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Old 07-31-2010, 12:13 PM   #1
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Making room up in attic


My attic has a pretty tall peak down the middle. Currently there are long, thin strips of plywood used as collar ties about 6' off of the floor. Here is what I was thinking:

Replace those collar ties with 2X6's 7' off of the floor, at that height they would be about 10' long.
Run a top plate down the length of the house on each side where the collar tie meets the roof rafter.
Put a bottom plate underneath each top plate and run studs the whole way, effectively making a wall on each side.

This would give me a room that is 10' by about 33', I would have attic storage on either side.

The attic floor is framed with 2X8's spanning no more than 13'. This room that I make would be directly above the main load bearing wall that runs down the center of my house.

Is this plausible? I would have this engineered if I went ahead with it, but for now I am just brainstorming.

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Old 07-31-2010, 02:07 PM   #2
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Making room up in attic


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Originally Posted by Proby View Post
My attic has a pretty tall peak down the middle. Currently there are long, thin strips of plywood used as collar ties about 6' off of the floor. Here is what I was thinking:

Replace those collar ties with 2X6's 7' off of the floor, at that height they would be about 10' long.
Run a top plate down the length of the house on each side where the collar tie meets the roof rafter.
Put a bottom plate underneath each top plate and run studs the whole way, effectively making a wall on each side.

This would give me a room that is 10' by about 33', I would have attic storage on either side.

The attic floor is framed with 2X8's spanning no more than 13'. This room that I make would be directly above the main load bearing wall that runs down the center of my house.

Is this plausible? I would have this engineered if I went ahead with it, but for now I am just brainstorming.
I did a similar project in my previous home. I think that I was required to have a ceiling height of 7'6".
What you are refering to as collar ties are usually called rafter ties. In my mind, collar ties are run from the top of the wall plates. Your 2X8 joists would be collar ties.
I'm not a framer, so maybe we both can be enlightened.

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Old 07-31-2010, 03:09 PM   #3
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Making room up in attic


"Rafter ties must be near the plates to be effective

Many builders confuse collar ties with rafter ties. Both are horizontal framing members that connect rafters, but that's where the similarities end. Collar ties (which are required by the Southern Building Code and no other) function to resist the pressures of wind uplift on a roof by holding the rafters together where they meet the ridge. As high up as they are, collar ties have no leverage to prevent the rafters and walls from spreading outward. That job is best done by the ceiling joists. The wrong and the rights of rafter tiesTo prevent roof loads from spreading the walls outward, rafter ties (or ceiling joists) must be in the lower third of the roof pitch. Collar ties are too high to keep walls from spreading and instead serve to resist uplift by holding the rafter together at the ridge.
If there are no ceiling joists or if the joists run perpendicular to the rafters, then the code requires rafter ties. Similar to a ceiling joist, a rafter tie is typically a 2x4 that runs parallel to the rafters, from outside wall to outside wall, and ties the rafters together as close to the top plate as possible. Rafter ties need to be installed every 4 ft. down the length of the roof.
Rafter ties do not have to be at ceiling height to be effective, but they must not be placed any higher than the lower third of the roof pitch. In other words: Measure vertically from the outside wall's top plate to the bottom of the ridge, and place the rafter ties within the lower third of that measurement. Once they get above that point, they lose their most effective leverage.
I've seen builders compound their mistakes when they try to use rafter ties as ceiling joists in semivaulted ceilings. For maximum headroom or aesthetic balance, they place the rafter ties halfway up the roof pitch, near the center of the rafter span where they're too high to be an effective tie. Applying the insulation and the drywall greatly increases the load on the rafters at their most critical point: midspan (what engineers call the maximum bending moment). This added load can cause the rafters to sag, pulling the ridge down and also pushing the exterior walls outward.
To avoid this problem, you'd need to engineer the rafters to carry the point load created by the additional weight being placed on them. You'd also need to design a ridge beam capable of supporting the roof load, just as you would if it were a cathedral ceiling, which essentially it is." From: http://myconco.com/ComEngProb.html

Most B.D. now require egress (escape) from an attic room. Proper stairs, handrail, HVAC, light and ventilation, insulation, etc.: http://books.google.com/books?as_brr...G=Search+Books

Be safe, Gary
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Last edited by Gary in WA; 07-31-2010 at 03:12 PM.
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Old 07-31-2010, 04:30 PM   #4
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Making room up in attic


My first read of this, I thought that, that clears up much! On 2nd reading, I'm a bit muddled!
It seems that collar ties hold the roof from pulling away from the ridge board..............

Rafter ties, must be installed no more than 1/3 of the distance from the floor to the ridge...........

Rafter ties are to be installed, parallel to the rafters, with a minimum of 4' centers............

Rafter ties are only required if the floor joists run perpendicular to the rafters............

Floor joists serve as rafter ties, if they run parallel...........

Am I correct in my understanding?????????????
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Old 07-31-2010, 04:56 PM   #5
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Making room up in attic


I understand it the same as you.

In my home, the ceiling joists run parallel to the rafters and the collar ties are up high. I would like to replace those collar ties with beefier lumber (either 2X6 or 2X4 if that'll work) and then run walls down each side.

I'd rather just have a smaller room with a squared ceiling than the typical angled ceiling and knee walls that you see.
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Old 07-31-2010, 05:08 PM   #6
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Making room up in attic


"It seems that collar ties hold the roof from pulling away from the ridge board" -- Yes. Mostly required in the Southern Building Codes.



All the others--- Yes. Sec. 2326.12.6. Rafter ties. Rafters shall be nailed to adjacent ceiling joists to form a continuous tie between exterior walls when such joists are parallel to the rafters. Where not parallel, rafters shall be tied to 1-inch by 4-inch (25 mm by 102 mm) (nominal) minimum-size crossties. Rafter ties shall be spaced not more than 4 feet (1219 mm) on center. From: http://www.mcvicker.com/resguide/page010.htm


Page #6: http://docs.google.com/viewer?a=v&q=...h1W5lElSFXE4_w

Proby, check with your B.D. if the collar ties are required or not. They prevent the rafter tops from uplift in high wind areas.

Be safe, Gary
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Last edited by Gary in WA; 07-31-2010 at 05:13 PM.
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Old 07-31-2010, 05:56 PM   #7
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Making room up in attic


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Originally Posted by GBR in WA View Post
Proby, check with your B.D. if the collar ties are required or not. They prevent the rafter tops from uplift in high wind areas.

Be safe, Gary
I would need the collar ties anyway since they would be the ceiling framing. I guess in that instance they wouldn't be called collar ties anymore, huh?
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Old 07-31-2010, 08:24 PM   #8
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Making room up in attic


As long as they are in the upper 1/3 of the total rise AND the B.D. requires them. Otherwise, if lower and not needed, they would be ceiling joists. Spans: http://www.awc.org/calculators/span/...orizontal+Span

Be safe, Gary

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Last edited by Gary in WA; 07-31-2010 at 08:24 PM. Reason: sp
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