skip to main content

Building a Home

Flat Roof: Put Torch Down Over Old Metal Roof?

12 years ago

I have a flat roof (pitch 1/8 inch per foot) with a 60-year old tin roof. I just got what seems like an unusual bid from a local contractor with a good reputation. He will put the new roof over the old metal without tearing out the old metal. Is this installation OK? What do you think? This is his plan:

Leave the tin roof in place (metal is steel coated with tin alloy, 60 years old)

2. Attach 1/2 inch rigid insulation over the old tin roof

3. Attach 3/8 or 1/2 inch of some type of sheathing board over the insulation

4. Adhere the torch down (also called modified bitumen) to that surface. (GAF smooth surface)

5. Paint the surface with aluminum paint to reflect heat away. Contractor says it needs to be re-painted only every 7-10 years.

Although EPDM and PVC are better, this is tempting because the installer is good and the price is less than half that of the other materials. There will be occasional walking on this roof and use of a ladder to service gutters on a higher roof, paint house, etc.

Is this installation OK?

Sort by:Oldest

Comments (4)

renovator8
12 years ago
Any membrane roofing system is only as good as the perimeter and penetration flashings and termination seals so that is what I would be asking about. PVC in a light color should not need to be painted. I'm not fond of open flames on a residential roof.
shw001
Original Author
12 years ago
Thanks for the response. The installer is very good, experienced, and will use a board over the installation, so the decking will not catch fire. I am confident that he will do terminations and seams well. My cheif concern is how a torch down (modified bitumen) roof will work in this type of installation where there could be some small puddles forming (about 1/8 inch deep)?

Renovator, you are correct that PVC would perform better and last longer. However, it is more than twice the price AND most local roofers don't offer it. For the contractos that do offer it, I have no information on their work quality.
Related Discussions
Putting Screws into a Flat Roof
Q
Comments (10)
Based on membrane manufacturers recommended standard procedures the installation is as follows (after removing old metal roof): 1. Inspect, clean up, wooden deck (3/4 inch lumber), replace bad wood, remove or nail in old nails or staples, etc. 2. install rigid board insulation (polyiso rigid boards 1-2 inches thick) using 3 inch metal plates and screws (about 16-20 per 32 square foot sheet). [THIS IS THE PART I AM WORIED ABOUT] 3. Sometimes a cover board (such as 1/4 inch plywood is installed on top of insulation. In this case I guess the 3-inch plates go on top of the cover board and screws go through the cover board > insulation > and deck. 4 As msyplx said, PVC membrane is glued down with a special adhesive on top of cover board or insulation. Seams are heat welded with a hot air gun. Step 2 is what worries me.
...See More
Questions on 'torch-down' roofs.
Q
Comments (10)
EPDM roofing for a smaller area will have only factory seams in the piece used, plus whatever cuts you have to make for things sticking through the roof. The life of EPDM is at least 30-40 years. There is no real supply of EPDM for the home market in the US (Firestone is a large manufacturer but could care less about residential work). Find a well recommended local installer and talk with them. If you are interested in trying the job yourself Resource Conservation Technology (Baltimore, MD) used to do turn key 'kits' based on dimensions and sketches. They supplied a piece of membrane made with hold down tabs on the back, and the rest of the items required to secure the edges. Flat Roof Solutions also sells everything you need and will help you decide what to order and how to do the job. They sell pieces of EPDM by size. You get a pieces large enough for the roof without any seams and cut it down as needed.
...See More
Flat Roofs - Which Materials to Use?
Q
Comments (3)
I just got what seems like an unusual bid from a local contractor with a good reputation. Although EPDM and PVC are better, this is tempting because the installer is good and the price is less than half that of the other materials. What do you think? 1. Leave the tin roof in place 2. Attach 1/2 inch rigid insulation over the old tin roof 3. Attach 3/8 or 1/2 inch of some type of sheathing board over the insulation 4. Adhere the torch down to that surface. (GAF smooth surface) 5. Paint the surface with aluminum paint, which he says needs to be painted only every 7-10 years. roof has very small slope (1%, or 1/8 inch per foot) Is this installation OK?
...See More
Flat Roof Materials
Q
Comments (4)
I just got what seems like an unusual bid from a local contractor with a good reputation. Although EPDM and PVC are better, this is tempting because the installer is good and the price is less than half that of the other materials. What do you think? 1. Leave the tin roof in place 2. Attach 1/2 inch rigid insulation over the old tin roof 3. Attach 3/8 or 1/2 inch of some type of sheathing board over the insulation 4. Adhere the torch down to that surface. (GAF smooth surface) 5. Paint the surface with aluminum paint, which he says needs to be painted only every 7-10 years. roof has very small slope (1%, or 1/8 inch per foot) Is this installation OK?
...See More
renovator8
12 years ago
I would consider a 1/8" per foot slope to be a dead flat roof so the membrane must be entirely waterproof so it will not leak even if it does not drain and that means no seams (or factory seams) which means the best material is fully adhered EPDM.

Any other membrane should be installed over tapered insulation so the slope is at least 1/4" per foot. You should include in all cost comparisons the probability of having to do it twice. See if the torch down contractor will replace the roofing if it leaks not just patch it.
shw001
Original Author
12 years ago
Do you think TPO will be better than EPDM? and worth an extra 15-20% over EPDM?

Related Stories

GREEN BUILDING Living Roofs Put Down Roots

No longer solely the domain of hippies — or hobbits — a green roof can be a hardworking partner in making your house sustainable

ARCHITECTURE Have Your Flat Roof and Your Snow Too

By Eric Reinholdt, Architect

Laboring under the delusion that flat roofs are leaky, expensive and a pain to maintain? Find out the truth here

ROOFS Roof Materials: Get an Old-World Look With Clay Roof Tiles

By Matt Clawson

The ancient roof material of choice remains the modern-day ideal for authentic Italian, Mediterranean and Spanish home styles

REMODELING GUIDES Materials: The Advantages of a Metal Roof

By Becky Harris

Metal reigns in roofing style, maintenance and energy efficiency

KNOW YOUR HOUSE Know Your House: Components of a Roof

By Bud Dietrich, AIA

Don't get held up by confusion over trusses, rafters and purlins. Learn about a roof's features and their purposes here

GREEN BUILDING 6 Green-Roof Myths, Busted

By Mariana Pickering (Emu Building Science)

Leaky, costly, a pain to maintain ... nope, nope and nope. Get the truth about living roofs and see examples from simple to elaborate

THE HARDWORKING HOME Where to Put the Laundry Room

By Mitchell Parker

The Hardworking Home: We weigh the pros and cons of washing your clothes in the basement, kitchen, bathroom and more

HOUZZ TOURS Houzz Tour: Under a Metal Canopy in Texas

By Becky Harris

New technology, reclaimed materials and an enormous protective roof combine in this Hawkins home for irresistible modern rustic charm

EXTERIORS Roofing Materials: Slate Makes for Fireproof Roofs That Last

By Rachel Grace

It stands up to weather and fire without losing its high-end look. But can your budget handle it?

ARCHITECTURE Design Workshop: The Shed Roof

By Eric Reinholdt, Architect

This popular — and versatile — form straddles the divide between contemporary and traditional styles

Sponsored

Columbus Premier Design-Build and General Contractor

More Discussions

Help please! re windows on Tudor

13

please help with designing ideas with siding and diff directions

20

What vanity countertop with this shower tile/vanity color?

5

Ranch House Exterior Design help!

14

Fireplace Built-ins Measurement and Window Selection Help

12