlayment comes in rolls of 250 feet at 48" wide, which means you can cover more area with one roll-out, approximately 1000 square feet under an incredible 40lbs, which compared to felt underlayment, weighs about six times more for the same coverage area.

·         Synthetic underlayment lasts significantly longer than felt roofing underlayment; this is because the chemical composition for synthetic solutions are more stable in response to ambient catalysts, therefore the degradation process is slower.

Looking at all the elements: safety, ease of installation, cost, efficiency in water-proofing, additional features, weight and ease of management and durability, it would seem that synthetic roofing underlayment wins the day, but then again, advantages do not have to prove viability or preference, cost constraints or construction specifications may dictate otherwise. 



Awesome post. Thanks for sharing. I really learned a lot. Keep it up.
Posted @ Sunday, June 09, 2013 11:07 PM by north carolina general contractors
Can syntheitic felt be used with concrete tiles? What is the best brand or type of synthetic felt?
Posted @ Saturday, February 01, 2014 11:08 AM by Phil Swanson
Are Synthetic felt better than paper felt to used on concrete tiles in a very hot weather during summer and 25 degrees during cold weather? if so what brand and how thick synthetic felt should I buy that conform to building standard
Posted @ Tuesday, April 08, 2014 9:33 PM by mario
good article for synthetic felt. 
Posted @ Tuesday, April 29, 2014 12:03 AM by pete thrift
Dear Sirs, 
  We have your name and adress from the internet and take this opportunity to set up business relations with you. Our company named as Baoding longjun Building Material Co.,ltd.It is located in Hebei province,China.We are a big factory deal with synthetic roofing underlayment and has meet or exceeds the applicable srandards of ASTM D226,ASTM d4869 Customers are quite satisfiled with our products since they are of good quality and competitive price. We want to have chance to cooperate with you. 
 Best regard, 
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Which synthetic underlayments are radiation resistant? Which metal roofs are radiation resistant?
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