We seem to be tearing off a lot of roofs lately where there was no felt underlayment used. The shingles, on average have lasted a very long time and the sheathing is in great shape.

“Its a vapor barrier”.

Can someone elaborate, without just referencing some link to a different page, on the purpose of felt underlayment in steep slope roofing.

Anyone that installs felt and wonders why, please don’t hide in the closet!

Btw, I’m from ‘the thumb’ of Michigan.

The only reason I need to install felt is that it will keep the interior dry if it starts to rain before I get the roof done.


Because asphalt shignle roofing need all the help it can get.

Vapor barrier is an oft-misused term.

hello drinc,
dont like the old copy paste gig huh?

so ditto on the previous two replys.
and for me a couple a reasons why i like felt paper on before shinglin.
your grip to the roof is much better, therefore much safer.
and the lines on the felt are very important to me.
i use them like a graph.
it is how i run my shingles strait across roof, without any horizontal lines.
but it is a pain to lay and really not nessecary on steep roofs.
lot a snow birds dont use it.

im older and scareder now, and i try to get titanium underlayment under my feet when ever i can.
stuffs like velcro. cant slide on it if you try.

good luck.


[quote=“gweedo”] i try to get titanium underlayment under my feet when ever i can.
stuffs like velcro. cant slide on it if you try.


get some snow or saw dust on it, then see how much you trust it. however i do use it on probably 50% of my roofs.

well im sure anythings slicker n owl piss with snow on it.
but i here ya marshall, i dont like the way the tools slide off the titanium.
but it does grip ya hangin over the edges.

heres a funny story for ya
when titanium first got on down here they did not want staples used to fasten cause of the hurricanes around here.
so they put on it “use plastic cap nails only”.
well that got misconstrude to mean you could not use metal cap nails either.
finnally everybodys startin to get it.


“Vapor Barrier” means it keeps the sheating from sucking the moisture out of the shingles and/or from on top of the shingle…

Hello from a fellow “thumber”

Are we talking moisture or waterproofing oils? Does wood decking sap oils from the shingles?

Unless it is solidly adhered with a moisture barrier compound, then you most likely have a vapor retarder.

paper keeps any resin from getting to the shingles on solid pine roofs and when I stripped mine there were places where the tar paper would not come off and it was because of pine resin that had bled out of the boards, not alot but several places.


Might it have been a heavily saturated asphalt felt?

all i know is that the manufactures say to use it…so i use it. after all, they spend millions on research and some companies (GAF for example) have been around since 1886. i however have only been around since 1973 (haha) so i think they might know more than me. :smiley:

The roof had been shingled before so the fact that I found tar paper stuck to pine boards meant it was still bleeding out in some places.

I used the Certainteed paper above the ice and water, why not for what it costs and to get the 5 star warranty thing.

In my mind putting the Roofers Select helped to bridge out uneven ness in the pine boards from board to board before the shingles went on.

Either way I had read that pine boards can bleed and some of mine so just passing it on.


yall are way over thinkin it.
just nail on any old under layment, throw some peal n stick in there if its showin outside and nail the shingles on allready.


The purpose of felt underlayment.

Standard Slope Application:

Proper application requires that a single layer of #15 felt underlayment be applied to decks with slopes of 4/12 or greater and consistent with all applicable building codes. This felt underlayment is required to achieve a Class A or C fire rating on the deck assembly.

Felt also helps to prevent leaks from wind driven rains that may, somehow, penetrate the shingles. Imperfections in the wood decking also can be a problem in the absence of felt underlayment. These imperfections will more readily telegraph through today’s thinner fiberglass shingles. Finally, many shingle manufacturers require felt to be used over a bare wood deck.

Certainteed Corp. which is a one of the best shingle manufacturers recommends that underlayment be installed but not require it except as noted below.

Low Slope Application: 2:12-4:12 (51mm/305mm)
On slopes 2" to 4" per foot apply a double layer of felt underlayment over the entire deck surface. Starting with 19" wide strip at eaves, overhanging the eaves 1/4" to 3/8", cover with full 36" strip providing a 17" exposure. Continue with 36" strips lapping each course 19" over the preceding course. End laps for low slopes shall be 12" and staggered 6 feet apart. Install drip edge over the felt underlayment at the rake and beneath the underlayment at the eaves.

Hope this helps :smiley:

nice copy & paste.