New metal roofing over asphalt shingles. Good or bad ?

[CalG]

I metal roofed the house. The usual 5 bar stuff with washer screws in the field.

One side of the house is an add on, and got full 1 inch board decking and black paper before the metal went down.
The other side was done as a "cold roof" with sleepers fastened through the original asphalt and 1x3 strapping purlins laid over those. (The roof is open cathedral on the inside with 1X6 t&g decking.)

The cold roof side is the dream roof. Cool in summer and snow slides in winter. The summer sun can make a bit of noise however.

The ice that comes with winter rains does pull fasteners. Every other year I go up on the roof with the nut runner and a tube of calk. It won't be many years, and I'll need to hire that done. Standing seam would eliminate that 2-3 hours labor in maintenance. That's likely at a rate of about $500 per hour. ;-)

eta I've been replacing the standard hex head fasteners with the internal wrenching low profile type. They are considerably more $ per fastener, but worth every penny!

 

[QRTRHRS]

I metal roofed the house. The usual 5 bar stuff with washer screws in the field.

One side of the house is an add on, and got full 1 inch board decking and black paper before the metal went down.
The other side was done as a "cold roof" with sleepers fastened through the original asphalt and 1x3 strapping purlins laid over those. (The roof is open cathedral on the inside with 1X6 t&g decking.)

The cold roof side is the dream roof. Cool in summer and snow slides in winter. The summer sun can make a bit of noise however.

The ice that comes with winter rains does pull fasteners. Every other year I go up on the roof with the nut runner and a tube of calk. It won't be many years, and I'll need to hire that done. Standing seam would eliminate that 2-3 hours labor in maintenance. That's likely at a rate of about $500 per hour. ;-)

eta I've been replacing the standard hex head fasteners with the internal wrenching low profile type. They are considerably more $ per fastener, but worth every penny!

Your post brings up another question. Screws in the field or through the ribs? I have seen it both ways on metal roofing.

 

[CalG]

you can't snug up on the ribs.

How can the seals be compressed?

The ribs make sense until you start to think that the "water seal" requirement in the field is EXACTLY THE SAME as it is on the ribs. And may be better!
Rain and snow fall pretty much equally over any area.

Look carefully at the "self drilled" holes, there is an upturn of the roofing metal. Enough to shed liquid water?

That's why a I would leave the present roof covering and build the "cold roof" system every time!

 

[finn1]

Another vote for sleepers over the existing shingles.

 

[s219]

The main reason the screw gaskets deteriorate is from overdriving the screws so that the rubber bulges out and is exposed. If the screws are snugged up right and the rubber just begins to puff out a teeny bit, but is still well shielded under the washer, then they will last a LOT longer.

 

[PILOON]

IMO sleepers are a must as metal will sweat and air must circulate to dry the sweat.
Therefor the thicker the sleeper the better the air circulation.

As to screws it stands to reason that there should be no or little water at the top of a ridge but always some on the flat.
Like a boat, a hole near the keel will leak while high on the side it won't.

Most current roofing fasteners rely on plastics to seal and as we know UV affects many plastics as well as over torquing can cause the seals to split.
I personally liked the old style lead seals as they did not split.

Also the power tool used to drive the screws should be adjusted so as not to over torque and crush the seals beyond 'nice and snug'.

 

[John Fitzgerald]

The contractors around here always put the screws in the flats. The washers will not seal on the ridges.

 

[/pine]

In these parts and also in FL...you tell the difference between a professionally installed roof and one that has the screws/nails in the flats...
....the heads should line up like corn rows...!

 

[ustmd]

I had a standing seam metal roof installed last Spring.

I talked to ~15 roofing contractors and got bids from 14 of those. Everyone one of the contractors required pulling off the old asphalt singles for them to warranty the installation of the roof.

 

[tcreeley]

I screwed down 2x4's running vertically with the rafters (2x10's) on top of the shingles. Then on that I ran 2x4's across and screwed the metal to that. Before that I used to get ice dams. After doing this, no more ice dams. Looks good, holds up well.