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-   -   Rafter framing code question (http://www.diychatroom.com/f19/rafter-framing-code-question-93001/)

anesthes 01-21-2011 09:36 AM

Rafter framing code question
 
1 Attachment(s)
I was hoping to see if you folks can tell me if this is code legal.

I'm adding an addition to my home, and I'm required to use R21 in walls, R30 in floor, and R38 in ceiling. The home is a ranch, 16' wide. To keep the roof at the same pitch, which is around a 4 yet allow ventilation in the attic from the soffet I have devised a crude drawing of my intended framing method.

Basically, I intend on using 2x6x16 ceiling joists, 16"OC with end bands (2x6) sitting on top of a double top plate of a 2x6 wall. I would then run a double 2x6 top plate on TOP of the ceiling joists for the roof joist/rafters.

Because the ceiling joists wouldn't attach to the rafters per code, I was going to add 2x4x16 rafter ties 48" OC.

Attached is my crude, ugly drawing. I need to maintain IBC code compliance of course.

The EXISTING part of the dwelling has 96" ceilings from the subfloor, however the walls appear to extend above the ceiling as the roof joists appear to sit roughly 9-10" higher. I'm assuming they constructed this home in a similar fashion but I have not torn open an eve to see for sure.


-- Joe

Gary in WA 01-21-2011 01:06 PM

Check with your local Building Department. Some incite on your exact situation; http://www.diychatroom.com/f14/cutti...-90944/index2/

Gary

anesthes 01-21-2011 01:22 PM

Quote:

Originally Posted by GBR in WA (Post 575044)
Check with your local Building Department. Some incite on your exact situation; http://www.diychatroom.com/f14/cutti...-90944/index2/

Gary

Aha!

My building department is a little odd. Originally I had intended on traditionally stick framing it, but a quick calculation proved R38 simply wouldn't fit in the proposed roof pitch. Since I'm making a ranch longer, I didn't want to have two different roof pitches. I asked them (building inspector) for a suggestion and they told me to ask an architect. eh!

As long as I can cite an acceptable method I'll pass inspection, but they make me do the homework, print code reference, etc.

From some of the links you provided in that thread, I believe I can strap it to resist the rafters pushing the walls out with metal ties, and omit the 2x4 rafter ties. I'll do more reading. Thanks!

-- Joe

Gary in WA 01-21-2011 01:34 PM

As the sites pointed out, the IRC only shows the rafter/joist attachment, nothing when the rafter is elevated. That pictured lumber manufacturer's site was good explaining the possible rotation of the ceiling joists without a rim or band joist to hold them in line. I would ask a local Structural Engineer for advice/price and submit the paper work to the B.D. for the liability now taken away from them. Worth the money and the paper trail satisfies your H.O. Insurance carrier if any problems later and at selling time...

http://www.homeenergy.org/archive/he...96/961110.html

Gary

Joe Carola 01-21-2011 04:45 PM

Quote:

Originally Posted by anesthes (Post 574919)
I was hoping to see if you folks can tell me if this is code legal.

I'm adding an addition to my home, and I'm required to use R21 in walls, R30 in floor, and R38 in ceiling. The home is a ranch, 16' wide. To keep the roof at the same pitch, which is around a 4 yet allow ventilation in the attic from the soffet I have devised a crude drawing of my intended framing method.

Basically, I intend on using 2x6x16 ceiling joists, 16"OC with end bands (2x6) sitting on top of a double top plate of a 2x6 wall. I would then run a double 2x6 top plate on TOP of the ceiling joists for the roof joist/rafters.

Because the ceiling joists wouldn't attach to the rafters per code, I was going to add 2x4x16 rafter ties 48" OC.

Attached is my crude, ugly drawing. I need to maintain IBC code compliance of course.

The EXISTING part of the dwelling has 96" ceilings from the subfloor, however the walls appear to extend above the ceiling as the roof joists appear to sit roughly 9-10" higher. I'm assuming they constructed this home in a similar fashion but I have not torn open an eve to see for sure.


-- Joe

When we frame this way you either use hurricane ties from the rafter to the plate or you nailed angle 2x4's from the ceiling joists to the rafter just above the birdsmouth of the rafter. Either way will work as spec'd by an architect or engineer where I'm from. This is a normal way to frame.

Joe Carola 01-21-2011 04:56 PM

1 Attachment(s)
Here's what I'm talking about. I showed both ways.

anesthes 01-21-2011 05:00 PM

Quote:

Originally Posted by Joe Carola (Post 575162)
When we frame this way you either use hurricane ties from the rafter to the plate or you nailed angle 2x4's from the ceiling joists to the rafter just above the birdsmouth of the rafter. Either way will work as spec'd by an architect or engineer where I'm from. This is a normal way to frame.


Would you happen to have any pictures of work you have done like that?

Edit: Thanks for editing my picture.

DO you need an engineer to sign off on that application, or is it a known method that is accepted ?

-- Joe

AndyGump 01-21-2011 05:14 PM

1 Attachment(s)
Why do any of that? You have enough to install R-30 insulation in the joist bays without resorting to extra work, material and headache.
This is conventional here, It does not include all notes and such as I would have but it gives you the idea.

Andy.

Joe Carola 01-21-2011 05:16 PM

Quote:

Originally Posted by anesthes (Post 575169)
Would you happen to have any pictures of work you have done like that?

Edit: Thanks for editing my picture.

DO you need an engineer to sign off on that application, or is it a known method that is accepted ?

-- Joe

It's on every plan I get stamped by Architects. Are you drawing your own plans for the town to see for permits and inspections? Where I'm from homeowners can do that. Everything they draw and present to the town will have to be approved. If they don't like something they will let you know. This type of framing is done every day where I'm from and meets code and always passes inspections. Don't know what your town will require you to do.

You can draw it either way for them and see if they question it. They might want you to get an engineer to sign off on it.

anesthes 01-21-2011 05:18 PM

Quote:

Originally Posted by AndyGump (Post 575175)
Why do any of that? You have enough to install R-30 insulation in the joist bays without resorting to extra work, material and headache.
This is conventional here, It does not include all notes and such as I would have but it gives you the idea.

Andy.

Hi Andy,

Minimum required by code is R38 for the ceiling. That is 10 1/4" deep.

-- Joe

Joe Carola 01-21-2011 05:27 PM

Quote:

Originally Posted by anesthes (Post 575178)
Hi Andy,

Minimum required by code is R38 for the ceiling. That is 10 1/4" deep.

-- Joe

You're only doing this for insulation reason? There's no need at all to do that like Andy said.

anesthes 01-21-2011 05:27 PM

1 Attachment(s)
Quote:

Originally Posted by Joe Carola (Post 575176)
It's on every plan I get stamped by Architects. Are you drawing your own plans for the town to see for permits and inspections? Where I'm from homeowners can do that. Everything they draw and present to the town will have to be approved. If they don't like something they will let you know. This type of framing is done every day where I'm from and meets code and always passes inspections. Don't know what your town will require you to do.

You can draw it either way for them and see if they question it. They might want you to get an engineer to sign off on it.

Hi,

Regarding plans. For everything I've built, I draw up quick plans showing wood type, spacing, etc and get the permit. They come out and inspect for code compliance. Never have anyone stamp plans ever.

The problem here is, this isn't a new construction - this is an addition to my existing ranch. I *want* to keep the same, lame roof pitch however I MUST run R38 insulation in the ceiling, and I must allow for proper attic venting.

In addition to that, the original dwelling, built sometime before I was born appears to have 106" walls from the sub floor to the top plate where the rafters are resting. I'm assuming the construction is very similar to what I'm proposing, although I have not opened up an eve to look. (4 feet of snow on the ground!).

I need to have my permits in order in a few weeks. When I went down initially, the inspector told me with that pitch I'm going to have a problem fitting the R38 in there. He said it absolutely cannot be compressed obviously and I must maintain ventilation to the attic. I asked him what he suggested and he told me ask someone else. :(

If I was building a new house, I'd just run a much different roof pitch, like 9:12 or something and I would be good.

Here is a picture of the end of the house where the addition is going.

-- Joe

AndyGump 01-21-2011 05:27 PM

I understand that, I have never had a problem with the above drawn method. The insulation is simply pulled back from the vent holes to allow air flow.
It is only brought back enough to satisfy air flow.

Andy.

anesthes 01-21-2011 05:30 PM

Quote:

Originally Posted by Joe Carola (Post 575184)
You're only doing this for insulation reason? There's no need at all to do that like Andy said.

How can I get a bat to fit with the 10 1/4" height without touching the roof sheathing?

One of the things the inspector said was the insulation absolutely positively MUST go to the top plate. He said that is the envelope or whatever where everyone tries to 'skimp' and the heat loss in a room is. He said he will bounce me if it doesn't go to the top plate and if there is no venting.

-- Joe

AndyGump 01-21-2011 05:31 PM

Roof pitch has nothing to do with this, I am leery of your inspectors requirement on this.

Andy.


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