Modified bitumen roof questions and answers.

This article series describes modified bitumen roofing materials, choices, installations, inspection, defects, roofing repairs, and product sources.

Page top photo courtesy of W. David Schwaderer.

Modified Bitumen Roofing Materials, Choices, Costs, Life Expectancy, Characteristics

These questions and answers about mod-bit roofs were posted originally

at MODIFIED BITUMEN ROOFING - be sure to revew that information given there.

Question: ok to face-nail the modified bitumen cap sheet?

(Dec 27, 2015) Gary said:
Can you face nail the cap sheet of a SBS or APP modified bitumen. I recently observed this on a home I inspected and thought it was incorrect.

Reply: dubious

I agree with you. All that's necessary is to find the manufacturer and product name, then take a look at the manufacturer's installation instructions for the modified bitumen roof.

On 2017-02-02 by (mod) - modified bitumen roof flapping in high winds

Corinne, clearly, yes as you observed the roof flapping.

It's worth some careful inspection - your roof is clearly not a fully-adhered system OR if it was supposed to be fully-adhered to the roof deck that adhesion has failed.

Air can get under a membrane roof at eaves vents if there is even a single gap or opening in the roof decking between the vented under-roof space and the roof covering, or if there are openings under roof edge flashing, or if there is an open seam that was missed and needs repair.

On 2017-02-02 by Corinne DeHamer

We have a touchdown roof on a flat roof house. On a day with sustained winds of over 20mp with gusts much higher, a roof inspector observed the roof "flapping". Upon inspection, the roof is securely attached all around the outside.

Is it possible for air to get under the roof through a vent, etc., and cause it to appear as if it was waving?

On 2016-09-03 by (mod) - difference between a tar and gravel roof and a modified bitumen roof?

Anonymous:

Sure, thanks for asking the difference between modified bitumen and tar and gravel - it's pretty easy to tell the difference:

Modified bitumen is a membrane roof, often coated with mineral granules (tiny fragments less than 1/16" in size) that is put down cold and glued or put down by using a torch to heat overlapping seams; You will see a continuous and fairly smooth surface and the individual courses of material will be about 36-39" apart. Except for the overlap at seams, a modified bitumen roof is a single membrane in thickness over the roof surface.

You will never see actual gravel (chunks of rock say 3/16" to 1/4" in size) on a modified bitumen roof.

A plain "tar and gravel roof" also referred to as a "built-up roof" or BUR is quite different from modified bitumen.

The tar and gravel roof is built-up of (typically) three to five layers of roofing felt. As each layer is applied and mopped down using hot tar between layers, we end up with not a single membrane but a multiple-ply membrane (3-5 plies).

The more plies that are used the longer will be the roof life and the more reliable will be the roof's performance against leaks. And since we're working with roofing felt, sold in 36" wide rolls, the width between the seams will always be smaller than a modified bitumen roof.

For example a 3 ply BUR roof will have (36/3) seams that are 12" apart.

On TOP of the BUR roof we might find only hot mopped tar, but a traditional "tar and gravel" BUR will sport a layer of gravel as I described above. The gravel has several functions including protecting the roof surface from photo-oxidation (sunlight) and sometimes serving as a ballast.

When you see gravel on the roof it's a "tar and gravel" BUR, and if you carefully sweep away some gravel you'll see the topmost layer of hot tar into which the gravel was spread. Some roof inspectors do this to see how much dust and dirt have settled down under the gravel as that's one (of several) indicators of the age of the roof.

Our much-admired friend Tom Byrne, a NY Home inspector, was on a tar and gravel roof with the building owner, lawyers, and the roofer who had just charged the owner for a "whole new built-up tar and gravel roof". There was an argument about whether the whole roof had been re-surfaced or if the roofer had just patched a section.

The roofer insisted the whole roof had been re-done. Tom bent over - which for him was an accomplishment as he was BIG - and swept back some gravel on the supposedly-two-day-old whole new roof. He pointed out several decades worth of mud and dirt under the gravel - there was no question that this roof section was old.

Tom stood up. "This is not a new roof" he said.

"Yes it is" said the roofer.

"Look at all this mud and dirt under the gravel. You said the roof is 2 days old. If that were true I'd see new clean black tar, not 20 years of mud and dirt" said Tom.

The owner glared.

The lawyer began to smile.

I asked Tom what happened next.

The roofer said "You don't know what the f@**@ you're talking about!" and stormed off of the site without another remark.

See BUILT UP ROOFS at https://inspectapedia.com/roof/Built-Up_Roofing.php for details about built-up roofs (BUR roofs).

On 2016-08-30 by Anonymous

Can you tell me the difference between a new modified bitumen roof system and a plain tar and gravel roof?

On 2016-09-03 by (mod) - Torch Down Solar III and then covering with Asphalt shingles

Jeanell:

Sounds as if you're ending up with at least 3 layers of roofing - perhaps less expensive than doing a tear-off.

How bad is the hail damage? Hail that scours off granules does shorten remaining roof life but unless there's other damage there's not an immediate leak problem, right?

"Torch down" may not be a specific product but rather reference to a torch-applied modified bitumen roof membrane. Why are we doing that followed by shingles?

Just for cosmetic reasons? If so, why do we need the membrane under the new layer of shingles.

This advice you report is confusing.

Watch out: some roof membranes such as ice and water shield underlayment products are specifically designed to seal around nails that penetrate the membrane as it's nailed to the roof surface.

Other roofing materials will not seal around nails. Nailing shingles over the latter on a low slope roof risks building a leaky roof that gives continuous trouble later-on.

On 2016-08-30 by Jeanell

To repair hail damage on a flat sunroom Roofer recommended putting down Torch Down Solar III and then covering with the same Asphalt shingles used on the rest of the house. Is this advisable?

On 2016-07-26 by Frank

Thanks

On 2016-07-25 by (mod) - more on mod-bit roof life

Frank, see MODIFIED BITUMEN ROOF DEFECTS & ROOF LIFE

and also

MODIFIED BITUMEN ROOF LIFE RESEARCH at https://inspectapedia.com/roof/Modified_Bitumen_Roofing.php#Mod_Bit_Life

On 2016-07-25 by Frank

Thanks. do you know where I might find more info (an article?) as to your opinion? It makes a lot of sense. tx

On 2015-11-17 by (mod) -

Tom:

"Legal" is a bit of a broad term; if you are asking if there are New York or model building codes prohibiting multiple layers of rubber roofing, no. But "torch down" ?

Something sounds very wrong with this sequence. Rubber roofs are glued, or mechanically-fastened and glued. They are not put down with a torch.

Modified bitumen is torched-down as might be traditional tar and felt or tar, felt and gravel roofs.

On 2015-11-17 by Anonymous

In ny tom

On 2015-11-17 by Tom

Is it legal to torch dowm rubber roofing over n older exsisting rubber roof???

On 2015-09-23 by (mod) -

Assuming the alligatoring is happening in the roof before you've applied a coating, the coating can help seal those cracks and may give you a few years more roof life before the roof needs replacement.

Why un-fibered? Perhaps to allow the sealant to soak into those hairline cracks? My OPINION is that the fiber-reinforced coating is thicker and more durable.

On 2015-09-23 by jamey

I have what I think is a mod bit roof about 15 years old. A pro roofer suggested about 2 months ago that I coat with un-fibered aluminum coating to help extend its life.

I was about to apply the coating but the material seems to have alligatoring over much of the surface which there seems to be more since the roofers inspection. Also, black dust from what I think is the drying out of the material has me concerned that the aluminum coating won't adhere very well. Any advice would be greatly appreciated. Thanks

On 2015-02-19 by (mod) -

Ken

Generally in a built-up roof, each additional ply will extend the life of the roof.

But I don't quite understand your question. Modified bitumen is a single-ply roofing system.

Multiple ply roofs using layers of felt and asphalt are described separately at

BUILT UP ROOFS at https://inspectapedia.com/roof/Built-Up_Roofing.htm

There you'll see that a common rule of thumb is each additional ply is worth about 5 years more of roof life.

On 2015-02-19 by Ken Wetcher

my roofer priced out 2 ply and 3 ply modified bitumen roofing system. how do I decide which to get?

On 2015-01-12 by (mod) -

Beth I can only SPECULATE since I don't know anything about the fire you describe nor how it was handled during the burning. But I speculate that a building fire only 50 feet away might indeed damage a bituminous roof by heat, causing loss of volatiles, even pitting or subsequent cracking, not to mention possible mechanical damage if debris fell onto the lower roof.

I'm reluctant to address the broad question of what the fire department should have done, given the absence of any information about the event. But you could certainly take that question to your fire marshall. Respectfully, Mod.

On 2015-01-12 by beth

how would high heat from a two story building burning down approximately 50 foot away affect a modified bituminous roof of a one story building? Would the heat alone from that distance or heat combined with water from fire trucks to prevent fire spreading to the nearby building in question affect the bituminous roof and how?
thanks

On 2014-10-06 by (mod) -

Can

I'm doubtful about this idea - both because parapet walls ask for leaks and because I'm not clear how we torch modified bitumen to fiberglass.

On 2014-10-01 by Can Modified Bitumen be applied to a fiberglass deck?

Hi I have a 4 yr old roof deck that is fiberglass closed in with parapet walls in which two horizontal 4" x 4" copper thru-wall boxes drain onto the adjacent flat Mod. Bitumen roof. They leak and have been sealed and resealed.

I want to remove the lower 8' section of the parapet wall and allow water to sheet flow from the glass deck onto the roof w/ no drains invloved.

this would entail patching /tying the glass to the main flat Mod Bit roof surface. Roofers are more than willing to take my money to do this but Can this be done and last ?

On 2014-08-14 by (mod) -

The number of layers of asphalt roofing or other roofing membrane materials is usually regulated by local codes and depends on what other layers and materials are present. Most roofers don't like to add layers because of various installation, wear and performance concerns. A typical local code limit might be 3.

On 2014-08-11 by l

how 'many times can you put modified on roof.

On 2014-05-22 by (mod) -

I would be reluctant to do that as you wii blow off the protective granules

On 2014-05-22 by Pat

White reflective coating now grayish black - can it be power washed before energy cote reapplied

On 2014-04-15 by (mod) - Can the existing roofing be cutback to the new edge and re-tourched down at that edge?

Anon, you will need to construct a new fascia, drip edge, and then use the same edge seal method that was installed on the original roof.

That means choosing the proper roof edge termination strip to match what's there. With modified bitumen it's easy to torch down a patch of the same material over the new drip edge and onto the adjacent remaining original surface. Be sure it's clean of course.

Using a small mod-bit detailing torch or equivalent is probably all you need; don't over-heat nor set the house afire.

DO not use a solvent-based roof mastic or patching compound nor a flashing tape - as many are incompatible with modified bitumen - without first checking with the manufacturer.

On 2014-04-15 by Anonymous

Have a flat Bituman roof that was torched down. I need to cut back a small corner of the overhang section of the roof (2'x4') to allow adjacent tree trunk clearance.

I have framed the new facia around the cutout. Once I cut the roof away, how do I deal with the Bituman roofing as far as re-sealing it down around the edges of the cutout area?

I will install new drip edge around the new cutout edges, but I don't know how to re-seal the edge of the roofing material at the new drip edge.

Can the existing roofing be cutback to the new edge and re-tourched down at that edge? Do I lay new roofing over the existing roof and torch it down at the new drip edge? or? Thanks for your help

On 2014-03-25 by (mod) -

Dawne I think your roofers are correct that modified bitumen is not compatible with a tar and gravel BUR. The right repair would be to use the same material as the original.

Rather than risk surprise leaks and water damage I'd ask a professional roofer to make the proper repair. Surely this is a small patch job.

On 2014-03-25 by Dawne

We had a company move our furnace to the attic which left venting holes in the ceiling. We have a mid century (1961) one story home with a tar and gravel built up roof. 7 eight foot tongue in groove slats were replaced on the vaulted ceiling.

The outer roof was repaired with modified bitumen roofing. Two roofers told me that the BUR was not compatible with a torch down repair. Will the repair last? It was the responsibility of the Heating and Air company to seal the roof.

On 2013-01-30 by george

I've recently discovered a problem in a Katepal-covered roof - water appears to be getting through the roof after 4 years.

The roof surface consists of Superkatepal shingles on top of a breathable membrane, on 6" x 1" roofing boards (as recommended). I'm currently following this up with Katepal, but I would appreciate any advice on the best way to resurface the roof, as it's beginning to look as though this will be necessary.

On 2012-08-30 by Alfred

In this article we can read:
"Modified bitumen is easily repaired without solvents or adhesives. It is compatible with asphalt shingles and asphalt compounds, although patching with roofing cement is not recommended."....
OK, solvents, adhesives and asphalt compounds, this is what NOT RECOMMENDED to use to repair the roof. What should DO RECOMMEND use then??

On 2012-08-03 by (mod) -

Robert

Take a look at EPDM, RUBBER, PVC ROOFING (article link in our ARTICLE INDEX) to see the properties of rubber or EPDM roofing - you'll see that modified bitumen is a very different product from rubber in thickness, composition, installation procedures, and most likely life expectancy as well.

On 2012-08-03 by robertsumnerjackson@yahoo.com

How does this product compare with rubber roofing?

On 2012-02-15 by Ahmed Waziry

what is the LEED's points for Bituminous modified reinforced waterproofing membrane?

...

Continue reading at ROLL ROOFING, ASPHALT & SBS - modified bituminous roofing, sold in rolls and applied to low-slope roof areas can be mistaken for mineral-granule-coated roll roofing, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• MODIFIED BITUMEN ROOFING - home
• DEFINITION OF MODIFIED BITUMEN
• IDENTIFY MODIFIED BITUMEN vs ROLL ROOFING
• MODIFIED BITUMEN PROPERTIES & INSTALLATION
• MODIFIED BITUMEN ROOF COATINGS & PAINTS
• MODIFIED BITUMEN SHINGLES
• MODIFIED BITUMEN ROOF DEFECTS & ROOF LIFE
• MODIFIED BITUMEN ROOF DEFECTS & ROOF LIFE FAQs
• MODIFIED BITUMEN ROOF WEAR & MAINTENANCE
• MODIFIED BITUMEN ROOF BUCKLING PROBLEMS
• MODIFIED BITUMEN ROOF LIFE RESEARCH

Suggested citation for this web page

MODIFIED BITUMEN ROOFING FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ROOFING

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