Framing Question (terminology)

tom418November 22, 2011

I live in a 2 1/2 story house (finished attic).

The sole plates of the side walls of my second story rest on the subfloor of the second story. The third story is a different setup. The floor is not as wide as the second story. Instead, it is 4 inches narrower on each side, and the sole plates of the third story end walls rest on the top plate of the second story end walls. In other words, the bottom parts of the wall frames are on the SIDE of the outermost floor joists between the second and third floors.

Is there a name for this type of construction? Advantages?

Thanks.

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renovator8

A 2 1/2 story house should have rafters framing onto the second story wall top plates on two sides and if there are end gable walls they should rest directly on the walls below. So, I'm not sure how your framing differs.

    Bookmark   November 22, 2011 at 1:57PM
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renovator8

The third floor/attic joists would rest on the top plate next to the rafters and would be just inside and nailed to the end gable wall studs.

It is possible for there to be a band joist around the level of the third floor/attic and joists that butt into it and floor sheathing on them. The rafters would then be installed on a plate sitting on the edge of the floor.

I prefer this alternate method because it raises the roof eave soffit higher on the exterior wall but it is unusual; yours sounds like typical "platform framing".

    Bookmark   November 22, 2011 at 2:07PM
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sierraeast

2nd to 3rd sounds like balloon framing which is pretty rare these days, at least in our area. In fact I don't believe it's allowed anymore.

    Bookmark   November 22, 2011 at 2:18PM
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renovator8

Both Platform and Balloon framing are shown in the framing diagrams of all editions of the IRC. In both cases the top plate supporting the rafters is configured the same and required by the code.

The only way to tell which method was used is to look at the second floor joist support or possibly the foundation sill detail.

    Bookmark   November 22, 2011 at 2:40PM
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tom418

OK Renovator, I think you've cleared things up for me.

I found a diagram of how my house is constructed (see link). I have a setup like the top diagram.

They describe platform framing, which is how my first and second floors are framed. But look at how the third floor is framed. Why didn't they let the walls rest on the third floor subfloor? Is there a reason for this?

Here is a link that might be useful: Diagram of my construction

    Bookmark   November 22, 2011 at 3:18PM
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renovator8

You have standard platform framing. Using a platform at the attic level would have been unusual because it would require more materials (band joists, etc.) which would only raise the rafter seats up and make the space under the rafters higher.

An architect might use it to increase the exterior wall height, allow higher top floor windows and more attic headroom but a contractor would usually not care.

    Bookmark   November 22, 2011 at 3:38PM
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tom418

Great! Thanks, Renovator8!!!!

    Bookmark   November 22, 2011 at 4:41PM
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sombreuil_mongrel

The best reason to set the rafters above the attic subfloor is that steep roof + big overhang = soffit sitting on top of the windows below. Rafters on top of rim joiust/subfloor and a plate raises the assembly high enough to add a frieze around the plate line if desired, and gives you about a foot more headroom or floorspace all around, depending on how you look at it.
Your type of framing has moved your 4' knee walls (or 8' ceiling clip line) inward by that amount, assuming a 12/12 pitch. Each room is 2' narrower than it would have been otherwise.
Casey

    Bookmark   November 22, 2011 at 6:07PM
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sierraeast

I took it that the op meant a literal 3rd story wall not a gable end wall, that's why the balloon framing comment which I haven't seen except for older period homes when it was fairly common.

    Bookmark   November 22, 2011 at 6:13PM
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tom418

Casey: Thank you for your reply also.
You are correct. My house is a stick built version of modular houses in my development whose third floors were added on site. Their third floors were as you described. When I opted for the stick built version, I was told about the reduction in square footage.

And Sierraeast: I should have called the gable wall by that name. I thought that I had implied that by calling my house a 2 1/2 story. Yes, I thought that balloon framing was done away with.

    Bookmark   November 23, 2011 at 7:40AM
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brickeyee

"Yes, I thought that balloon framing was done away with."

It requires significant fire stopping, and the availability of long studs has made it not very common.

Older balloon framed buildings used studs that extended from the foundation the top of the walls.
Even finding a 16 foot 2x4 straight enough for this type of construction is hard now. let alone longer.

    Bookmark   November 23, 2011 at 8:57AM
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