Ask Todd Miller *Metal Roofing Expert

Remove Roof Shingles Before Installing a Metal Roof?

Written by Todd Miller on March 26, 2015 | Filed under: Articles

I frequently am asked whether homeowners and contractors should remove roof shingles from a home’s roof before a new metal roof is installed. My answer often surprises people. However, it is based upon experience with tens of thousands of installations over many years.

My Experience

The vast majority of installations of the metal roofing systems produced by my company are over existing shingles. The low weight of metal roofing is one thing that encourages this. Steel shingles weigh about 1/4 what asphalt shingles weigh and aluminum shingles weigh about 1/8 what standard shingles weigh. I would say that in most cases, less weight is being added to the home by the new metal roof than what the current shingles have lost due to granule wear and oil evaporation. In other words, the total roof weight was probably greater when the last layer of shingles was installed than it will be when the metal roof is completed.

Asphalt Over Old Asphalt? No.

One important thing for folks to keep in mind if they are trying to decide what type of roof to buy is that new asphalt shingles should not be placed on top of old asphalt shingles. With most asphalt shingle manufacturers, doing so will void the warranty on the new roof. This is partly because the old shingles will not allow the sun’s heat to pass so easily into the attic so the new shingles end up staying at a warmer temperature, shortening their life.

Why is Metal Different?

That is not the case with metal — temperature does not damage the metal or the paint finish. The warranty on your new metal roof, at least from my company, will not be impacted at all by going over the old shingles.

In over 30 years and tens of thousands of installations over old shingles, I have yet to go back on a job later and find myself saying “Hmm … maybe the old shingles should have been removed.” It just never becomes an issue. And many of those installations actually have been over wood shingles and thinner wood shakes! I have also re-roofed personal properties with our products five times now over the years — every time was over the old shingles and no regrets.

I like going over the old shingles for 3 reasons:

  1. It stops the need to fill up landfills with old shingles. It ultimately increases the thermal resistance (R-Value) of the roof assembly, actually increasing energy efficiency compared to tearing off the old shingles. The benefit of this is during the summer.
  2. It allows the property owner to spend discretionary dollars on a better roof rather than on removing the old roof and disposing of it.
  3. Going over the old shingles also avoids the potentially damaging issues that can occur, like unexpected rainstorms, when old roofs are torn off.

Still, ultimately, it is the property owner’s decision but I would have no qualms about going over a layer of old shingles in most cases. It’s not uncommon to go over multiple layers either actually. On older homes, of course, I do put the caveat out there that if there are signs of an existing weight issue or old leaks, those need to be addressed and that may require removing the old shingles. If there are concerns about the integrity of the roof decking, then pull-out resistance tests using the roof fasteners can be performed.

One other thing to keep in mind is that building codes, where active, usually require no more than two layers of roofing of any type on a structure. There have been instances of building inspectors waiving that requirement but that is not an easy thing to get accomplished.

Remove Roof Shingles Before Installing a Metal Roof?

In a typical year, approximately 90% of the roofs our company manufactures are installed over old shingles. In my opinion, going over the old shingles is worthy of consideration because of the benefits of doing so. Every roof needs to be evaluated individually. Please feel free to email me your questions or circumstances for my input. My email is todd@asktoddmiller.com

75 responses to “Remove Roof Shingles Before Installing a Metal Roof?”

  1. toddmiller says:

    Thanks Allen. Metal roofing’s low weight can be a benefit to aging structures. And, of course, churches often have the long rafter lengths which can heighten weight concerns. This may be something that you’d want to have a structural engineer inspect. In many cases, metal roofs can be installed over old shingles but code requirements call for no more than two layers of roofing. I am going to email you direct with a copy of my ebook on How To Buy A Metal Roof. I think it may be helpful. Additionally, these videos may be helpful: https://www.youtube.com/playlist?list=PLMw9xVe_yEaVt4yv1i4LoDTlNKNd6boRd

  2. Allen Archer says:

    Hi Todd
    I have a large one story building that is 85 years old. It is solid structurally, but needs a new roof. It is a pitched roof, with shingles. I don’t know how many layers but I’m guessing more than one. I want to go with metal roofing for this (church) roof. I’m not sure about the integrity of the roof trusses. How should I approach this project. I’m in a cold climate so it won’t be done before spring or early summer.
    Thanks,
    Allen

  3. toddmiller says:

    Thanks. I do not know the full details of your home’s construction but, with most homes, the following applies:

    1) Metal roofs do not reduce the need for attic ventilation.
    2) Proper attic ventilation requires intake and exhaust vents. Intake vents are usually in the eave soffits and exhaust vents are in the roof at or near the peak / ridge.
    3) Proper ventilation helps make a home more energy efficient in the summer. It also reduces the risk of high moisture levels and possible condensation in the attic. In northern climates, it also reduces the possibility of winter ice dams on the roof.
    4) Attics generally require insulation on the floor, ventilation above that, and a vapor barrier behind the ceilings. You might get by without one of those things but rarely without two of them.

    I hope this helps. Please feel free to contact me anytime.

  4. Paul Amaral says:

    Todd,

    I have a question concerning installation of metal roofing.

    Have metal roofing on existing singles with an underlayment garment on top of singles

    The question is concerning the ventilation.

    With singles – there were 3 openings which was removed. Underlayment garment installed over the openings and then metal roofing. Is this correct? What is the correct procedure?

    Or should new ventilation be installed on each opening that pre-existed. But we metal roofing do not see a lot of openings on photos and other homes.

  5. toddmiller says:

    There are several considerations here including how bad the dip is and what type of metal roof you plan to install. Right off hand, I do not feel the boards are essential but I agree they could remove the visibility of the dip. In most cases, dips are more apparent rather than less once the new roof is installed. Feel free if you wish to email photos to me at todd@asktoddmiller.com

  6. Lance Hardcastle says:

    Thank you in advance. Our house was built in the early 30s. It currently has one layer of shingles over top of decking that is the original pine boards. 75% of the roof is straight and relatively flat. The remainder has a dip in it probably due to that being an addition. One roofer insists that 1 x4 underlayment be attached to the roof because the old boards are dry and screws may not hold in them. He also believes that the dip can be corrected with the underlayment of wood. The second roofer believes that the underlayment is an unnecessary expense and the dip would not be noticeable anyway. I really hate to have two opposite opinions. Can you offer yours? Thank you.

  7. toddmiller says:

    What you have described should not be done. In some cases, existing vents may be replaced on the roof by a different type of vent but in that case the old vent holes should be covered / blocked. Attic vents should come through the roof surface.

  8. George Bills says:

    My roof has a lot of vents on it for the roof to vent I see lots of videos showing removing the vent caps and leaving the holes and just going over the old vents doesn’t that create a problem with the roof venting and getting too hot in the inside?

  9. toddmiller says:

    Metal roofing is much lower weight than asphalt shingles. Aluminum roofing weighs about 45 – 65 pounds per 100 square feet and steel from 80 – 120. Asphalt shingles on the other hand weigh from 275 – 425. I can’t say this for certain but chances are that your home was built to handle the weight of at least two layers of asphalt shingles. Additionally, your existing asphalt shingles have lost weight due to granules wearing off and oils evaporating.

    One thing that you will need to know is the pitch of the roof on your home. Sometimes, double wides have lower pitch roofs. Most metal roofs can be installed down to 3:12 pitch but for lower pitches, you will need to choose a metal roof that is appropriate for your roof pitch.

  10. Keith McKenzie says:

    I have a double wide mobile home. Can I put a metal roof over the old shingles or will the metal be a weight factor?

  11. toddmiller says:

    In 30+ years I have never known it to become a problem. I do recommend a layer of underlayment on top of the old shingles and beneath the metal. Unless it is specifically a non vented situation by design, then the attic needs to have proper ventilation as well. A great source of ventilation information is at http://www.airvent.com

  12. Lorraine Bellamy says:

    If a steel roof is installed over shingles with some moss I know the moss dies but will it cause any rotting of shingles or wood underneath or will it dry and be inert. Thank you for a wonderful site.

  13. toddmiller says:

    Thanks Carole. Sounds like a great home and a great project. There are many things to consider here including moisture control. Do you know if the existing shakes are in spaced sheathing or solid decking? That is a big question. Furthermore, is there any actual ventilation on the attic / cathedral space including intake and exhaust vents. Here is my concern — the existing shakes are likely on spaced sheathing, meaning that they “breathe” very well. Anything you do to the roof, including covering over the shakes or removing them and installing solid decking will significantly tighten the home. Unfortunately that could set you up for condensation issues that did not occur before. There are a lot of unknowns here for me … I am happy to try to help but really need more information on the current situation. My email, if that is easiest, is todd@asktoddmiller.com Thanks so much.

  14. Carole Bartusiak says:

    We are currently looking at purchasing a home in the mountains of Colorado that can have high winds, hail, and temperature variances. The A-frame home was built in 1963 and has an original shake roof on the sloped portions and a flat roof everywhere else. We want to install a metal roof on the sloped portion but are unsure whether to install the roof over the existing shingles or have them removed first. There is a cathedral ceiling over the A frame portion but no attic in any other existing portion of the home. Can you please offer your opinion? I’d be happy to send you a picture of the home as well.

  15. toddmiller says:

    Thanks for your question. First of all, the International Building Code which is enforced in much of the USA but may or may not be enforced where this structure is located, requires no more than two layers of roofing. That is important to know and keep in mind.

    That said, the weight of a metal roof is pretty low. Most steel roofs weigh around 80 pounds for 100 square feet and aluminum is even less than that. Asphalt shingles by contrast are 275 – 450. Chances are that the last layer of shingles on the roof has lost more weight in worn off granules and evaporated oils than a metal roof will add back.

    The lumber weight is also not real great but it would require inspection and evaluation by a structural engineer to render an expert opinion on that. Undoubtedly this structure has been built to handle some pretty good weight from snow.

    As far as going over old shingles that are uneven … it can be done … more heavily textured and formed metal roof products such as corrugated sheets and metal shingles though are far more forgiving than is standing seam … standing seam can have ripples forced into it if it’s installed over an uneven surface.

    I hope this helps. Please contact me anytime. You can email photos of the roof and structure to me if you like at todd@asktoddmiller.com

  16. rebecca raymond says:

    I have a 12/12 pitch roof on an old 1930’s church, it has two layers of asphalt shingles on it, the top layer is really ragged on one side of the roof. Different roofers are telling me different things, …can I put metal over 2 payers of shingles even if one side of the roofs shingles has flaking off shingles. I know underlayment(synthetic is essential, and a roof vent), I’m concerned about the weight of new 2×4’s and the metal on my 2×6 old roof. I live in a cold and hot climate with major snows in the winter…but with my steep pitch is that a factor? Winter is coming, please help? Thank you

  17. toddmiller says:

    Congratulations on your new (to you) house. Your questions are not silly. Many many metal roof installations are over existing shingles. The low weight of metal encourages this. It is easier to do with more heavily textured metal roofs such as exposed fastened corrugated products and metal shingles. Standing seam roofs may have unevenness of the old shingles telegraphed through and cause ripples in the standing seam.

    Underlayment should be installed before the metal roof, regardless of whether the old shingles are removed.

    I can’t really say much on the old nails working their way up. Can’t say I have ever seen this before. So, I’d be very surprised if it is a real risk but ask your contractor what they think.

    As far as the wood condition … if you are not aware of active leaks and the contractor says the roof seems solid, it probably is okay. If there is bad lumber, they will know it when they try to fasten into it.

    I hope this helps. Please contact me anytime. My direct email is todd@asktoddmiller.com

  18. Susie says:

    Hi Todd, I am just having a metal roof installed as we have just bought an old house (with an old roof). I have a few leaks actually and had a contractor come out today to take a look. The contractor explained that because the roof was made with tongue and groove ship lap, as it ages and the wood hardens, the nails are being pushing up through the asphalt shingles. Now with the few leaks that I have, I was concerned with rotting wood. As the contractor walked on it he said it is in great confusion. He proposes taking a look at the insulation as it may have water damage but the wood is fine. Then he proposed adding the metal roof over the shingles. Now should I truly take his word for it that the wood is fine? Could I regret that decision if there is some water damage down the road? Maybe we should remove the shingles to check out the wood (not a substantial attic space to check from the underside)? Also what is to prevent more nails from being pushed out of the ship lap after we add a metal roof? I feel like my questions may be silly, but we are talking our first investment..

  19. toddmiller says:

    Thanks so much. First of all, if you wish, email photos of the roof to me at todd@asktoddmiller.com However, here’s my advice. Technically could it be done? Probably yes. Should it be done? Probably not. The wood shingles will be pretty broken up from the fasteners through them, etc. I would suggest tearing off the existing metal roof, the old cedar shingles … and then installing solid decking … unless sold decking is already in place beneath the cedar shingles. In any and all events, underlayment should be installed beneath the new metal roof.

  20. Shannon says:

    Hi. I’m clueless about roofs. I’m a lady (and that doesn’t mean we are all clueless) but while my husband is away for work 90% of the time I am left with the decisions about renovations etc. I have been burned in the past because of this, with a contractor for things we needed done on the inside of the house. Now it’s roof time. We have an older house, it’s been about 40 years since we got a new roof. It’s aluminum, but its already flying off so it has to be done. Now underneath are cedar shingles. I have had two very different quotes. One is for a quote that just includes the removal of old and putting new steel on. The other involves sheathing. The price difference is $1500. The company that wants to do sheathing swears up and down that new steel cannot be put over the old cedar, and the other company says it can. Not wanting to get ripped off, and not wanting a bad job done I am at a loss as to who to believe. My husband has nothing to offer for an opinion because this area is not his area of expertise. Who do I believe?

  21. toddmiller says:

    Thanks for your kind words. I think that you could do this. However, the ridge cap will need to be metal but then you could put the cedar ridge caps on top of that for “decoration”. As another thought … have you considered a steel shake facsimile? Something along the lines of http://www.kasselshake.com

  22. Todd says:

    This is such a great site and useful thread! I have a small 10×13 garden shed w cedar shingles that is about ready for a new roof. I like the appearance of the shingles, and would like to replace the side of the roof that faces the house with the same cedar shingles. However, the back side of the shed isn’t visible, as it faces a bluff, and collects a lot of tree debris. For purposes of longevity, ease of installation, and weight, I’d like to put a metal roof on the back side. Do you see any problem with cedar shingles on one side and a metal roof on the other? Can I use cedar ridgecaps at the peak, instead of metal? Thanks!

  23. toddmiller says:

    Thank you. Please call me at my office when you can. 1-800-543-8938 ext 201. You have a situation that we need to talk about a bit … I want to make sure that you do not do something which results in condensation where it did not exist before. I will be in the office tomorrow and Thursday.

  24. Tracy J says:

    Thank you for the quick reply! This is a double wide modular and we are in central Indiana. The metal is galvanized sheet metal that is roll formed and came in a steel coil.

  25. toddmiller says:

    Thanks. It depends a bit upon what type of metal roof you’re installing and where you’re located. In warmer climates, if you’re installing a vertical seam metal roof that rests largely against the underlayment, there is a risk of oils leaching out of the felt paper and sticking to the back of the metal. Then, as the metal tries to expand and contract with temperature changes, it can “bunch up” or tear the underlayment. Not good. My general advice is a layer of synthetic underlayment over the felt. This will act as a slip sheet and work well under virtually any metal roof. All of my advice is assuming there is nothing unusual about your home in regards to ventilation, cathedral ceilings, etc. Feel free to email direct to me with details or photos if you have more questions. todd@asktoddmiller.com

  26. Tracy J says:

    We are getting ready to install a metal roof on our home. We had to remove the shingles and replace the wood on the roof due to multiple leaks. We have put 30# felt paper down on top of the new wood but need to know whether or not we need to put anything else down (such as foam board or shingles) before we put the metal roof on. Any advice is appreciated! Thanks

  27. toddmiller says:

    It sounds like you have done much of the right research. Here is my concern though — the metal roof will potentially make the roof deck colder than it’s been in the past. This could cause condensation on the inside of the decking that has not happened before. Condensation occurs when warm moist air hits a cool surface. This would occur especially during evening in the fall and spring when ambient humidity is high yet temperatures get cool at night.

    So, to that end, leaving the old shingles is good. It also could be good to add insulation or a vented air space or even an air gap. These things will all help to create thermal breaks to keep the inside of the roof deck from getting too cold.

    Please realize that if you go over the old shingles, it could create unevenness that might force ripples into the standing seam panels.

    If you do anything in regards to insulation or ventilation, make sure that what you are doing is approved by the manufacturer of your roofing.

    Good luck and feel free to contact me anytime.

    All best.

  28. Brian says:

    Hi, I have a 1:12 pitch roof on my home with 2 layers of asphalt shingles. The home does not have an attic, as the interior ceiling matches the slope of the roof. With only a small insulated space between the ceiling and the roof I am not sure how to handle my metal roof install. I have found standing seam products rated for 1:12 pitch roofs but I’m not sure if I should leave old shingles on or not. I also am not sure about underlayment types or if I should add a space between the existing roof and the new metal roof. This home is in Boise, ID which is hot and dry in the summer and cold in the winter with low amounts of snowfall. Thanks for any help you can offer.

  29. toddmiller says:

    Thanks Karen. I will reply to you via email but, right off hand, you should be able to install over the existing, along with a layer of underlayment. Once the fungus is isolated from sunlight and moisture, it dies.

  30. Karen says:

    Hi, I was reading your info about covering asphalt shingles with metal. Would love to do this at our cabin. We have no leaks but do have moss. Should with remove it first with power washing. Worried that we’ll have to wait for it to dry out after the wash and it’ll slow us down. I think we’ll be using norclad. I sent photos via email.

    Sent from my iPhone

  31. toddmiller says:

    Thanks. It is still attic ventilation that concerns me. A vented ridge cap on a metal roof may not look significantly different from a non vented metal roof. Yes, if a ridge vent was installed, its purpose is to vent the attic, not the space between the steel roof and the old shingles. Therefore, to vent the attic, the ridge would have needed to be cut open. What did your contract call for as far as ventilation? Feel free to send photos to todd@asktoddmiller.com

  32. trevor says:

    sorry I may not have given you are the info and your answer may change.
    a steel roof was installed over very bad curled shingles with horizontal strapping. no vents were reinstalled and I don’t believe the shingle caps were removed.and if they were would the wood need to be cut for a vent cap. the top cap just looks like a cap and I wanted a vent cap. do they look different?.i have a picture if I could send it and you could tell me if it is a vent cap
    it is on a cottage roof. only used from May to October. the temperature would be 32F in the spring to 90F in the middle of summer. no air condition and no heaters. and it is on a big lake with very little trees.

  33. toddmiller says:

    In normal construction, proper attic ventilation is critical. It sounds like your attic ventilation has been diminished. Generally speaking that puts you at risk for higher air conditioning costs in warm weather, ice dams on the roof in snow climates, and greater risk of condensation and potential mold issues in the attic, particularly during the Spring and Fall months.

  34. toddmiller says:

    Thanks so much for your question. It’s important to think of condensation potential in terms of dew point. Condensation occurs when warm moist air hits a cool surface. Think of the glass of cold lemonade sitting outside on a hot day and the condensation on the outside of the glass. So, condensation requires a significant temperature differential and high moisture levels.

    Almost never does that sort of situation occur in the outer layers of a roof assembly — in those layers, you do not have a temperature differential that can cause condensation to occur.

    Condensation in a roof assembly is normally a risk in the attic space. Warm moist air originates inside the living space and raises to the attic. If the attic is properly ventilated, then it can not condense. However, if the warm moist air is not vented out and the roof deck cools down at night, it will condense. That condensation normally occurs on the under side of the roof deck.

    So, the question here has much more to do with whether you have good attic ventilation than it does with layers of the roof assembly. If you do not have good attic ventilation, and good attic ventilation can’t be achieved, then we need to talk some more and discuss options.

    The underlayment installed beneath is KasselWood roof is a moisture barrier from the outside which is a good thing. In essence should any water ever get beneath the metal roof or should the very rare chance occur of condensation, the underpayment prevents it from getting into the structure. But, again, that is pretty unusual to have happen.

    On the Decra products … there is an air gap between the metal and the roof deck. That acts as a thermal break. KasselWood has the same thing though the air gap may be smaller. It all depends on what Decra product is being considered. Some Decra products have greater air space than others. Very rarely are they installed though in a way which actively ventilates that air gap. More often it acts as a thermal break and perhaps a tiny bit of passive ventilation. Give me a call if you’d like to talk further. 937 773 9840 ext 201.

    All Best.

  35. Trevor H says:

    I had a steel roof put on over my shingles. They took my whirl bird venting off and now i have no venting.
    they did not take off the shingle cap and cut the wood to allow the heat through the steel cap. Is this a problem

  36. Alanna says:

    Hello!
    Do you have experience in very cold climates? I am in Quebec, Canada and it’s been known to reach temps in the high -20s to -30s F in the winter. If I install a metal roof over existing shingles, won’t there be a risk of condensation between the two?
    We are looking at two manufacturers; one is going to install a fabric between the two (Kasselwood), the other company (Decra) will install directly on the shingles saying they have ventilation channels in the product. I know you are biased to Kasselwood, but why are the techniques so different?

  37. toddmiller says:

    Can you send a photo to me along with details on the type of metal roof you plan to install? This can be done in some cases but may not always be the way to go. My email is todd@asktoddmiller.com

  38. Wayne says:

    Hi , just wondering if we can put a metal roof over existing shingkes that show signs of buckling and have moss on them. Thank You

  39. Chuck McKeon says:

    OK. Will do. Thanks again for your comments and advice. Really appreciate.

  40. toddmiller says:

    Thanks. I am not sure I am 100% following things but let me tell you my concern. When warm moist air hits a cold surface, of course, condensation occurs. A standing seam roof, in contact with the ship lap (even with underlayment between the two) can drop the temperature of the ship lap a few degrees compared to what it was with a different roof system. The metal just cools down more quickly than other materials. This couple of degree differential in rare cases has been the straw that broke the camel’s back and caused condensation that was not there before. Perhaps looking into a very thin insulation board between the metal standing seam and the underlayment / ship lap, would be helpful.

  41. Chuck McKeon says:

    Wow! That was quick! Thank you.

    Pitch is 4:12. Yes, using clamps.

    About 80% — or more — of the interior of the house is what we refer to in Hawaii as open beam (i.e. cathedral ceiling) — 4×6 rafters on 3′ centers, except for a 10′ addition (new rules) with 2′ centers. Attic spaces are over the kitchen/dining area, parts of two relatively small bathrooms, and three 2’+ deep linear bedroom closets. It has been my presumption that additional airspace would not be necessary.

    We have jalousie windows in most rooms just above floor level which are open 99% of the year. The roof ridge has a “homemade” vent framed with 2x4s — therefore, raised the height of a 2×4 on edge (3-1/2″) — which we built when we re-roofed 20 year ago. The cut-out of the shiplap along the ridge has a span of about 24″ running the entire length of the house — one straight ridge for the entire house. (The ridge vent “deck” runs down about 3′ on each side of the ridge line at the same slope as the “field” deck. For now, the ridge vent will remain — with some “tricky” flashing to keep the inner vent dry!)

    Any further comment you might have on the adequacy/(need) of (additional) ventilation would be most appreciated.

  42. toddmiller says:

    Thank you. Assuming the roof meets the minimum pitch required by the designed of the metal roof (probably 2:12), I do not see any issues with this plan. I assume you’re using clamps to attach the PV to the standing ribs. I am curious though … do you have a vented airspace beneath the ship lap?

  43. Chuck McKeon says:

    Honolulu, Hawaii. I am planning to install aluminum standing seam roofing (SHURLOCK 12″.032 ALUM LG MAUNAKEA WHITE-DURACOAT LOW GLOSS) after stripping off asphalt shingles applied to a 1×8 shiplap roof deck — boards are fairly tightly spaced. (I did the shingle install myself with 3 friends approx. 20 years ago.)

    Additionally the metal roofing will be installed only covering an area of approximately 20′ by 20′ starting from a rear gable end and ending 20′ where meeting a straight vertical cut-off of existing asphalt shingles. (There is estimated to be an additional 5-year life in the existing asphalt shingles.)

    This design is specifically to be a good, solid, long-term roof for under PV panels which will not, therefore, require any additional thru-roof protrusions. The seller, who forms the metal panels locally in his shop, recommends a synthetic underlayment (PALISADE SA UNDERLAYMENT 36″ X 66.7′-SELF-ADHERE 2SQ/ROLL).

    Cost is the primary “driver” of the design. The PV system is relatively small requiring 13 solar panels. (Have considered simply a new asphalt shingle roof under the PV panels — cheaper — but that would require many thru-roof protrusions for the PV tracks and I certainly want to avoid the cost of raising the PV panels at some later date.)

    The idea is to do, now, the minimum to get the PV up and running … face the question of how to complete the remaining 2,600 SF re-roof in 5 years.

    My question … Because I have not seen any discussion of re-roofing over shiplap, I am curious as to whether you might have any cautions or concerns given the situation described above.

  44. Zack says:

    Ok thank you very much for the advise. Have a good day.

  45. toddmiller says:

    I would never advise fastening into decking that has rotted or delaminated, jeopardizing the fastener pull out resistance. Therefore, it does sound like this needs to be addressed and, yes, you will have to use some material to build the roof up to the same level as the rest of the roof once that is done.

  46. Zack says:

    I am considering putting metal
    Over my existing shingles. I have a place in my roof where the decking was sagging and I basically bandaged it for 2 years. Do I need to replace that piece of decking before adding metal and if so do I need to replace the old shingles in that area so that it will
    Level out before adding metal to prevent wrinkling of metal?

  47. toddmiller says:

    The manufacturer of the roofing should specify batten size but it’s not uncommon for horizontal battens to be 1 x 2 or 1 x 4. Yes, cross battens would start with vertical battens on top of the decking but running on top of the rafters as “sleepers”. Then horizontal boards run and spaced as required by the metal roofing panel. Metal roofs that can be installed this way will have “load tables” that specify batten spacing. Cross battening provides vertically oriented chambers. Air can be brought in at the bottom and exhausted out at the top, creating good energy efficiency. In cold climates, this can also help avoid ice dams on the roof.

    Metal shingles also create a good option. These formed panels have an integral airspace between the metal and the roof deck. That airspace, while it may not be vented, does provide a thermal break which is also very effective for energy efficiency.

  48. Jay Sheeley says:

    What size wood would you use to make the battens? And by cross do you mean a vertical run from drip edge to peak and then full length horizontal boards on top of them running side to side?

  49. toddmiller says:

    Thank you. There should not be ice issues from installing over the old shingles. In fact, the R Value of the shingles will help keep interior heat from reaching the roof, and that can help prevent ice dams. You’re correct though on the possible shape issues. You could look for a structural standing seam that can be installed over battens. Apply underlayment over the old shingles, battens, and then the metal roof. The battens will even things out. You could “cross batten” by installing vertical battens and then horizontal battens. This allows for ventilation up the roof and can enhance energy efficiency. I hope this helps.

  50. Jay Sheeley says:

    I saw that some standing seem metal roofing companies remove the asphalt shingles and add ice guard before they install the roof felt. I was curious about any ice issues that could arise from doing new metal over old asphalt shingle. I would like to do standing seem over my old shingles or at least an option that conceals the fasteners from the elements. Is there any product that looks like standing seem with concealed fasteners but can be installed directly over existing shingles without shape issues?

  51. toddmiller says:

    I would remove the old shingles since they are in such bad shape. I would add a layer of synthetic underlayment, or more if required by code. Then install your metal panel. Make sure that the metal panel you install is approved for use on the pitch of this roof. If you wish, email me at todd@asktoddmiller.com and I will send you my ebook on How To Buy A Metal Roof.

  52. Mike C says:

    I have a pole barn with a shingled roof. The sheeting has a foil backed insulation attached directly to it on the underside inside the barn. This was done during construction because the insulation is a continuous length-wise roll sandwiched between the roof trusses and sheeting. Sort of creating a cheap insulated panel. The shingles on the south side of the building have cooked in the hot sun and are significantly curled and are now blowing off in high wind storms. What do you recommend for replacing this roof with steel?

  53. toddmiller says:

    Thanks Linda.

    Well seeing how my company manufactures metal shingles, I probably have some preferences. 😉 But, I will be objective. Most of these products will have Kynar / Hylar finishes which are my preference by far. I would look for products that have interlocks on all four sides and do not have exposed fasteners. Beyond that, though, you’re right — it comes down to proper installation. Make sure you’re comfortable with the installer. Call the manufacturer and make sure they can say good things about the installer. Go see past jobs, talk to past customers … and make sure that the installers on your roof will be the same as on the roofs you went to see. I will take a properly and well installed mediocre product over a poorly installed “world’s finest” product any day. Please feel free to email me direct if you have additional questions. tmiller@classicroof.com

  54. Linda says:

    We live in Central Florida and are researching using stamped metal shingles over our asphalt shingle roof. Do roofers need any special expertise to do this installation? Are there quality differences we should be aware of between the various stamped shingles? I realize the finish coating on the shingle is a factor to consider, but is there anything else we should know?

  55. toddmiller says:

    Thanks Jackie. It is good to hear from you. Here is a link to a comprehensive article I have written on this subject of going over old shingles:

    http://www.asktoddmiller.com/history/should-existing-asphalt-shingles-be-removed-before-a-metal-roof-is-installed/

    In normal situations, doing so absolutely will not lead to mold.

    Oak trees can drop sap and other stuff that can streak / stain any roof. On metal, provided the metal has a good coating, it is usually something that can be cleaned off. In some situations though there is no avoiding it because of the trees. A Kynar / Hylar paint finish on the metal roof will be most resistant to this dirt accumulation and streaking.

    As far as the blackness showing up without trees … I’d say that unless there is something very odd in the atmosphere in your area, that is related to a lower quality coating being on the metal roof.

    I will email you direct concerning a contractor in your area.

    Thanks much.

    All Best.

  56. Jackie Holt says:

    We r thinking about putting tin over shingles. There’s only one layer. But we have heard by doing this will cause mold. Is this true? What kinda maintenance is required w tin. Want to keep it looking good cuz we have oak trees around the house. We have other houses n our area w tin n their roofs have black on them. Wondering if this is mold or just dirty rain. These house do not have trees n their yard. Looking for someone w great prices material n to do the job right. We live n Clarksville Tn. I have two houses we r thinking about putting tin on. Please give me some advise n recommendations on material n mayb if u know of a company here. Thanks for help

  57. toddmiller says:

    Thanks Chuck. Removing the crown is difficult. Depending on the construction and exactly what is happening, he may be able to do some things from inside the attic — shore up rafters, etc.

    If there is “belly” going up the roof rather than crown, you could put down 2 x 4s as sleepers vertically up the roof over the rafters — before your horizontal battens are put down. That could take out some of the “belly”

    If there is “crown” going up the roof and it can;t be remedied from the inside, then it would require removing the decking and doing significant work.

    The problem with crown is that it will likely force ripples into the metal roofing panels. I am not sure what type of metal roof panel you’re installing? More textured and exposed fastened products may handle this situation better but then you’re dealing with exposed fasteners.

    Another option for crown would be to install a metal shingle roof as the shingle courses will usually accommodate the crown very well. Many of these products thought must be installed direct to the roof deck rather than over horizontal battens … so that could be an issue because you’d not be able to use the horizontal battens.

  58. chuck Richardson says:

    Thanks for your response.one last question for you. What steps should I take to take the crown out or is this even possible without tearing off the existing shingle roof?I was paid to frame it up and lay the metal on the existing roof. Should I inform the homeowner he should have a framer come in and fix this first or is there a way I can take the crown out as in doing it myself? Sorry more than one question. I’d email you these but I can’t find my password for my own email account!

  59. toddmiller says:

    Thanks Chuck. I assume that you’re installing a vertical seam metal roof and it is a vertical seam profile approved for installation over spaced boards. I assume, too, that your spacing of the boards is per the load table provided by the roofing manufacturer.

    What you’re doing will help take up any dips between rafters on the roof. It is not uncommon for this to be done just for this purpose. It will not of course resolve any crown that is in the roof … and that can be a big problem for vertical seam metal roofs.

    You will want to have one of your 2 x 4’s at the eave for the starter to be fastened to. That should create a pretty even surface there.

    Feel free to email me direct or even send photos if you have more questions. todd@asktoddmiller.com

  60. chuck Richardson says:

    I’m framing up over an existing shingle roof with 2″ by 4″ ‘s because the sheeting is sagging.I figured if I used 2by4 instead of 1 by 3″ it will help the metal lay even without taking shape of the sheeting that’s sagged.well after nailing one 2 by 4 up there I noticed there’s some spots where there’s gaps between the 2 by 4 and the existing roof in some spots from the sheeting sagging. Homeowner was addimant about laying over the existing roof even with the sagging in the sheeting!!! Is this OK or what? Also what’s the easiest solution to install drip edge over existing roof and still ensure the metal lays properly

  61. toddmiller says:

    It is my opinion that a drip edge should cover them but, in all honesty, I have no real reason for that. I do not think it is a code requirement. Not entirely sure I buy the “breathing” comment … doesn’t seem like much breathing will really happen. I’d probably just go on enjoying your roof as is unless this is an inspector that can require you to do something.

  62. Ian says:

    Please excuse typos…

  63. Ian says:

    I have a metsl stanfing seem roof over wood shingles and an inspector just claimed thst the edges where wood shingkes shiw under driipedge should be covered. It is a bout 1 inch exposed between fascia and metal but not out in open. I was told by one roofer that it is good to breathe and cutious if snother drip strip needs to be added? The current system has been in place for 9 years with no visible deterioration.

  64. toddmiller says:

    Underlayment should be installed beneath the new roof regardless. Yes, there is a risk of unevenness of the old shingles telegraphing through and causing ripples in the standing seam panels. The more textured the metal roofing is, the less chance of that happening. And, yes, walking on it or perhaps cascading or very heavy snow could cause damage to the metal roofing as well.

  65. angie says:

    should standing seam metal roofing not be installed over asphalt shingles due to telegraphing of the shingles underneath the standing seam panels?

    , when snow piles up on a standing seam roof that was installed over an asphalt roof, will the shingles likely make horizontal dents in the metal panels. Also, will expanding and contracting due to temperature changes cause rubbing against the stone coating on asphalt shingles. – could this eventually cause some corrosion on the underside of metal panels.

  66. toddmiller says:

    Every situation will be different but generally speaking, installing one of the more heavily textured metal roofs such as a corrugated vertical seam or or a horizontal metal shingle over your existing shingles, should not be a problem. You will want to install layer of underlayment between the old and new roofs. A true standing seam vertical roof, however, will require that either the old shingles be very smooth, they be removed, or battens be installed over them. This will help avoid showing ripples in the metal roofing panels.

  67. Kelly MacKay says:

    I have an old 20 year old asphalt roof that the shingles are in pretty bad shape. The roof itself it very strong. Can I put a metal roof on a roof that old?

  68. toddmiller says:

    Thanks Ruth. Not all metal panels can be installed on battens (furring strips) and only a select few products are designed so that they MUST be on battens. Always adhere to manufacturer recommendations.

    Regardless of whether or not battens are used, underlayment should be installed over the roof deck and / or existing shingles before the roof is installed.

    Generally speaking, the only benefit I see to battens is the thermal break they create to help stop heat transfer. However, to be really effective, you need vertical battens and then horizontal battens so that the resulting cavity can be actively vented.

    Now, other than that … if the attic has little or no ventilation and insulation, there can be benefit to battens.

    Each job must be analyzed individually. If you wish to share more details about your situation, I will be happy to weigh in with specifics related to your roof.

    My email is todd@asktoddmiller.com

  69. Ruth says:

    What are the pros and cons of installing metal rib panels onto asphalt shingles with furring strips vs without furring strips

  70. toddmiller says:

    Thanks Craig. Products that sit largely flat against the roof deck (standing seam primarily) are more prone to showing ripples from unevenness in the surface below them. Standing seam of course also doesn’t handle dips and swales in the roof as well as more heavily textured products will.

    That said, many standing seam roofs are installed over old shingles along with appropriate underlayment. It can be done. You just have to look at each job individually and consider the condition of the roof deck and surface.

    In most cases, existing metal valley pans are left in place and just covered over. If they have a pronounced V rib down the center, the new valley can be formed to accommodate that.

    As far as existing drip edges … new drip edges can be formed to go over the existing or the existing can be cut back to be flush with the fascia. If you do remove the drip edge, you’re correct … you may have to build that area back up with lumber or perhaps roofing membranes. Another option is to cut back the eaves (lumber and all) but 3.5″ and then place a 1 x 4 in that area. Many times the decking at the eave is sort of spongy … so putting press lumber there is never a bad idea.

    Thanks for your questions — they are great!

  71. Craig says:

    Great site. Does this also apply to click lock standing seam which uses a solid substrate rather than strapping? I’ve heard you can put a membrane over the shingles, then the metal, providing the deck is in good condition and the usual caveats are met. What are your views on this? If it applies, would you install the new valley over the existing aluminium valley (and membrane)? How is the existing drip edge dealt with? It seems like if you cut away the shingles to remove it, it would leave too much of a bump down. Thanks.

  72. toddmiller says:

    Hi Janine,

    Generally speaking, tile roofs will need to be removed and would not be suitable to be left in place with any no roof. Feel free though to send me pictures or more information and perhaps I can provide greater detail. My email is todd@asktoddmiller.com

  73. Janine says:

    I have a 70 year old house with flat ceramic tile roof. The ceramic tile is extremely high maintenance. Can I go over the tile with a metal roof?

  74. toddmiller says:

    Thank you for your comment. I visited your website and you have some good information on it as well. If there is ever a way in which I or my company might be of service, please let us know. Information on our products is available at http://www.kasselandirons.com

  75. Matt S says:

    Great article. The most commonly asked question by our customers is whether or not their new metal roof can be installed over pre existing asphalt roofing shingles.

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About Todd

Todd's expertise comes from his years of experience in metal roofing manufacturing. As president of Isaiah Industries, based in Piqua Ohio, Todd runs a several of the world’s leading manufacturers of residential metal roofing; Classic Metal Roofing Systems, Kassel & Irons, and Green American Home. His personal goal is to educate homeowners of the long-life benefits of metal roofing.

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