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  1. #1
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    Default Metal roofing over aging shingles - Correct way to install?

    I've installed metal roofing on barns 3 times, but never on a house, which is what I'm interested in doing now. My shingles are going on 20 years old, so I'd want to metal roof over them, if possible. I'd like to use the regular ol' galvanized silver 3'-wide 5-ridge metal roofing available at Home Depot/ Lowes.

    The house across from me just did the same, but I believe I saw (from the road) that the roofing company just tar papered over the old shingles, laid the metal roofing right on that, & screwed it down ... I expected to see them install a series of 1x4's over the old shingles first, & then lay the metal roofing on those & screw into them.

    With the metal I've used on barns, it's thin enough that I think laying it directly on shingles would let the wavy-ness of the shingles would make the flats of the metal also wavy. Laying the metal on tar paper over top of the shingles might help eliminate that, but I'm not sure.

    I also wonder if laying the metal right on the tar paper, like I think they did, would trap moisture between the two & eventually cause the metal to rust underneath?

    What do you think? Which way should it be done?

  2. #2
    Super Star Member brin's Avatar
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    I put a new roof on our old house and wanted the roofer to lay shingles over the 20 yr. old roof and he talked me into letting him tear the roof off....I am sure glad he did..it turned out that there was damage to some of the roof decking and it would have gone unnoticed had the old shingles not been taken off. I also had a shop on the farm with asphalt shingles that I installed metal roofing over...it leaked in several places and I could never get the leaks stopped...so finally tore it off and re roofed with metal from scratch and all was well...If you think about it ...which I did not....those old shingles under there will still continue to curl and disintegrate at varying degrees in various spots so your new metal roof would have to end up wavy and that would create leaks between the metal panels..Good Luck..
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  3. #3
    Super Member clemsonfor's Avatar
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    The correct way is to go to the deck and still use the stickers. I think the next correct way is to screw 1x4s or 1x3s to the roof then the tin. Although i know folks who have screwed directly to the shingles as well. You will hear it all, weigh the options and do what you like. I personally think i would put the 1x4s on my house and if it was any amout of roofing!

    Like on my 1300sqft farm house i will prolly just screw to the shingls if i do it.

    Also the 1x4 spacers allow air under there to act as extra insulation and allow the heat to flow from under to up to help keep the attic cooler, this is prolly what id do on my main residence.
    YM2000. MF dirt scoop,4' Jbar bushhog,boompole, LMC 12-16 disk harrow, 4' Atlas boxblade (with rippers). 1980 chevy K10,1990 ford ranger 2wd (285K miles),1997 saturn SL2 (twin cam!!),2001Toyota Higlander
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  4. #4
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    For a house, I would remove the shingles. For my barn I did this summer, I just went over the old shingles. A friend that does roofing suggested laying felt to prevent the shingles from wearing bare spots in the metal that could rust over time. But it’s a barn, so I wasn’t too worried about it. I can’t figure out how a metal roof could leak because of warped shingles underneath? I don’t think metal over shingles is all that uncommon.

  5. #5
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    Tks for the replies. Being a details stickler, I would prefer to tear off all the old & start fresh, including the ability to find & fix possible water damage to the sheathing. I probably will do that; it just seemed so much easier to roof over it, but easy seems to usually be the wrong way

    I just looked up the permit for the metal roof job across the street I mentioned - They have an older 2,800SF house plus garage & porches, & a 24'x44' detached garage, so 4,883SF total under new metal roof. The permit says the job cost is $21,850 ... again, that's without tearing off the old roof. & it's a fairly shallow pitch, probably 4/12, maybe 5/12, whereas mine is 8/12.

  6. #6
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    I just had my 2000sq ft of roof covered with screw down metal. $10k for stripping the original shingles off, covering the entire roof with snow and ice shield then the roofing.

  7. #7
    Super Member clemsonfor's Avatar
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    Quote Originally Posted by EHR View Post
    I just had my 2000sq ft of roof covered with screw down metal. $10k for stripping the original shingles off, covering the entire roof with snow and ice shield then the roofing.
    Is this 2000sqft of roof like you said or 2000sqft of living space under the roof? If it is like you say my roof would be in the $20K range. I am haveing my roof reshingled as we speak. Its around 4000sqft of shingles! My home is less that that of liveable sqft, more like 3000under the roof.
    YM2000. MF dirt scoop,4' Jbar bushhog,boompole, LMC 12-16 disk harrow, 4' Atlas boxblade (with rippers). 1980 chevy K10,1990 ford ranger 2wd (285K miles),1997 saturn SL2 (twin cam!!),2001Toyota Higlander
    1986 Cobia 177 sunskiff w/1981 Johnson 60 hp
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    Troybuilt 4 cycle & Echo 2 stroke,cold natured(need carb rebuild),MS390 Stihl, Northern tool pressure washer, mixes water into the oil in the pump(now dead, motor on a tiller). 5000 watt generator.

  8. #8
    Veteran Member johnrex62's Avatar
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    The only correct answer is " It Depends."


    Manufacturers make metal roofing designed to be installed in specific ways. The maker of your roofing will dictate how it can be installed and what the preferred method it.

    I have read installation guides that detail all of the methods mentioned so far, but have different product for each installation method. I do not know what makes on method technically right or wrong or how the products differ that makes one way or the other correct for that product, but I am convinced that if your roofing fails and your installation method is not the recommended way it will be impossible to get any type of support from the manufacturer or roofing company.

    I recently re-roofed my house and my product from Berridge specified either to be installed on solid decking or over existing not to exceed 1 layer of shingles. My initial quote was to do the roof overlay, but the roofing company decided to eat the additional cost and do a tear off so that the new roof would be less likely to oilcan from the uneven substrate. (my old roof was under 10 yrs old and only visibly wind damaged in a couple areas.)

    My house is just over 2500 sq feet and I have a 120 sq ft shed that were re-roofed. Both are 8/12 pitch hip roofs, only one valley and one fireplace to make things odd shaped. The total price was $13,700 from a company out of Austin Tx.
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  9. #9
    Super Member Robert_in_NY's Avatar
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    As JohnRex was mentioning, the metal manufacturer will list install directions. Most I have read do allow you to attach over shingles without any wood strips. Their requirement is you lay felt on the shingles so that the stones don't scratch the back side of the metal. The metal will hold up fine if your roof is fine and it won't curl and buckle unless you have actual structure problems. Just use a quality metal and do what your comfortable with and that is allowed by the manufacturer.

    We have installed just about every way possible. We have put strips down over asphalt, layed felt between the two on a different job, on another job the homeowner was providing labor and they stripped the first section, after that they had us go over the rest of the roof so we just used firring strips to hold the metal off the shingles. All of these roofs have been trouble free and the oldest roof is going on 10 years now. I don't remember doing any others before then but my memory is terrible.


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  10. #10
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    Default Re: Metal roofing over aging shingles - Correct way to install?

    Beginning several years ago, the "metal over shingles" craze took on locally. In recent years, I have seen many of these houses having to be re-re-roofed because the metal roofing is rusting from underneath.

    In most of the installations that I saw, the installers simply placed the metal over the shingles (no strips, no felt, no nothing) and screwed it in. I have helped replace a couple of these roofs (we took off the metal, stripped the shingles, firred the roof, and put on new metal) and another common problem was corroded fasters. The asphalt shingles would rust/decay the screws that held the metal on to the point that when we tried to unscrew them, they would break off about half the time.

    In my opinion, and my opinion only, I would never put a new roof over an existing roof. If it was a good idea and practice, then they would install two roofs when a house was built. The only reason to do it is to try to do the job cheaper. Once again, in my opinion, if a roof is in bad enough condition that it needs to be replaced, it needs to be removed.

    In your example, I would strip the shingles (if for no other reason than to inspect/repair the deck), fir the deck, and install metal, if you are indeed set on installing a metal roof.

    Good luck with whatever you choose and take care.

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