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-   -   venting choice? (http://www.diychatroom.com/f9/venting-choice-176875/)

taylorjm 04-11-2013 04:07 PM

venting choice?
 
So, I'm going to have my roof replaced, and I know my perforated soffit vents are gummed up from dust and dirt. So I'm getting quotes, and I think I have 2 choices.

1. Replace the soffits and add more perforated venting. Probably every other piece would be perforated. Slide baffles up in the cavities, make sure something is in place to hold back the blown in insulation from entering the soffits.

2. Use a shingle vent product, like smartvent as the first row. Add baffles, but not worry if the insulation enters the old soffit cavities.

My concern is does the smartvent allow enough airflow under that first foot of roof to prevent ice dams? I know if I replace the soffit entirely, the ice dam problem would go away, but that's more expensive than adding smartvent.

Thanks!

jagans 04-11-2013 08:17 PM

Replace with all vented soffit. I have yet to see any cfm data on "smartvent".

I think it is about as "Smart" as the "SmartCar" A combination auto and coffin

on wheels.

joecaption 04-11-2013 08:31 PM

How about a picture of the roof so we can see why that would even be an option.

Gary in WA 04-11-2013 10:38 PM

9 NFVA per foot or 1/2 of the ridge or correct portion of a 1/150 total system;http://www.dciproducts.com/html/smartvent.htm

Which will prevent ice dams; http://www.brainerdhomeinspection.com/roofve~1.pdf

You would still need to be careful of not blowing cellulose/fg in the baffle space...

The triple 4-center-vent-only punched soffit has 4.78 NFVA per foot (when clean- rarely) which would require a 2' deep soffit and 2 solids or 1' deep soffit and use the basket-weave triple vent; http://bluelinxco.com/Portals/0/docs...20Brochure.pdf They do tend to collect dirt from the moisture in the air that deposits there on the way in. Vents near the house will get moisture from the house as the air washes the siding and goes upward into attic. Optimum location is near the fascia board, pp. 615; http://books.google.com/books?id=Z8a...0vents&f=false

Gary

taylorjm 04-12-2013 07:40 AM

2 Attachment(s)
Here's pictures!

So, replace the soffits, or use smartvent? Keep in mind, we are in Michigan, so there's lots of moisture. It took about 25 years for the current soffit vents to clog up with moisture/dust/dirt. Not sure if new vents are any better/worse for this type of condition.

Windows on Wash 04-12-2013 08:28 AM

While the smart vent is an easier system to coordinate from a contracting standpoint because the standard roofing crew can do it in conjunction with the roof and does not require additional set up (i.e. siding pump jacks and access).

That being said, I think the truly vented soffit and properly baffled eave is the right way to go and will function more effectively, look better, and be more permanent.

taylorjm 04-12-2013 12:31 PM

Yeah, that seems to be the dilemma...do you go with the old way, tried and true, replace the soffits...or a new way with the smart vent.... From the way the quotes are coming in, to do the soffits will cost about $1200 more than the smart vent way. Total to fix the ventilation and reroof will be somewhere in the $8,000-11,000. So do you spend the extra $1200 for soffits, or save the money and go with the smartvent?

Brushjockey 04-12-2013 02:49 PM

I'd rip it out and re rock. Then you could add more outlets .

Gary in WA 04-12-2013 10:52 PM

IMHO, leave the soffit venting as is, add the smartvent. It would allow drier air coming in from wind blowing at the 3/4" high entrance edge, but not drive much moisture up as the intake sits 6" (after side baffles) above the drip-edge.You would have constant water running down/over during/after a rain... Did you do any other research on the product, as yet? The soffit vents stops most rain from entering but encourages more moisture toward the soffit from all ground wind, forcing it all against the house (picking up more moisture) and depositing it on soffit. Did you research the punched holes (effectiveness) in a soffit?

Either one for looks from the ground. Whether the air is supplied from under or over the soffit is not an issue, IMO. It will find either way easy, if the attic is air-sealed at the thermal/air barrier first. If one is too restrictive, it will draw from the other.

Gary

taylorjm 04-13-2013 12:50 PM

I've researched the smart vent, and it seems to be effective, but I never saw anything about the punched vents on a soffit. My biggest concern is that if I replace the soffit vents, in 20 years they are going to get clogged up again. If it clogged up in 20 years, what's to stop it from clogging up again in another 20?

Gary in WA 04-13-2013 11:17 PM

Are you showing signs of excessive moisture in the attic, warranting to change the ventilation from existing? Mold/mildew on the framing? Ice dams are caused from interior air below warming the roof deck sheathing below; http://www.buildingscience.com/docum...46-dam-ice-dam

Have you air-sealed the attic? http://www.familyhandyman.com/DIY-Pr...s/Step-By-Step

Do you have enough insulation to keep the heat from below reaching the attic? I think we are getting the cart-before-the-horse, here. We need more info... ventilation may not be the problem, or may only add somewhat to the solution, depends...; http://www.jlconline.com/cgi-local/v...170a32100a05c7

Gary

taylorjm 04-14-2013 12:09 PM

No moisture in the attic, but we do have ice dams. I assume thats due to the blocked soffits. There are very few penetrations into the attic except the normal electrical. We currently have about 8-10" of blown in cellulose and once baffles and the ventingn issues are solved we will be adding more blown in.

Mainly i am trying to decide whether to tear out the soffits and add more venting that way or leave them and save $1200 and go with a smart vent product.

Gary in WA 04-16-2013 03:57 PM

The ice dams are caused by the heat from below. Probably warm air rising through the ceiling/wall drywall joint that is only taped, or convective loops in low-density f.g. wall cavities- heating the top plates effectively and minimal insulation on the top-plate due to the sloped roof there. Add some foamboard at the perimeters to stop the ice dams; Fig.1; http://www.extension.umn.edu/distrib...ng/dk1068.html

Foamboard rather than foam/plastic baffle (that insulates (not touching sheeting) rather than conducts heat to the roof, first pic; http://www.buildingscience.com/docum...n-roof-venting

Be safe, check the drywall thickness, framing on-center before loading; https://docs.google.com/viewer?a=v&q...h3VLQNBaXp54rA

Gary


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