If you have enough soffit vents then the ridge vent should work well. I'm no roofer, but I don't know if venting more would fix your ice dam problem. I would think the only place you have to worry about with ice dams with a metal room are at the end of the roofing where it meets the gutter. If you get that fortified I would think you would be OK. You said you're putting the metal right overtop of the asphalt, can you put waterproof sheeting covering the shingles on the eaves, then if you get an ice dam it won't damage your house?

We've got a metal roof on our porch and what happens in the winter is, the snow stays on the roof until we get a sunny day then the whole shebang slides off. Sometimes it hangs from the gutter. I would imagine even if your attic is as cold at the outside, the snow and ice will still be hanging around your gutters. I suppose that's what snow birds are for, LOL.

Yes, we do get the ice dams where the gutter is.

We are hoping that most of the snow will be falling off the roof however the roofer said not to count on that. Ice dams can damage the metal roof in similar ways as an asphalt.

-renee

I would be skeptical about the "Low E and insulation barrier". It sounds like that foil-faced bubble wrap stuff that probably has an R value of 1 and virtually no radiant barrier effect. R-20 between the asphalt and metal roof would require over 3 inches of polyisocyanurate foam. Other foams would be over 4 inches thick.

The best way to avoid ice dams is to vent the space between the asphalt roofing and the metal roofing whether the interior insulation is vented or not. I would also expect to see a good underlayment in this space so water that gets through the metal roofing would drain out (unless you think the asphalt shingles will be able to do this).

Perhaps you should get a design professional to help you with moisture migration, energy conservation, and ice dams rather than relying on a roofer trying to market his services.

The metal roof space will be vented (passively of course) and the Low E barrier is not bubble wrap. He did give us a sample. the Low E barrier is R 8 then there is a layer of insulation board (about R 4) then more Low E (R 8).

The new metal roof should NOT leak. If it did, the water would run out the eaves. We are expecting the asphalt shingles would help prevent water damage. However, if the metal roof did leak this is an installation problem. These roofs should not leak.

I am not sure what you mean by "design professional".

thanks,
renee

All roofs leak eventually.

"Low E" is a term used to describe extremely thin low-emissivity coatings on glass that are mostly transparent to visible light but reflect most of the infra-red light. The use of this term to describe any part of a roof assembly sounds highly suspicious to me. If there is an aluminum foil radiant barrier it should be called that and it would need to have an inch of unobstructed air space above or below it.

A design professional is someone who designs buildings and/or their component systems rather than selling materials and/or their installation.

Here is a link that might be useful: Low E

sorry, the product is called Low-E (maybe it stand for low energy??)
http://www.low-e.com/products/products_view.php?Product=Low-E

dumb name, I know.

sure, all roofs may leak eventually but we are trying to have a roof that won't leak for 30 years or more.

Our current roof is not leaking (that we know) but it is fatigued and we need to replace it. We want to do this before our house is damaged.

I asked my husband why we never have ice on our roof like our neighbors and he said because we have really good insulation in the attic on the second floor ceiling and really good ventilation in the attic. So the snow never melts except from the sun and then it is warm enough outside to drip off and not turn to ice.
We too have an old asphalt roof (40+ years, plus older layers underneath) and are thinking of metal roof in the next 5 to 10 years. Current roof doesn't leak, thought the porch roofs (flatter) did and dh replaced those about 15 yr ago. Dh said we would rip off the asphalt roof(s) though. I'm wondering how one makes the decision to keep the old or get rid of it. Would be expensive to dispose of the old thats for sure.
kathy

Well, there is a law in certain areas on how many roof layers you can have. We have one asphalt layer however we do have other layers (not asphalt). Legally we can not have more than two asphalt roof layers on our house. So, even if we had two layers of asphalt we could add the steel roof over them. (you just can't add another asphalt layer)

We made the decision to keep the asphalt roof because it would be thousands more dollars to rip off the old roof and dispose of it and we are not required to rip off the old roof. Ripping off the old roof, according to our research, would not benefit us or extend the life of the new roof.

Many people around here have metal roofing now and luckily I have seen them being installed. Every one I have seen installed has been installed over the original asphalt roofing. Most likely people did this as a cost saver. This is one of the benefits of metal roofing.

The cost of the metal roof is nearly the cost of a complete tear-off plus the new installation of an asphalt roof. if we had to do a complete tear-off we would not be able to afford a metal roof.

There are two types of metal roofing. Ones that can be installed directly on the roof deck and those that are meant to be spaced between the roof deck w/ purlins. These roof are more rigid and usually cost more. We wanted the metal roof to be installed over purlins because this leaves an air gap = more insulation for our house.

If you need repairs to the roof deck you would have to remove the shingles in that area of the house. Maybe that is why your husband is in favor of the tear-off??

So, we came to the decision to not do the tear-off because:
-it was more affordable
-not required
-did not harm the house or new roof

-renee

We do not need a new roof yet, but when we do, it will be the metal roofing. For one thing, you have a benefit from the insurance company both for fire, and for better resistance to hurricane damage.

In south Alabama, we do not worry about ice dams. Of course, this last winter we had thirteen days in a row when temps were below freezing, but no ice dams.

Clay roofing tiles would work nicely with our stucco house, but be more expensive to purchase. I doubt they would have an advantage over metal roofing in a hurricane prone area.

We put a metal roof on our Victorian 15 years ago. Over the old shingles - for noise dampening, among other things. Rain can be loud. Also: insulation, avoid mess and cost for now, back-up in case of any metal roof problems, etc.

I live in the PNW and don't even know what an ice dam is! But I wonder if a hooded gutter with your metal roof would solve your problem. Snow sliding off the roof (it's steep) ripped off some of our regular gutters. We got them replaced with a hooded system (not L**f G**rd) last fall - no snow to test them this winter of course!! But it should be better.

KarinL