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TOPIC: Standing Seam roof

New metal over old metal

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I own a 100 year old house which was built over a 10 year period. The first roof was cedar shingles then the present roof is a metal one. Its very flat and is made up of 12"x12" squares that are crimped together then nailed on. Half of the house has oak purlins and the other half is sheeted with 1"x12"pine boards, the tar paper is totally torn or gone. There is 5" of blown in insulation and there is no condensation problems at all, even though there is no ridge vent or eave vents, the temperature in the attic is consistent with the outdoor temperature. Here are my questions; 1) Can I put a standing seam roof over the old one. If so would I put tar paper on top of the old roof. 2) Or would it be better to tear off the old and put on the new. Money wise I can only afford sheet metal, not tiles. 3) I plan to upgrade the insulation to r-38, so would roof vents and gable vents be okay, eaves vents would be very difficult.
Guest User

6/25/2002
It appears as if you received a very effective service life out of your current metal roof. I would be curious to know why you are having to reroof as identifying the cause will help insure that you correct the problem. Most of the original attics had some type of ventilation, be it the space in the sheathing, louvers etc. Some buildings relied on the heat loss to keep the snow off the roof. I am assuming by your desire to increase the insulation that you are in the northern climate. I am surprised that given the description that your attic is not hotter than you describe although the metal may be reflecting a lot of the suns heat and you may be surrounded by trees etc that help. I am assuming that the old hand seamed panels that you have are allowing some air to migrate through and if you install the new roof over the old you should install a moisture barrier of some nature to catch the condensation such as a 30 lb felt paper. I would also then give consideration to installing an ice and water shield up from the eaves to a minimum of 3 ft inside the exterior walls. Ventilation is always important and I would strongly recommend it. The best is to have a balanced 50-50 between ridge and eaves. If this is impossible then you must double the amount of opening if you use gable or ridge. This will require a minimum of 1 sq ft of ventilation for every 150 sf of attic area. Watch the prevailing winds and install a good quality system that keeps the snow out. Remember the old houses had no air barriers on the inside which leads to heat loss and condensation in attics. If you renovate the ceilings install one or alternately paint with a good quality oil base paint and seal the penetrations around light fixtures etc. Good Luck.
Allan Reid
Dura-Loc Roofing Systems, Inc.

6/26/2002
Thanks for the info. I believe your right about the seamed roof allowing air to get into the attic and I do live in Ohio so that's why I'm increasing the insulation. The metal roof is in good shape, except for a litle rusting by the gutters. The reason I need to replace it is because I put on a two story addition and I cannot find a match to the old roof, and there are three shed roof additions that have all asphalt shingles. So I want to have the house covered in one style only. I get that it is okay to go over the metal with new metal? Or would you suggest tearing the old one off first. I'll be doing the job, so money and time is not an issue. I just want to do it the best way. Thanks very much.
Guest User

6/26/2002
We live in the Pacific Northwest where the climate is cool and wet. We are considering a stone-coated steel tile roof to replace our present shake roof that is 15 years old. Two questions: (1.) Two contractors recommended installing the new stone-coated steel tile roof over the old one without removing existing shakes - is this a good idea? (2.) Some areas, especially in So. Cal., require a fire-resistant layer material between the old roof and the new steel one - is this a necessary material and expense in this area?
Guest User

7/11/2002
Many metal roofs are designed so that they can be successfully installed over existing roofs including over wood shingles and shakes. The group of products you're talking about (stone coated steel tile) has a long history of these applications. I am sure that the installers in your area can point to many such applications in your area which are performing very well. Ask for some jobs you can go see -- talk to the homeowners. As with any product, you want to have an experienced and well-trained installer. Local building codes dictate what, if any underlayment, should be used over the old wood shingles. Additionally, you can check with the product manufacturer for thir suggestion to see if, for any reason, they suggest you go beyond what the code is requiring. In recent years, we have seen some reversal in building codes as they pertain to the requirement of fire resistant underlayments under metal roofs. Fact is, steel roofing will be very resistant to the typical airborne sparks which might land on it. All Best. Todd Miller
Todd Miller
Isaiah Industries, Inc.

7/12/2002
I own a 50 year old camp on a small lake in south louisiana. The existing roof is corrogated galvanize secured with the old lead head nails, nailed on top of the humps. Thick felt supplies the barrier between the roofing & 1" solid sheets bag/as board.(Bag/as sheets came from local sugar house leftover product of sugar cane)The old corrogated metal roof is showing signs of rust & getting thin. I have already extended the life 7-10 years by moping on a cool sealant. Water has not made it's way to the solid sheeted wood yet. I have already purchaced the new metal roofing & understand the importance of the venting process. My question is can I lay down my 2x4 lats over the existing roof then install the new metal roof? The roof pitch is 3 1/2 on 12, old roof still reliable, & good attic space. thanks Rudy
Guest User

8/17/2002
Log home with screwed-down metal roof over sandwich (rigid insulation) without sofits. Winter brings ice build up, sometimes as much as 1-2 feet at the eves. Space is completely heated, therefore there is no unheated attic. Considering standing seam over old metal roof using nailers to create breathing space (sofit space) to lessen ice build up. Is this a good, or bad idea. If recommended, how much space needs to be created with the nailers, how far apart, and what guage metal should be used to prevent denting by foot traffic and falling ice?
Guest User

8/19/2002
Log home with screwed-down metal roof over sandwich (rigid insulation) without sofits. Winter brings ice build up, sometimes as much as 1-2 feet at the eves. Space is completely heated, therefore there is no unheated attic. Considering standing seam over old metal roof using nailers to create breathing space (sofit space) to lessen ice build up. Is this a good, or bad idea. If recommended, how much space needs to be created with the nailers, how far apart, and what guage metal should be used to prevent denting by foot traffic and falling ice?
Guest User

8/19/2002
Log home with screwed-down metal roof over sandwich (rigid insulation) without sofits. Winter brings ice build up, sometimes as much as 1-2 feet at the eves. Space is completely heated, therefore there is no unheated attic. Considering standing seam over old metal roof using nailers to create breathing space (sofit space) to lessen ice build up. Is this a good, or bad idea. If recommended, how much space needs to be created with the nailers, how far apart, and what guage metal should be used to prevent denting by foot traffic and falling ice?
Guest User

8/19/2002
Yes you are on the right track. I would suggest that you ensure that you 1)ventilate the space between the old and the new, 2) ensure that the fasteners you use on the strapping get a good hold into the structure to protect from wind uplift. Depending on your rafter spacing, you may want to consider srapping vertically over the rafters with a 1x3 and then fastening your 2x4 strapping down through into the rafter. Check on the local building code requirements.
Allan Reid
Dura-Loc Roofing Systems, Inc.

8/20/2002
You are obviously experiencing heat loss which is melting the snow and as it migrates down to the eaves where it is cooler, it freezes and creates your ice damming. One must look at the roof assembly to study what is not working. First and formost you need a good quality air barrier on the inside of the insulated panel. Typically a min 6 mil poly sheet is used with all the joints sealed. This is to stop the warm moist air from moving through the assembly. Second you need a moisture barrier under trhe roofing which breathes but traps condensation and moisture on the surface. Coupled with this the building codes require a minimum of 1" free air space over the insulation and it needs to be vented. It appears as if you minimum do not have the air space and installing one at this point will help elliminate your problem. One has to be careful in installing the new roof over the old in cold climates that you do not create another air barrier on the outside of the insulation where it can collect condensation and rot the decking. Given your problem I would remove the old roof and old moisture barrier if there and inspect the decking. Then strapp the roof vertically with a 1 1/2" board to allow for air flow.Then install a good quality ice and water sheild up from the eaves to a point wher the ice collected before and at least 6 feet and then use a good quality breathing membrane from there up to the ridge taping around all penetrations. Now you can strap the roof horizontally to accept the new metal roof. Ensure that you ventilate the eaves and ridge. There are a number of products out there made from a profiled mesh to do this that keep the bugs out. Chose a style and guage of metal roofing by talking to the manufacturer that will help you set the strapping spacing correctly to set it for foot traffic and falling ice. If you have a section where there is an upper roof shedding onto a lower roof, I would place a rof of plywood in lieu of strapping under the metal roofing in this area. Remember, the air space will now allow any heat loss through the assembly to vent out the ridge and minimize ice damming. Good luck.
Allan Reid
Dura-Loc Roofing Systems, Inc.

8/20/2002
Homeowner has a 100 year old typical A-frame house with a standing seam metal roof installed over 1" x 8" boards approx. 2" apart. There is no evidence of underlayment between the roof and boards, condensation is an issue. There is no overhang at eaves, and no additional ventilation. He wants to preserve the existing characteristics of the attic space, and have a new copper roof system installed. We propose installing new wood nailers vertically along the rafter, installing a new plywood roof deck, then installing 30 # felt, red rosing and copper panels. Will this create any problems ?
Guest User

1/14/2003
You will want to make sure that the application procedure is appropriate for the copper panels you're installing; please check with the roofing manufacturer. Beyond that, condensation is the result of warm moist air hitting the cool underside of the roof. I would strongly suggest getting good ventilation in the attic space. A vapor barrier and insulation on top of the celing below the attic would also be helpful. Todd Miller
Todd Miller
Isaiah Industries, Inc.

1/14/2003