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Old 03-08-2011, 01:14 PM   #1
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Roof ventilation baffle/insulation question


I recently got dragged into a project involving part of my second floor. The house was built in 1920 and is a 1.5 story cape type house (or bungalow).

On the "sloped" part of the ceiling, the area I'm working on was "finished" at some point with old Kimsul insulation and covered with flimsy wood paneling. No drywall or plaster. The flat part of the ceiling is drywalled and insulated from above.

While the whole 2nd floor is very cold in the winter, this area was even worse. So I pulled all the paneling and insulation from the sloped area and found evidence of moisture issues on the roof decking due to poor insulation and no ventilation. The space out to the eaves was blocked off with blocks of wood.

The whole second floor should really be totally rebuilt to allow for more insulation and headroom but there's no way I'm getting into that at this time.

So I ran these baffles from the eaves to the overhead area:



The new looking "mini" knee wall is just a replacement of the old one except with a bottom plate. I pulled a few floor boards and insulated and draft stopped in the joist bays under that area.

So my question is, should I have the baffles running out into the eaves like shown above? I know in a larger unconditioned knee wall attic, they would begin near the top of the kneewall but this little space between the kneewall and the outer wall is pretty narrow. Afraid the insulation for the knee wall may interfere with the baffles since I may just pump it full of celluose insulation once the drywall is up.

I put those pieces of insulation around the baffle at the top plate to block the draft while the area is open.


Last edited by Zedman53; 03-08-2011 at 01:18 PM.
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Old 03-08-2011, 05:34 PM   #2
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Roof ventilation baffle/insulation question


Do you have a ridge vent? If not, there is no sense in running baffles in any cavity that does not have a roof vent.... or... adding a ridge vent if you dont have one would be ideal. Yes you do want the baffles extended down into the eave. That is their purpose, to connect the soffit vents to the roof venting... Are there gaps between those baffles? That will short circuit the air flow when you blow cellulose in there... Your fg that you stuffed in at the top plate is good though. If you fill up the whole kneewall area with cellulose that will keep it from flowing down into the eave, and prevent wind wash.

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Old 03-08-2011, 07:28 PM   #3
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Roof ventilation baffle/insulation question


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Do you have a ridge vent? If not, there is no sense in running baffles in any cavity that does not have a roof vent.... or... adding a ridge vent if you dont have one would be ideal. Yes you do want the baffles extended down into the eave. That is their purpose, to connect the soffit vents to the roof venting... Are there gaps between those baffles? That will short circuit the air flow when you blow cellulose in there... Your fg that you stuffed in at the top plate is good though. If you fill up the whole kneewall area with cellulose that will keep it from flowing down into the eave, and prevent wind wash.
I currently have 4 square vents near the ridge. House needs a roof soon so I'd have a continuous ridge vent installed at that time.

I left a 1 inch gap per the instructions between each baffle. I was actually just going to use fiberglass insulation on the sloped ceiling and MAYBE use cellulose in the kneewall area......but I started installing the batts in the rafters and found they are not even close to square with each other. For example, one rafter bay is 17 inches wide near the flat ceiling and it drops down to 15 at the bottom. ...........a huge pain in the a to cut and fit the batts in there properly.

Would it be possible to forget about the batts and install ridgid foam board over the rafters, strap over that, drywall, and then dense pack cellulose into the rafter bays and kneewall?? This is turning into a real cluster you know what, lol.

Thanks!

Last edited by Gary in WA; 03-10-2011 at 12:27 AM. Reason: keep our "G" rating
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Old 03-10-2011, 12:26 AM   #4
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Roof ventilation baffle/insulation question


Find your Zone on the map or closest City below the map; http://publicecodes.citation.com/ico...001_par001.htm

Zone tells how much insulation required; http://publicecodes.citation.com/ico..._11_sec002.htm

If not venting that roof sloped section; http://publicecodes.citation.com/ico...006_par003.htm
You will need vents at the upper attic space. Furr the rafters down to get required insulation thickness, whichever way you go.

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Old 03-10-2011, 11:15 AM   #5
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Roof ventilation baffle/insulation question


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Originally Posted by GBR in WA View Post
Find your Zone on the map or closest City below the map; http://publicecodes.citation.com/ico...001_par001.htm

Zone tells how much insulation required; http://publicecodes.citation.com/ico..._11_sec002.htm

If not venting that roof sloped section; http://publicecodes.citation.com/ico...006_par003.htm
You will need vents at the upper attic space. Furr the rafters down to get required insulation thickness, whichever way you go.

Gary
Yeah, I'm going to have about an R42 in the flat ceiling when I'm done but furring down the rafters to achieve R38 ain't happening. An already cramped, awkward, and barely useable room will become pretty much useless. They are only 2x4's. The rafters will be somewhere in the R20's when I'm done as opposed to R nothing before.

At some point we may expand this and other areas upstairs with a big shed type dormer so I don't want to get too involved right now since it will all have to be ripped out at that time. Already got way more into this than I wanted to, lol.

But I figured out a somewhat easy method to compensate for the crooked rafters while insulating so I'll just go with the vented roof setup. Thanks.
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Old 01-01-2012, 10:30 AM   #6
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Roof ventilation baffle/insulation question


Wow! looks to me like you did a perfect job! (however no gaps between the baffles.. insulation can get in and block air flow! just add pieces of new baffle to bridge the gap)

Make sure to add soffit and ride vents in the future.

I recommend you use closed foam spray insulation as you don't have much space to add insulation.
In colorado, where i live i have R-59 of fiberglass. closed foam with give you the highest insulation per inch.. but its expensive.. well worth the cost however in the long run.

also use plastic vapor barrior under the sheet rock.



Good Job!


Last edited by vanwahlgren; 01-01-2012 at 10:33 AM.
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