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Baffles needed?


azzurri's Avatar
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Join Date: Jan 2002
Posts: 136

10-29-03, 03:02 PM   #1  
Baffles needed?

I just had my kitchen expanded. The new part extends out 10' x 24' and has a sloped ceiling. The new roof meets the original part of teh house (the vertical second floor wall) about 2' higher than where the old extreior kitchen wall did. The builder installed soffit vents along the roof overhang. The part of the roof that meets the house has roof shingles all the way up to the wood shingles of the wall it meets (plus a 4-5" metal sheet to prevent leaks above the last row of roof shingles).

So, this is unlike an attic, which, in addition to the soffit vents, would also have a ridge vent. Now I understand that in attics you would install styofoam baffles all along the length of the rafters from soffit to ridge before insulating, in order to allow air to circulate freely.

Can anyone confirm that I DO NOT in fact need to use baffles in my kitchen ceiling? My assumption is based on the fact that since there is no outlet for the air entering from the soffit vents, I wouldn't be accomplishiing anything.

Also, the soffits are a good 10" away from the exterior plywood of the new kitchen wall. Given this, I woudl assume also that I can just stop the insulation at teh imaginary plane that woudl represent a continuation of the plywood into the rafter cavity. Yes? Or just go all teh way to the soffit vents and plug that area to keep bugs and such out?

As I am typing I'm realizing "what is teh point of this soffit vent, anyway?"

Thanks!

 
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resercon's Avatar
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NJ

10-29-03, 08:47 PM   #2  
http://www.certainteed.com/cvent/cvav00401p.html

On this site look at the "FlashFilter Vent". This is innovative way of providing vents where the high part of a roof that meets with a wall of the house. This goes or replaces where they put that 4-5" sheet metal to prevent leaks.

You are correct, the soffits are basically useless if you do not have the higher vents installed on the roof. It has the same effect as if you dipped a straw into a fluid, put your finger on the end of the straw, took the straw out of the fluid. All the fluid inside the straw remains. This illustrates the air under the roof without the high vents. Release your finger from the end of the straw and all the fluid leaves the straw. This illustrates what will happen to the air under the roof once you install the high vents.

As far as the baffles are concerned, it depends if the insulation is obstructing the air flow from the soffits to the high portion of the roof. For example, if the rafters are 2' x 10' and the insulation is 6 inches thick, you would have a little bit more than a 3 inch gap between the insulation and the roof. This would be a more than sufficient air passage from the soffits to the high portion of the roof.

 
azzurri's Avatar
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10-30-03, 08:32 AM   #3  
Thanks. I plan on using 6" insulation so I will in fact have some air space between the roof plywood and insulation...but only about 2" as the rafters are 2x8s, not 2x10s.

Can you please clarify if leaving this 2" channel for air will be sufficient? In this scenario, air would pass up through the soffits and along the bottom of the roof, but would have no exit, except from where it entered. I assume it is too late to add a vent such as type you identified on the link. Is this okay?

Thanks again.

 
resercon's Avatar
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10-30-03, 10:43 AM   #4  
You could still install the vent mentioned on that site but there are other options which might be less expensive to do, like roof vents installed on the high portion of the roof. Unfortunately it appears that the insulation will be instaled between te rafters all the way up the rafters, which means you would have to a roof vent between every rafter on the high portion of the roof. If this is the case, then call the contractor who installed the roof and have them install the "FlashFilter vent" for you. It is not that hard to do.

Since you are using 2 x 8's and 6 inch thick insulation, the air gap between the insulation and the underside will be less than 2 inches. Because the styrofoam baffles are inexpensive and easy to install, I would recommend installing the baffles just to make sure of the air passage from the soffits to the high vents of the roof.

 
azzurri's Avatar
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11-03-03, 10:04 AM   #5  
Anybody with ideas on how far into the overhang I should install the insulation? The soffits are about 10" past the exterior plywood of the wall and the baffles that I just installed reach about 4 inches shy of the soffits. So, the baffles extend past the exterior wall (into the cavity that is the overhang), but not quite all the way to the soffits.

My guess is to just go about even with exteior wall (imagining it to extend up into the cavity).

 
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