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TOPIC: Roofing over existing roof

metal over shingle

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I have an existing shingle roof that I'm going to be covering with standing seam metal. The roof has to straightened because of some "bows" in the rafters. My question is how high up (2X4 or fur strips or ???) off the existing shingles (minimum) do I need to be???? ALSO, do I need to put a water barrier between the new and old roofs(#15,#30,Ice and Water)???? Please I need answers!!
Guest User

9/5/2002
I have an existing shingle roof that I'm going to be covering with standing seam metal. The roof has to straightened because of some "bows" in the rafters. My question is how high up (2X4 or fur strips or ???) off the existing shingles (minimum) do I need to be???? ALSO, do I need to put a water barrier between the new and old roofs(#15,#30,Ice and Water)???? Please I need answers!!
Guest User

9/5/2002
First off you should contact the manufacturer of the product you have chosen to get their advice. The size of the furring strips and the location is related to the product attachment requirements, rafter spacing and local codes. Typically you will be shimming over and attaching down through into the existing rafters. I would ask you to investigate why the existing rafters have sagged and appreciate that you are adding additional weight onto them. Certain wind uplift and snow load requirements will change the equation as well. Again I would strongly suggest contacting the manufacturer as well as the local building official for their advice. As to the stand off. if your roof assembly is a cathedral ceiling then you are required by code to have a minimum 1" air space that is vented. As to the underlayment requirement, unless the product is tested you are required to have a minimum 30 lb underlay however, if the existing shingle roof is in reasonable condition and water tight you can use this as your underlay. If you contact me back directly with the roof configuration, pitch, climatic area then I can provide more meaning information. Good Luck.
Allan Reid
Dura-Loc Roofing Systems, Inc.

9/5/2002
My contractor is telling me it is perfectly safe to install metal directly over shingles with no fur strips. My shingle roof is in fair condition. He says with the new metal that has some laminate on both sides, it is safe not to use fur strips. Can you give me some advise?
Guest User

9/11/2002
We have 30+ year old wood shingles on our roof. If they are ok to leave under the metal roofing will it increase the insulatiing factor? And if we remove them and put on the metal roof how does it compare for insulation to wood or other shingles? I don't want the upstairs to be hotter, as it is an open ceiling.
Guest User

9/12/2002
We have 30+ year old wood shingles on our roof. If they are ok to leave under the metal roofing will it increase the insulatiing factor? And if we remove them and put on the metal roof how does it compare for insulation to wood or other shingles? I don't want the upstairs to be hotter, as it is an open ceiling.
Guest User

9/12/2002
We have 30+ year old wood shingles on our roof. If they are ok to leave under the metal roofing will it increase the insulatiing factor? And if we remove them and put on the metal roof how does it compare for insulation to wood or other shingles? I don't want the upstairs to be hotter, as it is an open ceiling.
Guest User

9/12/2002
First it is always best to ask the manufacturer. Some panels are designed to go and over however the building codes have certain requirements. Check to see if the code allows it and check the manufacturer. Code do call for a moisture barrier under roofing material and if your existing roof is in good condition it can perform this function. On the down side the existing roof material could telegraph up through ans felt does help stop this. You did give the region of the country and you may want to consider the added insulation benefit the air space provides especially if it is ventilated. It can cut down considerably on utility bills especially air conditioning. Hope this helps.
Allan Reid
Dura-Loc Roofing Systems, Inc.

9/12/2002
It would help if I knew what region you are in but here goes. It sounds like you have what I refer to as a "cathedral" ceiling assembly where the ceiling follows the rafter line and there is no attic. If the house is older, it may not have been constructed correctly however her goes. The new codes require a minimum of 1" vented air space under the roof material. This will provide the best energy saver of all. The shingles provide a little R value but not that much.There are also some reflective sheet underlayments that can help boost the energy savings as well that can be incorporated at the same time. If the existing wood shingles are in good condition then some companies like ourselves have various assemblies tested to go over wood shingles so check with the manufacturer and see if they have a building code evaluation report that supports this. You want to sure to renail loose shingles and install a good moisture barrier over them. Make sure that the new strapping provides the air space and that they vent it. Some areas like California require structral upgrades for earthquakes when re-roofing and/or certain fire ratings so again make sure they have an approved assembly.
Allan Reid
Dura-Loc Roofing Systems, Inc.

9/12/2002
Sory I just found this one. Hope this helps. Some companies like ours have systems tested and approved for installations over wood shingles and provide fire ratings. The main reason they roof over is that they do not want the dust and debris associated with the removal of the wood shingles. Leaving them does add a certain insulation factor. If you have comfort problems now in the summer, a metal roof on strapping will help you in this regard however here are a few things to consider. First the building codes call for ventilation now especially on your type of roofs with open ceilings. Basically they require a minimum of 1" under the roof material. I would suggest that you consider tearing off the old roof and checking for dry rot. Then install some ridgid insulation with a good moisture barrier and then the strapping. They can use vented closure strips to ventilate the chamber. If you contact me directly indicating your climatic region I cn give you better details. Good Luck.
Allan Reid
Dura-Loc Roofing Systems, Inc.

10/28/2002
I HAVE REMOVED THE OLD SHINGLES, AND LAYED 30 LB FELT PAPER OVER THE ROOF. DO I NEED TO STRIP OR CAN I LAY THE METAL OVER THE FELT?WHICH WAY IS BEST?
Guest User

11/3/2002
It really depends upon what type of metal roofing you're installing. Many, but not all, of the shingle style metal roofs do require solid decking. There are other styles of metal roofing which can be installed over lathe and, with some products in particular some through=fastened panels, ventilation beneath them can extend their life. I suggest choosing a roofing product and then posing this question to the manufacturer. Todd Miller
Todd Miller
Isaiah Industries, Inc.

11/3/2002
In the south texas area, do building codes allow the placement of aluminum shingles directly over wooden shingles, and do insurance companies often balk at this situation if "solid decking" is not used in this construction?
Guest User

6/21/2003
This is done fairly frequently with aluminum shakes going over wood shingles up to about 1- 14/" thick. A quality underlayment should be installed over the wood shingles. Also, the eave and gable edge shingles, especially if they are rotted at all, should be cut back and the area filled in with new dimensional lumber for secure perimeter fastening. On applications like this, the low weight and formed thickness of aluminum shakes allows it. With thinner aluminum shingles, you will not be able to go over as thick of wood shingles. Some manufacturers offer special fastening methods which even ensure fasteners into every course of lathe beneath the wood shingles. I do not think your insurance company will have a problem with this sort of application. The best thing might be to inquire first though. Additionally, if you are in a coastal area, an engineer will probably be signing off on your installation. Make sure before the job is started that there is an engineer who will sign off on it. Again, in my experience, this sort of application is done fairly frequently. I have never seen a job done this way where I later had doubts as to whether it was the right thing to do. Todd Miller
Todd Miller
Isaiah Industries, Inc.

6/22/2003
In a metal shingle over existing wood shingle re-roofing installation, does it require to install drip edge along the rake of the roof? If fascia board is installed along rake, should the drip edge be installed on-top of the fascia board or behind the fascia board? Should the metal shingle be completely overlapping the fascia board so that the fascia board is not exposed to rain?
Guest User

6/23/2003
If the wood shingles are in bad shape, they should be cut back and removed along the gables and eaves. The cut back should be, in most cases, 3-3/4" and then this area should be filled in with dimensional lumber. Most metal shingle systems include some sort of gable trim and drip edge. In most cases, the drip edge will hang down over the fascis board by 1-1/2 - 2". The remainder of the fascia board below that will be exposed. If the fascia board has an aluminum or other cover on it, that fascia cover should extend up under the roofing drip edge. Additionally, before the drip edge is installed, I suggest that the roofing underlayment be installed so that it hangs over the end of the roof. This excess will then be folded down under the roofing gable drip edge. If a cover is installed on the fascia, it should extend up and under the underlayment as well. There are a variety of ways in which the gable drip edge will then interact with the roofing to close off the end of the roof. This varies between the various metal shingle systems and, in some cases, options are available from individual manufacturers as well. In some cases, the gable drip edge is integral to a channel which the roofing slips into. In other cases, the roofing might somehow lock into or over the channel. In other cases, individual caps or other trim might be added to close off the metal roofing shingle ends. Todd Miller
Todd Miller
Isaiah Industries, Inc.

6/24/2003
I purchased a house that was built in the 1930's that originally had a tin roof nailed directly to the support beams and now has an asphalt roof on top of the tin. The support beams are exposed from the attic and appear to be in great shape. Can a vertical panel metal roof be put on top of the two existing layers? Thank you, Stevon
Guest User

6/26/2003
National building codes which are enforced in many areas dictate a "two layer" maximum when it comes to roofing. If you're in an area where you would need a permit for re-roofing, this will be an issue. If you wish, hire a professional engineer to visit the home and give an opinion on this. I personally would be concerned about achieving secure attachment of the new roof. Todd Miller
Todd Miller
Isaiah Industries, Inc.

6/27/2003
Guest User

8/7/2003
Subject:retrofitting steel panels over exisitng shingle roof:....Roof is to be stripped over shingles with 1x4s with steel panels applied to the 1x4s. One contractor says need I insultion between 1x4s or will get condensation like in a metal building..... which could deteriorate 1x4s and roof............ Second contractor says insulation is not necessary and not to worry....Is the first contractor just trying to sell me insulation or should I be concerned?.....Will felt applied between the 1x4s and steel solve any potential condensation problem?...where can I find reccomended installation details for this type of reroof installation.
Guest User

8/25/2003