Thread: # of layers allowed

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As far as the second layer is concerned, as AFAIK, the codes give only general guidance:

IRC R907.3 Recovering versus replacement. New roof coverings shall not be installed without first removing existing roof coverings where any of the following conditions occur: 1. Existing roof or roof covering is water-soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.

So, what’s “adequate”?

You pretty much going to have to look to the manufacturer for more specific information.

Owens Corning installation instructions and warranty are pretty typical:

From the OC warranty :

WHAT IS NOT COVERED
Damage to the product due to any cause not expressly covered herein. After our shingles leave our manufacturing facility, they are subjected to conditions and handling beyond our control that could affect their performance. This warranty does not cover any problems with non-defective shingles caused by conditions or handling beyond our control. Some examples of conditions not covered by this warranty include:
1. Acts of God, such as hail storms and winds in excess of wind levels listed in the chart at the end of this warranty;
2. Foot traffic on your roof or damage caused by objects (such as tree branches) falling on your roof;
3. Improper or faulty installation of your shingles. Installation must be in accordance with our written installation instructions;
4. Discoloration caused by algae, fungi, lichens or cyanobacteria (unless are pretty typical:

From the installation instructions:

If old asphalt shingles are to remain in place, nail down or cut away all loose, curled or lifted shingles. Sweep the surface clean of all loose debris just prior to applying the new roofing. Ensure proper size and length of fasteners. If roofing over old wood shingles, cut back the old shingles at eaves and rakes and apply wood edging strips. Some local building codes may require the use of a No. 30 asphalt saturated felt over the old wood shingles prior to reroofing. Consult local building code authorities. The surface must be smooth before shingles are installed. Make deck smooth by nailing down all loose and curled shingles, protruding nails, etc. Install beveled wood feathering strips, if necessary.

So, if you client has OC shingles, and problems after a roof-over, and the old roof was not "smooth"...

Originally Posted by Clay E White

It is correct that at most, only two layers of asphalt composition shingles are allowed?

Also, when installing a second layer of comp. shingles on top of the first layer, do you install underlayment in between the two layers? Or is it not needed and the second layer lays directly on top of the first?

I am fairly certain that here, you can go over the existing shingles twice, three layers total. At least that is what it used to be. It may have changed after all of the hurricanes hit here. Yes, an underlayment is required. Think of it a re-roofing the roof without tearing off the shingles.

The problems come in when the go over is done over a roof that should have been replaced in the first place. Rarely, do they ever nail all of the cupped shingles down.

I have had several calls after I failed a shingle roof about going over the existing roof. My simple answer is "I recommended replacement of the roof covering". That is exactly what I mean. From what I have been told, the go overs only last around 10 years anyway. Not to mention all of the extra holes in the roof decking from all of the added nails.

My own personal opinion is to replace the roof covering.

Check your local codes. My state does not allow any more than 2 layers.

Originally Posted by Eric Van De Ven

I am fairly certain that here, you can go over the existing shingles twice, three layers total.

Re-roof once, two layers total.

For a long time.

It has basically nothing to do with 'the shingles' themselves (regarding life expectancy of the shingles), but with 'the weight' of the shingles. Each additional layer weighs that much more than the original rafters/trusses were designed for.

Thus, when you stop and think about it, the more layers, the more likely the roof sheathing is likely to 'stay in place'.

Originally Posted by Jerry Peck

Re-roof once, two layers total.

For a long time.

It has basically nothing to do with 'the shingles' themselves (regarding life expectancy of the shingles), but with 'the weight' of the shingles. Each additional layer weighs that much more than the original rafters/trusses were designed for.

Thus, when you stop and think about it, the more layers, the more likely the roof sheathing is likely to 'stay in place'.

Thanks Jerry.

I thought it was back in the late 70s or early 80s where you could go three total. Although the decking may stay in place, the trusses may not support the additional weight. Although, most of the older homes could support either a shingle or tile roof so the weight factor may be a non-issue.

Originally Posted by Eric Van De Ven

so the weight factor may be a non-issue.

I can see it now - new hurricane preparedness technique ...

When a hurricane comes, run over to your local Big Box store and buy up all the shingle bundles, take 'em home and spread the bundles (still bundled) out over the roof.

Might just hold that sucker down!

Originally Posted by Jerry Peck

I can see it now - new hurricane preparedness technique ...

When a hurricane comes, run over to your local Big Box store and buy up all the shingle bundles, take 'em home and spread the bundles (still bundled) out over the roof.

Might just hold that sucker down!

And if that doesn't do it, just elastomeric the heck out of it!

3 LAyers also has to do with the fire rating as 3 layers make it much more difficult to vent the roof properly during a fire.

Originally Posted by Clay E White

thanks everyone, but do you need to put an underlayment between the two layers?

Yes. It is just like re-roofing the house, except for the tear-off.

Eric, do you have an appropriate source that says an additional underlayment is needed?

It may be different in Florida, but out here shingles directly on top of shingles is OK.

I believe what Martin stated is correct everywhere...

Overlayment without additional underlayment

Originally Posted by Martin lehman

Eric, do you have an appropriate source that says an additional underlayment is needed?

It may be different in Florida, but out here shingles directly on top of shingles is OK.

From the Florida Building Code:

1521.17
Asphaltic shingle assemblies may be applied over one existing layer of asphaltic shingles having not more than 1/ 8 -inch (3.2 mm) difference in level in the existing shingle material. Recover over an existing shingle system shall be with a product having a Product Approval as prepared roof covering, in strict compliance with the application method detailed in the product approval.

When you get to the "product" and "product approval" part, you the refer to the section pertaining to installations which says:

SECTION 1521
HIGH-VELOCITY HURRICANE ZONES—REROOFING

1521.1 General.
Materials and methods of application used for recovering or replacing an existing roof covering, system or assembly shall comply with the requirements set forth in Sections 1512 through 1525 .
1521.9
One additional roofing system may be applied over an original roofing assembly, providing the existing roofing assembly complies with the requirements of Section 1521 .

1518.2 Underlayments.
Underlayment shall be as defined in Section1513. Underlayment shall be installed in compliance with the roofing component Product Approval and shall be in compliance with the following minimum requirements:

1518.2.1
Underlayment shall be attached to a nailable deck in a grid pattern of 12 inches (305 mm) between the overlaps, with 6-inch (152 mm) spacing at the overlaps.

1518.2.2
Where the architectural appearance of the underside is to be preserved, the underlayment shall be secured in accordance with Section 1519.5.2 .

1518.2.3
Tin caps and nails or cap nails shall be applied as defined in Section 1517.5.2 .

1518.2.4
Underlayment nails shall be as defined in Section 1517.5.1 .

1518.3

If the underlayment is a self-adhering membrane, the membrane shall be applied over a mechanically attached anchor sheet, attached in compliance with Section 1518.2.1 .

1518.4

All underlayment applications for prepared roof coverings shall be applied in compliance with the manufacturer roofing assembly Product Approval, and shall be not less than one of the following: (1) A double layer of an ASTM D 226 Type I, with a 19-inch (483 mm) headlap; or (2) A single layer of an ASTM D 226, type II with a 4-inch (102 mm) headlap; or (3) A single layer of an ASTM D 2626 coated base sheet with a 4 inch (102 mm) headlap, and (4) All endlaps shall be a minimum of 6 inches (152 mm).


1521.11
If the recover roofing assembly is mechanically attached through either a base sheet or insulation layer, the attachment assembly shall be field tested for fastener withdrawal resistance, in compliance with TAS 105, and laboratory tested for pull-over resistance to insure compliance with wind uplift requirements set forth in Chapter 16 (High-Velocity Hurricane Zones) of this code. Test results shall be submitted with the uniform roofing permit application. Recover roofing assembly anchor sheet or base sheet shall not be mechanically fastened directly to existing gravel roof unless all gravel is completely removed.

eCodes

Eric,

You w-a-y over reached on the codes there, going far beyond where it told you to go. Combine that with the fact that that section is *only for* Miami-Dade and Broward counties.

I will look it up in few minutes and reply with the code as it is stated.

Eric,

From the Florida Existing Building Code.
- Section 511
- - Reroofing
- - - 511.3 Recovering versus replacement.
- - - - New roof coverings shall not be installed without first removing existing roof coverings where any of the following conditions occur:
- - - - - 1. When the old roofing is water-soaked or deteriorated to the point that it is not suitable as a base for additional roofing.
- - - - - 2. When blisters exist in any roofing, unless blisters are cut or scraped open and nailed down before applying additional roofing.
- - - - - 3. When the existing roof surface is gravel or the like, the gravel shall be thoroughly removed or all loose gravel removed and approved base material installed before applying additional roofing.
- - - - - 4. When existing roof is slate or the like.
- - - - - 5. When sheathing or supports are deteriorated to the point that the roof structural system is not substantial enough to support recovering.
- - - - - 6. When existing roof has two or more applications of any type roofing material. Conformance with this item shall make replacement mandatory.
- - - - Exceptions:
- - - - - 1. Building and structures located within the high-velocity hurricane zone shall comply with the provisions of Sections 1512 through 1525 of the Florida Building Code, Building.
- - - - - 2. When the structural deck is concrete and the existing roof is firmly attached to the deck, then the roof shall be removed down to a minimum of three plies of moisture-free felts.
- - - - - 3. When otherwise approved by the building official.
- - - - - 4. Wood shingles or shakes shall not be placed over more than one application of wood or asphalt shingles. Wood shingles or shakes may be placed over existing shakes when installed in accordance with Cedar Shake and Shingle Bureau recommendations.
- - - 511.4 Roof recovering.
- - - - Where the application of a new roof covering over wood shingle or shake roofs creates a combustible concealed space, the entire existing surface shall be covered with gypsum board, mineral fiber, glass fiber or other approved materials securely fastened in place.
- - - 511.5 Reinstallation of materials.
- - - - Existing slate, clay or cement tile shall be permitted for reinstallation, except that damaged, cracked or broken slate or tile shall not be reinstalled. Existing vent flashing, metal edgings, drain outlets, collars and metal counterflashings shall not be reinstalled where rusted, damaged or deteriorated. Aggregate surfacing materials shall not be reinstalled (high-velocity hurricane zones shall comply with Sections 1512 through 1525 of the Florida Building Code, Building).
- - - 511.6 Flashings.
- - - - Flashings shall be reconstructed in accordance with roof covering manufacturer‘s installation instructions. Metal flashing to which bituminous materials are to be adhered shall be primed prior to installation (high-velocity hurricane zones shall comply with Sections 1512 through 1525 of the Florida Building Code, Building).

Your post was from the non-longer-existing 2001 Florida Building Code, not the 2004 Florida codes.

When talking about "re-roofing", that is something which is current, i.e., "now", which means the current code.

Be that as it may, let's say you were referring to a home which had the roof re-covered prior to the effective date of the 2004 Florida Building Code, then, where you posted "§1521.9 One additional roofing system may be applied over an original roofing assembly, providing the existing roofing assembly complies with the requirements of §1521.", you promptly stepped outside 1521, referring to other code sections.

Jerry,
That was from the 2004 building code. The 2001 isn't on line anymore. Follow the link in my post.

Chapter 15 deals with roof installations.

Martin had asked if it was OK to just put the shingles on top of the other shingles. Where I live, it isn't because of this line in your code reference:

1. Building and structures located within the high-velocity hurricane zone shall comply with the provisions of Sections 1512 through 1525 of the Florida Building Code, Building.

Since I live in a High velocity hurricane zone, what I posted is correct.

Getting back to the original question, the number is two, or is it?

6. When existing roof has two or more applications of any type roofing material. Conformance with this item shall make replacement mandatory.

In any event, if the roof was in good shape and had no leaks or rotted wood, why would you do anything to it?

In most of the cases I have seen, the homeowner did a go-over because they had leaks. I have found on every one of them that the roofer did not replace any of the rotted wood. If they didn't replace the rotted wood, say in a valley, I would have to guess that they didn't bother with the flashing either.

And, six months after your Client buys the home and the roof leaks, three roofers come out and say "you need a new roof, didn't your inspector tell you?"

I have never seen a go-over that I didn't fail. Maybe that will be my new slogan!

FHA does not allow more than 2 layers of 3-tab shingles on a roof.

Eric,

Are you sure that was from the 2004 and not the 2001?

When I looked in the 2001 Florida Building Code, your wording is exactly what was there.

That does not really matter, though, as the 2004 Florida Building Code series also includes the Florida Existing Building Code, which is what I quoted from, and is what applies to roof recovering, i.e., 'on an existing building'.

Originally Posted by Jerry Peck

Eric,

Are you sure that was from the 2004 and not the 2001?

When I looked in the 2001 Florida Building Code, your wording is exactly what was there.

That does not really matter, though, as the 2004 Florida Building Code series also includes the Florida Existing Building Code, which is what I quoted from, and is what applies to roof recovering, i.e., 'on an existing building'.

Yes, Jerry, that is where I got it from. Here is the link: eCodes

I looked in the section you quoted first and when I saw that it said: Building and structures located within the high-velocity hurricane zone shall comply with the provisions of Sections 1512 through 1525 of the Florida Building Code, Building.

I went to those sections and brought over the pertinent sections instead of all of the chapters. Anyone can go there and read it themselves.

I also seem to remember reading something about a section of the roof must be pulled up to verify the proper nailing pattern. So if the nailing pattern was not correct, then they couldn't do a go-over anyway. If it was correct, after pulling up a section of the roof, trying to get that area repaired so it is the same level with the rest of the roof, wouldn't be practical, so either way, re-roof.

Eric,

Follow your link to Chapter 34.

CHAPTER 34
- EXISTING STRUCTURES
- - SECTION 3401
- - - GENERAL
- - - - 3401.1 Scope.
- - - - - Alteration, repair, addition, relocation and change of occupancy of existing structures and buildings shall comply with the provisions of the 2004 Florida Existing Building Code .

Do you have a link to the Florida Existing Building Code?

How many is 2-many?

Maximum # of layers allowed...Two, (2), Dos, Zwie....From the IRC....

R907.3 Recovering versus replacement. New roof coverings shall NOT be installed without first removing existing roof coverings where ANY of the following conditions occur:

1. Where the existing roof or roof covering is water-soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.

2. Where the existing roof covering is wood shake, slate, clay, cement or asbestos-cement tile.

3. Where the existing roof has TWO or more applications of ANY type of roof covering

There are two exceptions that deal with metal roofing.


Thus,,if you have TWO existing roof coverings you may NOT install a new covering without having first removed the old one......

and I only traced this back 30 years but few ashphalt roof coverings exceed that age today..

As always your mileage may vary!