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Just want to start by saying you guys are great for taking the time to answer our questions. I have a couple of questions. I am having a new roof put on my 1909 home. It has one cedar shake and 2 asphalts. I know it needs to be re-decked but what I was wondering is do you guys take off the original 1xs or just osb over the top? another quetion is I have a ridge vent now and 4 turtle vents down low on a hip roof the lower vents get clogged by birds nests did the previous roofer put these lower vents in to use them as intake vents? I have aluminum soffits with vents but dont know if there are actually vents cut under them.
 

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Grumpy and Aaron will be along.
 

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Drewzer,

We are happy to answer your questions to the best of our abilities. I have met Grumpy, and I sincerely beleive he comes to these forums to perpetuate quality in the trade, as do I.

Now onto your house.... My father has a circa 1900's house which had the same roofing types and layers as you. I tore them down to the spaced sheething and installed new 3/8" plywood over the top. There are a few things to remember....the spaced sheething will continue to be the structural roof decking. The plywood siumply provides for a smooth flat surface to apply the new roofing to. I have done a couple of these and it has turned out fine both times. Be sure to affix the sheething to the rafters as you would normally, ending all sheets on a rafter half. If you do not do this, there is a great risk of fastener back-out of the 6d or 8 d nails if they only penetrate the spaced sheething.

I have found that most hip roofs do not have enough ridge to properly vent with ridge vent. I am a big fan of passive ventilation, but on most hip roofs, attica fans seem to be the best way. It is very possible that the last roofer installed the vents low to perform the duties of intake ventilation....I doubt it is sufficient, since the turtle vents youre referring to only provide approx. 1/3 foot of net free vent space per vent. That gives you 1 1/3 sq. ft. of net free vent space. This is ample ventilation for my doghouse. You may have to remove some soffit panels to check for soffit venting, and if there is, you need vented soffit along with it. New soffit ventilation is either really easy or really difficult to inastall. The 1:150 rule usually provides ample ventilation..

One square foot of net free vent space for every 150 square feet of attic floor space will do the trick in a balanced system, meaning one foot in (intake) and one foot out (exhaust).

I hope I was able to help.



This is not legal advice.
 

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Discussion Starter #4
Thanks AAron, so should I install a power vent and forgo the ridge? I am aware that I will still need to take care of the soffits What about a poer vent and a ridge?
 

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Typically I leave the 1" boards installed and I install CDX over the boards. I do NOT use OSB. The CDX is fastened THROUGH the 1" boards and INTO the rafters. Make sure a drip edge is installed at the gable ends or the plywood will be visible and prine to water infiltration and rot. I usually use 1/2" but in this case 3/8" would be adequate because you have the support of the orignal 1x boards and the plywood really is nothing more than a nailing base. Make sure there is a 1/8" space between all sheets of plywood for expansion contraction purposes.

I am personally not a fan of mushroom/turtle vents being installed low on the roof. These vents are installed as an intake but can actually cause more harm than good in some cases. These cases being snow infiltration in the winter, and water during a heavy storm. A ridge vent ONLY works with equal or greater intake ventilation. If you don't have the proper over hangs then you may consider a different method of ventilating your attic. What I mean is if you can not create an intake ditch the idea of a ridge vent and install 1 mushroom/turtle vent for every 150 square feet of attic floor space. As aaron said, most hip roofs shouldn't have ridge vent in the first place. www.rollvent.com www.airvent.com

Instead of removing the soffit panels, you can probably see into the roof through the spaced decking when the cedar has been torn off. It would be a real bummer if you tore off the soffits and saw that there were vents! OOps! Personally if it were me I'd pay the "Wait and see" game. Tear off the roof, peek inside, if no soffit vents then tear off the soffits and create your ventilation.

Always hire a professional roofer to take care of your roofing projects. Roofing is not as easy as it appears and one mistake can cost you thousands $$$ in repairs of interior damage. Your roof protects your house and everything inside. You owe it to yourself and your family to have a professional roofer roof your home.
 

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What is a poer vent? Do you mean power as in FAN?

No!!! Hiss Boo! Boo hiiss! Evil bad.

NEVER and I mean NEVER mix an attic fan and ridge vent. You will cause more harm than good. Air chooses the path of least reistance. What this means is your ventilation doesn't care where it gets it's air. It's up to your professional roofer to design your ventilation system. Many roofers don't understand the principals of attic ventilation. I know I didn't up until 4 years ago. I spent 6 hours in a room locked up with a bunch of engineers who explained it to me in disgusting detail. I am now certified by Air vent, a major manufacturer of some of the best attic ventilation products in the world.

As I said, air chooses the path of least resistance. When your fan is OFF it will act as an intake for your ridge vent because it is the closest and largest opening to the ridge vent. This defeats the purpose of having soffit vents. Only a small part of your attic, the top part, becomes ventilated. That's bad.

When the fan is ON it becomes the exhaust. All it knows is that it needs to suck air. it doesn't know it's supposed to get that air from the soffit vents. Instead it is lazy and takes the air from the closest vent being the ridge vent. Again; Only a small part of your attic, the top part, becomes ventilated. That's bad.

Either situation creates what I call negative ventilation. No it's not a vacuum, but your sofit vents become useless either way! This is actually what the manufacturer's call "ventilation short circuit".
 

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Discussion Starter #7
Thanks again Grumpy. I will for sure hire a professional, for I know nothing about these things and am afraid like a little girl of heights. I was trying to educate myself through you guys. Thanks again. Andy
 

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You need three mushrooms for every 150 sq ft of attic floor space, and you can dis-assemble soffits with out tearing them out.

$.02
 

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Aaron the rule of thumb is one square foot of ventilation of every 150 square feet of attic floor space. correct?

A mushroom vent is one square foot of ventilation. No?

If no I've been undersizing many roofs by 1/3 for many years. I'm running of to do some research now because that's how the engineers explained it to me. I want to make sure I understood properly.
 

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According to my Lomanoca chart, if I were to have a 1500 square foot attic, I would need 8 of their 750 static roof louvers, which are also known as static/turtle vents.

My airvent chart says I need between 5 and 19 depending on vent and slope for a 1500 sq ft attic. 14 is the average.

According to my charts I had the forumals correct, but I'm waiting for replies form the manufacturers. I have sent e-mails to Lomonaco, Airvent, and Obydyke. I'll try GAF and Tamko just for the fun of it and post their replies.
 

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The masterflow vents are sized like the rest. They state 50 sq. inches. There are 144 square inches within a square foot.
 
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