metal over shingles

Richard Howard
8/8/2013
I asked this question yesterday but am not sure it made it to you. I am about to put a metal roof over two existing layers of shingles. I have gotten some mixed messages regarding metal over shingles from different sources. Is the consensus that old shingles should be removed first? Also, if I keep the old shingles and put metal on top of that will the roof and house tend to build up and retain more heat than if i strip the old shingles and have metal only? Also will this three layer system tend to collect condensation? My roofer wants to use Feltex.
Todd Miller
Isaiah Industries, Inc.
8/8/2013
Good attic ventilation is the key to both your condensation and heat build up questions. If you have proper ventilation, those will not be issues. (In fact, I could easily make the argument that existing shingles help reduce attic heat gain and also help reduce the chance of condensation because of the R Value they offer.) Now, in most areas, building codes say no more than two layers of roofing -- any roofing. Your insurance company may also want to weigh in on that because, when roofs get destroyed by hail, they do not like having to pay for multiple layers of old roof removal at that time. So, you need to think about number of layers and whether you're in an area where building codes are enforced. The low weight and design of metal roofing though can encourage installation over old shingles even multiple layers. This also avoids landfill disposal and allows homeowners to spend money on an upgraded roof rather than on old shingle removal and disposal. The more heavily textured metal roofs will be less likely to show an unevenness from the old shingles if they are left in place. Do know, however, that that can be an issue especially if the old roof is real rough or uneven. Curled shingles are usually not a big issue.
Guest User
8/8/2013
Thanks Todd. My insurance company has no problem with the three layers. I am still waiting to hear from the building code people. My house is a fifty year old Cape Cod. It had a ridge vent up til I re-roofed 20-25 years ago and the roofer talked me into two galvanized turbines. I have experienced no early shingle failure or any other problems that I might suspect would come from such a poorly ventilated roof. My current roofer wants to add a ridge vent when he re-roofs with metal and he wants to remove the turbines. Since you feel that keeping the old shingles may reduce heat gain and reduce condensation, should I just go ahead and save $1500 and tell the roofer to leave the old layers on?
Todd Miller
Isaiah Industries, Inc.
8/8/2013
Thanks Richard. Obviously I am going off of limited information and the ability to see it first hand but provided the building inspector is okay with it, I have seen lots of successful installations like this in the past. As far as ventilation, make sure that you have proper intake vents at the soffits to feed a ridge vent. Sometimes that is an issue on capes. If you do not have intake vents, let me know. We may want to stick to the turbines. Also, if you like, you can email photos to me at [email protected]
Eric Novotny
An informed customer is the Best Customer!
8/11/2013
Richard, Depending on the added expense of the removal, I would take them off. Ventilation will alleviate any moisture concerns and should be pro-actively handled regardless. The roof will hold more heat with the asphalt roof regardless and it will store that heat later into the day as compared to over a solid plywood deck. The ventilation will mitigate that heat build up but it still will retain more heat that if there was no old shingle layers. Post up a picture and we will tell you how to best ventilate the roof. Turbines are often flawed solutions to a poorly balanced ventilation approach. If you can stay passive (i.e. ridge with soffits), that is best.
mary ann grasser
8/12/2013
I have the same question, we are thinking of a metal roof versus shingle, this house was built in 1995 & have shaker style shingle it was suggested that they be removed, however it was our understanding that metal could be placed over any existing shingle. We had 2 roofers come out, one said to remove the other said no, so I am confused on which way to go.
Todd Miller
Isaiah Industries, Inc.
8/12/2013
Based upon what I see and what you have told me, I'd be comfortable installing over your existing roof, along with a layer of underlayment. Now, a standing seam roof may show some extra ripples from going over your old shingles. A through-fastened metal roof or one of the textured shake, shingle, slate, or tile facsimile products should not show anything.
Guest User
8/12/2013
Thank you for your input, I received my first estimate with shingle removal & metal roof 7,7700.00 which I feel is high on such a small house for shingles 10% off that price, I am going to have more estimates done.
Eric Novotny
An informed customer is the Best Customer!
8/13/2013
Mary Ann, Either application will work on your home. As far as the pricing goes, that is market dependent. I would guesstimate your home at around 18 - 20 squares if I were just throwing out a rough estimate. At that quantity, that would be a supremely cheap price for most metal applications in my market.

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