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Figure 2-16 re roofing starter course (C) J Wiley, S Bliss Re-Roofing Asphalt Shingle Roofs - Best Practices

Asphalt roof shingle re-roofing advice:

This article discusses how to prepare an existing asphalt shingle roof for a roof-over or for re-roofing with new asphalt shingles. This article series discusses best practices in the selection and installation of residential roofing.

We also discuss Proper asphalt shingle roof preparation for a roofover job. Roof-over details for multiple layer asphalt shingle roofs.

Characteristics of asphalt shingle roofing materials. Best practices for roofing material installation, flashing, ventilation, nailing, underlayment

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Reroofing Options on Asphalt Shingle Roofs

Shingles 3 layers (C) Daniel FriedmanAdapted/paraphrased with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) , chapter on BEST ROOFING PRACTICES:

Reroofing saves the cost, trouble, and risks (water damage while the roof is exposed) associated with a tear-off.

If the roof is structurally sound, most building codes allow for two layers of asphalt shingles and some allow for a third on roofs with a 5:12 or steeper pitch.

Here is a typical excerpt limiting the number of shingle layers on a residential roof to two:

Roofs that already have two layers of 2 shingles should not be roofed again. Remove the existing shingles, then roof with
new shingles. - FHA Single Family Housing Policy Handbook, cited atReferences or Citations

If the original shingles are not badly curled and the sheathing is sound (check for bouncy areas), then a reroof is a good alternative.

Shingle Type Recommendations for Re-Roofing Asphalt Shingles

The heavier the shingle on the new layer, the less likely it is that irregularities in the surface below will telegraph through.

Laminated or other heavy-textured shingles work well, as they do not need to be carefully fitted to the existing shingles, and the irregular texture will conceal any small bumps or dips from the original roof.

Prep Work for Re-Roofing Over Asphalt Shingles

Watch out: Check roof deck condition: if you are stripping roof shingles entirely from a roof deck, either because of their poor and rough-surface condition (not suitable to shingle-over), or because portions of the roof deck itself need to be replaced (perhaps due to rot, insect damage, water damage), be sure that you properly identify the type of roof sheathing used and its condition over the entire roof deck.

Don't even think about roofing-over a structure whose roof deck is in the condition shown in our photograph at left. But a careful inspection may be required to detect more subtle but dangerous roof deck conditions.

Watch out: Life Safety Issues: Walking on an old water-damaged roof with an un-sound roof deck can result in serious injury if a worker steps into a soft area and falls through the roof - a hazard more likely with thin plywood sheathing (on some low-cost homes as thin as 3/8" or even 1/4") and also more likely where the roof is known to have been leaking, or finally, where fiberboard roof sheathing has been used.

Best Practices Guide to Residential Construction continues:

Starter Course for Re-Roofing Asphalt Shingles

Figure 2-16 re roofing starter course (C) J Wiley, S BlissIf laying three-tab shingles over three tab shingles, it is important to nest the new shingles against the old to create a flat surface as Friedman elaborates just below.

This process starts with a 5-inch starter strip fit along the eaves and set against the second course of existing shingles (see Figure 2-16).

DF Notes:

Notice that in re-roofing the starter strip is an inch less in width than when installing new shingles over a fresh roof-deck, shown in our asphalt shingle roofing guide

at ASPHALT SHINGLE STARTER COURSE INSTALLATION

That's to avoid a raised ridge and to let the new full shingle course lay flat atop the original shingles. In essence when I [DJF] installed shingles over an existing roof, for maximum roof life I want the shingles to lay flat - raised ridges in asphalt shingle mean bending that means wear that means shorter shingle life.

So the upper edge of each new shingle course butts against the lower edge of the appropriate existing shingles on the roof above the course being installed. That will let the shingles lay flat on the roof. Only the first course needs support below - that's why we cut a special starter strip of more-narrow width than for a new roof installation.

The special starter strip width is equal to the exposure width (usually 5") of the existing roof.

Even before installing the starter strip or underlayment you should install drip edge flashing along all roof edges.

See DRIP EDGE FLASHING for ROOFS

Next install a course of shingles cut down to 10 inches wide, so they fit against the bottom edge of the existing third course (this creates a new 3-inch first course). After that, shingling should proceed normally, fitting each course up against the bottom of an existing course.

Fastening / Nailing Details When Re-Roofing with Asphalt Shingles

Use galvanized roofing nails long enough to fully penetrate the sheathing, typically 1-1/2 inches for a second roof and 1 3/4 inches for a third. Nesting each new row below an existing one keeps the new nails 2 inches below the existing, which will help minimize any splitting of the sheathing.

Flashings for Re-Roofing Asphalt Shingles

Depending on their condition and accessibility, some flashings can be reused. New shingles may be able to tuck under existing step flashing, chimney flashings, and front-wall flashings. If they are deteriorated, they must be replaced along with vent boots.

See FLASHING ROOF WALL DETAILS and FLASHING ROOF-WALL SNAFU for specifications of roof-wall flashing and for some photo-examples of troubles with existing step and counter flashing when re-roofing an existing structure.

Valley Details for Re-Roofing Asphalt Shingles

Any type of valley flashing will work and simply lays over the existing flashing (except in a tear-off, where all flashings should be replaced).

Unless a metal valley flashing is used, the first step is to line the existing valley with a new underlayment consisting of either 90-pound roll roofing or a more durable modified bitumen membrane. Then install either a closed or woven valley as described above.

See roof valley details at ASPHALT SHINGLE VALLEY FLASHING.

- - Adapted with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) .

Resources: Roofing Materials & Equipment Suppliers

Manufacturers

Asphalt Shingles

Ridge Vents

Venting Underlayments

More Information about Roofing Materials, Methods, Standards

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) , by Steven Bliss, courtesy of Wiley & Sons.

Also see the roofing article links listed at the ARTICLE INDEX the bottom of this article and our roofing home page: ROOFING INSPECTION & REPAIR.

- - Adapted with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) .

 

Reader Q&A on Re-Roofing with Asphalt Shingles

On 2020-03-31 - by (mod) -

Roll of aluminum flashing metal used on buildings & roofs e.g. from zoro.com - at InspectApedia.comI'm sorry, Todd as I want to be helpful, but I don't understand the question. What wrap-around metal - wrapping what, where?

In general, metal flashing including formable or bendable flashing metals in aluminum, galvanized steel, lead, stainless steel, copper, and other metals are provided by your roofing suppliere or by a building supplier.

A simple example of a roll of aluminum flashing from Zoro.com is shown here.

On 2020-03-31 by Todd

Where do you get the wrap around metal for a go over roofing project

On 2019-05-03 by (mod) - reroofing be done over wet shingles

Yeah that's a bear. IF there is not working space either the rooftop unit has to be lifted - which is horrible as it'll be expensive and require removing and replacing refrigerant (unless the installer left flexible line slack) -

Or you'd install a suitable membrane under the unit and flash the upper end and sides at the roof

On 2019-05-03 by RICHARD

how to re-roof under air-conditioning units which are on top of roof

On 2018-11-30 by (mod) - reroofing over wet shingles

Not if you're following the manufacturer's installation recommendations.

On 2018-11-29 by Diane

Can reroofing be done over wet shingles

On 2018-05-09 by Christie

Can you have 1 layer of asphalt shingles on one side and 2 layers of shingles on the other side?

On 2017-05-11 by (mod) -

Ed

You want a drip edge - as we detail at DRIP EDGE FLASHING for ROOFS - https://inspectapedia.com/roof/Roof_Drip_Edge_Flashing_Specifications.php

Often I'll add (or a roofer would add) a second drip edge right atop the existing shingle layer before laying on the second shingle layer. Or you'll rely on the existing drip edge.

The article I cite above gives details that help assure that the drip edge works properly

On 2017-05-11 by Ed Willson

On re-roofing, I presently have drip flashing, do I need to re-install new drip flashing over old roof?

On 2017-04-09 by John Baker buy some 5" starter strip

Looking for a source to buy some 5" starter strip for reroofing over shingles. All I have seen so far is 7 " wide.
Thanks

On 2017-02-17 by Gabriel folded over shingles along the edge of my roof

I have folded over shingles along the edge of my roof from the last roof repair I had done. They replaced all comp shingles along the ridge and edges, no metal drip edge is there at all, and wind is blowing debris and rain into the folded shingle.

Why would they do this? Is this correct? I can't find anything online that speaks to why they would fold a shingle in half and then nail it down along the edge, other than as a decorative edge. It looks like a water trapping nightmare, and now I have leaks 3 years later. Is this something they should come back and fix?

On 2016-09-28 by (mod) -

No Sylvia I can't make sense of what you describe. The ridge is at the peak or highest point of a roof while the fascia board is found along the eaves or lowest edge of the roof.

On 2016-09-22 by Sylvia Leduc

On my roof, directly over the ridge area, are exposed nails driven directly into the shingle and through the fascia board. Does this sound correct?

On 2016-04-13 by (mod) - whether I can attach OSB roof sheathing over the battens of a cedar shingle roof

As long as the OSB is nailed to the rafters not simply randomly to battens, I don't see a problem in going over the battens once the old wood shingles are removed. Just double check the flashing details - which I can't know for your roof.

When you tear off the shingles and then add 1/2" thick OSB roof sheathing followed by felt and asphalt shingles, the upper surface of the finished roof might be close enough to the original level of the upper surface of the prior roof that no flashing amendments are needed - eg at chimneys - or maybe not.

Same goes for tearing off the battens: you're lowering the upper surface by about 3/4" - IMO even more likely to be trouble.

On 2016-04-13 by Pete Wingrove

I need to replace my original cedar shake roof (3/4 inch split shakes), which is installed over wood battens. I plan to replace the roof with architectural asphalt shingles, and am working with several roof contractors to get estimates.

The roofing contractors are giving me different opinions about whether I can attach OSB roof sheathing over the battens, or I have to remove the battens entirely and attach the OSB sheathing directly to the rafters.

Can I install OSB sheathing over the roof battens, or do I need to remove the battens?
The who are giving me different information about whether I need to

Question: average cost for a tear-off re-roof job for 2200 sq.ft.

(Apr 30, 2011) Anonymous said:
Please what is the average cost for a 2200 sg ft ripe off roof,gaf,timberlin,ice shiels ,etc.?

Reply:

Details on Estimating Roofing Costs.

A very general number for re-roofing with asphalt shingles might be $100/square or about a dollar per square foot. BUT you cannot use this number reliably.

Roof replacement costs vary widely by area of the U.S. as well as by factors peculiar to the individual building such as building height, roof slope (very steep, can't walk-on, more costly to re-roof), and the need for incidental repairs of roof decking and flashing. Also the complexity of the roof is an important factor - a single simple gable roof with no intersecting roofs and valleys is easier, faster, less costly to re-roof. Finally the cost to dispose of the torn-off shingles may vary widely by area too. So you will want estimates from two or three local roofers. Be sure to read bids carefully as there may be differences in what is included in the work.

(Oct 12, 2011) Anonymous said:

I dont know where alot of these roofing job bids are coming from but $100 isn't even realistic any more. Be careful if a contractor is that low, they may be using seconds. it rumored the some of the big home improvement sores are selling these
My whole sale price has crossed the $100/sq for most products. With labor, the average 20 square roof can easily cost 10k.

Also check your local building requirements fo tearoff requirements,ice and water shield,wind requiements.
Most areas require all damaged layers are removed to the deck befor a new layer is installed
Other than just old age, most roof damage is covered by your homeowners policy. You might try calling a claim with the help of a trusted roofing contractor. This can greatly reduce your out of pocket costs.

Question:

Jan 14, 2013) Jerry said:
I was told by a friend that you can not put the "architectural" sytle shingle (fiberglass type) over any old roofing. I have the 3 tab style on my house, and needs to be covered, they are fairly nice and tight and flat, very little to no cupping or curled, just worn. Can I do this, as it's only a single layer, and would be nice not to deal with the tear off, clean up, rain, etc . . . or do I have to use 3 tab again over these?

Reply:

It is common practice to add a second layer of shingles over an existing single layer provided the roof decking is intact and the roof surface is flat. That can be either architectural shingles or conventional 3-tab shingles. But check the shingle warranty from your shingle manufacturer. Some warranties may be affected by a mult-layer installation.

Question:

(Sept 17, 2014) Anonymous said:
I'll be re-roofing an addition soon. Going over an existing roof(single layer).
I have a question on the 'hip' in this roof. (roof is an L -shape)
SHould I remove the existing HIP shingles before I start, or should I go right over them?

ALso, I am thinking longer nails? Is 1-1/4 OK. Or should I use 1-1/2?
The existing roof is also 25 year 3 tabbers.

Question: ok to re-use blown-off roof shingles?

(May 22, 2015) Bruiser said:
We had a 3 tab asphalt shingle blow off. Is it ok to reuse the shingle with no damage?

Reply:

Sure, Bruiser you can re-use an un-damaged roof shingle that blew off, but you may want to add a few dabs of roof cement in the proper location to glue down the tabs to avoid wind-blow-off again.

Question: How do you re roof with timberline shingles now that they are 13 inches in width

(June 1, 2015) Anonymous said:
How do you re roof with timberline shingles now that they are 13 inches in width

Reply:

The shingle exposure in a re-roof job needs to match the shingle exposure of the under-layer of shingles or you may see ripples or lines parallel to the eaves telegraphing through the new roof layer - and ultimately those lines may become early wear points.

On 2015-06-01 by Anonymous

How do you re roof with timberline shingles now that they are 13 inches in width

On 2015-05-23 - by (mod) -

Sure, Bruiser but you may want to add a few dabs of roof cement in the proper location to glue down the tabs to avoid wind-blow-off again.

On 2015-05-23 by Bruiser

We had a 3 tab asphalt shingle blow off. Is it ok to reuse the shingle with no damage?

On 2014-09-17 by Anonymous

I'll be re-roofing an addition soon. Going over an existing roof(single layer).
I have a question on the 'hip' in this roof. (roof is an L -shape)
SHould I remove the existing HIP shingles before I start, or should I go right over them?

ALso, I am thinking longer nails? Is 1-1/4 OK. Or should I use 1-1/2?
The existing roof is also 25 year 3 tabbers.

Thx in advance

On 2013-01-14 by Jerry

I was told by a friend that you can not put the "architectural" sytle shingle (fiberglass type) over any old roofing. I have the 3 tab style on my house, and needs to be covered, they are fairly nice and tight and flat, very little to no cupping or curled, just worn. Can I do this, as it's only a single layer, and would be nice not to deal with the tear off, clean up, rain, etc . . . or do I have to use 3 tab again over these??

On 2011-10-12 by Anonymous

I dont know where alot of hese bid are coming from but $100 isn't even realistic any more. Be careful if a contractor is that low, they may be using seconds. it rumored the some of the big home improvement sores are selling these

My whole sale price has crossed the $100/sq for most products. With labor, the average 20 square roof can easily cost 10k.

Also check your local building requirements fo tearoff requirements,ice and water shield,wind requiements.

Most areas require all damaged layers are removed to the deck befor a new layer is installed
Other than just old age, most roof damage is covered by your homeowners policy. You might try calling a claim with the help of a trusted roofing contractor. This can greatly reduce your out of pocket costs.

On 2011-04-30 - by (mod) -

Details on Estimating Roofing Costs.

A very general number for re-roofing with asphalt shingles might be $100/square or about a dollar per square foot. BUT you cannot use this number reliably.

Roof replacement costs vary widely by area of the U.S. as well as by factors peculiar to the individual building such as building height, roof slope (very steep, can't walk-on, more costly to re-roof), and the need for incidental repairs of roof decking and flashing.

Also the complexity of the roof is an important factor - a single simple gable roof with no intersecting roofs and valleys is easier, faster, less costly to re-roof. Finally the cost to dispose of the torn-off shingles may vary widely by area too. So you will want estimates from two or three local roofers. Be sure to read bids carefully as there may be differences in what is included in the work.

On 2011-04-30 by Anonymous

Please what is the average cost for a 2200 sg ft ripe off roof,gaf,timberlin,ice shiels ,etc.?


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