raising collar ties - DIY Chatroom

ajoantmug · 03-10-2007, 07:34 PM

Hello,
I am going to finish my attic space and am very interested at raising the collar ties. My roof is a double gable or intersecting gable. One side is 22 feet wide and 11 feet high at center. The other side, which intersects, is 20.5 feet wide and 10 feet high at center. The existing collar ties are at 7 feet. I would like to raise them to 8 feet. The rafters are 16 inches on center and are 2 inches by 6 inches. Is what I want to do possible or will it compromise the structure? Oh, and the rafters rest on the exterior, brick walls.
Thanks in advance!

**AtlanticWBConst.** · 03-10-2007, 07:38 PM

Quote:

Originally Posted by ajoantmug

Hello,
I am going to finish my attic space and am very interested at raising the collar ties. My roof is a double gable or intersecting gable. One side is 22 feet wide and 11 feet high at center. The other side, which intersects, is 20.5 feet wide and 10 feet high at center. The existing collar ties are at 7 feet. I would like to raise them to 8 feet. The rafters are 16 inches on center and are 2 inches by 6 inches. Is what I want to do possible or will it compromise the structure? Oh, and the rafters rest on the exterior, brick walls.
Thanks in advance!

Yes... It is do-able, because you will most likely be installing knee-walls as well. Between the knee-walls (giving vertical support to the rafters at probably 40" - 50" up) and the collar ties (moved up to 8')...You will have a solid rafter structure.
Done it many times on attic remodels with building inspection approval.

Example:

BEFORE:

AFTER:

ajoantmug · 03-10-2007, 07:44 PM

Yes, I am planning on four foot knee walls. But will this place too much, if any of a load on the floor joists below?

**AtlanticWBConst.** · 03-10-2007, 07:52 PM

Quote:

Originally Posted by ajoantmug

Yes, I am planning on four foot knee walls. But will this place too much, if any of a load on the floor joists below?

Collar ties are not installed for vertical loads, they are installed to re-inforce the rafters and roof structure from upward wind pressure and roof loads that can cause rafters to spread apart outward.
Installing knee walls would not be for weight or load support, but aid in keeping the rafters from spreading.
Thus, you are not adding any of the rafter's weight loads to your floor joists.

To illustrate: Take 2 playing cards, or 2 books, and lean them end to end to form an "A"....Where is the weight load? At the peak and at the bottoms. They support each other....there is no downward or vertical weight load under the areas of the 'A' form.

ajoantmug · 03-10-2007, 07:59 PM

They are 1 5/8 by 7 1/2.

**AtlanticWBConst.** · 03-10-2007, 08:09 PM

Quote:

Originally Posted by ajoantmug

They are 1 5/8 by 7 1/2.

I changed my response to your question about knee walls in regards to the floor joist sizes.
Please re-read my edited answer above.... in regards to any rafter weight load on the knee walls.

BTW, yes: you have 2x8's which will properly support any live loads with your attic remodel....

ajoantmug · 03-11-2007, 12:24 AM

This is sounding good. Should the collar ties be connected with a carriage or lag bolt or is nailing sufficient? Should the knee walls be tied in directly to the floor joists or can they be framed on top of them? The current collar ties are on every other rafter, should the new ones be the same or do they need to be on every one? What dimension lumber should be used for both the collar ties and the knee walls?

**AtlanticWBConst.** · 03-11-2007, 09:39 AM

Quote:

Originally Posted by ajoantmug

This is sounding good. Should the collar ties be connected with a carriage or lag bolt or is nailing sufficient?

Nailing is sufficient- use 10d or 12d nails for 1x6 or 2x4 collar ties.

Quote:

Originally Posted by ajoantmug

Should the knee walls be tied in directly to the floor joists or can they be framed on top of them?

They may be framed on top of them.

Quote:

Originally Posted by ajoantmug

The current collar ties are on every other rafter, should the new ones be the same or do they need to be on every one?

What you could do is install new 2x6 ceiling joists (see last point in my reply)...onto every rafter for your ceiling framing. These will also serve as your new 'stronger' collar ties.

Quote:

Originally Posted by ajoantmug

What dimension lumber should be used for both the collar ties and the knee walls?

Knee walls: Simple 2x4's
Collar ties: normally, you can use 1x6 or 2x4's, but read the next point:

However:
As mentioned, I would simply suggest using 2x6's attached across to each rafter to serve a double purpose....(as your ceiling joists and collar ties) Using the 2x6's would be going over what is required for collar ties, but accomplishes 2 missions. Using the 2x6's rather than the 2x4's for the 'ceiling joists/collar ties'....helps to eliminate sag over that span (which you don't want since that is your ceiling). You can attach strapping perpendicular across the new 'joists/collar ties' to finish the framing structure for your new ceiling.

ajoantmug · 03-18-2007, 06:41 PM

thank you for the advice.

**AtlanticWBConst.** · 03-18-2007, 07:15 PM

Good luck on your project...