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Old 01-08-2015, 10:15 AM   #1
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Re-insulating Attic


Planning on blowing cellulose insulation into the attic this weekend and had a few questions before getting started. We purchased the house in June, this being our first house, I'm still learning a few things. House was built in 1956, single story ranch, 1285sq ft, brick outside with framed walls on 16" centers with 16" rafters, hip roof design, attic is unconditioned space and not livable. 2x6 wall and rafters. Sheetrock on the walls and ceiling (this one surprised me).

1. I'm not seeing a vapor barrier below the current insulation, should I be putting one down before blowing cellulose?

2. The current insulation looks original and has 0 fluff to it, I'm not even sure it is insulation. When installing our ceiling fan into the living room that previously had no light fixture at all, I had to cut through it, but as I was touching it, it was crumbling apart. It has a reflective shell on both sides of it, and some type of fibers between that. I have attached a small picture from our inspection report, as it is all I have at the moment. In the picture it does not look shiny, its just covered in dirt/dust. Any idea what this stuff is if its not insulation? Is it safe to blow over this?

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3. I will be air sealing the attic before blowing the insulation and installing soffit baffles along the roof. Do these baffles only need to be placed where the soffit vents are located, or in every ceiling bay? We do not have a continuous soffit vent, only vents in a few locations with the roof mounted vents on the back and side of the house.

4. As our house has a hip roof, the front porch (5 x 8) and back porch (10 x 10) are covered by the roof, do these areas need to be insulated as well? If not, do I need to build some type of barrier out of rigid board/XPS to block them off? I have not had a chance to look into the areas that cover the porches, but on the outside of the house, there is only eave coverings that make up the ceiling on them. Both porches are not enclosed and have exterior doors leading to them.

I did search for assistance to question 3, but couldn't find a definitive answer, and as always, any help is greatly appreciated!
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Old 01-08-2015, 11:26 AM   #2
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1. If the attic is vented and you air seal the attic floor, it isn't needed in my opinion.
2. Picture is tough to see, but you should remove and/or move it in order to properly air seal.
3. Ideally you should have soffits in every rafter bay so I would plan on that eventuality and install baffles in each and every one.
4. If the porches are not conditioned, they do not require insulation. I would be wary of moisture in those areas percolating into the attic and condensing on cold surfaces. I would still air seal them and insulate them if it were me.
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Old 01-08-2015, 03:43 PM   #3
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Thank you for the reply WoW, I do plan on moving the current material to air seal the ceiling. When installing the baffles, I have read that one should stuff a piece of fiberglass batting at the bottom near the top plate to make a barrier for the wind, would it be better to use R15 Roxul ComfortBatt? It's not much more than a package of FG.

I will try to get a better picture of the attic later tonight, particularly over the porches, for a better opinion on what to do.

Thanks again!

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Old 01-08-2015, 04:58 PM   #4
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Do not stuff a bat down there and certainly not roxul.

If the baffles are installed properly and you seal the outer top plate, wind washing is not an issue and even less so if you use cellulose.
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Old 01-09-2015, 07:47 AM   #5
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Sounds good - thanks WoW.
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Old 01-09-2015, 03:58 PM   #6
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" Both porches are not enclosed and have exterior doors leading to them."----- I would not insulate them.... unless trying to stop solar radiation from the slab to attic (minimal) through the ceiling framing to the ventilated attic. Gary
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Old 01-09-2015, 04:28 PM   #7
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Not required like Gary said.

I was more concerned with humidity percolating into the attic and adding moisture to the attic venting (depending on the porch ceiling type).
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Old 01-10-2015, 11:47 AM   #8
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I'd leave the porches alone, air seal them only to stop bugs any smaller than the screening on your existing vents. Sounds like you need more venting at the soffits, here is where the porch air leaks will help ventilate the attic on a small scale, but only cracks by the exterior beams/soffits. Much better to locate the supply vents at house perimeter, at every rafter bay to wash every area along exterior walls, including the porches. Ventilate the porches, if needed due to missing soffits there, etc., but you need more ventilation especially with way more insulation; http://www.airvent.com/homeowner/pro...it-specs.shtml

Far as the vapor barrier, first find your Zone, Fig. 1----- then read Figs. 6,7 -? (Foil is similar to poly); http://web.ornl.gov/sci/roofs+walls/...papers/143.pdf They are not required per code in attics over 1' high as the wind/passive ventilation will remove any minimal moisture from diffusion with the supply air wash. The baffles also keep the blown-in insulation from touching the colder roof sheathing; resulting in an R-value loss from conduction.

WoW: "I was more concerned with humidity percolating into the attic and adding moisture to the attic venting (depending on the porch ceiling type)." do you have a link for me to understand that better?

Gary
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Old 01-15-2015, 10:20 AM   #9
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Thanks WoW and Gary, for all your replies. Unfortunately, our local blue apron store had already rented out the blower for the insulation this past weekend so we were unable to get the insulation done. We did get the baffles in place on all the rafter bays and air sealed the attic, we plan to go back and do the insulation this weekend.
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Old 01-15-2015, 04:19 PM   #10
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Sounds good.

Post up some "after" feedback. It helps for future readers.
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Old 01-15-2015, 09:23 PM   #11
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Great, let us know the outcome...


Gary
PS. WoW, "I was more concerned with humidity percolating into the attic and adding moisture to the attic venting (depending on the porch ceiling type)." even with a high permanence material like fiberboard, you would need a vapor pressure driving force or big difference in temps to "percolate" (diffuse) any moisture through two space at close to the same air pressure/temperature....capillarity wouldn't apply ------- maybe if you soaked the soffit with water from garden hose on a hot day in afternoon as attic would be hottest... your thoughts?
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Old 07-07-2015, 11:13 AM   #12
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OK... 6 months later, still working on this project.

Wife and I decided it would be best to install new vented soffit panels before blowing the insulation (which has been in our basement for 6 months). After thoroughly looking at the soffits which are aluminum, we realized we just didnt have nearly enough ventilation going on. So I went down to our local ABC supply and picked up some vinyl soffit material 50/50 vented/solid and started the install over the holiday weekend. As i started ripping down the aluminum, I found solid 3/8 plywood behind it, of course this isnt going to work so now I am in the process of cutting it all out with a circular saw and jig saw to get between the "soffit joists". At the time we only had 3 soffit vents measuring 30x16", but behind those there was only a slot about 5x16. This is in a run of approx. 180 linear ft of total soffit! (Hip roof)

My questions:

1. The new soffit material i purchased is rated at 5.87 sq in per sq ft, seeing as my soffits measure 16" out from the house, am I correct in assuming that it will be 7.91 sq in per linear ft?

2. Currently we have 8 roof louver vents, unknown NFA, but by my calculations we should have at least 360 sq in. of exhaust, should I upgrade these vents to be sure of their NFA?

FYI I will be using the 1/300 rule per our local building codes that state if we have soffit intake you do not need to follow 1/150. This will put me at about 530-710 sq in of NFA for soffit intake (depending on whether it is 5.87 or 7.91 sq in per foot).

BTW yes, I know the color doesnt match, thats what I get for "eyeing it" off their keychain colors. Wife and I plan on painting freize board covers to match.
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Old 07-07-2015, 11:52 AM   #13
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Quote:
The new soffit material i purchased is rated at 5.87 sq in per sq ft
Is it 5.87 square inches per sq foot or per linear foot?

In any case I think you have 7.83 square inches in each 16 inch panel.

Quote:
we have 8 roof louver vents, unknown NFA
some of them have the net free stamped along the bottom edge at the roof line.
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Old 07-07-2015, 11:54 AM   #14
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According to manufacturer, it's 5.867 per sq ft. Napco brand.
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Old 07-07-2015, 12:03 PM   #15
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are those triple 4's as in 12" wide?
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