Venting with vaulted ceilings problem

mixer

25 x 27, 6-12 pitch gable roof. Used new O.C. corrugated strip low profile ridgevent (12.5 sq in./foot) on entire 25 foot ridge. Existing soffit vents on both sides total up to 700 sq in.

OSB sits on 2x8 on 24". Below OSB, 2 inches of airspace, then insulation (rigid+fiber). No attic since this is vaulted.

Same soffit vents (no change/no blockage). Different ridge vent (who knows what the old one was?

Customer says room is now much hotter and doesn't cool down at night for hours.

Ideas?

Ed the Roofer

I kow you already saw my reply on Roofing.com but it is a worthy discussion to add to here for additional input too.



The "Foot-Print" of the attic space is used to determine the NFVA in square inches.

If you wanted to calculate the total amount of Cubic Volume, then ASHRAE has a calculation for that, but that is not the one referred to in the building codes.

You said 25 feet of ridge vent. Is that the entire length of the ridge? If not, you need to do the entire length.

Also, it doesn't matter what NFVA of square inches you came up with if the soffit intake venting is not 100% continuous.

Every single chamber in every individual rafter bay needs its own Intake and it's own Exhaust, hence, both systems need to be continuous and provide an equal amount for every lineal foot.

Everything that has the name, "Ridge Vent" attached to it does not necessarily mean that they all perform the same.

The Shingle Vent II from Air Vent provides 18 Square Inches per lineal foot.

What size Intake Vents do you have in place and how far apart are they spaced?

Get rid of the cruddy ridge vent and install one that works with higher NFVA per foot numbers.

You seem knowledgeable about this stuff, so how did you allow this to be the specification provided for you?

Ed

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mixer

Thanks again. It's good to know that there are some folks out there with years more knowledge and experience.....and combined at that!

Grumpy

I'd like to see a photo or sketch of the structure to give advise.

It's funny "it wasn't like that before" is something that always irks me. Did you even notice before?! Grrrr.... Why were you replacing the ridge vent in the first place? I am not a fan of the OC ridge vent.

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-Grumpy
Chicago Gutters Chicago Roofing

mixer

Well I guess I can't "grrr" back as well , but it is definitely hotter (albeit, unscientific) in the room. I checked it out. But, the more definitive thing is that it stays hotter longer.

Was it hot before? Sure, but not this hot.

As for my description, I was hoping I could "paint" a good mental image, but here is my rough sketch below.

The reason the ridge vent was replaced was a new roof.


I thought about this a lot in the last 24 hours and my theory is that the hot air is simply "pooling" inside the top of the ridge. A lot more cooler air coming in at the soffits (700 sq in.) pushes the rising hot air up and when it hits the ridge vent (300 sq in.) then it stops and cooks even more.

Note: Technically these are not soffit vents but rather vents placed in blocking which is in-between each rafter over then exterior wall (the rafters are not enclosed or boxed)

Attached Images

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Ed the Roofer

You need to install a better ridge vent.

If that triangle up there is all the way across, then even eliminating the ridge vent and installing Powered Attic Roof Ventilators or Solar Powere Roof Ventilators would be better.

My opposition to the PAV's is that if the CFM is too high, they actually cost you more money and energy due to vacuuming out the interior climatically controlled air from the liveable environment.

When they are not running, they are the same as a large static air mushroom vent.

The ridge venting performs continuously, even after the sun has set, yet radiant heat remains in the upper attic compartment.

Also, I strongly disagree with Dennis on Roofing.com about installing the powered attic vent in addition to the ridge vent.

Just think about it.....Where will the PAV draw it's air from? The nearest source, which is the path of least resistance of course.

Ed

__________________
Just Wait A Minute, I Will Be Right Back With A Link For That.
http://www.rightwayroofingcompany.com/ www.rightwayroofingcompany.com
Roof Estimates, Roof Repairs, Roofers, Roof Leak Help, Elgin, Carpentersville, East Dundee, West Dundee, Sleepy Hollow, Algonquin, South Elgin, Huntley, Lake In The Hills, Illinois

mixer

Thanks Ed for your thinking and research on this.

Roofsafe

Mixer, I have a way you can vent it but you need to use a better ridge vent, the rollout vent will plug up, use the SVII or something equal, then take the filter out, or it will plug up as well, anything with a filter will eventually plug up.
I'll have to find some pictures and I will be back with them.

Roofsafe

mixer, this is one pic of what I do to vent vaulted ceilings, under the deck is where baffels have been put, insulation then rocked. When you make an entry for air it will circulate through the whole area creating air flow.
Posting these pics seems to be harder now, hope I don't lose this again.
The air intake is at the bottom just up from the wall, on the roof, the entry from the soffet is nill as the soffet area is closed off. This works really well.



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Ansel

That is EXACT SAME CONSTRUCTION as my house in Northern Illinois .... Couple options ......

#1 - Vent only Upper Attic Section with Gable end vents and depending on length of ridge and location one or both of the vents may need to be power ..... Super insulate everywhere else you can ....

#2 - Insulate and vent on top of the roofdeck - which is what I did on my house as I need more insulation than I could get between my rafters and ceiling and still have a clear ventilation space .....

After 10 years it still works perfect and my ice problem and snow melt issues are all but gone .... If I was to do over again I would up the insulation to 4.5 or 6 inches verses the 3 inches I went with and that would save even more energy monies ....

Best,
Ansel