# Purpose of Felt?



## BamBamm5144 (Jul 12, 2008)

What is the real purpose of felt?


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## Tom Struble (Mar 2, 2007)

didn't we just do this?:blink:i think it's to warm you up for carrying shingles up:thumbsup:


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## Randy Bush (Mar 7, 2011)

Felt!! what is felt?? Never heard of the stuff.:whistling


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## Tom M (Jan 3, 2007)

Its the second line of defense


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## kage (Aug 17, 2008)

backup man..


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## Sar-Con (Jun 23, 2010)

A less expensive alternate for deck armour.


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## BamBamm5144 (Jul 12, 2008)

Sure? Thought it was just another way for manufacturers to make more money, just like ice and water.


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## JWilliams (Nov 11, 2008)

It's a waste of time and space just like this thread... Just Kidding bam


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## GRB (Feb 23, 2009)

It's primarily to provide a slip sheet between the shingles & sheathing. I've torn roofs of that had no underlayment & the shingles were fused to the sheathing in some areas. Imagine the sap coming out of board sheathing when that roof is baking in the sun - that's mostly what you're trying to prevent. In addition, the asphalt in the shingles can get driven into the roof deck by the sun if there's no underlayment in place. 

And yeah, it's also a second line of defense, but not a very good one once the shingles are installed, as the felt's then full of nail holes.

Edit: Out of curiosity, I just Googled this & found a couple interesting opinions...

http://arrowheadroofing.com/news/roofing-felt-its-real-purpose/

http://en.allexperts.com/q/Roofing-1598/Roof-paper.htm

Interesting how the two responses seem to have been written by the same person, huh?


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## JWilliams (Nov 11, 2008)

Something else to make the price of petroleum go sky high.


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## Randy Bush (Mar 7, 2011)

I find it interesting that he says that the felt never wears out, I have done roofs where the felt just crumbed in removing, would that not be wore out?


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## GRB (Feb 23, 2009)

Randy Bush said:


> I find it interesting that he says that the felt never wears out, I have done roofs where the felt just crumbed in removing, would that not be wore out?


The question is who's "he"? 

And whoever "he" is, has apparently never done any tearoffs. 

I'm with you, Randy - we've seen a lot of felt that did its job & took one for the team. That's its purpose. :thumbsup:


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## DaVinciRemodel (Oct 7, 2009)

Felt keeps the floor from getting scratched when you move the furniture :thumbsup:


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## JWilliams (Nov 11, 2008)

dude sounds like a dumbass. :thumbsup:


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## DaVinciRemodel (Oct 7, 2009)

JWilliams said:


> dude sounds like a dumbass. :thumbsup:


You talking to me? :laughing:


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## E-Centric (Aug 30, 2007)

I have to call out the scientific portion of the provided links... bitumen, by design, is not supposed to be permeable.

"Although many roofing felts are now marketed as being vapour permeable, until recently almost all felts were impervious. Roofing felt was introduced primarily to act as a secondary barrier against wind-driven snow and rain, but its use also causes a reduction in air movement within the roof space, particularly if the roofing felt is impervious, and this effect is often compounded by the introduction of insulation."

http://www.buildingconservation.com/articles/roof/roof-ventilation.html

I'm not going into detail about vapor pressure, just that the general concept of felt being permeable was a loose interpretation, at best.
--CWP


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## Tom Struble (Mar 2, 2007)

interesting link,but i don't see how it applies to modern built /insulated roofs


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## E-Centric (Aug 30, 2007)

Tom - if you're referring to the link I shot out, it really doesn't apply to modern roofs. I just wanted to refute the mis-information about felts use as a vapor-permeable barrier for the roof. It simply wasn't intended for that, originally.

--CWP


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## katoman (Apr 26, 2009)

There has always been two types of felt - standard and perforated.

The perforated is made for bsmt. walls. For air infiltration. I've never heard of it used on roofs.

But there's always been two types.


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## Tom Struble (Mar 2, 2007)

i don't know about basements or why it would be good there but the perf felt was used in built up hot mop roofing to help prevent air entrapment in the layers


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## r4r&r (Feb 22, 2012)

Well the few times I have had to repair an unexplainable leak smack in the middle of a roof, meaning no penetrations anywhere near the leak or above, I have pulled shingles to find no felt in that area, most times I have found it appears as though they did a deck patch after the felt and didn't bother felting the patch. Once I put felt down there is no more leak. 
So to me that is the biggest reason for felt, cuz some water will find a way under the shingles sooner or later.


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## Friscoblue (Jun 17, 2009)

I install mostly Slate roofs!
felt is to keep structure watertight during the Slate installation!!!!

When the felt is no more, the Slate roof will be watertight for many years!! providing it was installed and flashed properly!!!!!


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## Tom Struble (Mar 2, 2007)

:thumbup:!!!


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## kage (Aug 17, 2008)

when i first did cedar roofs we didnt use any felt except 30# along eaves, then they changed it to per. felt for whole roof,(so it could breathe..they said) now its open game on what you use for underlayment as long as its on there...cedar shouldnt have any underlayment IMO..its friggen cedar..it needs to breathe!!


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## hdavis (Feb 14, 2012)

Tom Struble said:


> well if you follow thru with e-centrics link stating that at one time felt was more or less vapor impermeable it may have made sense


I'd challenge this. Since I was a kid, 15lb would always leak water eventually if you let it pool on it.


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## Tom Struble (Mar 2, 2007)

maybe he wasn't talking 15lb?...how the heck old are you anyway?:blink:


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## superseal (Feb 4, 2009)

you guys got it all wrong - felt prevents squeaking whilst walking upon a roof :whistling


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## GRB (Feb 23, 2009)

No such thing as 15 lb felt any more. It's around 8 or 9 lbs./square last time I checked. The manufacturers now have to refer to it as #15, rather than 15 lb. Just like cereal & Struble, felt's been shrinking. 

Oh, yeah... 


!!! !!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!


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## Tom Struble (Mar 2, 2007)

it's not even felt anymore:sailor:


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## GRB (Feb 23, 2009)

Tom Struble said:


> it's not even felt anymore:sailor:


You're kidding!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

:laughing:


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## Tom Struble (Mar 2, 2007)

i thought that was way to subtle for you to get:laughing:


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## [email protected] (Apr 12, 2010)

*moisture barrier*

it keeps the water from leaking in to the house !!!!!:whistling:no::no:


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## Tom Struble (Mar 2, 2007)

then does it keep water from leaking out of the house?:sad:


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## hdavis (Feb 14, 2012)

Tom Struble said:


> maybe he wasn't talking 15lb?...how the heck old are you anyway?:blink:


I was roofing in the 60s. The guy's wrong about the permeability: http://www.buildingscience.com/docu...t-humid-climates-and-asphalt-roofing-shingles


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## Tom Struble (Mar 2, 2007)

davis you are too much:laughing:


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## TNTRenovate (Aug 19, 2010)

It's there for many reasons. None of which I have been able to track as the original intended purpose. It's a barrier before shingles are installed and after they are installed. It is a barrier to prevent the wood from drawing out the petroleum in the shingles. It is a slip sheet allowing the shingles to expand and contract separately from the roof decking. And it makes tear off a whole lot easier.


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## Tom Struble (Mar 2, 2007)

Rob answered it case closed:thumbup:




but do you need it?:whistling


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## hdavis (Feb 14, 2012)

Tom Struble said:


> Rob answered it case closed:thumbup:
> 
> 
> 
> ...


Depends:whistling


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## GRB (Feb 23, 2009)

hdavis said:


> Depends:whistling


A definitive answer. 

Game, set, & match. 

:laughing:


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## katoman (Apr 26, 2009)

Last month one of my customers called me asking for a referral for a roofer. I had my guy call him. He quoted the job at $13,500. It's a tear off, steep roof.

The HO got two other quotes - one for $12,000 and one for $11,500.

He went with the guy at $12,000. I know them, and they do good work. But I asked the HO if they quoted the same work. He told me that my roofer was the only one who recommended tar paper be installed.

Now it's not required by code due to the steep pitch, but I think it gives a better job. TNT nailed most of the reasons.

Needless to say I was not too happy with my customer, but what are you going to do?


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