irodetoday
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| 04/15/2009 3:43 PM |
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| I'm about to put a standing seem metal roof on my house. One guy wants to remove the 22yo shingles....the other guy wants to put the metal right overtop the shingles. What should I do? |
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Alton
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| 04/15/2009 3:52 PM |
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You need to determine if there are any spongy spots on the roof although you may not have seen any leaks. You can have rotted decking and not be able to tell it from below. If someone will walk all over the roof, then it will be easy to feel soft spots. I was working on a roofing job where one of the roofers fell through a soft spot. This showed us where to replace the bad decking. So whoever walks the roof should be made aware that deck boards can be weak.
If no spongy spots or leaks, then ask the metal roof supplier what they recommend. |
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Alton C. Keown
Residential Designer and Construction Technology Consultant
Auburn, Alabama
E-mail: alton at auburn dot edu |
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wes
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| 04/15/2009 4:17 PM |
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A lot depends on the type of metal roof you are using. You say 'standing seam' but a lot of people use that term for any type of metal. If it is a true standing seam, then I would suggest removing any shingles and underlayment, repairing any weak spots, and installing new underlayment (preferably something other than 'felt'). This is because the sheets of metal are relatively flat with the edges turned up for seaming. This profile is very flexible and suseptable to showing any irregularity under it. The terms 'telescoping' or 'oil canning' are sometimes used to describe this action.
If, however, you are using the more commerical type metal roofing, typically 36" wide panels with a series of ribs formed into it, then these panels can be layed over an existing roof, because these panels are much stronger and less likely to allow any irregularities to show through. |
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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ICFconstruction
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Posts:638
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| 04/15/2009 8:33 PM |
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I would remove the old shingles, can't go wrong.
Would the granules would be tough on the underside of the metal? With expansion and contraction I have seen many things wear through roofing materials. |
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Brad Kvanbek - ICFconstruction.net |
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mac31313
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Posts:20
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| 04/15/2009 9:03 PM |
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if codes allow
remove cap, place 1x4 fir strips over existing 2'-3'o.c., nail to joist (ring shank nails) attach metal to battens per mfg. requirements
foil bubble insulation can also be added under battens if needed
air space allows for moisture removal, old shingles provide some insulation value,and no landfill trips
mac
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Polycore
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Posts:64
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| 04/16/2009 4:40 PM |
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Correct me if I am wrong, but you are using a "standing seam" metal roof, because it will not leak, and will last 100 years. Take the time to take off the shingles, make sure all the sheeting is in good condition, make any necessary replacements and secure your "standing seam" metal roof. There is no point to put the metal roof over the shingles. First of all you won't find any existing damage or leaks without removing the shingles. Secondly, you are already on the roof and have paid for a far superior product, do it right the first time and you won't have to worry about it. If it is done right it may need to be painted every 25 years and be good for 100, that's what you paid for.
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Polycore Canada Inc.
www.polycorecanada.com
1-877-765-9267 |
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coldtrail
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Posts:2
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| 04/17/2009 9:59 AM |
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I would strip the roof out over the decking with either 1x4's or 2x4's every two feet. Screw these directly to the truss or rafter. I would inspect the decking, but I would depend on the rafters and strips to hold the metal to the roof.
The strips will take out alot of the wavey decking. Of coures we dont have a code or inspector. |
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angel
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Posts:10
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| 10/14/2009 3:49 AM |
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Hello,
It is better you said that how to put the metal, i can help you out if you are letting me know about the exact position of your house, or you can post a pic
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Quality Roofing
Colorbond Adelaide
House Roofs |
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SimonD
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Posts:94
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| 10/14/2009 3:02 PM |
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| One way to decide wether to remove your shingles or not would be how complex your roof is. If your roof has valleys, dormers, lots of roof penetrations like skylights, chimneys and vents, then these are the areas where water may have gotten in and damaged your roof deck. Another issue is if your area is prone to rain storms and severe weather, water may have been forced under your shingles at the edges and ridge and has done damage. If your roof is old, that matters too. If none of the above applies and your roof is simple, not old and in an area with mild weather then leave the shingles on, but make sure the guage and the profile of metal roofing you have chosen is sufficient to be placed directly over shingles otherwise the shingles will 'telegraph' through the metal roofing and look rippled and not smooth. Your roof deck needs to be in good repair before you put the metal roof on because that's the last roof you will need in your lifetime. |
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Building Designer
PANELfusion, LLC, Tampa, FL
simon@panelfusion(dot com)
"Metal SIP Advocate" |
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irodetoday
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Posts:2
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| 10/14/2009 9:06 PM |
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| Thanks. I live in Pittsburgh, PA. Roof is 20 plus years old. I want to remove the shingles. I just know there will be some decking that will need repair.
Another question. One of the roofers is recommending to go with a more "industrial" panel. He says it would be much cheaper and more durable than Standing Seam. It doesn't look quite as good as Standing Seam but if cost is 50% less I think I would consider it. Would you?
Also, what underlayment do you recommend....bubble or closed cell foil like Prodex?
Thanks. |
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cmkavala
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Posts:1415
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| 10/15/2009 1:55 AM |
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Posted By irodetoday on 10/14/2009 9:06 PM
Thanks. I live in Pittsburgh, PA. Roof is 20 plus years old. I want to remove the shingles. I just know there will be some decking that will need repair. Another question. One of the roofers is recommending to go with a more "industrial" panel. He says it would be much cheaper and more durable than Standing Seam. It doesn't look quite as good as Standing Seam but if cost is 50% less I think I would consider it. Would you? Also, what underlayment do you recommend....bubble or closed cell foil like Prodex? Thanks. Prodex is not a roofing underlayment, use whatever the roofing mfg. recommends
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Chris Kavala
chris@southernsips dot com
1-877-321-SIPS |
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wes
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Posts:637
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| 10/15/2009 6:47 AM |
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irodetoday,
Several steel roofing suppliers make 'snap lock' panel designed for residential use. It resembles the true 'standing seam' products, but are somewhat less expensive. It is still more expensive than the industrial panels, but it is worth checking out.
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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big hammer
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Posts:16
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| 10/15/2009 7:40 PM |
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| I would strip off the old roofing and replace with a good architectural roofing. Has a 50 year warrantee. Metal roofs here in my area will not last nearly as long as what some here are saying. Plus metal roofs are difficult to do anything with after the installation, such as in a remodel, addittion, repair, cleaning the chimney, etc. Sometimes the paint gets scratched during the application, that is where the panel will fail. RUST is the enemy! Once it gets scratched, the rust starts. Think about the little rock stuck in the sole of a shoe. s c r a t c h... |
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toddm
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Posts:170
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| 10/18/2009 8:11 AM |
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This will give you an idea of the snap-together metal roofing systems: http://www.mcelroymetal.com/content/products/ I put on a Mcelroy roof in 2001 and was quite happy with it. Your standing seam contractors will probably be scandalized that you'd consider panelized roofing. I am sure the lead pounders in the plumbing world had the same reaction to PVC pipe.
While Big Hammer is right about rust, paint will keep a metal roof going forever. I am sure there are roofs here in Philly that are well over 100 years old. |
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Rio
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Posts:75
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| 10/19/2009 8:30 AM |
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Take off the shingles first, repair and prepare and then install the metal.................................
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DallasBill
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Posts:140
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| 10/27/2009 3:27 PM |
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I would remove the shingles first, and for a reason nobody has mentioned....
One of the major benefits of a metal roof is the fact that it offloads heat at night a LOT faster than asphalt shingles do. That results is a far less heat load on your house after the sun goes down and the temp starts to drop. Your AC does not have to run as much. Leave the shingles on and you negate that benefit. This is obviously a lot more important the farther south you live, but it is a benefit nonetheless.
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Dana1
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| 10/28/2009 8:50 AM |
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Posted By DallasBill on 10/27/2009 3:27 PM
I would remove the shingles first, and for a reason nobody has mentioned....
One of the major benefits of a metal roof is the fact that it offloads heat at night a [b]LOT[/b] faster than asphalt shingles do. That results is a far less heat load on your house after the sun goes down and the temp starts to drop. Your AC does not have to run as much. Leave the shingles on and you negate that benefit. This is obviously a lot more important the farther south you live, but it is a benefit nonetheless.
The emissivity of asphalt shingles is usually quite high- around 0.9, but the emissivity of bare or plated matals is usually low, around 0.1-0.3. Painted/coated it will vary- the emissivity of the paint/coating is the determining factor, but 0.4-0.7 is pretty common. Metal roofs don't shed heat via radiation NEARLY as quickly as asphalt shingles, only 1/2-3/4 as fast.
The R-value of metal is quite low compared to asphalt shingles, as is it's thermal mass, but unless you have 3 layers of shingles up there or no other insulation in the attic/ceiling it'll be hard to measure the difference in total conducted heat flux from that secondary effect. But they do not shed heat more quickly than asphalt shingles- quite the
contrary, and the overall nighttime heat shedding is largely unaffected
by the insulating & thermal mass aspects of a fully-shaded layer of
shingles under the metal. The R-value of the roof decking itself is
usually at least 4x the R-value of the shingles.
The biggest difference in cooling season performance between typical metal vs. asphalt roofing is the difference in solar reflectivity. Asphalt shingles tend to have reflectivities only in the 0.1-0.25 range, whereas metal roofs' reflectivity is typically over 0.5, and some with "cool roof" ceramic coatings will exceed 0.75, while retaining moderate emissivity. Basically it boils down to absorbing less than half the heat of asphalt during sunlight hours while retaining some ability to shed heat at night. It's the ratio of reflectivity to emissivity that determines it's overall performance. If it absorbs only 1/4-1/3 of the heat of shingles, but sheds it only 1/2-3/4 as fast, it's still a HUGE performance win.
But strip 'em anyway- they're just dead weight inhibiting the drying capacity of the roof deck, both obscuring & potentially creating moisture damage issues.
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Dana1
Registered Users
Advanced Member
Posts:702
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| 10/28/2009 8:51 AM |
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Posted By DallasBill on 10/27/2009 3:27 PM
I would remove the shingles first, and for a reason nobody has mentioned....
One of the major benefits of a metal roof is the fact that it offloads heat at night a [b]LOT[/b] faster than asphalt shingles do. That results is a far less heat load on your house after the sun goes down and the temp starts to drop. Your AC does not have to run as much. Leave the shingles on and you negate that benefit. This is obviously a lot more important the farther south you live, but it is a benefit nonetheless.
The emissivity of asphalt shingles is usually quite high- around 0.9, but the emissivity of bare or plated matals is usually low, around 0.1-0.3. Painted/coated it will vary- the emissivity of the paint/coating is the determining factor, but 0.4-0.7 is pretty common. Metal roofs don't shed heat via radiation NEARLY as quickly as asphalt shingles, only 1/2-3/4 as fast.
The R-value of metal is quite low compared to asphalt shingles, as is it's thermal mass, but unless you have 3 layers of shingles up there or no other insulation in the attic/ceiling it'll be hard to measure the difference in total conducted heat flux from that secondary effect. But they do not shed heat more quickly than asphalt shingles- quite the
contrary, and the overall nighttime heat shedding is largely unaffected
by the insulating & thermal mass aspects of a fully-shaded layer of
shingles under the metal. The R-value of the roof decking itself is
usually at least 4x the R-value of the shingles.
The biggest difference in cooling season performance between typical metal vs. asphalt roofing is the difference in solar reflectivity. Asphalt shingles tend to have reflectivities only in the 0.1-0.25 range, whereas metal roofs' reflectivity is typically over 0.5, and some with "cool roof" ceramic coatings will exceed 0.75, while retaining moderate emissivity. Basically it boils down to absorbing less than half the heat of asphalt during sunlight hours while retaining some ability to shed heat at night. It's the ratio of reflectivity to emissivity that determines it's overall performance. If it absorbs only 1/4-1/3 of the heat of shingles, but sheds it only 1/2-3/4 as fast, it's still a HUGE performance win.
But strip 'em anyway- they're just dead weight inhibiting the drying capacity of the roof deck, both obscuring & potentially creating moisture damage issues.
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ICFconstruction
Registered Users
Advanced Member
Posts:638
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| 10/30/2009 12:43 PM |
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| Is an underlayment recommended under metal roofing? I have heard of ice and water shield over all the sheathing and the metal on that. |
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Brad Kvanbek - ICFconstruction.net |
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cmkavala
Registered Users
Veteran Member
Posts:1415
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| 10/30/2009 3:03 PM |
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Posted By ICFconstruction on 10/30/2009 12:43 PM
Is an underlayment recommended under metal roofing? I have heard of ice and water shield over all the sheathing and the metal on that. There are HI-Temp brands that can be used in direct contact with metal
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Chris Kavala
chris@southernsips dot com
1-877-321-SIPS |
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