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Roofing underlayment - roofing felt requirements:
Is roofing felt required? Who says? Felt details for various roof slopes & conditions
This article series discusses roofing felt, specifically addressing the roofing code or roofing manufacturer's requirements for use of an underlayment, such as roofing felt, tarpaper, or other underlayment products beneath asphalt shingles and other roofing materials.
We review these roofing felt questions: Is roofing felt needed under asphalt shingle roofs? Roof shingle warranty requirements for roof shingle underlayment. NRCA recommendations for roofing felt underlayment. Permeability of felt underlayments in hot humid climates. What are the benefits from using roofing underlayment or felt? What problems can occur when using a roof shingle underlayment?
We also discuss the moisture permeability of roofing underlayments in hot humid climates.
Our photo (page top) shows felt underlayment in good condition as a worn out roof was being stripped. It looks as if the installer of asphalt roof shingles (still visible at below right but now worn out) may have placed roofing felt on top of a still older wood-shingle roof.
Above is a peel-and-stick mineral surfaced roofing underlayment shown during installation of a metal standing seam roof. Photo courtesy Galow Homes.
The roof deck should be sound and level before laying the underlayment. Fifteen-pound or heavier felt underlayment is required by code in some areas. Whether or not it is required, underlayment is cheap insurance against problems. There are several good reasons to install underlayment:
It protects the roof deck from rain before the roofing is installed.
It provides an extra weather barrier in case of blow offs or water penetration through the roofing or flashings.
It protects the roofing from any resins that bleed out of the sheathing.
It helps prevent unevenness in the roof sheathing from telegraphing through the shingles.
It is usually required for the UL fire rating to apply (since shingles are usually tested with underlayment).
Our OPINION is that on new asphalt shingle, tile, fiber cement, slate, and many wood roofs, most roofing contractors apply an underlayment membrane of roofing felt ("tar paper"), or fiber-reinforced roofing felt. A special underlayment may be recommended by the manufacturers of specific roofing product and hybrid products.
Our photo (left) shows new felt underlayment in place during an asphalt shingle roof installation in New York.
While the requirement for felt underlayment beneath asphalt roof shingles seems to be a topic of almost timeless argument subject to much arm-waving and little reading of manufacturer's instructions and warranties, various sources recommend or require installation of a felt underlayment over the roof deck before asphalt roof shingles are installed.
Booth & Roberts reported at length on the uses of underlayments on asphalt shingle roofs, citing (quoting):
Asphalt shingle underlays are commonly used throughout North America. The National Roofing Contractors Association’s (NRCA’s) definition of underlay(ment) includes some important functions:
To separate the roof covering from the roof deck
To shed water
To provide secondary weather protection
The authors point out that
"Resins from green lumber roof decks have been known
to interact with roof shingles, and a separation layer of
underlay can be useful. Underlays are quickly applied and
they can provide temporary roofing before the roof shingles
are installed. Underlays have remained intact after
shingles have blown away, thereby providing temporary roofing .
Underlays provide secondary weather protection
in ice-dam situations, when water backs up over the
head-laps of shingles.
Other functions of underlays have been reported .
Two of the more important ones are air-flow resistance and
Air-flow resistance reduces windblown
water penetration from the outside and moist air penetration
from the inside of a roof. Moisture storage provides
temporary storage for small amounts of leak water, which
subsequently evaporates in dry weather. We know of no
experiments that quantify these advantages.
There are disadvantages to underlays. Felt materials can
wrinkle and buckle, and these imperfections can telegraph
through the finished shingle layer [8,9].
that underlays reduced the life of roof shingles in
California due to heat build-up . Explaining how an
underlay will act as secondary weather protection when it
has shingle nails through it every 8 inches (203 mm) or so
can be a challenge.
The liquid water transmission test in
ASTM D 4869 for asphalt felt underlayments for shingles
 includes the following note:
“Take care to ensure that the
staples do not protrude at the front surface of the plywood board so
as not to puncture the test specimen,” this is hardly realistic.
Slipperiness and poor ultraviolet (UV)"
NRCA, Building Code, & Manufacturers Recommend or Require Felt Underlayments on Shingle Roofs
Booth & Roberts and other sources also report that underlayment is required or recommended below shingles. [Reference numbers are to references in the cited document.]
NRCA: NRCA recommends underlays on all shingle roof systems
without exception . A 1990 survey indicated that
79 percent of U.S. roofing contractors always used underlays
Roof Warranty: The absence of underlays can invalidate some
manufacturers’ warranties and roof system fire classifications
Manufacturer's Requirements: typical requirements found in roof shingle manufacturer's installation instructions specify the use of underlayment:
Non-perforated, [Type I, No. 15] [Type II, no. 30], asphalt saturated felt complying with ASTM D 226, ASTM
D 4869 or ASTM D 6757. - Oakridge Pro30™ shingle instructions.
Canadian building codes do not require general (full
roof) underlays under roof shingles. Many Canadian roofing
contractors use general underlays, while others do not.
Typically, underlays are used more over wood plank roof
decks and less over plywood. Underlays are more likely to
be used on lower-sloped roof systems than on steeper
There also are provincial preferences, for
example, Ontario roofing contractors tend to use underlays
less than their neighbors in Québec.
Local building code requirements: here is an example from Coon Rapids, Minnesota
All dwellings, structures attached to dwellings, and all conditioned (heated and/or cooled) structures, require eave
flashing to be installed at the eaves and extending on the roof to a point even with 24” past the inside wall line
barrier shall consist of at least two layers of underlayment cemented together, or be a self-adhering polymer modified
bitumen sheet (many times referred to as ice dam protection or ice and water shield).
It must be installed the full length
of all valleys. On roof slopes of 2/12 to 4/12 the remainder of the roof shall be two layers of 15# felt (applied in shingle
fashion), or 1 layer of ice dam protection. On 4/12 or greater slopes, the balance of the roof shall be one layer of 15# felt.
Five Best-Practices Reasons for Using Roofing Felt Underlayment
Roofing underlayment or felt protects the roof deck from rain before the roofing is
Roofing underlayment or felt provides an extra weather barrier in case of blowoffs
or water penetration through the roofing or
Roofing underlayment or felt protects the roofing from any resins that bleed out of
Roofing underlayment or felt helps prevent unevenness in the roof sheathing from
telegraphing through the shingles.
Roofing underlayment or felt is usually required for the UL fire rating to apply
(since shingles are usually tested with underlayment).
The roof deck should be sound and level before laying the
underlayment. Fifteen-pound or heavier felt underlayment
is required by code in some areas. Whether or not it is
required, underlayment is cheap insurance against problems.
Underlayment On Standard Slopes where Asphalt Roof Shingles are Installed
On roofs with a slope of 4:12 or
greater, use a single layer of 15 lb. asphalt-saturated felt,
starting at the eaves and lapping upper courses over lower
by a minimum of 2 inches. Vertical joints should lap a minimum
of 4 inches and be offset by at least 6 feet in successive
rows (see Figure 2-2 at left).
Secure each shingle course along seams and edges with
enough corrosion-resistant nails to hold it in place until
the roofing is installed.
In high-wind areas, apply fasteners
a maximum of 36 inches on-center along overlaps.
For best protection against leaks, run felt 6 inches
over ridges and hips, from each direction, and 6 inches
up any adjoining walls. Valleys should be lined with a
full width of roofing felt (or bituminous membrane)
pushed tight into the valley so there is no slack.
Asphalt shingles can be used on roofs with
a slope of 2:12 to 4:12 if double-coverage underlayment is
Start with a 19-inch strip of 15 lb. asphalt-saturated
felt along the eaves, and lap succeeding courses by
19 inches as shown in Figure 2-3.
Wherever there is a possibility of ice or snow buildup
or the backup of water from leaves or pine needles, install
a self-adhering bituminous membrane along the eaves that
extends up the roof to a point at least 36 inches inside the
interior wall line.
An alternative approach, not widely used
anymore, is to seal all laps in the lower courses of roofing
felt with lap cement or asphalt plastic cement.
In areas with extensive snowfall or windblown rain,
the best protection against leakage is to cover the entire
low-slope roof area with a bituminous membrane, as
shown in Figure 2-4.
Vertical end laps should be at least 3 inches and horizontal
laps 6 inches. If the roof changes to a steeper slope,
for example, where a shed dormer joins the main roof, extend
the membrane 12 to 18 inches up the main roof slope.
Bituminous membranes are self-healing around nail holes,
and because they bond fully to the sheathing, any leaks
that occur cannot spread.
As a safeguard against expensive
callbacks, many roofers now apply membrane to the entire
surface of any roof with a slope of 4:12 or less.
Eaves Flashing Recommendations for Asphalt Shingle Roofs: using ice & water shield
The best defense against ice dams in
cold climates is a so-called “cold roof,” consisting of high
levels of ceiling insulation separated from the roof surface
by a free-flowing vent space (see “Preventing Ice Dams,”
page 97 in the printed text Best Practices Guide to Residential Construction).
Where a cold roof cannot be achieved due to
complex roof shapes, unvented roofs, or retrofit constraints,
ice dams may form during severe winters, in some cases,
causing pooled water to wet wall cavities and interior
Where adequate insulation and ventilation cannot be
assured, self-adhering bituminous eaves flashing should
be installed. The membrane should go from the lower edge
of the roof to a point at least 24 inches inside the interior
wall line ( Figure 2-5 at left).
Where two lengths of eaves flashing meet at a valley,
run each across the valley, starting with the length from
the roof with the lower slope or lesser height. The valley
flashing should later lap over the eaves flashing.
Install Drip Edge Flashing Below Underlayment or Ice-Dam Membranes at Roof Eaves & Gable Ends
[Click to enlarge any image]
Our photo above illustrates several details of roof drip edge, eaves flashing, and gable end flashing at an asphalt-shingle re-roof job we documented in Dutchess County, New York. From left to right:
Green arrow: points to the white aluminum drip edge installed at the lower roof edge. Drip edge is also sold in brown, black and some other colours.
Drip edge flashing directs roof runoff away from the roof fascia and edge and into gutters or at least not down the fascia board (if no gutters are installed) and it is recommended by roofing standards, manufacturers, and experts.
Orange arrow: points to the installation of ice and water shield along the lower roof eaves - protecting against ice dam leaks that are common on un-vented roofs in cold-weather or snow-climates.
Install the ice and water shield membrane so that it laps securely over and bonds to the surface of the drip edge. The membrane does not have to extend fully to the outer edge of the drip edge flashing, but it should be on top of the upper surface of the drip edge in a best-practices roofing installation.
Otherwise as we repeat just below, some water is going to run under the drip edge rather than be directed off of the roof surface.
Watch out: if the roof is not using peel-and-stick eaves flashing membrane (ice and water shield), you will use roofing felt in this location. In that installation the lower edge of the felt must be on top of, not underneath the drip edge.
That is, the drip edge flashing is the first item installed onto the roof sheathing (or atop old shingles in a multi-layer shingle re-roof job). If you install the drip edge on top of the felt, any condensation or water running down the roof surface between shingles and felt will run underneath the drip edge, down the fascia, and perhaps into the building soffit or walls - not a nice thing.
Blue arrow: points to the first course of 15# roofing felt on this roof. The lower edge of the felt is overlapped 3-4" on top of and over the upper edge of the lower course of ice and water shield.
Brown arrow: points to the first shingle course, doubtless installed as a reference point for this roof job.
Install the starter course (normally a 3-tab shingle installed upside down or a solid asphalt strip) so that its low edge is parallel to the drip edge and extends no more than 1/4" past the drip edge itself. Longer overlaps of asphalt shingles past the drip edge will hang over into the gutter, will send roof runoff off of the roof rather than into the gutter, and will eventually crack, break, and look gross.
See OVERSHOOTING GUTTERS
Just below we illustrate shingles installed with too much overhang into the gutter.
Pink arrow: at the right of the roof along the gable end we see more drip edge being used to flash the roof gable end fascia / trim and roof edge.
I prefer to install the gable drip edge under the felt though that detail is less critical than at the lower roof edge or eaves. When understanding all metal flashings on buildings it makes sense to consider the direction in which water wants to flow: normally "down" (though small up-flows occur by capillary action).
Roofing Felt Installation Details - omitted felt & felt specifications for various roof pitches or slopes
Reader questions on roofing felt installation specifics
(June 28, 2014) Anonymous said:
Hi Dan, a couple of roofing questions:
1) We often see roof felt stopped short of the eaves. Builders argue its not a problem. I once had a written opinion from NRCA stating felt needed all the way to the eaves but can't find it anymore. Any known reference clearly indicating need to felt to eaves?
2) Asphalt shingles on less than 2:12 pitch, builder says ice&water shield under it, I know that's not OK but again any reference source you may know of?
Hope all is well in NY land, nice here in Raleighwood. - Steve Smallman - [Mr. Smallman is a professional home inspector in Raleigh NC - Ed.]
Thanks for the important questions Steve:
1. Felt underlayment omission from some roof areas: this defect - taking a shortcut by leaving off some roofing felt, is an example of a wider problem: building codes & standards writers have given up on trying to anticipate every possible way that people can make a mistake, shifting instead often to "performance" codes that give the general intent of the code. So we'll have trouble finding an explicit citation for your question part 1.
But a reading of roof shingle manufacturer's specifications for using an underlayment (and the article above which is nicely researched) does not find any exceptions that allow leaving out some of the coverage area.
I'd excuse the omission of felt at the eaves and at rake edges of a roof IF instead the roofer is installing a stick-down impermeable barrier such as ice and water shield. Otherwise it's a mistake.
Quoting from NRCA you'll notice that nothing in NRCA's language refers to an "exception" for some roof areas where underlayment is required:
"Underlayment (or "felt paper" as it is frequently called) is installed over the roof deck before the application of asphalt shingles. An underlayment performs two primary functions: it provides temporary weather protection until the asphalt shingles are installed, and it provides a secondary weatherproofing barrier if moisture infiltrates the asphalt shingles."
2. Applying shingles on low slope roofs (< 4:12) is discussed in detail at inspectapedia.com/roof/Low_Slope_Roofing.php
please take a look. ice and water shield over the entire roof should work ok and would be an update to the older method described by carson dunlop associate's sketch at inspectapedia.com/roof/0016s.jpg
for asphalt shingles, NRCA recommends a single layer of no. 15 asphalt-saturated underlayment be used with roofs having slopes of 4:12 (18 degrees) or greater.
for roof slopes between 3:12 (14 degrees) to 4:12 (18 degrees), NRCA recommends a minimum of two layers of no. 15 underlayment. if you are installing a heavier-weight shingle with a projected long service life, using no. 30 underlayment instead of no. 15 would be appropriate.
Inadequacy of Roofing Felt as a Vapor Barrier for Asphalt Shingles in Hot Humid Climates?
A Building Sciences Corporation report [at the citations section of this article] lso elaborates the usefulness of placing a vapor barrier on the roof deck below shingles in hot humid climates. BSC points out that: [some paraphrasing -DF]
Unvented roofs with asphalt shingles in hot humid climates require a vapor
barrier between the asphalt shingles and the roof deck. This is because asphalt roofing materials
store water from dew or rain. Thus asphalt shingles
form a water reservoir not unlike wood shingle or shake roofs.
The report argues that this stored moisture is driven inwards [presumably as water vapor, not liquid water] when sun strikes the damp or wet roof surface, and it continues to argue that moisture is driven through vapor-permeable roofing paper, felt, and plywood or OSB roof decking, thus ultimately into the attic space
But unlike an asphalt shingle roof nailed [over felt] directly to a roof deck, a wood shingle or shake roof that has been installed using best practices includes a disposal path for water absorbed in the roof surface: an air space between the wood roofing and the roof deck, or the installation of wood roofing over spaced nailers or "skip sheathing".
In cool or temperate climates this does not present a problem because the combination of heavy wetting from due or rain i snot combined with solar heating at high outdoor temperatures, say the authors who go on to argue that that buckled roof shingles observed in the morning (caused by moisture migrating back up from the roof deck) relax during the day.
But on an un-vented roof moisture driven inwards [through the shingles, roofing felt, and OSB or plywood roof decking] in hot humid climates, needs to be addressed.
This phenomenon can
typically be ignored in climates other than hot humid climates because the combination
of extensive dew formation and solar heating at high outside ambient temperatures is not
common. In vented roofs, this is often manifested in the buckling of shingles early in the
morning as the moisture migrates in to the roof deck sheathing and the joints close. This
is followed by relaxation and opening up of the roof sheathing later in the day—the
But in un-vented roofs in hot humid climates, the authors argue that water from the roof surface is drawn upwards in liquid form, by capillary action, between plies of overlapped shingle courses where it passes ultimately through the vapor barrier and through the roof decking to the roof cavity interior.
The driving force of moisture through the roof and into the building is by solar heating according to the authors.
[OPINION-DF: from exterior roof inspections at all times of day and seasons, we have not observed this time-related morning roof shingle buckling in the Northeastern U.S. nor in Florida, nor the Southwest, though the authors report the phenomenon.
It is possible that the authors are not quite correct that daily buckling and relaxing of roof shingles can be ignored on a vented roof as harmless, since certainly the product is expected to remain flat, and flexing daily might reduce its anticipated wear life.]
With unvented roof assemblies, this inwardly driven moisture must
be addressed. The preferred method is to prevent the moisture from entering the roof
deck material via the installation of a vapor barrier.
Asphalt shingles are quite impermeable to the passage of liquid water directly through
them. However the geometry of their installation allows wicking at overlaps. This inwardly driven capillary water is the source for the wetting of the
roofing underlayment and roof sheathing.
The material properties of shingles change
under elevated temperatures and moist conditions due to their hygroscopic nature. The
large vapor pressures resulting from incident solar radiation and the changed material
properties are sufficient to drive moisture inward through the shingles.
Roofing felts or underlayments vary greatly in their permeability to water vapor; the
typical underlayment used under asphalt shingles in residential construction is quite
[QUESTION-DF: we note that the test chamber constructed by BSC was itself in an enclosed, air-conditioned space, and that the underside of the test chamber roof was at least in part exposed to the air conditioning. It seems possible that the reduced humidity and lower temperatures on the "interior-side" of the test roof may have contributed to moisture behaviors that vary from what occurs in the field.
Attics and under-roof spaces such as in an un-vented "hot roof" cathedral ceiling are certainly not exposed to cool dry conditioned air. BSC may have addressed this concern but we did not find it in the referenced article.
The conclusion of the BSC report is an argument for installation of an impermeable moisture barrier underneath roof shingles, perhaps in place of the traditional and permeable roofing felt.
What are the differences between the test roof and a roof's behavior in the field?
How does the impermeable moisture barrier under roof remain impermeable when perforated by shingle nails or staples? What will be the market effects of suggesting entire roofs be underlaid first with a moisture barrier unaffected by roof shingle fasteners such as ice and water shield?
Why not recommend that all roofs and roof cavities include ventilation in their design, not only solving the possible driven-moisture problem discussed by BSC but also providing for longer shingle life (cooler roof surface) and in cooling climates, possibly reduced building cooling costs?]
History of Roofing Felt & Underlayment Codes or Specifications
11 Sept 2015 Doug Nader said:
When was it made code to have tar paper/felt under shingles?
"Code" is a bit vague of a question as to come up with a "first required" date for roofing felt in the building codes we'd need to say what code you are asking about: your local, state, country, or model code or what? Most modern codes require complying with the manufacturer's recommendations even if a specific detail or component is not addressed directly in the code. The history of tar paper or roofing felt goes back to at least the 1800's. I have not found an exact citation but I believe you'll find the discussion of felt underlayment in the earliest roofing codes. The first U.S. building codes date from 1859 (Baltimore, MD). - Wikipedia ret. 12 Sept 2015
Building codes in the U.K. obtained impetus with the first significant building regulations passes as the "Rebuilding of London Act" passed by Parliament after the Fire of London in 1666. For a U.S. history of the use of and requirements for roofing underlayment or felt see the following patent (I've edited and cleaned up some typographical errors in the Google patent version of this document to restore Josiah Jowitt to his position of honor).
Jowitt, Josiah or Stanley, Felt, Roofing. "Roofing-felt and its manufacture." U.S. Patent 318,910, issued May 26, 1885.
Note that this patent refers to long-established earlier roofing felt processes. Excerpting:
Roofing-felt as usually made consists of two or more, usually three, layers of felt-paper which have been separately saturated with with coal-tar pitch and pressed together. The layers are thus coated by passing them in extended webs through a tank of hot ,pitch.
They are then passed between pressure-rolls to press them together and squeeze out the excess of pitch, and they are then cooled and dried, and finally wound up in a 'compact roll for the market. As all the layers are coated with the pitch, the contacting convolutions in the roll are liable to adhere together, particularly in warm weather when the pitch is [softened] by the heat, and when this occurs the material becomes practically valueless, because of the impossibility of unrolling it.
To prevent this adherence of the superposed couvolutions, various expedients have been devised for preventing their contact, such as rolling up a web of Manila paper with the roofing-felt, or sprinkling upon the felt some absorbent powder which is rolled up with it. These precautions are somewhat effective, but entail considerable expense and annoyance both in the manufacture and use of the felt.
The principal object of my invention is to produce a roofing-felt or other similar material which shall be in all respects equal to that heretofore made, and which shall be cheaper,
more durable, and heater to handle, and
which, above all shall have a non-adhesive
surface, so that the convolutions in the roll will not adhere together.
To this end I make the .felt with a dry outer surface, containing only enough tar or pitch to make it waterproof or weather-proof, and confine the heavier or cementing coating of tar or pitch to the interior of the felt-between the surfaces which entirely to the edge of the fabric, but by preference I leave the layers uncemented along each edge, so that the pitch cannot ooze out at the edges of the fabric and cause the confelt made according to my invention.
Other roofing felt history, development, patents & code citations
Berg, Bo. "Method of laying roofing felt and means therefor." U.S. Patent 5,526,624, issued June 18, 1996.
Ernst, Boley. "Roofing nail." U.S. Patent 1,435,134, issued November 7, 1922. - for fastening roofing felt to the roof deck
Hugh, Lucas Parsons. "Roofing." U.S. Patent 2,205,307, issued June 18, 1940.
An object of my invention is to provide a slate -roof structure wherein the slate units in each course are laid to expose relatively large areas to the weather so as to p rovide coverage for a relatively large roof area with a relatively small amount of slate, thereby reducing the cost of the roof as well as the load of the slate coverage.
Roofing felt or equivalent material underlies each course of slate for cushioning purposes in addition to providing an effective seal against the entrance of moisture.
I also provide novel means for rendering splices between adjoining strips of roong felt moisture-proof to the end that the roof structure may have moisture-proofed properties throughout in addition to permitting the use of strip material of shorter lengths than the width of the roof.
ICC, International Code Council, Section 1507, Requirements for Roof Coverings
UNDERLAYMENT. One or more layers of felt, sheathing paper, nonbituminous saturated felt or other approved material over which a steep-slope roof covering is applied. ...
Underlayment shall be two layers applied in the following manner. Apply a minimum 19-inch strip or underlayment felt parallel to and starting at the eaves, fastened sufficiently to hold in place.
Starting at the eave, apply 35-inch-wide sheets of underlayment overlapping successive sheets 19 inches and fastened sufficiently to hold in place.
Unless otherwise noted, required underlayment shall conform to: ASTM D 226, Type II; ASTM D 2626 or ASTM D 249 Type I mineral-surfaced roll roofing.
1508.3.3.1 Low-slope roofs.
For roof slopes from 21/2 units vertical in 12 units horizontal (21-percent slope), up to four units vertical in 12 units horizontal (33-percent slope), underlayment shall be a minimum of two layers applied 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 fastened sufficiently in place.
1508.3.3.2 High-slope roofs.
For roof slopes of four units vertical in 12 units horizontal (33-percent slope) 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 mm), fastened only as necessary to hold in place.
Overbury, Frederick C. "Process of making roofing felt or like material." U.S. Patent 1,558,495, issued October 27, 1925. Abstract excerpts:
This invention has for its object to produce a fibrous material which will possess strength and flexibility and also marked fireproof qualities....
According to my invention and to meet the object thus specified, I provide a multiply sheet formed of layers of paper felt and asbestos, the fibers of the several layers being intermingled and adherent, so 25 that the sheet is an integral structure.
In the manufacture of this sheet, the paper felt layer a is formed of cotton and wool or other suitable fiber in the usual manner, into a wet pulpy web, upon which is deposited a wet pulpy web of asbestos fiber b.
These'may be then subjected to a felting action in a machine or apparatus of the ordinary construction, or be dried in the usual dryin machine, thus producing a sheet, one face of which is paper felt (so-called) and the other face of which is asbestos, the two layers being interlocked I together by the intermingling of their fibers without the use of any foreign binder or cement.
It is quite apparent that the sheet may consist of more than two layers of the asbestos and of the Wool fiber, as for instance the layer of asbestos can be laid between the layers of Wool felt, or vice versa.
After the sheet has been dried into a porous absorbent condition, it then may be saturated with asphalt or any other of the usual waterproofing compositions which are employed in the manufacture of prepared roofings, and then faced, preferably on the wool-felt side, with a layer of high-meltingpoint asphalt or .pitch a, as shown in Figure Renewed November 14, 1919. Serial No. 338,118.
produce commercially a roofing material which is substantially fireproof.
It has been proposed to cement together, as by the use of pitch, sodium silicate, or the like, a layer of asbestos upon a layer of roofing felt, but this increases the cost of production of the roofing material.
Sheet asbestos, when sufiiciently thin to be used alone, does not possess the necessary tensile strength, whereas wool felt alone, while relatively slow-burning when impregnated as described, does not really possess the desirable fireproof qualities.
According to my invention, I provide a single integral sheet, in which the strength is afforded by the felt layer, and the fireproof qualities of the asbestos layer.
It is unnecessary herein to describe the operations by which the raw material, cotton ,or wool rags, or the asbestos, are disintegrated and reduced to awet fibrous pulp, or the machines by which they are formed into webs 01'' layers, as the same are well known.
If desired, the sheet may have only the felt layer saturated or coated, or both, with a waterproofing or non-heat-conducting compound, or the asbestos layer may be saturated or coated, or both, in either instance leaving the other layer untreated, this being of course subject to particular requirements.
While the composite sheet as herein described is particularly applicable for use in the manufacture of flexible waterproof roofing, yet its use is not confined thereto, as it may be employed for a variety of other uses. For instance, but without limitation, the sheet may be'employed for the purpose of insulation, or as a flooring, or for other purposes.
For some purposes, the sheet may be so treated as to saturate with a waterproofing or non-heat-conducting compound only the fibrous layer, leaving the asbestos layer unsaturated, or vice versa.
What I claim is The herein described method of producing-a flexible composite sheet of fibrous material, consisting in bringing into face contact two layers of wet pulpy felted fiber and asbestos fiber, causing the said fibers of said layers to interlock, and then drying the sheet thus formed.
Wilson, James. "Apparatus for laying roofing-felt." U.S. Patent 1,278,272, issued September 10, 1918.
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did omission of felt underlayment contribute to shingle blow-off in windy conditions?
(Aug 18, 2011) mike callahan,lake erie roof&sid said:
I have encountered a roof with absolutely no felt in what way did this contribute to the seal of the roofing if any? Shingles are blowing off constantly! The roof was installed in 1998
Mike, the article above quotes authoritative sources on why we want felt below asphalt shingles on a roof. But I haven not found any reference to a connection between shingle blow-off and the absence of felt. If shingles are blowing off of a roof it's most likely because
- the self-sealing tabs did not seal
- the shingles were not properly nailed
- the roof is exposed to particularly high winds
On the other hand, the omission of felt underlayment may increase the roof leaks that occur during a storm when shingles blow off of the roof.
(Dec 12, 2011) Jon Wright said:
Are there any OSHA, IRC, NRCA or other regulations about using stronger than 15 lb. felt on steeper roofs to protect the installer?
15# felt is the minimum recommended felt thickness. Other specifications are in the article above.
[delete] (Aug 16, 2012) Anonymous said:
My name is Dennis from Deco roofing systems ltd.
I am looking for a board which is between 10-12mm thick to be used as an under layer material for the Shingles.
Mostly what we use is silvachip board which is a recycled material from tetrapak.
Kindly advice on whether we can get a material which can be nailed on the roof and if possible it should be waterproof.
We are considering importing several containers for our running projects.
Looking forward to hearing from you soon.
(Oct 12, 2012) Mike said:
can you install new felt over the old felt? what negative effect can it have?
No particular problem except if you leave a mess or old half-driven nails or old rippled, torn or folded felt you may have a rough surface that punctures new felt and shingles or causes the new roof not to lie flat. One needs to make a field decision based on the on-roof conditions.
(Nov 19, 2012) Maria form Cancun said:
I live in McALlen Tx. In april, we had a historic hail strom. My 2 rental houses' roofs were replaced by a cheating Roofing Company. Contract said: 25 Owens Corning, but he installed Tamko 20year; and all wrinkled. Now he wants to offer me what the original contract said: Ownes Corning 25 years. My question is: 1500 shingles x 5 nails each one = 7500 extra holes the plywood will have. I do not like the idea of having a strainer as a roof. I want this cheating roofer to install new plywood as punishment for being a thief.Pleas,e help me with yor answers. Maria from Cancun
It is common to install three or even more shingle roofs atop the original roof sheathing without worrying that the sheating has been damaged by prior nails.
Just be sure that the OLD roofing is first removed. Mulit-layered shingles on a roof often have a shorter life. ALso that will allow an actual inspection of the roof decking or sheathing - any rotted or damaged sections should be replaced.
(Feb 6, 2013) Anonymous said:
I inspected a home today that was originally a shake roof, now a concrete tile roof. The structure is reinforced 2X6 so I am not as concerned about the weight, as I am the underlayment. I found the roof had metal hat channel screwed to the skip sheathing and a heavy paper, almost cardboard type underlayment between the hat channel and concrete. I saw no battens supporting the tiles and all the fastener at the ridge and valleys were exposed screws. Has anyone seen anything like this? The roof was installed in 2004
(Apr 12, 2014) Jonathan said:
We just started manufacturing roofing underlayment in india and we are trying to find dealers on north America who can market this product.
Please advice or comment over how to go ahead or can some one be bridge between us and end users.
(July 1, 2014) Anonymous said:
Would it be safe/wise to insulate a cathedral ceiling with, say, styofoam/then sheeting, then asphalt shingles from the outside and how would you vent the heat out of the interior - gable end vents? I'd prefer not to insulate from the inside. I'd like to keep the look of the interior cathedral boarding (3.5" fir).
I've installed a design that placed foam insulating board atop rafters, followed by plywood, then roofing; we left an air space between the plywood deck underside and the top of insulation placed between the rafters in an effort to obtain a very high-R roof. It seemed to me to have been a waste to place that uppermost layer of foam insulating board. However there has been more recent research on the effects of and benefits of heat transmission through top-insulated roofs.
If you don't want to disturb the interior finished ceiling you indeed have to insulate from above. Some approaches include
- installing insulated strutural panels onto the rafters or over an existing roof deck (after tearing off old roofing) - making either a hot roof design or using insulating panels that inclde a vent path from eaves to ridge vent
- tearing off decking, insulating between rafters - foam or fiberglass - leaving (or not) an air path (hot roof or not)
- Nailing high-R solid foam atop rafters (or existing bare decking) then plywood, then roofing, venting the rafter space from eaves to ridge
(July 8, 2014) greg o said:
hi. who is responsible for step flashing caulking when a new roof has been installed? thanks
In my opinion the caulking of the upper edge of step flashing, if the design requires that sealant use, is certainly part of installing the step flashing itself, not a separate job. Usually roof flashing installation is part of roof installation, though there could be exceptions such as when a roof penetration is installed *after* the roof has been installed. Then proper flashing should be part of the installation of whatever that subsequent thing was - a chimney, plumbing vent, etc. If the installer does not know how to install flashing then s/he needs to arrange with a qualified roofer or other person who knows how to install flashing - else the job will leak and thus have been improperly executed.
Question: remove existing flashing to install ice and water shield properly
(Oct 24, 2014) Leslie said:
I am having my roof re-shingled and I am worried about my skylights. I asked the roofer if we should install ice & shield around my skylights but he said it's not necessary as he doesn't think it's a good idea to remove the skylight flashing. He said the ice & shield goes under the flashing and he's reluctant to replace the current skylight flashing since it is not leaking. Is this true or is he just trying to avoid extra work? Other roofers I received quotes from said I should install ice&shield and new flashing around skylights.
He's got a point that it is difficult to install ice and water shield under existing flashing. He' d have to remove and reinstall the flashing to do a good job. That's what I'd prefer.
Question: felt underlayment on concrete tile roofs?
(Mar 29, 2015) Sam S. said:
My house has a concrete tile roof where the tiles were nailed directly to the spaced sawn wood stripping that is nailed to the roof rafters. There was no felt underlayment used and no deck to apply it to. This roof is now 36-years old and has never leaked, at all. Would felt underlayment improve this assembly and how would it be installed?
Sam you don't say where you live - as concrete roof tile installation requirements or specs vary by jurisdiction.
At any event, there is no cost-reasonable way to add felt below the existing concrete tile roof. Leave it alone and bring this up again at re-roof time - if we live that long.
Question: is tar paper required by building codes?
(May 9, 2015) Debbie Cleland said:
I need to know if tar paper is a must under the building code...My roof was reshingled in 2008 and this year had a leak...the roofer who fixed leak said there is no tar paper under my shingles..Is this against the code...can the contractor be fined and made to bring my roof up to code? I live in Elliot Lake Ontario canada
Roofing manufacturers recommend using roof underlayment. It does not have to be specifically "tar paper" as other products are also available.
If your local building codes require following the manufacturer's installation instructions then underlayment is probably requried where you live.
Question: installing new shingles direct on plywood?
(June 19, 2015) Norma said:
We moved into a home in a newer subdivision (10 yrs. old). When we bought the house 4 years ago that would have made the shingles/roof 6 years old. We, along with several other neighbours are now faced with having to re-shingle our roofs. Some quotes from a variety of roofers are saying we don't need a membrane under the new shingles. We feel the current problem we are all having is because there is NO underlay or membrane on the roofs.
We live in a cold/hot climate in Canada and because of those types of weather conditions (which are sometimes very very severe) we feel the membrane is necessary. Some owners have decided to go ahead and apply new shingles to just the plywood. Is this a good choice?
1. follow the shingle manufacturer's recommendations to install underlyament
2. in freezing climates like Canada I'd like to see liberal use of ice and water shield at eaves, valleys, and other leak-prone areas.
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"Unvented Roofs, Hot-
Humid Climates, and
Asphalt Roofing Shingles
Research Report - 0306
Building Science Corporation", Building Science Corporation, 30 Forest Street,
Somerville, MA 02143
Quoting from the article abstract:
"When constructing unvented roofs with asphalt shingles in hot-humid climates, a vapor barrier must be
installed between the asphalt shingles and the roof deck." - Web Search 5/21/2010
NRCA Roofing & Waterproofing Manual, 5th Edition, National Roofing Contractors Association, 10255 W. Higgins Road
Rosemont, IL 60018-5607
Telephone: (847) 299-9070 Toll Free: (866) ASK-NRCA (275-6722), e-mail: firstname.lastname@example.org. - http://www.nrca.net/rp/pubstore/details.aspx?id=243&c=9
Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: email@example.com or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
Steve Smallman, Raleigh, NC, Email: firstname.lastname@example.org, Website: http://stevesmallman.com/ - Quoting: Steve Smallman Property Inspections (SSPI) inspectors have performed or supervised over 25,000 inspections since we introduced home inspections to the Triangle area in 1980. Mr. Smallman is a contributor to InspectApedia.com and has commented on or provided information on plumbing traps, commercial FPE electrical panels and DIY Tests of FPE equipment,, roofing underlayment, and building exteriors.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Green Roof Plants: A Resource and Planting Guide, Edmund C. Snodgrass, Lucie L. Snodgrass, Timber Press, Incorporated, 2006, ISBN-10: 0881927872, ISBN-13: 978-0881927870. The text covers moisture needs, heat tolerance, hardiness, bloom color, foliage characteristics, and height of 350 species and cultivars.
Green Roof Construction and Maintenance, Kelley Luckett, McGraw-Hill Professional, 2009, ISBN-10: 007160880X, ISBN-13: 978-0071608800, quoting: Key questions to ask at each stage of the green building process Tested tips and techniques for successful structural design
Construction methods for new and existing buildings
Information on insulation, drainage, detailing, irrigation, and plant selection
Details on optimal soil formulation
Illustrations featuring various stages of construction
Best practices for green roof maintenance
A survey of environmental benefits, including evapo-transpiration, storm-water management, habitat restoration, and improvement of air quality
Tips on the LEED design and certification process
Considerations for assessing return on investment
Color photographs of successfully installed green roofs
Useful checklists, tables, and charts
Roofing The Right Way, Steven Bolt, McGraw-Hill Professional; 3rd Ed (1996), ISBN-10: 0070066507, ISBN-13: 978-0070066502
Slate Roofs, National Slate Association, 1926, reprinted 1977
by Vermont Structural Slate Co., Inc., Fair Haven, VT 05743, 802-265-4933/34. (We recommend this book if you can find it. It
has gone in and out of print on occasion.)
Roof Tiling & Slating, a Practical Guide, Kevin Taylor, Crowood Press (2008), ISBN 978-1847970237, If you have never fixed a roof tile or slate before but have wondered how to go about repairing or replacing them, then this is the book for you. Many of the technical books about roof tiling and slating are rather vague and conveniently ignore some of the trickier problems and how they can be resolved. In Roof Tiling and Slating, the author rejects this cautious approach. Kevin Taylor uses both his extensive knowledge of the trade and his ability to explain the subject in easily understandable terms, to demonstrate how to carry out the work safely to a high standard, using tried and tested methods.
This clay roof tile guide considers the various types of tiles, slates, and roofing materials on the market as well as their uses, how to estimate the required quantities, and where to buy them. It also discusses how to check and assess a roof and how to identify and rectify problems; describes how to efficiently "set out" roofs from small, simple jobs to larger and more complicated projects, thus making the work quicker, simpler, and neater; examines the correct and the incorrect ways of installing background materials such as underlay, battens, and valley liners; explains how to install interlocking tiles, plain tiles, and artificial and natural slates; covers both modern and traditional methods and skills, including cutting materials by hand without the assistance of power tools; and provides invaluable guidance on repairs and maintenance issues, and highlights common mistakes and how they can be avoided.
The author, Kevin Taylor, works for the National Federation of Roofing Contractors as a technical manager presenting technical advice and providing education and training for young roofers.
The Slate Roof Bible, Joseph Jenkins, www.jenkinsslate.com,
143 Forest Lane, PO Box 607, Grove City, PA 16127 - 866-641-7141 (We recommend this book).
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones