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-   -   How to attach a piece of 2x to the bottom of plywood roof deck? (http://www.diychatroom.com/f19/how-attach-piece-2x-bottom-plywood-roof-deck-148357/)

miamicuse 06-26-2012 06:57 PM

How to attach a piece of 2x to the bottom of plywood roof deck?
 
I have to attach a piece of 2x6 lumber to the bottom of the roof plywood deck. The purpose is to sister that to a piece of rafter that has been damaged by water and termite.

I can attach the face of the 2x6 to the face of the existing rafter, using nails or screws. However, what is the best way to attach the top face of the 2x to the bottom face of the roof deck? The roof deck is I think 3/4" plywood, and I don't want to use nail or screws that may end up puncturing the deck and poke holes in the roof's water proof membrane under the concrete roof tiles.

Should I glue it with construction adhesive?

Someone at Home Depot told me I could use something called an "L CLIP" but I have no idea what he was talking about and he can't describe it to me either. I did a search for L-CLIP and came back with this.

http://strongtie.com/graphics/cfs/large/SCW5.gif
But I am not sure how that helps me it will still require screwing through the plywood.

oh'mike 06-26-2012 07:28 PM

Unless the old rafter is completely rotten it should still be holding down the roof deck--so sistering in a new one will not require adding fasteners from the new sister to the deck.

I would use PL Premium adhesive between the new sister and the roof decking for good measure any way---it is cheap insurance---Mike---

joecaption 06-26-2012 08:41 PM

Mike's right but post a picture to see if were missing something.

miamicuse 06-27-2012 02:58 AM

I will try to illustrate but will be a bit long winded.

Here is a series of trusses as viewed from below.

http://i173.photobucket.com/albums/w...1020670-OV.jpg

Trusses are marked 1, 2, 3, 4.

Truss 1 is OK, as shown.

http://i173.photobucket.com/albums/w...P1020676-1.jpg

http://i173.photobucket.com/albums/w...P1020677-1.jpg

Now truss 2 has some rotted damages on top.

http://i173.photobucket.com/albums/w...P1020678-2.jpg

You can see someone previously had nailed a 2x6 on the back side of it. It seems only 3 nails were used, but I didn't want to pry the 2x6 out for fear it may damage the rotted member more. I would have cut a trapezoidal plywood gusset and cover both sides, sandwiching the damaged member in the middle.

http://i173.photobucket.com/albums/w...P1020679-2.jpg

What I want to do is to do a better repair of this. I am trying to figure out:

(1) Is there some materials I can use to fill in the "void" between the damaged member and the roof deck? Some sort of structural putty or filler?
(2) If I sister another piece of lumber on the front side, nailed to the damaged member and somehow attached to the bottom of the roof deck, and may be drill 3/8" holes through all three pieces then tie them together with nuts and bolts.

oh'mike 06-27-2012 06:12 AM

Bolting all three together looks like the best plan.

Adding a ripper of 2x material at the top of the rotted rafter may be needed to keep the new sister from rolling when the bolts are tightened.

It's a shame that the previous owner let the roof go for so long before repairing.

Wildie 06-27-2012 08:50 PM

Perhaps as you mentioned, a pair of pressure treated, plywood gussets used to sandwich the truss would work!
I would use both construction adhesive and carriage bolts to fasten the gussets to the truss.

miamicuse 06-27-2012 08:52 PM

Quote:

Originally Posted by oh'mike (Post 952460)
Bolting all three together looks like the best plan.

Adding a ripper of 2x material at the top of the rotted rafter may be needed to keep the new sister from rolling when the bolts are tightened.

It's a shame that the previous owner let the roof go for so long before repairing.

I agree, I wish they did a proper repair but now I am dealing with it.

I am not sure I can rip a piece of 2x to match the top portion that is gone. It's too irregular. I think I am going to use a multi-max tool to trim off the loose wood up top, then may be use some epoxy filler mixed to the texture of toothpaste and putty them in? I am not sure what else can be filled into the void to take some compressive strength when I put another sister plywood on the other end and tighten them with bolts.


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