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Looking to have roof layover - will this effect ventilation?

Looking to have roof layover - will this effect ventilation?

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  #1  
Old 03-04-14, 10:28 AM
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Looking to have roof layover - will this effect ventilation?

Hello! Let me paint the picture as best as I can - I have no pictures.

House is a ranch, 1 layer of shingles on it now, no issues - they're just old. It's about that time Probably get another year or two out of the shingles before they start to curl, and all the neighbors have pretty architectural shingles and are all updated so why not me? It's all tongue and groove wood, no plywood - looks gorgeous from the attic underneath it.

Got a couple estimates so far, but my question has to do with differing opinions between these guys as far as ventilation in the attic after the layover. The house is essentially a sort of "T" shape, and is 70 years old - all stone, great shape, BUT - no soffets. I guess they just didn't do that back then. And there's nowhere to PUT them, so, we're soffetless. I've got a brand new attic fan installed before we bought it last year, it has a ridge vent running along the large length of the top, and 3 gable vents, located at the "X" spots below -

House:

. . X
X -|----X

One of these contractors is concerned that it might not ventilate properly with a second layer, and recommends a tear off and start from the wood. Otherwise, he says mold might grow up there.

Another saw no issues but suggested that when he does it that he also install another ridge vent running perpendicular to the existing one on the short length of that "T" above to help it ventilate, but didn't think it would be much of an issue.

I almost feel like the one contractor is just trying to sell me a tear off that I might not really need. I mean... I've got a brand new attic fan, ridge vent, and 3 gable vents and no indoor appliances vent to the attic. It would surprise me to find mold up there, if the old floor/ceiling joists up there were thicker than the old school 6" ones that they are I'd almost make it another room.

Thoughts? Oh - roof is 20 squares. So we're not talking about a huge attic here. But I don't have the sq ft of it, sorry.
 
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Old 03-04-14, 11:10 AM
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Not a great plan to just go over the old roof for several reasons.
There's no way to inspect the sheathing for damage.
It's not going to lay as flat.
Far more prone to shingles blowing off because there not going to seal right.
It's going to cost twice as much at some point to remove 2, layers when it gets reroofed.
And there is a way to add soffit venting. Having no soffit vent is like sucking on a straw with your finger over the end of it.
SmartVent by DCI - The #1 Choice for Attic Intake Ventilation
 
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Old 03-04-14, 02:26 PM
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A layover can be done without major problems resulting if the original shingles are laying flat and the roof has no major defects. Depending on location, ventilation, and insulation, the extra heat built up by 2 layers of shingles can accelerate wear and reduce the life of the roof. It is hard to quantify precisely, and whether it is worthwhile to go that route will vary on a case by case basis. Many experts believe the penalty in roof lifespan is less in colder northeast climate than it is in hotter regions. Some people have problems, but for some others the roof functions and looks good for 15 or more years after a layover.

That being said, some roofers just don't do them. Not necessarily because they want to up-sell you, but because they have seen problems and warranty issues with layovers that cause them to shy away from any jobs where they don't get to tear everything off and assess all sheathing and flashing before putting new stuff on. One thing all tradesman despise is getting called back to fix problems with their work free of charge. That takes money right back out of their pocket. To cut the likelihood of it happening a lot of them stick to specific processes and materials that they know from experience work well. One guy may have done a bunch of roof-overs without a problem and feel comfortable with it. Another may have done a few and had to go back and do warranty repairs because of things that were missed due to not ripping off the old layer. After getting burned enough times they decided they would rather just decline any job that is not a tear off than risk those headaches again.

I would say the guy who wants to do the tear off isn't necessarily pushing it just to get more money out of you. It's more that he feels most comfortable when he can assess and/or replace everything underneath to his own standards so he knows he won't be responsible for surprises under there that aren't his fault. However if the guy who is willing to do the layover seems competent and has a good plan for ventilation you can probably get away with it. The fact that he wants to add a vent is a good sign.
 

Last edited by eharri3; 03-04-14 at 03:37 PM.
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Old 03-04-14, 03:41 PM
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Personally, I would tear off instead of adding another layer.
 
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Old 03-05-14, 01:43 PM
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Thanks for all the insight! Yes, I have read that tearing off is the best way and if I had infinite $$$ then I'd maybe entertain that idea. But with the budget being what it is, a layover is what I can afford to have done, and the shingles and roof are in good enough shape / flat enough to be a great candidate for it (per the contractors). A couple of them where just concerned whether or not the ventilation might be effected to an extreme degree, what with the 3 gable vents, ridge vent, and attic fan installed already.

Thank you again!
 
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Old 03-05-14, 08:02 PM
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Before committing to just a layover without tearing off the old stuff, get the manufacturer of the shingle brand and style you intend to use, to give it their OK, in writing. Several of them that I've dealt with over the years will not provide any product warranty if their shingles are installed on top of existing shingles. Especially true for architectural-grade shingles. They won't lay and self-seal properly, in addition to not lasting as long with the added heat build-up in the attic.

So your 40-year roof will instantly become a zero-year roof.
 
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Old 03-06-14, 12:26 AM
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Roofing

I have been walking on a roof since I was a teenager, and I am now 38. Yes you will get about 5 more years out of the roof if you tear it off and put the shingles directly on the decking. It is A LITTLE give or take depending on the pitch. Of course, the steeper the pitch, the less likely that the wind can get underneath the shingles. The shingles will lay down flat if the roof is done correctly. Those that are saying that the shingles won't lay down flat and the shingles are going to fly off and the roof won't last but about 5 years aren't roofers. If they are, they haven't been in the business long enough to know that this isn't true. They are going by bad roofing jobs and here say.

This roofer may not be trying to get the extra money, but I have a friend of mine that does a lot of shingles as well, and he pushes the tear off because he wants the extra money. It has nothing to do with right or wrong, he just wants more from the job. That is just him though.

Again, it may be better and you will get a little more life out of the roof, but don't let anyone convince you that it is WRONG to do a lay over like that. It isn't. In fact zoning codes let you do so if it is done correctly in almost every state in the U.S. - They wouldn't let this happen if it was WRONG. If you can't afford the extra money, just put the shingles on top of the other shingles. Everything will be fine. Just make sure that you get longer roofing nails to make up for the extra thickness (it will only be about 1/4 inch) and DON'T make the mistake of putting tar paper inbetween the two layers. You will have moisture build up between the two roofs and that will ruin it for sure.
 
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Old 03-06-14, 12:11 PM
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I don't see anyone saying the roof would only last five years this way so I'm not sure where that comment came from but the idea here is the roof will not last as long this way. How much less? Impossible to say with certainty. Bridgeman's point, however, is that you may have no warranty on your shingles this way.

Can you do a layover? Sure. Would I? No. That's what we're saying.
 
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Old 03-06-14, 01:11 PM
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He didn't say a roof done this way would only last 5 years. He said it would probably last about 5 fewer years than a tear off. I have heard from a bunch of roofers that had nothing but trouble with these and don't do them anymore. A few others who push tear-offs to make the extra money, and still others who do roof-overs all the time and hear that the roof is still fine 10-plus years later.
 
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