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Tubafore 06-18-2013 12:55 PM

Rafter seat cut options
 
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Traditionally most rafters have a birds mouth cut where they rest on the top plate (as shown on the left).
Is there any reason not to cut the seat as shown on the right with the rafter tail reduced in height?
Is there a code or practical reason for sticking with the birdsmouth?

I want to use the style on the right to leave more room for air to circulate in the eaves and eliminate the need for continuous soffit vents in a cathedral ceiling.

joecaption 06-18-2013 01:07 PM

I'm not seeing anyway the one on the right is going to give you more.
Looks like a lot less to be.
Unless your going to have this ceiling spray foamed I see no way your going to fit the required amount of insulation plus the baffles in that small an area.
http://www.energystar.gov/index.cfm?...sulation_table

Tubafore 06-18-2013 01:20 PM

1 Attachment(s)
There will be a build down framework on the interior to give me the needed insulation depth.

tony.g 06-18-2013 01:44 PM

Structurally there is no problem with the detail on the right.

Willie T 06-18-2013 01:49 PM

You do understand that no matter the point of narrowing the rafters, a smaller fascia makes the house look cheaper. That's why trusses with just 2x4 top chords (tails) have larger 2x6 or 2x8 "hang-down" sub-fascias added to them.

Tubafore 06-18-2013 02:08 PM

The fascia will still be about 7" tall. This is an addition and it will match up well with the existing house.

Willie T 06-18-2013 02:13 PM

Quote:

Originally Posted by Tubafore (Post 1203365)
The fascia will still be about 7" tall. This is an addition and it will match up well with the existing house.

Then I see no problem.

Tubafore 06-18-2013 02:33 PM

Awesome, thanks.

GBrackins 06-18-2013 03:59 PM

I take it you are doing the work yourself? I ask because the additional time required to build down the ceiling for more insulation space.

Tubafore 06-18-2013 06:04 PM

Quote:

Originally Posted by GBrackins (Post 1203433)
I take it you are doing the work yourself? I ask because the additional time required to build down the ceiling for more insulation space.

Yes I will be doing the work myself. There are a few reasons I chose this design. Even a 2x12 wouldn't give me the depth I needed for insulation without pricey spray in foam.
With R-38 batts plus the 1" foam board I will be using to create an air space this will give me a total R-44 value. Plus the drop down will break the thermal bridging that happens through solid lumber. All at a pretty reasonable price tag.

GBrackins 06-18-2013 06:08 PM

sounds good, thanks for sharing


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