Allowable roof loads for framing

plummen

Quick question guys since Im no pro carpenter i figured Id ask you guys.
Helping some friends remodel a house with an upstairs attic that was converted to bedrooms probably 50 plus years ago.
They gutted all the plaster room walls in the attic so I could start wiring ,but as I was l was laying out plug boxes I started noticing existing framing that I would call questionable at best!
So no we have it stripped completely down to basically 4 5' exterior walls and a roofline.
The roof has what im going to estimate as being a 8/12 pitch as best i can tell and is framed with 2x4s that somebody covered with new osb and shingles before they bought the house.
My question is how much of a span can those 2x4s really span on a roof like that in a god forsaken place like omaha ne where it tends to snow really good when it does snow?
Im thinking about doubling up all the 2x4s with 2x8s from where the land on top of the walls to the peek,and replacing the spindly 2x4s that run between the side to side to support the ceiling with 2x6s .
Does this seem like a good idea or have i gone off the deep end again from too many years of commercial/industrial wiring and plumbing?

joecaption

Well the house is 50 years old and it have not came down yet.
See any cracked or bowed rafters?

plummen

Looks like a ski jump on one side!

joecaption

Without removing the whole roof and old rafers how do plan on installing new ones?
With that bad a curve I see no way to set them in place.
Not a bad idea to do it, just a lot more work then your thinking it is.

plummen

Im thinking about jacking them back up a little and nailing them in beside to stabilize whats already there

joecaption

Well, here's what's likly to happen when you have 50 year old wood that's bent, some are going to crack, as your lifting some of the nails are going to pop where there toe nailed, and it's very likyl to also mess up the shingles.
It's also going to be a real pain to try and lift something on an angle.
I'm sure someone else here will come up with an idea but I'm thinking if you built knee walls it would keep the roof from sagging any further.

plummen

The walls that are there now are roughly 5' where the ceiling starts.
Im not trying to make it perfect by any means,I just want to push up enough on the 2x4s enough that once i take the pressure back off them the 2x8s will be basically preloaded/stressed so it shouldnt get any worse.
If they want it perfect they need to knock the roof off and start over!

abracaboom

I agree with Joe. More likely to mess things up than to make things better.

If you still want to do it, I'll draw a picture for you showing the best way to persuade those rafters to move (with 2x4s and a hammer).

mae-ling

IF and that's a big If you can get rafters up there is one piece you can sister new ones beside the Old. Or it sounds like maybe you are wide open underneath? Find out what you need for your roof pitch, size and snow load. Take them up in the attic and sister new one beside old one. Do not try to staighten old ones, leave them sag and push up the roof sheeting. nail new rafter to old one. Nail on New collar tie. And plywood gusset at the top. Do this for each one. Go on roof and nail sheeting (or whatever is up) there into the new rafters. You will need to re-shingle.

Another option is to build a roof on top of the existing roof.

AndyGump

It sounds like you are setting up a 'non-vented attic' situation too.

Have you considered that too?

Andy.

titanoman

I agree with Joe. You can't straighten 50 year old lumber.
Put purlins in to prevent further sag.

Gary in WA

"My question is how much of a span can those 2x4s really span on a roof like that in a god forsaken place like omaha ne where it tends to snow really good when it does snow?"------ they could span about 6' horizontal measurement. That figuring a 25# snow load for your location and 10# dead load, chart #(5) here: http://publicecodes.citation.com/ico...002_par023.htm Depending on species and grade of 2x4.....

The knee-wall is probably not bearing on another house wall below, very common framing years ago. Which means, if adding bulk (weight) to the rafters, they should span from house exterior walls to ridge board. Otherwise you will be adding that new roof load to the knee wall- and ultimately the floor joists to carry it all safely. When adding collar ties for ceiling joists in the top 1/3 of total rise, gussets would not be needed then.
The biggest concern is the size/span of the attic room floor joists to carry minimum 30# per sq.ft. (plus the combined roof/wall/floor/ceiling loads, if so, could not use this chart): http://publicecodes.citation.com/ico...002_par017.htm

Hopefully they have a permit for this......

Gary

__________________

mrgins

First of all, what is the total clear span? If there are 5' ext walls, are there collar ties? If so, at what height off the floor? Can you post some pics?
After that, we can give you better advice

AndyGump

Practically speaking, the OP and the HOs do not really need advice on what lumber size to use, but they need someone qualified to look at the whole roof, walls and floor framing system to come up with a good over-all solution that will last a good ling time.

Andy.

plummen

Thats one reason I want to use the 2x8s sistered to the 2x4s is so the insulation isnt sandwhiched between the ceiling and roof sheething like it is with the 2x4s with no way for it to breath.
Im planning on running 2x6s from one side of roof to other in place of the existing 2x4s also to support the ceilings.
Im definately going to install the triangles in the peek make from 3/4" plywood to tie things together as well