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Old 02-26-2010, 08:35 AM   #1
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Cathedral ceiling


1930 house, currently a pitched roof, have 2x6 joists in ceiling and in roof truss.
I am going to make the master bedroom a vaulted ceiling.
There are 9 rafters on both sides. Carpenter is going to sister these rafters with 2x8.
Instead of collar ties, he was going to sister 2 of the 2x6 joists and keep them across the room span.
There are no soffit vents of any type of ventilation in this section. There is only one window in the north side of the house, this ceiling will be in the south side of the house, now with a wall separating it from the north side and window.
Are the 2x 8 enough to allow for proper insulation and ventilation?
Is this design good for structure? Carpenter told me he did a couple of neighbors in the past year this way and it worked well.

Thanks you.

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Old 02-26-2010, 09:34 AM   #2
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Cathedral ceiling


What sort of Insulation do you require?
Where are you located?
Is there ridge venting in place?
2 x 10's or 12's would be better... IMHO

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Old 02-26-2010, 01:46 PM   #3
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(Discussion moved to another thread)

A roof truss is different from a roof rafter
Trusses generally can not be modified

Need more info & post a picture of the framing
How big is this room ?
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Old 02-26-2010, 10:35 PM   #4
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Cathedral ceiling


Location: long island, NY
I plan on putting in fiberglass. Spoke to insulator today, he said he can do an R 21 in the 8", with the ridge vents.
I will be putting in the ridge vents, and adding soffit vents shortly.
Hopefully the R21 will suffice. the 10 or 12" are too wide to fit off the top plate. Will have to cut about 6" "bird's beak" with a 12". So I decided to stay with the 8"

Scuba they are not trusses. Just 2X4 spanning 11.5' to the center ridge vent. This is what I will sister with the 2X8s.

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Old 02-26-2010, 10:54 PM   #5
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Cathedral ceiling


You are in zone 4 by NY chart:

http://www.dos.state.ny.us/code/ener...Provisions.pdf

You need R-38, R21 is not good enough
You are going to have heat loss thru the ceiling which will probably cause ice dams
You need 2x12's unless you are going with spray foam insulation

By removing the ceiling joists you are weakening the roof/wall assembly
I'm not sure putting in additional support on only 2 of the joists will work long term
There have been a number of roofs that have collapsed under the recent heavy snows
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Old 02-26-2010, 11:18 PM   #6
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Cathedral ceiling


"Is this design good for structure? Carpenter told me he did a couple of neighbors in the past year this way and it worked well." ----- Whoa, slow down.

Start with the basics: http://books.google.com/books?id=E5S...raming&f=false

Ceiling joists are required, OR rafter ties – every 4’ apart on a non-structural ridge roof system. This is per MINIMUM building safety code. (IRC 802.3.1) Google it….

If the pitch is low, the rafters need to be engineered, per code again. (IRC 802.3)

You really need to run this by your local Building Department, not the local carpenter, at least for the liability for insurance purposes…


Be safe, Gary

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