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.