what are the reasons why felt padding (and its many successor
materials) are used in constructing a roof?

On Mar 8, 6:34 am, wrote:
what are the reasons why felt padding (and its many successor
materials) are used in constructing a roof?

The primary reason is to prevent shingles from adhereing to the
plywood. This was driven home to me once when I inspected a roof that
had been shingled without felt. The seams between the plywood sheets
telegraphed through to the shingles and they tore. Whole roof had to
be replaced even though it wasn't that old.

marson wrote:
On Mar 8, 6:34 am, wrote:
what are the reasons why felt padding (and its many successor
materials) are used in constructing a roof?

The primary reason is to prevent shingles from adhereing to the
plywood. This was driven home to me once when I inspected a roof that
had been shingled without felt. The seams between the plywood sheets
telegraphed through to the shingles and they tore. Whole roof had to
be replaced even though it wasn't that old.

How did the plywood seams tear the shingles?

Matt

"Matt Whiting" wrote in message
...
marson wrote:
On Mar 8, 6:34 am, wrote:
what are the reasons why felt padding (and its many successor
materials) are used in constructing a roof?

The primary reason is to prevent shingles from adhereing to the
plywood. This was driven home to me once when I inspected a roof that
had been shingled without felt. The seams between the plywood sheets
telegraphed through to the shingles and they tore. Whole roof had to
be replaced even though it wasn't that old.

How did the plywood seams tear the shingles?

Rafters move around, especially on a stick-framed roof. Plywood expands and
contracts in the sun at a different rate than the shingles. If the shingles
are completely stuck to plywood accross a crack, and the crack gets bigger,
the shingles can tear. If the rafters are 24" OC, and the roof is decked
with the current cheap 7/16, if someone heavy steps on a horizontal crack,
one sheet can flex where the one above or below doesn't, and again you get
tearing. I'm pretty big, and my roof is flimsier than I would like. Up
there, I only wear clean tennies, and walk as gently as possible, even
though the roof is less than a year old. (I got spoiled as a kid- on the
houses my father designed and built, the roofs were overbuilt by modern
standards, and felt as solid as any of the floor decks. And he used 2x10s
for those, not 2x8s like the cheap builders.)

aem sends....

It's purpose is to protect the roof deck from rain, snow and ice.

On low-slope roofs (2:12 - 4:12) rain water drains slowly and creates the
potential for water to back up under the shingles. Also, wind-drive rain can
force water under the shingles,wetting the deck. Because of this, two layers
of underlayment are required to ensure the deck remain weathertight.

On roofs over 4:12, a single layer of 15 lb underlayment has been found to
be sufficient to protect the deck.

In areas where the average daily temperature is 25 deg or less, there's also
the additional possibility for ice damming at the eaves. So the codes
require additional requirements of having two layers of 15 lb underlayment,
cemented together to a point 24 inches up from the exterior wall. (Could
also use one layer of 30 lb, self-adhering material in place of two layers
of 15 lb felt.)


wrote in message
ups.com...
what are the reasons why felt padding (and its many successor
materials) are used in constructing a roof?

On Mar 8, 4:42 pm, "Dennis" wrote:
It's purpose is to protect the roof deck from rain, snow and ice.

On low-slope roofs (2:12 - 4:12) rain water drains slowly and creates the
potential for water to back up under the shingles. Also, wind-drive rain can
force water under the shingles,wetting the deck. Because of this, two layers
of underlayment are required to ensure the deck remain weathertight.

On roofs over 4:12, a single layer of 15 lb underlayment has been found to
be sufficient to protect the deck.

In areas where the average daily temperature is 25 deg or less, there's also
the additional possibility for ice damming at the eaves. So the codes
require additional requirements of having two layers of 15 lb underlayment,
cemented together to a point 24 inches up from the exterior wall. (Could
also use one layer of 30 lb, self-adhering material in place of two layers
of 15 lb felt.)

wrote in message

ups.com...

what are the reasons why felt padding (and its many successor
materials) are used in constructing a roof?

Never heard of two layers of 15#. Shingle wrappers still talk about
two layers of 30# mopped with tar on 2/12 or less and on eaves, but
noone does that any more--ice and water shield is used in those cases
where water can get under the shingles. 15# is very prone to tearing
and is a poor choice for protection. Again, 15# is used to prevent
shingles from bonding to the plywood.

On 2007-03-09, marson wrote:
On Mar 8, 4:42 pm, "Dennis" wrote:
It's purpose is to protect the roof deck from rain, snow and ice.

We've got a house (in southern CA) that has NO felt at all -- and
concrete tiles for the roof material.. We've got quite a few cracked
tiles now (after 15 years) and have leaks in quite a few places.. Needless
to say it's my opinion that the roof was installed incorrectly (no plywood
sheathing is down either -- just well spaced slats) and so the rain just
comes into the attic. If there was a layer of felt and plywood sheathing,
the rain would stay out.. Oh well.. I wasn't around when the current roof
was installed or I would have caught it.. Needless to say, it's going to
be ripped off soon and done properly.

On Mar 9, 3:11 am, "Rick F." wrote:

We've got a house (in southern CA) that has NO felt at all -- and
concrete tiles for the roof material.. We've got quite a few cracked
tiles now (after 15 years) and have leaks in quite a few places.. Needless
to say it's my opinion that the roof was installed incorrectly (no plywood
sheathing is down either -- just well spaced slats) and so the rain just
comes into the attic. If there was a layer of felt and plywood sheathing,
the rain would stay out.. Oh well.. I wasn't around when the current roof
was installed or I would have caught it.. Needless to say, it's going to
be ripped off soon and done properly.

There are plenty of instances where a felted and plywood-sheathed roof
leaks. A poor installation is a poor installation.
The skip sheathing (spaced slats) was the standard way to do roofing
for centuries. Roof felt is not waterproofing and should not be
relied on to stop a roof from leaking.

R

On Mar 9, 6:40 am, "RicodJour" wrote:
On Mar 9, 3:11 am, "Rick F." wrote:



We've got a house (in southern CA) that has NO felt at all -- and
concrete tiles for the roof material.. We've got quite a few cracked
tiles now (after 15 years) and have leaks in quite a few places.. Needless
to say it's my opinion that the roof was installed incorrectly (no plywood
sheathing is down either -- just well spaced slats) and so the rain just
comes into the attic. If there was a layer of felt and plywood sheathing,
the rain would stay out.. Oh well.. I wasn't around when the current roof
was installed or I would have caught it.. Needless to say, it's going to
be ripped off soon and done properly.

There are plenty of instances where a felted and plywood-sheathed roof
leaks. A poor installation is a poor installation.
The skip sheathing (spaced slats) was the standard way to do roofing
for centuries. Roof felt is not waterproofing and should not be
relied on to stop a roof from leaking.

R

Yep. I don't know where the idea that the felt is the primary
waterproofing came from. Anyone who has ripped off an old roof knows
that the heat over the years pretty much destroys any waterproofing
the felt had at installation. If water is getting as far as the felt,
the roof has problems.

Harry K

"marson" wrote in message
oups.com...
On Mar 8, 4:42 pm, "Dennis" wrote:

Never heard of two layers of 15#. Shingle wrappers still talk about
two layers of 30# mopped with tar on 2/12 or less and on eaves, but
noone does that any more--ice and water shield is used in those cases
where water can get under the shingles. 15# is very prone to tearing
and is a poor choice for protection. Again, 15# is used to prevent
shingles from bonding to the plywood.

There seems to be a lot on nonsense spread around on this; but the fact is,
it's there to protect the deck, both before the shingle installation and
after; whether asphalt or wood shingles and wood shakes are used. It has
nothing what-so-ever to do with shingles sticking to two different deck
panels.

To reply to your question, *two layers* of underlayment are required BY CODE
when any roof slope is between 2:12 and 4:14 (low slope roof). Again, this
is related to the degree-angle of the roof deck, not the type of shingle.
The finished roof materials may have their own requirements, which may
exceed these.

A single layer is required for asphalt roofs over 4:12 because the drainage
is fast enough to dissipate the rain.

In addition to the slope, two layers are required when the winter design
temperature in January is below 25 deg F (basically Atlanta and south).
These layers are to be 100% cemented together - (more commonly used, but
more expensive) a single layer of self-adhering-polymer sheet is used.
Commonly referred to as ice-barrier or similar.

These requirements are code, not something that's to be done when an
installer feels like it. It's code throughout the US. In the IRC, it's in
Sections R905.2.7. In the UBC it's covered in Section 1507.2.8.

This is also well covered in the Asphalt Shingle Manufactures Associations
"Residential Asphalt Roofing Manual" (the so-call bible of the asphalt
roofing industry.) From the section under "Underlayment", and although NOT
covered in International Codes, in the ARMA manual it specifically states
that one should NOT use "coated felts, tar saturated materials, polyethylene
or laminated waterproof papers" as "could act as a vapor retarder (barrier)
"..which could.. "trap moisture or frost between the covering and the roof
deck". (This is response to another posters' reply of wanted a vapor
retarder felt.) As WVT is not a requirement of the ASTM underlayment
requirements, I don't what the permeability is but I would imagine that the
unperforated underlayment is a vapor retarder and the perforated type is
not.

In the ARMA manual, the commentary given for using underlayment is ".... it
provides two functions:
It keeps the deck dry until shingles are applied, thereby precluding any
problems that may result is shingles are placed on a wet deck,
If shingles should be lifted, damaged or torn by winds after their
application, it provides secondary protection by shielding the deck from
wind-driven rain and preventing water from reaching the deck".

Also keep in mind that the IRC and the UBC Codes always require the roofing
installer to install the roof coverings "in accordance with the manufactures
installation instructions" (which are printed on each package of shingles.)
Those are not suggestions, they are required to be followed by code.

Originally I referred to the underlayment as 15# and 30#, however these
actually no longer exist. The proper designation is ASTM D226 Type I or
D4869 Type I. (Type I is still commonly called 15# and Type II is assumed to
be a 30#. Currently Type-I runs about 11# / 100 sqft and Type-II is 26 # /
100 sqft.)

It has
nothing what-so-ever to do with shingles sticking to two different deck
panels.


I have seen with my own eyes shingles adhered to a plywood roof deck
(with no felt) where the shingles broke in a 4 x 8 pattern
corresponding to the sheets of plywood. Please explain why this
happened and then I will bother to read the rest of your post.

Marson I don't know why it happened. Paper thin (inexpensive fiberglass)
shingles, deck waterproofed with roofing cement (I seen this on an
inspection and the guy responsible told me he thought it was better than
underlayment), shingles had been on for too many years in a hot climate,
deck not installed properly, etc. All-in-all it doesn't matter, the purpose
of underlayment is to protect the deck. If if masks the deck lines (it
shouldn't be necessary) so much the better.


"marson" wrote in message
ups.com...


It has
nothing what-so-ever to do with shingles sticking to two different deck
panels.


I have seen with my own eyes shingles adhered to a plywood roof deck
(with no felt) where the shingles broke in a 4 x 8 pattern
corresponding to the sheets of plywood. Please explain why this
happened and then I will bother to read the rest of your post.

On Mar 19, 6:30 pm, "Dennis" wrote:


There seems to be a lot on nonsense spread around on this; but the fact is,
it's there to protect the deck, both before the shingle installation and
after; whether asphalt or wood shingles and wood shakes are used. It has
nothing what-so-ever to do with shingles sticking to two different deck
panels.

To reply to your question, *two layers* of underlayment are required BY CODE
when any roof slope is between 2:12 and 4:14 (low slope roof). Again, this
is related to the degree-angle of the roof deck, not the type of shingle.
The finished roof materials may have their own requirements, which may
exceed these.

Although you sound like quite an expert, I would point out that
according to both NRCA and ARMA, a "steep slope" roof is anything that
can be shingled. This is either 2/12 or 3/12 and steeper, depending
on who you listen to. A "low slope" roof cannot be shingled, and is
known in common parlance as a "flat roof". Low slope roofs require
EPDM, modified bitumen, standing seam steel or the like. Check out
their web sites if you doubt me.



In addition to the slope, two layers are required when the winter design
temperature in January is below 25 deg F (basically Atlanta and south).
These layers are to be 100% cemented together - (more commonly used, but
more expensive) a single layer of self-adhering-polymer sheet is used.
Commonly referred to as ice-barrier or similar.

What are you talking about here? The two layers cemented together or
self adhering membrane are required only on the eaves 3 feet into the
heated space in cold climates. You talk like it is supposed to be on
the whole roof. Also, the polymer sheet is only more expensive if you
are using volunteer labor!


This is also well covered in the Asphalt Shingle Manufactures Associations
"Residential Asphalt Roofing Manual" (the so-call bible of the asphalt
roofing industry.) From the section under "Underlayment", and although NOT
covered in International Codes, in the ARMA manual it specifically states
that one should NOT use "coated felts, tar saturated materials, polyethylene
or laminated waterproof papers" as "could act as a vapor retarder (barrier)
"..which could.. "trap moisture or frost between the covering and the roof
deck". (This is response to another posters' reply of wanted a vapor
retarder felt.) As WVT is not a requirement of the ASTM underlayment
requirements, I don't what the permeability is but I would imagine that the
unperforated underlayment is a vapor retarder and the perforated type is
not.

In spite of what the ARMA manual might say, ice and water shields are
sold to be used IN LIEU of the two layers of felt mopped together.
Check out http://www.icc-es.org/reports/pdf_files/UBC/5433.pdf

In the ARMA manual, the commentary given for using underlayment is ".... it
provides two functions:
It keeps the deck dry until shingles are applied, thereby precluding any
problems that may result is shingles are placed on a wet deck,
If shingles should be lifted, damaged or torn by winds after their
application, it provides secondary protection by shielding the deck from
wind-driven rain and preventing water from reaching the deck".

Well, seems like you got me there. I'm still skeptical. Most roofers
run the felt just prior to shingling. Unless you take the time to
lathe it, 15# is really pretty useless as protection. Also, as I am
sure you know, 15# must be torn off if it gets wet because it wrinkles
so bad. Also, do you really believe that it would have any value in a
windstorm? If a wind can take shingles off, it will surely rip off
the felt as well. If water protection was the issue, then 30# would be
in common use. As other posters have said, 15# is well nigh useless
as a water barrier. I will stick to my theory of preventing shingles
bonding to the plywood. I've seen that one with my own eyes.

Originally I referred to the underlayment as 15# and 30#, however these
actually no longer exist. The proper designation is ASTM D226 Type I or
D4869 Type I. (Type I is still commonly called 15# and Type II is assumed to
be a 30#. Currently Type-I runs about 11# / 100 sqft and Type-II is 26 # /
100 sqft.)

Heavens, I have been wrong about this all this time! Wonder why it
said "30#" on the wrapper on the roll I bought a couple months ago?

Although you sound like quite an expert, I would point out that
according to both NRCA and ARMA, a "steep slope" roof is anything that
can be shingled. This is either 2/12 or 3/12 and steeper, depending
on who you listen to. A "low slope" roof cannot be shingled, and is
known in common parlance as a "flat roof". Low slope roofs require
EPDM, modified bitumen, standing seam steel or the like. Check out
their web sites if you doubt me.

A low slope roof is one, that is defined by the IRC code, (the code adopted by most of the country, but hte UBC reads the same), as 2:12 to 4:12. Roofs with these slopes are required, BY CODE, to have two layers of underlayment installed. They have specific installations requirements, but are not required to be cemented together. The Code reference is R905.2.7, and here is exactly how it reads:

R905.2.7 Underlayment application. For roof slopes from two units vertical in 12 units horizontal (17-percent slope), up to four units vertical in 12 units horizontal (33-percent slope), underlayment shall be two layers applied in the following manner. Apply a 19-inch (483 nun) strip of underlayment felt parallel with and starting at the eaves, fastened sufficiently to hold in place. Starting at the cave, apply 36-inch-wide (914 mm) sheets of underlayment, overlapping successive sheets 19 inches (483 ram), and fastened sufficiently to bold in place. For roof slopes of four units vertical in 12 units horizontal (33-percent slope) or greater, underlayment shall be one layer applied in the following manner. Underlayment shall be applied shingle fashion, parallel to and starting from the cave and lapped 2 inches (51 mm), fastened sufficiently to hold in place. End laps shall be offset by 6 feet (1829 mm).

Section R905.2.7.2 of the IRC, deals with ice protection. It also requires two layers of underlayment, but they must be cemented together, up to a point 25" in from the sidewall. There is an option to use what's commonly called ice shield (or simular). Anyway, here is how it reads:

R905.2.7.1 Ice protection. In areas where the average dally temperature in January is 25°F (-4°C) or less or when Table R301.2(I) criteria so designates, an ice barrier that consists of a least two layers of underlayment cemented together or of a self-adhering polymer modified bitumen sheet, shall be used in lieu of normal underlayment and extend from the eave's edge to a point at least 24 inches (610 ram) inside the exterior wall line of the building.


As far as the rest of your remarks, I would never make any kind of statement referring to myself as an "expert". I do however hold certificates in all phases of residential and commercial inspection and plan review from the ICC; including building, electrical, plumbing, mechanical, fire protection and energy. I'm also licensed in several states.

In reference to ARMA concerning "slope", ARMA's Residential Asphalt Roofing Manual reads (under Slope): "In general, asphalt shingles may be used on roof slopes between 4 inches and 21 inches per foot using standard application methods. Beyond this maximum slope, special steep slope application procedures must be used." To my knowledge, they do not define slope anywhere else in the book.

I don't have a copy of the National Roofing Contractors Association's publications; so i can't respond to this one. However I would point out that none of their publications are considerd recognized standards or are adopted codes books. (And the codes always govern.) Given the NRCA's reputation however, I would imagine that the Membrane Roof Systems Manual is an excellent publication.

In the IRC, Section R905.3.3.1 and R905.3.3.2 clearly details what a low & high slope and high slope roof is.

R905.3.3.1 Low slope roofs. For roof slopes from two and one-half units vertical in 12 units horizontal (2-1/2:12), up to four units vertical in 12 units horizontal (4:12), underlayment shall be a minimum of two layers underlayment applies as follows:
1. Starting at the eave, a 19-inch (483 mm) strip of underlayment shall be applied parallel with the eave and fastened sufficiently in place.
2. Starting at the eave, 36-inch-wide (914 mm) strips of underlayment felt shall be applied, overlapping successive sheets 19 inches (483 mm), and fas*tened sufficiently in place.

R905.3.3.2 High slope roofs. For roof slopes of four units vertical in 12 units horizontal (4:12) or greater, underlayment shall be a minimum of one layer of underlayment felt applied shingle fashion, parallel to and starting from the eaves and lapped 2 inches (51 ram), fas*tened sufficiently in place.

Thus you can clearly see that a roof is considered "low slope" from 2:12 to 4:12, and "high slope" for any roof over 4:12.

In all fairness, a low-slope roof is listed as any roof 2:12 in the IBC, but we are talking residential roofs here.

In spite of what the ARMA manual might say, ice and water shields are
sold to be used IN LIEU of the two layers of felt mopped together.
Check out http://www.icc-es.org/reports/pdf_files/UBC/5433.pdf

If you re-read what I said, you will see that I state that the ice barrier was an option to two-layers, cemented together. Personally I prefer this product and if you look back in one of my earlier posts, you will see where I had it used over my *entire roof* when I re-roofed two years ago. (Less chance of ever developing a leak was my thinking.)

Well, seems like you got me there. I'm still skeptical. Most roofers
run the felt just prior to shingling. Unless you take the time to
lathe it, 15# is really pretty useless as protection. Also, as I am
sure you know, 15# must be torn off if it gets wet because it wrinkles
so bad. Also, do you really believe that it would have any value in a
windstorm? If a wind can take shingles off, it will surely rip off
the felt as well. If water protection was the issue, then 30# would be
in common use. As other posters have said, 15# is well nigh useless
as a water barrier. I will stick to my theory of preventing shingles
bonding to the plywood. I've seen that one with my own eyes.

I agree, but it's only a minimum code requirement. If I was a roofer (and I'm not), I probably would use ice shield over the entire roof (if I could convince the home owner to pay the slight extra costs (piece of mind and all that.) But yes, 15# felt (now called Type I) is a pain the ass to work with, esp. on a wind day.

As far as 30# felt (properly called Type II), only use (again from the code) is in closed valleys. (Actually Type II or Type III is specified.) Personally I would error on the edge of durability; especially in any valley.

Heavens, I have been wrong about this all this time! Wonder why it
said "30#" on the wrapper on the roll I bought a couple months ago?

It should also state that it's ASTM D224 Type II. References to 30# is because that what it used to be known as and everyone still calls it by that term. Just like electricians calling nonmetallic sheathed cable as "ROMEX" (a brand name developed by the Rome Wire Company and now owned by General Cable.) It's actually a trademark, not a cable type, but thousands of electricians still refer to this type of cable as Romex.

Nice talking with you,
Dennis