sagging rafter, installing sister

[transferguy]

posted by: paulmars

How to install rafter sister?

If I make it the same length as the existing ones, it wont fit. There will be no way to install it w/o removing the roof plankings.

My only idea is to make it shorter and cut the piece that sits on the block wall, cut the angle 1.5" higher. This will allow me to slide it in further, then lift up the ridge end and pull it into place. Then place a 2x4 below the angle cut on the block wall side. Clear?

My jpg shows a drawing of existing rafter with the red line how Im thinking of cutting the sister. It would be weaker, but this is all that i can think of. If I do this I will attach it with screws and glue to the block wall top wood and bolt it to the existing rafter two bolts 1' apart at each end.

better ideas?

pics and my drawing: IMAGES NO LONGER AVAILABLE

please ignore the incorrect jpg drawing. I cant figure out how to delete it. No wonder I stopped using photobucket a long time ago!

what about the sag? I'm gunna have to PUSH it flat with this new rafter. Will not the old sagging rafter push against the new, maybe sagging it too?

[transferguy]

posted by: paulmars

three rafters where the roof sags have a measurable curve to them. 3rd one is totally destroyed by termites. Every place that I touch it, it crumbles.

[transferguy]

posted by: dkerr

I hope someone jumps in that is more knowledgeable on this than I, but you are right a same size rafter would involve removing some roof boards to drop it in place, now that is an option if you also need to redo the singles on the roof itself but if it is in good shape you may be reluctant to do that.

You likely should have cross pieces along the bottom of the rafter mid may up which may help prevent sages curves from developing like what you would see on the bottom or between joists on basement ceiling (floor joists). Adding that now may help further curving / sages.

All the weight support on the outer side is on top the wood / brick wall not on the outside part of the rafter, the outside is really supporting that outside foot or so of the roof. If the sister rafter gets to the outside edge of the outer wall I believe you still have the same support at that point.

I assume it is the inside portion of the rafters that is the problem weak area? If you need to add additional sister rafters to compensate for weak areas as that should distribute roof weight across more rafter support. Certain types of wood is stronger than others too.

[transferguy]

posted by: paulmars

Posted by dkerr

You likely should have cross pieces along the bottom of the rafter mid may up which may help prevent sages curves from developing like what you would see on the bottom or between joists on basement ceiling (floor joists). Adding that now may help further curving / sages.

pictures please. I been thinking that I need some type of support. This is in garage and their are no joists, but i can add some. I might even add a support down to the floor. I dont like the idea of adding four more rafters, that is a lot of added weight.

maybe I need to attach the rafter ends better. These on this old house are just toe nailed in place. pics attached.

[transferguy]

posted by: pushkins

Adding 4 more sistered rafters is not any added weight that needs to be worried about in any way whatsoever.

Building a wall to support a rafter/s wouldn't normally be a valid option either, the sag was created by either the termite issue or undue load at some point in the roofs past, replacing the suspect rafters with new rectifies the issue without the need of a wall.

[transferguy]

posted by: pushmars

4 rafters side by side, all have large knot in same location, causing sag. 3rd one is termite damaged and actually has less of a sag.

Still looking for ways to fasten these better.