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TOPIC: Roofing over existing roof

INSTALLING METAL ROOF OVER SHINGLES

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In order to install a metal roof over an existing shingled roof, is it best to have the roof "stripped" with strips of wood, or just place metal right on top of shingles? Also, for a home, is 26 guage metal okay?
Guest User

1/5/2005
You should always put a new underlayment over the old shingles. Whether boards are put down or you go direct over the old shingles is very much a function of the metal roofing product you choose. You will need to confirm with the roofing manufacturer how their product has been tested and how it is to be installed. Metal gauge, again, is dictated by product design. Check into what testing your metal roofing has passed.
Guest User

1/6/2005
Can you apply A 26 gage metal roof directly over exzistig shingles
Guest User

2/17/2005
In many cases, yes. It depends largely upon the design of the metal panel. Check with the manufacturer for a final answer.
Todd Miller
Isaiah Industries, Inc.

2/17/2005
can i install metal over asphalt shingles
Guest User

2/26/2005
This will be determined by the condition of the shingles and the type of metal roofing being installed. The manufacturer of the roofing you choose should be able to help with this question. Generally, the more heavily formed metal roofing profiles are better suited for this.
Todd Miller
Isaiah Industries, Inc.

2/26/2005
Some of the less textured metal roofs in particular might show unevenness if installed over old shingles. Also, in any event, you need to take steps to ensure secure fastening through the old shingles.
Todd Miller
Isaiah Industries, Inc.

2/26/2005
Is ther a chance of the asphalt singles melting under the new metal roofing?
Guest User

3/9/2005
I have never run into anything even remotely like that.
Todd Miller
Isaiah Industries, Inc.

3/10/2005
I have heard that if you don't provide an air space between the metal and shingles, mold/mildew could occur in that space because of condensation. Comments?
Guest User

3/16/2005
I have never seen this occur in 20+ years in the industry. That said, though, I am a firm believer in new underlayment beneath every new metal roof and I am also a firm believer in good attic ventilation.
Todd Miller
Isaiah Industries, Inc.

3/16/2005
I was called to inspect problems a homeowner had after having this roofing installed on a 35 yr. old FmHA house. New panels were screwed directly to existing single layer of asphalt shingles on approx. 4 in 12 pitch hip roof with one hipped wing turned out to cover a front porch. The roof looked OK from the outside, except for some swag on one of the hip ridges that probably pre-existed the metal. Owner showed me photos of water streaming down the inside surface of one whole exterior wall. In addition, the inside surfaces of the plywood roof decking had become black, apparently from mold, though they felt dry to the touch. A manufacturer's site (Fabral) I checked recommended furring strips over existing shingle roofs, but only as a "best case" scenario. Contractor did eliminate two turbine vents from the house without replacing them, and soffit vents were in place but occluded by deep dish fiberglass batts. The loss of vent looks to me like a reason for blackening of decking, but as for water streaming down outside wall I am at a loss. I suspect that blown rain may be finding a way below tops of panels at hip ridges, and don't know the condition of the covered shingles. Have any of you seen problems associated with this kind of roofing?
Jim Baird

4/8/2005
Bad things can happen when good products are not installed properly. Obviously, there is an issue with ventilation and moisture control. Next, there is a problem in that no underlayment was installed over the old shingles. Finally, I do suspect there may be some flashing problems allowing water intrusion as well. Feel free to email me pictures (close up) of the flashings, etc. My direct email address is below. I really suspect this whole roof will have to be removed and re-installed. [email protected]
Todd Miller
Isaiah Industries, Inc.

4/8/2005
Hello, Mr. Miller: I'm thinking of having a metal roof installed over my office of ~1600 sqft. The existing hip roof is not steep and not extremely flat and is in need of repair. The contractor I contacted told me he'd put the 1x4 wood strips and install the metal over that. I see you recommend an "underlayment". What is that and what material is it made of? I have a ridge vent in the old roof and have extreme heat problems in the summer. Will a metal roof installed this way improve the situation? Thanx. Jim
Guest User

4/9/2005
Jim, Thanks for your question. I am assuming that the existing roof and decking will be left in place. In that case, I would cover it with underlayment and then vertical battens followed by horizontal battens. This is provided that you choose a metal roof which can be installed over battens. The reason for vertical battens first is that this will create an air chamber which can be vented from the bottom to the ridge. You will want to work in an eave detail which allows for venting at the bottom. This vented air chamber will help keep your office cooler and it will also help to avoid any accumulation of unwanted moisture. As far as underlayment ... 30 pound roofing felt is normal but there are also many good synthetic underlayments available today. A quality roofing contractor will know what these are. A couple of other things -- it sounds like your roof is low pitch. Make sure that the metal product being installed is approved for use on roofs that are the same pitch as yours. You may wish to explore the full world of metal roofing products before making a final decision. Keep in mind the many differences in product appearance, metal, finish, warranty, and installation details. Always choose an experienced and qualified installer with good references. Note to other readers: My response is particular and specific to Jim's situation. Please do not assume that what I have described here is the way to go in all situations. I have had readers before sense that I was inconsistent in my answers. I try my best to be consistent but every situation is different and may merit a different response. Todd
Todd Miller
Isaiah Industries, Inc.

4/9/2005
Mr. Miller: I have a roofing problem similar to one described by Jim (message from 04/09). Briefly I want to install metal shingle roof over two layers of old aspalt shingles on my cottage. Roof slope is 3:12 and there is no attic. Would it make sense to add foam insulation between old roof and new metal shingles to keep house cooler in a summer. Also would it reduce room between old roof and metal shingles and affect roof ventilation? Thank you, Vadim
Guest User

5/15/2005
Most, but not all, metal shingle style products require solid decking. I understand your need for insulation but I would not choose insulation over ventilation. If the structure can handle the weight, you could do something like build up with foam and an airspace and then new decking on top of that. Vent the airspace. You may wish to get a structural engineer involved to do some analysis.
Todd Miller
Isaiah Industries, Inc.

5/15/2005
Im installing a 26 ga metal roof on an exsting asphalt roof . I put 30 felt down and after installing 5 panels there is uneveness is this typical or should the aspalt be removed for a better fit ?
Guest User

6/23/2005
This is pretty much impossible to answer "long distance" but, yes, going over the old shingles is likely a contributing factor.
Todd Miller
Isaiah Industries, Inc.

6/23/2005
can i put a metel roof over a roof that has a layer of ceder shakes and two layers of asphalt shingles is there a load restriction
Guest User

6/24/2005