Standing seam metal roofing over existing asphalt shingles?

[Diggin It]

OK, you're talking about a roof square of 100 square feet. That figures better. I read that as a square foot. That's where punctuation helps.

 

[s219]

I've always wondered what you do about flashing when replacing or covering an asphalt roof with metal. If it's a simple roof then it's not an issue, but if you have dormers or porches or first-story rooflines butting up to second-story walls, how do you handle the flashing?

 

[TnAndy]

I've always wondered what you do about flashing when replacing or covering an asphalt roof with metal. If it's a simple roof then it's not an issue, but if you have dormers or porches or first-story rooflines butting up to second-story walls, how do you handle the flashing?

Nearly the same as you do with shingles.

Open valley using metal piece they make for that where you have intersecting roof.

"L" shaped (inside 90 bend, matching roof color on the inside) flashing against a wall, covered with siding on the wall withing a couple inches of the bottom of the L, or a sawed joint in a brick wall with a small bend in the top of the L inserted 90 degrees into the saw cut and caulked.

Gable ends us an outside (color wise) 90 degree bent rake trim pc that laps over the metal couple inches and down the gable fascia a few inches.....screwed both edges.

 

[Diggin It]

^^ The guys that did mine said they usually try to pull the siding and set metal flashing under it. Mine was too old and brittle and the existing shingles were essentially bonded to it with black roof tar. End result was to bond the metal flashing to the surface of the siding. Not ideal, but functional.

 

[jfh28]

can you do it....yeah probably.....should you do it....probably not......metal roofs are designed to be installed on a flat surface.....asphalt shingles are not flat.....over time the undulations of the asphalt shingles will telegraph thru the metal roof and a nice roof will look terrible......also anyone walking on the metal roof will leave indentations as the metal will dent to the asphalt shingle profile where they walk.......won't be much but you will notice it.....like a hail storm dent on a car...26 gauge metal even 24 gauge is not that strong...you're spending a good amount for metal roofing but trying to save what maybe 2k in demo costs.......don't do it.....strip the shingles and get down to flat sheathing and start from there......metal roofs can last a very long time......do it right once and be done with it......Jack

 

[lilranch2001]

can you do it....yeah probably.....should you do it....probably not......metal roofs are designed to be installed on a flat surface.....asphalt shingles are not flat.....over time the undulations of the asphalt shingles will telegraph thru the metal roof and a nice roof will look terrible......also anyone walking on the metal roof will leave indentations as the metal will dent to the asphalt shingle profile where they walk.......won't be much but you will notice it.....like a hail storm dent on a car...26 gauge metal even 24 gauge is not that strong...you're spending a good amount for metal roofing but trying to save what maybe 2k in demo costs.......don't do it.....strip the shingles and get down to flat sheathing and start from there......metal roofs can last a very long time......do it right once and be done with it......Jack

I am contemplating a standing seam roof as well, and I think I have come to this conclusion as well.

I have been around to many barn metal roofs that tend to leak like a sieve!

 

[M5farms]

It's according to what shingle he has 3 tab shingles are flat and 90% of roof overs are done over them . Architectural shingles are only about a 1/8" rise over 5" . So technically they are considered flat. I have never seen shingles imprint a metal roof.

 

[Stimw]

OP doesn't show his location?
I had a new metal roof installed last April by a licenced roofer, permitted and inspected.
It is galvalume 3' panels and the roofer has his own (expensive!) roll former and Brake to make the panels and trim at his shop.
I had him install it over non-leaking shingles with synthetic felt under it.
They vented the ridge and capped it. My house was cooler last summer too.
They per-drilled the panels and screwed down through the ribs, approved by engineers.
He said less chance of leak on rib verses the flat.
It cost me about $260. a square, several thousand less than closest estimate.

 

[QRTRHRS]

When I read one of these threads on metal over shingles using furring strips, Cor-A-Vent comes to mind. Not sure but I do not think that they make a product for roof decks like their wall applications. I know that they make ridge vent material. Seems like that kind of air flow would be better than what goes through the rib area?

Dents on metal roofing? I had a place with a barn that was built using 3/4" screws to fasten the 5 rib tin over poplar purlins cut on the property so they were likely green when installed. Always replacing those 3/4" screws with longer ones, I would walk on the purlin areas wearing sneakers. Never had an issue with dents.

Awhile back, Fine Homebuilding had an install article about Atas International, Allentown, PA's metal roofing. Interesting product.

 

[QRTRHRS]

OP doesn't show his location?
I had a new metal roof installed last April by a licenced roofer, permitted and inspected.
It is galvalume 3' panels and the roofer has his own (expensive!) roll former and Brake to make the panels and trim at his shop.
I had him install it over non-leaking shingles with synthetic felt under it.
They vented the ridge and capped it. My house was cooler last summer too.
They per-drilled the panels and screwed down through the ribs, approved by engineers.
He said less chance of leak on rib verses the flat.
It cost me about $260. a square, several thousand less than closest estimate.

Screws through the ribs vs the flat; always a good topic for discussion.

 

[M5farms]

Screws through the ribs vs the flat; always a good topic for discussion.

The only panels that rib application is acceptable the r panel or pro panel where the ribs flat and does not have the pencil rib on top. This style rib is designed with anti syphon channels.the r panel requires butyl tape. The reason manufacturers recommend the flats is because most people over tighten the screws and cause splits or deformation to the ribs. Either is acceptable is installed correctly.

 

[PILOON]

Screws through the ribs vs the flat; always a good topic for discussion.

My take is water will always run down the flats but not on the ribs.
Like the ribs are usually abot 1 inch above the flat are, hence you'd need 1 inch of water before any could penetrate and on a sloped roof that is almost impossible.

That's how I understand it and all my tin roofs are installed with screws on the ribs and so far no problems.
When it comes to metal siding that;s a different question, screws go on the flat area.

 

[s219]

Nearly the same as you do with shingles.

Open valley using metal piece they make for that where you have intersecting roof.

"L" shaped (inside 90 bend, matching roof color on the inside) flashing against a wall, covered with siding on the wall withing a couple inches of the bottom of the L, or a sawed joint in a brick wall with a small bend in the top of the L inserted 90 degrees into the saw cut and caulked.

Gable ends us an outside (color wise) 90 degree bent rake trim pc that laps over the metal couple inches and down the gable fascia a few inches.....screwed both edges.

I know how you'd do it for new construction, but picture a modern home with Hardy siding (panels or lap) that had everything flashed for an asphalt roof before the siding was installed. I can't see how you will be able to re-flash that properly for a metal roof without trashing the siding.

 

[Diggin It]

I know how you'd do it for new construction, but picture a modern home with Hardy siding (panels or lap) that had everything flashed for an asphalt roof before the siding was installed. I can't see how you will be able to re-flash that properly for a metal roof without trashing the siding.

You put the roof down with trim, caulk well then use flashing flexible enough to conform to the siding. In my case, they put roof metal J channel down first, then set the panels inside it. That captures and directs whatever hits the roof directly. Between the J channel and the siding is filled with silicone caulk. Over that is foil tape (typical used for HVAC) that bonded to the J channel and siding. That can be painted to match the siding if desired. There are other products available now that would do that last step better that I didn't know about at the time. One at Lowes is called 'Peel & Seal' that has a thicker foil surface and a polymer adhesive underside that bonds to almost anything. HD has a version too. Pretty sure both are made by the same company and labeled with store brand names.

 

[M5farms]

In most applications you would just cut a reglet channel. Its roofing not rocket science

 

[TnAndy]

I know how you'd do it for new construction, but picture a modern home with Hardy siding (panels or lap) that had everything flashed for an asphalt roof before the siding was installed. I can't see how you will be able to re-flash that properly for a metal roof without trashing the siding.

I'd pull the nails loose at the point they contacted the old flashing, and slip the new flashing under the siding, then re-nail. Would likely involve repainted, but if the siding was on as long as the old shingles, it probably could stand a coat of paint anyway.

 

[tcreeley]

I had old shingles I did not want to remove. I added a 2x4 above each joist and screwed it down. Then I lay 2x4's across that and the metal roofing was screwed to it. I vented the metal roofing and it had a good air flow. My ice damns disappeared. Worked well. No condensation issues.

 

[IHDiesel73L]

I had old shingles I did not want to remove. I added a 2x4 above each joist and screwed it down. Then I lay 2x4's across that and the metal roofing was screwed to it. I vented the metal roofing and it had a good air flow. My ice damns disappeared. Worked well. No condensation issues.

I like this idea as I think it would allow you to easily put spacers in between the rafter nailers and the purlins to correct any sag or unevenness-the twist I would put on it is that I would use one of the new PVC trim products for the nailer over the rafter rather than wood. This way any condensation or moisture has a straight run down the roof between the nailers and the only thing touching the roof is a material that doesn't rot. At that point would do 5/4 x 3 purlins over the PVC nailers.

 

[aczlan]

Anyone ever do this? We have an older farmhouse that had a major renovation done 20 years ago in which some new roof was installed over the new addition and the old roof was torn off and replaced over the existing house. The shingles are standard 30 year three tab that are 2/3 of the way through their life, I'm just thinking ahead and if we have the money to do it in the next couple of years I'd like to cover them with metal roofing rather than wait for a leak to develop. We don't have any leaks currently, but we do battle with grey squirrels and flying squirrels which have chewed through flashing and fascia boards and found their way into the attic and soffits. This is one of my motivations for metal roofing aside from the look.

We are out in the woods with no other houses around so we're not worried about "fitting" with the neighborhood. Our barn has grey colored standing seam roofing that is old and weathered and I'd like the house to have the same look. The barn roofing was simply bought in 12' x 3' sections and installed over purlins spaced 2' OC. The runs on the roof are 12' and 16', so with 12' panels on the 16' runs I would just plan to lap the section closest to the peak over the lower section according to manufacturer specs, seal the joints with silicone, and stagger the seams (ie: 4' panel at peak, 12' panel to edge of roof, 12' panel at peak, 4' panel to edge of roof, etc...). It seems to me that this would probably the last roof I'd ever put on this house (I'm 37 years old and plan to stay here for rest of my life)-am I missing anything here?

Ask your supplier about 16' panels, no piecing panels together that way and less places for leaks to start.

Aaron Z

 

[PILOON]

Ask your supplier about 16' panels, no piecing panels together that way and less places for leaks to start.

Aaron Z

When we built a 60 x 100 barn they supplied all our roofing in one length and the pitch was 3 1/2 in 12.
Trusses were all one piece as well.