Aluminum shingles/poor ventilation

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Old 12-29-10, 12:50 PM
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Aluminum shingles/poor ventilation

I'm looking at redoing my soffits/eavestroughs thing spring.

I purchased a house a few years back and it has an aluminum shingled roof. Awesome life on it but I'm confused beyond on heck why at the time of installation in last 90's the house kept two roof vents (not powered, non turbine) instead of installing, IMO, two more.

After bumling in the attic this fall I noticed that no light passes up in the soffit area so I started going around the house with a broom stick and even though the soffits are fully vented outside there must be solid plywood underneath blocking any sort of air movement in the attic.

Although I didn't find the attic temperature horrible or anything out of the ordinary I find it quite odd that someone would get an expensive roof like that and not vent it right.

I understand the use of aluminum in terms of reflecting heat etc but it wreaks havoc in the winter after a snow storm and the roof heats up, melting the layer of snow on the roof and basically causing the whole sheet to slide right off. Fortunately it hasn't damaged the eaves' yet but I do have to go up in the spring and hammer some of the nails back in (hence time for eaves replacement to add some more downspouts ... only 2 on a 1200 sq ft house! .... and to get new eaves overall anyway).

It may be stupid to ask because I know it's important to vent but is there any other reason other than stupidity that this wouldn't have been done when installing an aluminum shingled roof?

My plans are soffit and cut out the plywood, new eaves, install a couple more roof vents, and then look at adding insulation in the attic.

I live in southern ontario so the summers get pretty hot (90s and usually stay that way while the nights stay in probably the mid 70s).

Thanks!
 
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Old 12-29-10, 03:26 PM
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The ratio that most places recommend for attic ventilation when you have soffit intake and roof exhaust is 1:300. In other words, 1 sq ft of ventilation for 300 sq ft of attic space. That 1 sq ft is roughly divided in half, with half being intake and half being exhaust. So using that ratio, if your house is 1200 sf, that means you would need 4 sq ft of ventilation. 2 sq ft of intake and 2 sq ft of exhaust. 2 sq ft of intake is not much, it would likely be one small 6x12 opening in the plywood (.5 sq ft) on each side of the house. I would think that would be easy for you to miss. You often can't see the openings in the plywood soffit because the angle of the rafters doesn't allow you to see them directly. And the light coming in them is indirect if the holes are covered by your soffit panels. They won't shine like a spotlight from inside the attic.

At any rate, ventilation is often overblown as to it's importance. When houses have bad ventilation it is usually obvious, because they have a frost problem in the winter, or their shingles get too hot and burn up in the summer, or humidity and heat causes plywood edges to curl up as that humidity tries to escape. If you have no apparent problems due to excess heat or humidity I would suggest you find something else to worry about. Not trying to be offensive, just suggesting that it is probably not as big of a deal as you think it is.

In the climate you are in some roofers might install even less ventilation than they do down here, due to the possibility of snow. More ventilation means more chances for snow to blow into your attic and melt, causing a nice puddle on top of your ceiling. You wouldn't want that either.
 
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Old 12-29-10, 06:35 PM
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You are probably right, it probably isn't a big of a deal as I think it may be but when I had a house inspection done, he recommended more ventilation. Doesn't mean I need to go crazy but I just have a hunch that the limited ventilation coupled with the aluminum roof adds to the snow landslides on the roof in the winter that one day will probably tear my eaves off and get some back heat in from the attic in the summer. Most houses around here have some combination of turbine vents, powered vents or just several air vents. Usually I'll see houses similar to my size of roof including pitch etc and see 4-6 on it. I have two, hence the reasoning for the concern. Lack of ventilation around here usually melts the asphalt shingles, which obviously isn't much of a concern for me.

Our summers are somewhat humid and hot. I've never went up in the attic in the summer to actually check anything (who wants to be in the attic in the summer!) but like I've said I've been up a few times and do know I could benefit from more insulation.

I just want to get a heads up before spring and get some quotes. I'm looking at new soffits/eaves as they're pretty much do and I had already intended to add two more downspouts (only have two on the whole house, want 4).

Thanks for the reply so far.
 
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Old 12-29-10, 07:02 PM
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Turbine vents definitely move more air than your standard lomanco style "can" vents, so you could switch to those. But if you are going to do some work to the soffit next year you sure can check to make sure you have some soffit venting, as mentioned before.

3-4 lomanco style can vents would be needed as exhaust to match four 6" x 12" intake vents in your soffit.

If ur up in the attic you could check to ensure that your top plate is insulated, and all penetrations like holes for electrical wiring are sealed shut (good place for foam). A lot of air can come down interior walls this way too.
 
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Old 12-30-10, 06:16 AM
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Are the snow avalanches common with a metal roof? When a whole sheet of snow comes off, it comes off with a thud.
 
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Old 12-30-10, 07:10 AM
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Yes, that's pretty common with any metal roof. Not only is metal a slicker surface, but it conducts heat better. This is why you always see metal roofs in snow country, because they are usually self-cleaning.
 
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Old 12-30-10, 11:39 AM
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Thanks XSpleeper! Again, probably more concerned than I need to be but want to make sure I'm on the right track when it comes time in a few months to get everything redone. I'm sure the extra insulation in the attic isn't going to hurt.
 
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Old 12-30-10, 11:56 AM
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Women don't usually like their bushes getting crushed, so notice where the snow piles up and don't let them plant anything there.
 
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Old 12-30-10, 12:06 PM
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We've learned that the hard way....

And I'm the one shovelling the compacted stuff after it falls off the roof. I've been more concerned about my dog taking a load on his head or now that we have kids, having them play outside and getting dumped on. I do check but it can go at every time.

I remember the first time my wife and I experienced the avalanche. We both woke up to this rumble and then our bedroom window went black for a few seconds and then the light let in again. We were like WTF?
 
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Old 12-30-10, 08:13 PM
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I've seen metal roofs in snow country that have what looks like fences at the bottom. The idea is that these "fences" prevent the avalanche of snow hitting someone by stopping it, and letting it melt slowly, then passing it as it reaches a certain size. Perhaps your roof needs this detail added.
 
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Old 12-30-10, 08:24 PM
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Probably wouldn't hurt but we're talking a whole side of a roof sliding on off....I'm sure it's doable ....
 
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