Metal roofing over aging shingles - Correct way to install?

[chopped]

1After Katrina this is how I did my roof and my attic is 20 degrees cooler in the summer than it was before. The roof is very quiet in a rainstorm. You can not hear rain falling on the metal. I'm sure your Florida weather is similar to our Louisiana weather and the extra insulation pays future dividends. I did this roof completely by myself and pocketed 2/3 of the money the insurance company gave me for the repairs.[/QUOTE]

Nice job I noticed the 'board' attached to the trim on the lower part. thats to hold the sheets from sliding I assume, did it also aid in getting them on straight?Getting them to run traight seems to be the chore..
thanks.

 

[tallyho8]

Nice job I noticed the 'board' attached to the trim on the lower part. thats to hold the sheets from sliding I assume, did it also aid in getting them on straight?Getting them to run straight seems to be the chore..
thanks.

Since I was doing the job by myself, I temporarily screwed those boards on to hold up the metal until I screwed it down. They also helped hold it straight. Getting the first sheet straight is the most important part about installing a metal panel roof.

 

[Smallplot]

Am I missing something? I'd say the fire is a bigger issue than trapping heat.

Yes you are missing something let's see if I can explain it. With wood/shingle construction if a fire starts inside the fire will be quicker to burn through the roof causing a vent therefore letting the temprature drop allowing firefighters to get access to the contents inside.
Now put a metal skin over the top of that roof. All that heat will in essence be reflected back inside the structure raising the internal temperatures quicker which leads to the real possibility of a flash over. This is where the contents temps reaches the point they burst into flames at the same time. Bad news for firefighters and owners.
Another added con is firefighter access through the metal covering to keep the fire from spreading. Also considering if there are voids fire will quickly travel through them (this is why walls usually have vertical piece of wood between the wall studs.

Another con if there is a fire, fireman use water. Water on a metal roof can be very hazardous to fireman. This creates fall hazards when a shingle surface still allows firemen to keep solid footing.

I am not saying firemen can't or are not equipped to deal with a metal roof. They can and have to but every second they have to use special equipment, and yes special equipment takes longer to use, is that much longer the contents are being destroyed by fire.

Couple all the above with a good majority of the people on this forum living in rural communities served by volunteer departments, which only means longer response times.

Just my 2 cents.

 

[tommu56]

Speaking from experience...My barn has metal roofing screwed/nailed directly to the original wood shakes. We get some nasty windstorms through here every spring, and every spring, without fail, I've got to go up and nail the roofing back down the best I can (If it hasn't been blown completly off..., I've got three tarps up there now). When I re-roof (Soon!), I am taking it down to the sheathing and starting fresh, screwing directly to the 1" or better thick white oak sheathing boards-this should prevent losing any more roofing. Based on this, IMHO, I would not even consider roofing over old roofing, at least not in Tornado Alley.

Dan

Use screws double them up put then on both sides of the ridges in the valley