Joist Hangers or not? Attic opening.

[Kelemvor]

Don't know if anyone has experience with this or not but here goes...

We have an attic in our house with a square opening to crawl up into. I'm putting in a pull down ladder thing which requires a larger opening. This means I have to frame out a larger hole (perpendicular to the joist direction) which involves cutting a couple of the joists.

When I put in the longer piece to frame the opening, I could just use large screws to connect it to the ends of the joists I have to cut or I could use joist hangers. Anyone know if there's any pros or cons to either way? It's be faster to just put 3 long deck screws (or something similar) into each joist but if using the joist hangers would be beneficial for some reason, then I would consider that.

Anyone have any experience with this?

Pic: https://www.dropbox.com/s/y969x0c8adgj999/2015-06-20 17.53.10.jpg?dl=0

In the picture, the dotted lines are where I am expanding the opening. The circles are where I could use joist hangers or could just screw the boards together. The current opening is just done with nails but is from 30+ years ago.

 

[boomerang]

I'm no expert by any means on construction but if it were my house I would look at it from this perspective. If the framework defining the existing opening does not use joist hangers, I would not be concerned about using them for the alteration. My only concern is if the cuts you will be making will be into the bottom member of roof trusses. Right now, only one truss is compromised. When you're done, three will be compromised and they are adjacent to each other.

The pro of using joist hangers in this situation is that you have more fastening surface. More fasteners will be holding the same joint together. I'd think that would be advantageous if the joist, as the bottom chord of a truss, is a stressed member. But even with hangers, the weakness is in the 2x lumber you will be using to frame the opening. Whether the fix for that is to double those up or to use a single and slap an additional piece of 2x lumber laying flat across the top of the joists that frame the opening is not something I would be comfortable giving advice on. Although that's probably how I'd do it if it were my place. Slap one on the top but have it longer to lay on top of at least one uncompromised joist on either end. Screw it all together and it should be good and strong.

Hope what I'm saying is clear.

 

[Greenman]

If it's truss framing don't cut anything, live with the small opening. If it's stick construction and you intend to cut out 3 joists you should double the joists at each side because they will be carrying increased load. Use joist hangers, screws (with one or two exceptions) aren't structurally rated.

 

[boomerang]

^^^^^^^^^
This guy knows far more than I ever will. Take his advice over mine.

 

[Greenman]

^^^^^^^^^
This guy knows far more than I ever will. Take his advice over mine.

Don't sell yourself short.
I've been swinging a hammer for 39 years, it's impossible not to learn something in all that time.

 

[tracerbullet]

Agreed on not cutting it. I'm guessing there's a reason drop-down stairs are made to go in between joists, not across them. Also I want to say those pieces are in tension, not compression, and I don't see how you can easily replace the work performed by the chunk you cut out in the way you might for example if you took out some studs to put in a window.

 

[Greenman]

I never thought about the tension loads on the ceiling joists. Great catch.

 

[Humpy]

Agreed on not cutting it. I'm guessing there's a reason drop-down stairs are made to go in between joists, not across them. Also I want to say those pieces are in tension, not compression, and I don't see how you can easily replace the work performed by the chunk you cut out in the way you might for example if you took out some studs to put in a window.

Assuming it's a pitched roof, it's essentially the same idea, transfer/spread the loading to the rest of the structure. The difference is vertical compression versus horizontal tension but the solution would use similar techniques as wall construction using collar ties, structural sheathing, and "headers" to do the work. The harder part is figuring out exactly where and how much is needed.

 

[skyking]

It would not be a happy retrofit, that much I can say.

 

[mizzou]

This is how peope uncover home renovation nightmares years down the road when you are long gone. No offense sought, its something all of us are guilty of when doing major or minor renovations.

I always am eager to do my own work.....but when it comes to structural integrity and safety...i wont touch it unless i know 100% what im doing. Im sure you could do it just as you planned but who knows when and how the house will respond over time.

 

[Greenman]

If you could draw a section and plan view I could probably tell you how to make it work.