Is roof ventliation important if the attic is conditioned?

pcampbell

If so could someone just briefly explain the purpose? Is it to keep moisture away from the wood?

Dale Chomechko

Conditioned as in air conditioned?
As long as air moves in & out (replacement air not recycled)
Good example: a crawlspace heated with forced air is ok as long as you put in a return air.
Dale Chomechko
DC Roofing Inc

pcampbell

Yes air conditioned, like if it were kept within normal human temperature ranges all year round (60-75F). Our system is forced air hot and cold, so that would be moving air, but it seems like it's just recycled air.

jogr

Attic ventilation or roof ventilation? Some use the term interchangeably but if you are talking about a conditioned attic then there is a difference. Since the attic is conditioned you obviously don't want to ventilate out your conditioned air. For conditioned attics some people have the insulation directly against the roof sheathing and there is not "roof" ventilation. Others will design in a "roof" ventilation system by keeping a gap between the sheathing and the insulation or even adding a second layer of sheathing raised on furring strips.

Whether you need the "roof" ventilation depends on your local climate, codes, the detail of your construction and the shingle manufacture warranty. It's a good topic to generate a lot of strong opinions.

pcampbell

OK.

We have a cape cod with no overhangs, so there is no option for rafter ventilation that goes up the rafter cavities and up to the ridge that I am aware of with a metal (not asphalt) roof, which we plan on getting.

Then the plan is to finish the attic, that is to say to make it into livable space where the temperature is normalized like 60-85F.

What I am trying to figure out is what should we be doing in terms of roof ventilation as all of the roofing contractors want to know if I want a ridge vent, if I want to keep my attic fan, etc.

Right now there isan attic fan, so that is attic ventilation, but as-is there is basically NO roof ventilation as far as I can tell, especially considering there is insulation pushed up against the rafter boards.

So moving forward, what would be the smart/correct thing to do?

Even if we pulled the insulation away from the rafter boards , there is no air flow, since there's no roof overhang.

jogr

Your metal roofing contractor should be able to tell you whether it needs to have ventilation under it (I suspect not). If he says it's not needed for the metal roof warranty then what you have would be well suited to fiiling up the rafters with insulation and putting a good vapor barrier on the inside before applying drywall. But I would encourage you to google conditioned attic and learn all you can first.

Hopoefully one of the roofing contractors here has experience with metal roofs and can fill in some pros/cons.

Sounds like your current setup has the ventilation on the wrong side of the insulation.

Dale Chomechko

How large are the rafters, a 2x10 rafter will give you some clearance for ventilation. I have also seen the fascias dropped down 3/4" & screened to let in soffit ventilation.
Have also seen spray on insulation with baffles tacked on to the underside of the roofdeck & sprayed around them completely.
You may want to check the local buiding codes as well as talk to a metal roofing contractor. Take your time you don't want to pay for this twice!
Dale Chomechko
DC Roofing Inc

pcampbell

The rafters are 2X6. Due to cost, we are reconsidering asphalt shingles.

We would also intend to remove the attic fan and install a ridge vent since as you said, yes we are venting on the wrong side as of right now!!!

There is an option for this "air vent" thing which puts these intakes at the edges of the roof and that matches up with a Ridge vent. If we take the insulation down and put in the baffles (whatever it is calld that keeps insulation from being pushed up against the plywood under the roof) and spray foam on top that would be the way to get the most dense possible in a 2X6, probably.

Previous owners put R-11 in there now and R-11 is really not enough I don't think(?).

jaros bros.

Instead of the chutes, rip sheets of rigid insulation and adhere two inch strips of it on either side to make a chute. They won't collapse with spray foam as easily and will also give you much better airflow than those egg carton style chutes. You will also need much more insulation than a 2x6 can provide for your area. I am guessing that you need anywhere from 30-40 in your attic in New Jersey. You don't necessarily need to vent. You could just use spray foam and screw some extensions on to your rafters to allow for more insulation. Code now allows this. It is called a hot roof. Shingle manufacturers used to not warranty their shingle because they felt the roof would get too hot, but I don't think any of them have this exclusion anymore. The reason for attic venting is to release built up heat and moisture. Conditioning the air does both of these, as long as during the winter you have some way to mitigate the moisture buildup with an air exchanger or you have an old leaky building.

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Ed the Roofer

The product from www.AirVent.com is called TheEdge Intake Vent and another alternative which I have personal experience with is called Smart Vent from DCI Products Inc., @ http://www.dciproducts.com/html/smartvent.htm

I have successfully used that version since 1991 and it works fabulously well and is easier to install, with less of a hump in the roof than TheEdge product.

But, for the Ridge Vent choice, I would solidly recommend the Air Vent version called Shingle Vent II over any other for a multitude of reasons.

Ed

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