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rafter tie question

red1212's picture

rafter tie question (post #192811)

red1212 on Wed, 08/25/2010 - 18:23
in

Live in Maine have a colonial house with unfinished full attic, 8:12 pitch roof., 20 years old.

Looks like when roof was framed they basically decked over the floor of the attic (second floor ceiling) with plywood and then placed the rafters on top of this deck with a birdsmouth cut on edge.  Ridge is non structural, no collar ties.

I recently pulled up all the plywood, and removed existing fiberglass insulation to blow in cellulose at a greater depth, covering the top of the 2x10 floor joists which I presume act as rafter ties.  I found that the floor joist was not a continuous 2x10 but rather two separate pieces of wood overlapped about 4' on a load bearing wall, toenailed to top plate of bearing wall.  They were not nailed to one another.  There is cross bracing for the joists

I nailed them to one another with a dozen or so nails where they overlap.  I also added collar ties 1/3 of way down from ridge.  Since I am not putting the plywood back down due to increased insulation depth, I am wondering if it will create any problems with spreading.  Was the plywood playing much of a role keeping the overlapped floor joists/rafter ties from spreading?  Now I'm wondering if I should go back and try to really secure the overlapped 2x10's together rather than just a few nails - bolts or metal strap?

Maybe I just am worrying too much and if it has been fine for 20 years with plywood in attic it will be just as  fine without plywood.
Any thoughts would be appreciated.

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Other than the plywood, your (post #192811, reply #1 of 8)

by DanH in reply to red1212 [original] on Wed, 08/25/2010 - 18:36

Other than the plywood, your roof is standard construction for the era.  If you want to play it super-safe the simplest thing to do would be to take about a 8-inch wide slice of that old plywood and nail it across the joist overlaps, running the length of the roof.


This country will not be a permanently good place for any of us to live in unless we make it a reasonably good place for all of us to live in.  --Theodore Roosevelt

Does the plywood add much or (post #192811, reply #2 of 8)

by red1212 in reply to DanH [original] on Wed, 08/25/2010 - 18:40

Does the plywood add much or is most of the "work" done by the toenailing into bearing wall?

The toenailing is probably (post #192811, reply #3 of 8)

by DanH in reply to red1212 [original] on Wed, 08/25/2010 - 19:09

The toenailing is probably sufficient, except that it's often hard to tell how well the toenailing has been done (especially at this distance) and whether an edge is apt to tear out.  The flat nailing is iffy since the joists are likely not really cheek-to-cheek.


This country will not be a permanently good place for any of us to live in unless we make it a reasonably good place for all of us to live in.  --Theodore Roosevelt

attic (post #192811, reply #4 of 8)

by k1c in reply to red1212 [original] on Sun, 08/29/2010 - 16:35

Adding collar ties was all you needed to do.  Although because of your roof pitch and some luck, your roof did not sag after all these years.  Your inner walls also hold the perimeter together.

The attic floor joists are toenailed at the outer walls as well so securing the overlap in the middle will not add more strength.  The plywood probably did little to hold things together.    

Engineer advice (post #192811, reply #8 of 8)

by ENGINEER10 in reply to red1212 [original] on Sat, 10/16/2010 - 20:59

The plywood held the joists and rafters toghether to prevent them from spreading out in opposite directions.


Now that you have added the collar ties below the roof ridge it replaced the role of the plywood and you should be fine providing that you have sufficient nailing/fastening  of ties to rafters which depends on the location below ridge, roof pitch, width of house in the direction of rafters, weight of roof, amount of snow and how strong are the winds in your area.

 

www.CHMconsultants.com/Light-GaugeSteelS...

 

Looks like when roof was (post #192811, reply #5 of 8)

by Framer in reply to red1212 [original] on Mon, 10/11/2010 - 01:39

Looks like when roof was framed they basically decked over the floor of the attic (second floor ceiling) with plywood and then placed the rafters on top of this deck with a birdsmouth cut on edge.

When doing that there has to be a 2x4 or 2x6 plate nailed to the top of the ceiling joists. You have to nail hurricane ties to every rafter and plate or nail angled braces from the ceiling joists to the rafters at the plateline with or without the plywood code wise.

Joe Carola

Half of what you have read (post #192811, reply #6 of 8)

by Piffin in reply to red1212 [original] on Sat, 10/16/2010 - 20:04

Half of what you have read here is wrong, but you are fine with what you have now

 

 


or try this site for the whole gang

http://forums.delphiforums.com/breaktimeclass/start

Agreed.  The collar ties do (post #192811, reply #7 of 8)

by DanH in reply to Piffin [original] on Sat, 10/16/2010 - 20:28

Agreed.  The collar ties do little to address the spread potential, but so long as the splices in the joists are good then the structure is as sound as it was with the plywood.  Things like hurricane clips would probably be required in new construction, but millions of homes have been built without them and aren't falling down.


This country will not be a permanently good place for any of us to live in unless we make it a reasonably good place for all of us to live in.  --Theodore Roosevelt