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Old 06-29-2020, 09:00 PM   #1
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Insulating a vaulted ceiling


Hello, we are renovating a 1908 craftsman's style house. It's a 1.5 story, with the second story have knee walls and a pitched roof.

The framing is 2x4 lumber which only gives me 4" depth in the cavity between the framing. I live in climate zone 3 and minimum insulation r value is R30 to meet code. There are no soffit vents or roof vents on the house. The second floor will have a ceiling with attic space above, which we plan on filling with cellulose.

The best option would be to have the cavities spray foamed, but we unfortunately don't have that much room in our budget.

Another option I thought would be 2 layers of 2" foam board in the cavity and then 2" foam board over the studs to reach r-30. I read a lot about vent and non vented roofs and I see a lot about needing to leave air space down to the eaves, but I'm not sure if this would apply to my situation. Would I be able to attach 2" foam board directly to the underside of my roof and then seal all edges with spray foam, as well as tape all joints on the foam board?

Thanks.
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Old 06-29-2020, 09:08 PM   #2
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Re: Insulating a vaulted ceiling


Your best bet is to spend some time, really looking at what it would take to get the low and high venting.
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Old 06-29-2020, 09:25 PM   #3
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The low wouldn't be too big of an issue, we are planning on redoing all the soffits anyways. The high I'm not to sure about, it has a never roof and they don't have any ridge vent shingles.
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Old 06-29-2020, 11:47 PM   #4
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Re: Insulating a vaulted ceiling


You are talking about a 2x4 rafter vaulted ceiling??? Very unusual. First thing I would do is check span tables to see whether the 2x4s are over-spanned. In my climate zone 5, a vaulted 2x4 rafter is only good for a 7' span. In your climate zone, a 2x4 rafter might be good for 8' or 8.5' span. You might need to sister on 2x8s just for strength, and then that solves your cavity size issue.
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Old 06-30-2020, 12:13 AM   #5
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Re: Insulating a vaulted ceiling


Quote:
Originally Posted by Xandrew227x View Post
The low wouldn't be too big of an issue, we are planning on redoing all the soffits anyways. The high I'm not to sure about, it has a never roof and they don't have any ridge vent shingles.
it would not be a problem t open a ridge vent or even add box vents
Opening the soffet is usually the tricky part.
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Old 06-30-2020, 07:06 AM   #6
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Not sure if it changes anything, but it's a pyramid hip roof, true 2x4 on 24". About 3/4 of the way up the roof structure on the interior it has framing that braces the roof structure.

There are 4 dormers built into the roof, it is a balloon style framing where the wall from the first floor extends into the second floor and the roof then sits on that.

We had an engineer look at our place since we had some laminate beams sized, he looked over the entire house and the roof structure wasn't an issue to him, so I'm not sure if that was just a common way to build them here.
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Old 06-30-2020, 06:37 PM   #7
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Re: Insulating a vaulted ceiling


Quote:
Originally Posted by Xandrew227x View Post
Not sure if it changes anything, but it's a pyramid hip roof, true 2x4 on 24". About 3/4 of the way up the roof structure on the interior it has framing that braces the roof structure.

There are 4 dormers built into the roof, it is a balloon style framing where the wall from the first floor extends into the second floor and the roof then sits on that.

We had an engineer look at our place since we had some laminate beams sized, he looked over the entire house and the roof structure wasn't an issue to him, so I'm not sure if that was just a common way to build them here.
]


It's been OK for over 100 years.
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Old 06-30-2020, 06:46 PM   #8
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Re: Insulating a vaulted ceiling


Quote:
Originally Posted by Xandrew227x View Post
Hello, we are renovating a 1908 craftsman's style house. It's a 1.5 story, with the second story have knee walls and a pitched roof.

The framing is 2x4 lumber which only gives me 4" depth in the cavity between the framing. I live in climate zone 3 and minimum insulation r value is R30 to meet code. There are no soffit vents or roof vents on the house. The second floor will have a ceiling with attic space above, which we plan on filling with cellulose.

The best option would be to have the cavities spray foamed, but we unfortunately don't have that much room in our budget.

Another option I thought would be 2 layers of 2" foam board in the cavity and then 2" foam board over the studs to reach r-30. I read a lot about vent and non vented roofs and I see a lot about needing to leave air space down to the eaves, but I'm not sure if this would apply to my situation. Would I be able to attach 2" foam board directly to the underside of my roof and then seal all edges with spray foam, as well as tape all joints on the foam board?

Thanks.

You are never going to get a straight answer of how to do these houses. A 1.5-story cape should be disallowed by code and made illegal to build. I wish I had just built a 2-story colonial that was nothing but two rectangular 8-foot boxes stacked on top of one another with a 6/12 gabled roof. Would have made life easier...
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Old 06-30-2020, 08:02 PM   #9
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Yeah I know exactly what you mean, it's been a real pain trying to layout the second floor with the sloped ceiling.

I'm waiting to hear back from the building inspector about what I can do. I'm hoping he doesn't decide I need to bring the roof up to code, we aren't changing anything structurally with it, so I'm hoping he will let it slide.

Guess we will wait and see.
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