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Old 07-21-2009, 11:35 AM   #1
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Rafter vents & insulation question


Hey guys, need your expertise....again.

We put a dormer on one side of our cape cod and took the insulation off of the opposite side's rafters. We intended to put rafter pro-vents in every rafter to enhance airflow. When we pulled away the insulation we realized that the old wood on the roof (which is now covered by new plywood) is rather dry and not-so-solid. What kind of nails are recommended for using to install the rafter vents? Or small screws? They're not heavy, so I was just going to use 3/4 inch galvanized nails. Is that too short? Would you recommend using longer nails to drive into the newer plywood?

Also, we noticed that since the ventilation was so poor previously, there's a pretty good layer of black "soot-looking" stuff on the old insulation and inside of the rafters. What is is? Is this mold? Harmful?

Any input on the two questions above would be great!
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Old 07-21-2009, 01:56 PM   #2
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Rafter vents & insulation question


3/8" staples with a hand squeeze staple gun, like those from Arrow Manufacturing, sold at Home Depot would be sufficient to hold the light weight material in place.

Do not overlap them, as they need interval spaces of about 1/2" to allow for any minute condensation build up to not accumulate to a waterfall like scenario when it graduates to the lower proper vents over the soffits, if you are installing them the entire length of the rafters.

Ed
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Old 07-21-2009, 02:42 PM   #3
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Rafter vents & insulation question


Thanks Ed! Very helpful. I will keep them spaced by a 1/2 inch. Didn't know that.

Any idea what the black stuff may be? I'm worried someone may say "mold"...
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Old 07-21-2009, 02:51 PM   #4
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Rafter vents & insulation question


Quote:
Originally Posted by Ed the Roofer View Post
Do not overlap them, as they need interval spaces of about 1/2" to allow for any minute condensation build up to not accumulate to a waterfall like scenario when it graduates to the lower proper vents over the soffits, if you are installing them the entire length of the rafters.

Ed
Now you tell me
I was thinking you would want any water to drain down to the soffits
At least the addition rafter venst will be installed properly
Do you have a pic of the black stuff?
If its anything like what I have seen its just years & years of dust/dirt
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Old 07-21-2009, 03:18 PM   #5
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Rafter vents & insulation question


I'll take a picture tonight when I'm there and send it to you later. Thanks.
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Old 07-21-2009, 04:21 PM   #6
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Rafter vents & insulation question


Quote:
Originally Posted by k.kuenn View Post
Thanks Ed! Very helpful. I will keep them spaced by a 1/2 inch. Didn't know that.

Any idea what the black stuff may be? I'm worried someone may say "mold"...
It may be the beginning growth of Black Mold.

Air-flow and reduced humidity will stifle it's growth.

More Info:
http://www.epa.gov/mold/moldresources.html

Ed
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Old 07-21-2009, 04:24 PM   #7
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Rafter vents & insulation question


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Originally Posted by Scuba_Dave View Post
Now you tell me

You didn't ask.....

There should be instructions from each of the products manufacturers.

I installed it incorrectly on multiple occassions before I became aware of that precaution and have not heard back from anyone regarding any negative consequences, so it is probably a very minor issue, but still an issue that should be done correctly.

Ed
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Old 07-21-2009, 04:46 PM   #8
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Rafter vents & insulation question


I guess I need to read more, makes sense

Quote:
1. Install RAFT-R-MATE in each rafter
cavity beginning at the soffit area, to
assure the vent remains open, and
continue up the cavity to the ridge vent
or to a common air space.

2. RAFT-R-MATE should be installed with
an approximate 2" gap between the ends
of adjacent pieces to allow moisture to
escape more readily into the air channel.

3. Install cavity batt insulation such that the
ends of the insulation do not occur in the
area of the 2" gap. This precaution
minimizes the potential of the insulation
expanding into the air channel and
restricting airflow.
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Old 07-21-2009, 05:03 PM   #9
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Rafter vents & insulation question


Wow!!! A 2" gap? I don't recall it having to be that large, but as long as the insulation does not peek through and restrict the air-flow, I see that it really wouldn't matter.

The reasoning that I read some time ago, was that a slight amount of humidity will condense enough to just form little droplettes, but, if you allow all of them to accumulate and flow uresticted bonding together, then you have created a cascading water-fall at the bottom of the Proper Vents, aka, Insulation Baffle Vents.

Ed
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Old 07-21-2009, 09:07 PM   #10
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Rafter vents & insulation question


Actually Ed, You did tell Dave, 4 months ago! Attic Ventilation Channels with Skylights

Problem is, Dave didn't read it......... BUT it was 18 days later to Dave's post!! So we'll let it slide, Dave. chuckle.

Be safe, G
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Old 07-21-2009, 09:13 PM   #11
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Rafter vents & insulation question


Ah, I think I caught the end of that thread
I usually do make notes when I see something like that
I guess I have to let Ed off the hook too
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Old 07-21-2009, 09:25 PM   #12
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Rafter vents & insulation question


Don't feel bad, Dave, here is one I learned today. I knew face stapling insulation is better than side stapling, as you don't compress it. That was what I answered in that poll a while ago. Even the manufacturer says- either way or use tension fit insulation batts. Well, I was looking for support showing Kraft paper on batts will allow some water vapor to move through, which it will, and I found this- too. [502.1.4.6] Inset Stapling Faced Batts is not Allowed. If faced batts are
used (kraft paper or foil facing material) and if they have a
stapling tab, they must be stapled directly to the face of the
stud. Stapling to the side of the stud compresses the insulation
and creates a convective air channel that reduces the
effectiveness of the insulation (see Figure 4-3).

Makes sense to me. Be safe, G
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Old 07-21-2009, 09:30 PM   #13
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Rafter vents & insulation question


Quote:
Originally Posted by GBAR in WA View Post
Actually Ed, You did tell Dave, 4 months ago! Attic Ventilation Channels with Skylights

Problem is, Dave didn't read it......... BUT it was 18 days later to Dave's post!! So we'll let it slide, Dave. chuckle.

Be safe, G
Quote:
Originally Posted by Scuba_Dave View Post
Ah, I think I caught the end of that thread
I usually do make notes when I see something like that
I guess I have to let Ed off the hook too
Thanks for making me laugh guys.

Ed
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Old 07-23-2009, 12:38 PM   #14
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Rafter vents & insulation question


Okay, here are the pics of the black stuff. Thoughts?

and, one last question....

What is your recommendation for insulating the ceiling in our finished attic.....faced or unfaced insulation? The guy at Lowe's sent us unfaced, but I was expecting faced so that I could staple it up. Currently, I don't have a ceiling up, yet in the living space. So I'm not sure whether I just didn't understand that I'd have to put the insulation up after the ceiling???
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Rafter vents & insulation question-rafter1.jpg   Rafter vents & insulation question-rafter2.jpg  
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Old 01-29-2011, 07:19 PM   #15
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Rafter vents & insulation question


I thought these vents mount in between the rafters??
I don't get where the two inch spacing comes in effect
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