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How To Roof Over Shingles

You Dont Know About The Condition Of Plywood Under Shingles

How to Install Roof Shingles | Ask This Old House

The first and most obvious problem that you will have to face is that you cannot find out about the condition of plywood unless you dismantle the old shingle roof. Of course, you can inspect the inside of the house, and roughly assess the general condition of the deck, but it is worth understanding that while the asphalt roof is installed, you do not see the full picture.

If the plywood is damaged in one place, then in the future this part will turn into a stress point. It should be understood that the presence of such vulnerable parts of the roof can affect its integrity and service life.

Disadvantages Of Metal Roofs

Like most other things, there are a few disadvantages of choosing metal roofs. Otherwise, they would be found everywhere! The disadvantages include:

  • Metal roofs can be much more expensive than shingles. Even with their durability, which helps increase value and balance over the expense over time, many homeowners simply cant afford to install metal.
  • They provide excellent protection against the elements, but in many cases, rain and hail sound very noisy under a metal roof. A layer of soundproof insulation can help, but it adds to the cost even more.

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Can You Put New Shingles Over Old Ones

If you know its time for a new shingle roof or even a tile roof on your home, you may have heard that you can just put a new layer of shingles over the existing one. But is this true? In short, the answer is yes, but doing so may not always be a good idea.

In this article well explain:

  • When roofing over your existing shingles can be a good idea
  • When you should tear off your roof and start from scratch, instead.

Contact Legacy Service To Schedule An Appointment

Classic Ribbed Metal Roofing

At Legacy Service, we love just about everything about this type of roofing. When they are installed correctly using the right materials, they can withstand just about anything. And since it reflects heat from the sun, it can help you save significantly on energy costs. Its also 100% recyclable, making it eco-friendly. We have decades of experience when it comes to installing this type of roofing, and we can actually custom-make every panel for your project. We also offer a lifetime warranty, which makes for a sound investment. If youd like to learn more about metal roof replacement, contact our Legacy Service team today to schedule an appointment.

Posted on Oct 19, 2019 in Roof

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A lot of elements play a role in maintaining the integrity of the roof, but as a homeowner, the most important components to pay attention to are the underlayment, ventilation, and material.

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Fold Flashing Over The Peak

Cut the flashing back to the peak along each crease. Then fold the flashing over the peak and cover the cut ends with self-stick underlayment. Roof valleys channel a lot of water, so they need extra protection. Start by installing self-stick underlayment on the decking. This process is much easier with two people. Cut the underlayment to size , and peel off the entire plastic backer. With a person on each end, fold the underlayment in on itself, sticky side out. Then lay it into the valley and unfold it. Try to push it down into the crease of the valley as tightly as possible. If this self-stick ice-and- water underlayment bridges both sides of the decking, leaving a gap underneath, it could tear once you install the metal valley flashing. Run the underlayment past the drip edge at the eaves, and trim off the extra with a utility knife. Once it’s smooth, nail it down on the outside edges.

Finish installing felt paper on the rest of the roof, overlapping the self-stick underlayment. Be careful when you trim back the felt paper so you don’t slice into the underlayment. Photo 7 shows the underlayment covering the felt on one edge a couple of inches. This will keep water farther away from the inside corner of the fascia. You can extend the center out even more but not so far that water overshoots your gutters if you have them.

Your Decking Is Covered Up By Your Old Asphalt Roof

When you get a full roof replacement, your old roof is torn down to its decking. This gives your contractor a chance to inspect the deckings integrity to see if it can handle your new roof.

If you install a metal roof over your asphalt roof, theres no opportunity to inspect your roofs decking. If your contractor cant test your deckings integrity or inspect for rotten boards, it could lead to a costly problem down the road.

I understand everyone is on a budget, but if youre investing in a metal roof you might as well tear-off your old asphalt roof to avoid this problem.

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Cut And Install New Shingles

Any installation of the new shingles must follow manufacturer recommendations. For example, there must be an adequate amount of overlap, and the fasteners must be properly positioned. It is important to use experienced roof technicians who know how to cut new shingles to precisely fit around vents and other roof penetrations.

When Tearing Off The Old Roof Is A Better Option

Asphalt Roof Shingles Installation

Even with all the benefits of installing new shingles over old ones, there are times when its better to tear off the old roof and start fresh. Here are some reasons to do that.

  • There are already two layers of shingles on your roof – Most building codes only allow two layers of any type of roofing on your home. So if there are already two layers, the choice is made for you. You need to tear off the roof and install a new one.
  • Current shingles are curling or in bad shape – The new shingle roof should lay flat on your old one. But if the current roof is curling, this isnt possible. Youre better off removing the old roof.
  • Your roof leaks when it rains – If your roof is leaking, its usually better to get rid of the old roof so you can find the source of the problems and fix them. Putting a new roof over a leaking roof wont remove the leaks.
  • Your roof is soft and spongy feeling – If, when walking on your roof, the majority of it feels soft and spongy, you may have some problems with the underlying sheathing of the roof. To fix it, youll need to remove the existing roof.
  • Your roof cant support the weight – Shingles might not seem like they weigh much, but the shingles needed to cover a typical 2000 square foot roof can weigh in around 5000 pounds. Thats more weight than a typical SUV. So make sure the underlying structure of your roof can support another layer before installing over your existing roof.

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Roofing Over An Existing Roof: What You Need To Know

When you start noticing issues with your roof, orwhen it is nearing the end of its lifespan, it is probably time for some bigdecisions. You may wonder about the roofing options you have, and which onewill be the best solution for you. The best thing to do then is to call in aprofessional roofer and discuss it with them, as they have both the neededexpertise and experience to steer you in the right direction.

If the condition of your roof is such that a fewrepairs will not suffice to get it back into shape, but it is still functionalenough that it doesnt need to be completely torn off and replaced, then youshould think about reroofing, i.e. installing a new roof over your existingone. Reroofing is not the same as roof replacement and there are certainconditions that your roof needs to satisfy in order to be a viable candidatefor reroofing.

Keep reading to find out all you need to know aboutreroofing, including how it differs from a roof replacement and what its mainadvantages are.

Can You Install A Metal Roof Over Shingles

Everyone at some point has heard of the saying out with the old, in with the new. But when it comes to roofing, a new roofing material does not necessarily mean you have to get rid of the old one.

A home that removed asphalt shingles and installed a standing seam metal roof

If youre getting ready to make a big roofing change from asphalt shingles to metal, youll have to first make a decision on what to do with your old shingle roof. One option is that your old shingles can be removed prior to the new metal roof being installed, but that is not your only choice. It may come as a surprise that a metal roof can actually be installed over your existing shingle roof.

But just because something can be done, does that mean you should do it?

At Western States Metal Roofing, we have over two decades of experience with customers upgrading from asphalt shingles to a metal roof that are faced with this exact decision. We believe that this choice should be made on a case by case basis. It depends on different factors and every roof is going to be different from the next.

In this article, youll learn more about re-roofing . We will also go over 4 factors to consider when deciding if you should remove your asphalt shingle roof before you install a metal roof.

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Install Ice And Water Barrier

When water backs up behind an ice dam, it can work its way up under the shingles and possibly into the sub-roofing. Therefore, northern NJ homes often benefit from the addition of an optional waterproof barrier along the eaves and anywhere ice dams may form. It is often possible to safely install this waterproof barrier right over your existing shingles.

Is It Cheaper To Get A Metal Roof Or Shingles


Youre probably wondering about the cost to install a metal roof over shingles. While its cheaper to purchase shingles , metal roofing may provide you with better value in the long-term. Not only do they look beautiful and unique, but theyre also designed to last decades longer because of their durability. In fact, a metal roof thats built properly will be able to handle anything Mother Nature throws at it. You will most likely never have to purchase another roof again in your lifetime.

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Why Not Add New Roof Shingles Over Old

As suggested above, the potential cons of re-roofing tend to outweigh the potential pros, but it all depends on your situation. The following list includes some universal reasons not to reroof as well as some considerations or things to check out if you’re seriously considering adding new roof shingles over old ones.

1. Shingles are designed for flat surfaces. They don’t do a good job of bridging over gaps, dips or humps, including the stepped texture created by overlapping shingles. Re-roofers have tricks to lay new roof shingles over old so that the same step-ups between courses are maintained, but if any old shingles are cupped, curled, or otherwise misshapen, those defects will “telegraph” through to the new layer. Many roofers recommend using laminated, or dimensional, shingles for re-roofs because they’re thicker than standard shingles and often have a staggered edge profile that helps hide any dips or high spots in the old roofing.

3. No visual inspection of roof sheathing. Without a tearoff, roofers can’t see what the decking looks like. A good roofer will perform a careful “walking” inspection for spongy areas and other problems, and they can make localized repairs before re-roofing. A not-so-good roofer might be less conscientious.

5. Re-roofing may affect the warranty on the new shingles. Pretty self-explanatory. Be sure to check with the shingle manufacturer regarding all warranty issues and installation requirements before re-roofing.

Can I Install A Metal Roof Over Shingles

Yes, in some cases, you can install a metal roof over asphalt shingles. Always check with your local building code officials first. Some codes dont allow this at all and some only allow 2 layers of roofing in total, so if you already have 2 layers, the code will not allow going over it again with metal. If allowed, per your local code, there are still a few things to consider before proceeding.

You will want to make sure the plywood under the existing shingle roof is in good shape, meaning it has no soft spots. It is important to have a solid deck for the fasteners to attach to. You wouldnt want to rely on rotten wood to hold your metal roof on in a windstorm.

You will need to confirm with the metal roof manufacturer, their recommendations for installing metal roofing over shingles. Some products are approved to go straight over non-compromised asphalt shingles. Others will require a new layer of underlayment over the entire roof. And some may require both underlayment and wood strapping secured to the roof deck. Be sure to follow the manufacturer instructions accordingly.

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Waterproof The Vent Pipes

  • 10.1 – Install shingles right up to the vent pipe.
  • 10.2 – Trim shingles so that they fit around the pipe, then nail.
  • 10.3 – Insert pre-formed flashing around the vent, then glue with plastic roof cement. The boot should extend 4″ over the lower shingles, rise 8″ on the vent, and extend 6″ on both sides.
  • 10.4 – Colmater l’espace entre le tuyau et le solin avec du ciment plastique.
  • 10.5 – Continue installing shingles, taking care to completely cover the upper edge of the flashing.
  • 10.6 – Glue all parts of shingles overlapping the flashing with plastic cement.
  • 10.7 – Coat exposed nails with plastic roof cement

Remove The Old Shingles

How to Install GAF Ridge Cap Shingles at Roof Transitions | GAF Pro Series
  • 1.1 – Remove the old shingles and roofing felt with a roofer’s shovel. Pry out nails.
  • 1.2 – Sweep the roof as clean as possible and run a scraper over the decking to check for nails that might have been missed.
  • 1.3 – Inspect the plywood or particle board and replace any damaged or rotten boards. Panels must be at least ½” thick.
  • 1.4 – Nail down or screw in any boards that are raised or loose.
  • 1.5 – Install a metal or vinyl drip edge directly on the plywood the length of the eaves. Nail at 12″ intervals and lap each section by 2″. Use snips to cut the corners.
  • 1.6 – Verify that soffit and ridge vents are not obstructed.

Also Check: How Long Should An Asphalt Shingle Roof Last

Installing A Metal Roof On Wooden Planks

In climates with frequently changing temperatures, moisture can form between the layers of the roof. And how to install metal roofing over shingles to prevent condensation? To do this, you need to create an air cushion between the two layers of the roof.

This air cushion is created when wooden planks are used before installing a new metal roof. These quarter-inch wooden planks are installed directly on the asphalt roof, and a metal roof is already attached to them.

This installation method is very common because it avoids several problems at once. First, you reduce the chance of dents and bends in the metal roof. Secondly, the correct installation of the planks allows you to create an open-air space between the two roofs and will not allow moisture to accumulate.

For such a roof to function correctly, the wooden planks must be installed parallel to each other. If some of them are vertical, and the other part is horizontal, then in some places closed air pockets will form. This will disrupt the natural circulation of air and condensation will form.

Flashing And Additional Rows Of Shingles

Flashing must be installed correctly around elements, such as vents or chimneys, that penetrate the roof, as well as in valleys where different parts of the roof meet. When doing a layover, the thickness of the layers can make it difficult to use any method other than metal valley flashing. To install, line the valley with underlayment secured with roofing cement. Cut the flashing into 6- to 8-foot lengths to help prevent buckling after installation. Apply roofing cement to the back of the flashing, then nail it into place, keeping all nails a minimum of 6 inches from the flashing’s centerline. The edges of the valley flashing should be under the new shingles. Continue installing the rest of the shingles by butting each new row snugly against the bottom of the existing row of shingles immediately above and nailing into place.

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Step : Install Rubber Or Foam Closure Strips

Looking for advice the wind blew and tore off some of the ...

When working with any overlaps , you must install rubber or foam closure strips that match the shape of the metal to keep water from penetrating during violent rain storms or heavy snowfalls.

You also have the option of laying down and attaching rubber strips for any plumbing vents. The goal here is to prevent any water damage later.

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