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Old 03-11-2014, 08:29 PM   #1
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Attic Insulation with a new roof


Ok, here's the current situation:

1920s house with a steep slate roof. The attic (3rd floor) is finished with knee walls. There is no roof venting. The knee walls are uninsulated. There is paper-backed batt insulation in the rafter bays directly under the decking. The attic floors are uninsulated. The ceiling is insulated with some sort of fiberglass.

Here's what's changing:

The roof has done its time and is going to be replaced with asphalt shingles. The plan is also to also cut in a ridge vent. What I am thinking is that it makes sense to remove the insulation from the rafter bays if we're attempting to vent the space, and to also add in shingle over intake vents.

I figure I'll then go back and insulate the kneewalls and the attic floors behind those walls.

Does this make sense?

A variety of other options I've seen:
-Remove the insulation, do not vent the roof, spray in foam insulation
-Do not remove the insulation, just cut in the ridge vent
-Do not remove the insulation, do not vent the roof

I should mention that this is in Pittsburgh, PA -- so we do see all temperatures and levels of humidity.

At the moment, I'm not overly concerned with energy efficiency, as I plan on leaving access to behind the kneewalls pretty open and can always make changes, but I am mostly concerned with the longevity of the room and preserving the roof boards.

I greatly appreciate the assistance and please ask questions about the existing conditions if anything isn't clear!

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Old 03-12-2014, 06:39 AM   #2
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Attic Insulation with a new roof


What is the decking like under the shingles and will it be coming off?

Best would be to create a vented space and the corrected insulation schedule if possible. Best of both worlds.

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Old 03-12-2014, 09:02 AM   #3
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Attic Insulation with a new roof


I am no expert, but if you put in a ridge vent, you pretty much have to move the insulation to the attic floor. Insulating the attic floor should be more efficient than the roof, since there is far less square feet for heat to escape from. Make sure you air seal the attic floor before putting in the insulation. I think you are suggesting ridge vent plus roof mounted vents. This may not provide good ventilation because air tends to flow in the static vents, across and out the ridge vent, without moving any air from the bottom half of your attic. Normally, soffit vents at the bottom of attic and ridge (or roof vents, but not both) at the top.
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Old 03-12-2014, 09:47 AM   #4
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Attic Insulation with a new roof


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What is the decking like under the shingles and will it be coming off?

Best would be to create a vented space and the corrected insulation schedule if possible. Best of both worlds.
As far as I can tell it's in pretty decent shape, so I'm not planning on having it removed. It's thick ~2x6 planking. There's a chance we may go over it with OSB if we run into some rotted areas, to assist with nailing but I don't anticipate it will be too bad.
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Old 03-12-2014, 09:50 AM   #5
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Attic Insulation with a new roof


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I am no expert, but if you put in a ridge vent, you pretty much have to move the insulation to the attic floor. Insulating the attic floor should be more efficient than the roof, since there is far less square feet for heat to escape from. Make sure you air seal the attic floor before putting in the insulation. I think you are suggesting ridge vent plus roof mounted vents. This may not provide good ventilation because air tends to flow in the static vents, across and out the ridge vent, without moving any air from the bottom half of your attic. Normally, soffit vents at the bottom of attic and ridge (or roof vents, but not both) at the top.
This is my understanding as well, that the rafter bays need to be open for typical venting to work as that's where the airflow is needed.

The soffits will be difficult to get consistent access to to add intakes, so I'm looking at products such as the Coravent Invent and the DCI smartvent for use as intakes, which can be rather easily installed from the outside.

http://www.cor-a-vent.com/in-vent.cfm
http://dciproducts.com/html/smartvent.htm
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Old 03-12-2014, 01:11 PM   #6
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Attic Insulation with a new roof


Those are interesting vents I never seen them before. If you dont have a soffit you dont have a choose but if you have soffits just add vents. I assume you have plywood or solid soffits. You can get 2 inch round vents that install in about 5mins each.
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Old 03-12-2014, 03:12 PM   #7
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Attic Insulation with a new roof


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Those are interesting vents I never seen them before. If you dont have a soffit you dont have a choose but if you have soffits just add vents. I assume you have plywood or solid soffits. You can get 2 inch round vents that install in about 5mins each.
The soffits are about 24" or so deep and it can be difficult to get to from inside the attic space -- I'll have to investigate more thoroughly -- shooting for using traditional soffit vents where I can (ie where I know a clean hole can be cut from outside) and the shingle over vents where I can't.
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Old 03-13-2014, 02:05 AM   #8
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Attic Insulation with a new roof


DCI works well in the situations we have used it in FYI.
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Old 03-13-2014, 11:55 PM   #9
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Attic Insulation with a new roof


I haven't read any rave reviews on the roof intakes, may want to research that more, if I were you..."Contractor Talk" is a good one.

Why is the soffit material not accessible for continuous soffit louvered/screened? Pages 615-618; http://books.google.com/books?id=Z8a...0vents&f=false

The 2" round have a NFVA of 0.803 sq.in. each = 11 required per lineal foot to make 150 min. (9 NFVA per ft, to balance with ridge at 18 and other side of roof); http://www.ventmastersstore.com/2-ro...ned-vent-mill/

Your choice: http://oikos.com/esb/51/sideattics.html

ADA the drywall on the knee wall, air seal under it; http://www.habitat.org/env/pdf/ceiling_and_attic.pdf

http://www.buildingscience.com/docum...wall-approach/ Air seal attic first, as said.

Gary
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Old 03-15-2014, 02:34 PM   #10
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I haven't read any rave reviews on the roof intakes, may want to research that more, if I were you..."Contractor Talk" is a good one.
Gary
They work fine and do help balance the system.

9 NFVA on most of the systems.
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Old 03-18-2014, 06:33 PM   #11
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Attic Insulation with a new roof


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ADA the drywall on the knee wall, air seal under it; http://www.habitat.org/env/pdf/ceiling_and_attic.pdf
Excellent resources Gary, thank you. Can you clarify what you mean by "ADA" in this context?

Thank you!
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Old 03-18-2014, 11:22 PM   #12
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Attic Insulation with a new roof


Knee wall is a major source of air infiltration/exfiltration (with outside air on other side of wall without sheathing/WRB benefits), so much so that codes now address it; http://publicecodes.cyberregs.com/ic...002_par021.htm

http://publicecodes.cyberregs.com/ic...002_par022.htm

ADA; http://www.buildingscience.com/docum...wall-approach/

Further ideas; http://oikos.com/esb/51/sideattics.html

Caulk the bottom plate/sub floor joint, protect the sloped ceiling insulation ends at knee-wall from wind-washing, add foamboard to attic side of knee, cover is local codes require it against fire.

Gary

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