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-   -   2x4 rafters sufficient? (http://www.diychatroom.com/f19/2x4-rafters-sufficient-168621/)

Lupus71 01-08-2013 05:26 PM

2x4 rafters sufficient?
 
Hey guys I have a 16x24 shop ive built that needs a roof but im running low on cash, I'm wondering if 2x4 rafters with a 2x6 beam will be strong enough to hold a roof with 4/12 pitch, asphalt shingles, 7/16 osb, and felt paper. I did some calculations lastnight and came up with 4.6 lbs psf. I would be using whitewood(whatever that is) lowes wood no.2 . Also I live in ga so no snow not much wind. Thanks, I can't find much on the net.

jaydevries 01-08-2013 05:48 PM

try this
http://www.awc.org/calculators/span/...rcalcstyle.asp
or
http://www.wclib.org/pdfs/SimpSpanTbls.pdf

Lupus71 01-08-2013 06:28 PM

Thanks! That's actually the one I used to get 4.6lb psf. I'm just not sure how to get the deflection.

cleveman 01-08-2013 09:45 PM

The ridgeboard is inconsequential. It can be a 1x.

I think you'll be fine spanning 8'. We span 12' with 2x6's 2' oc with a 4/12 roof and we have 1' of wet snow sitting on it now/have had more in the past.

joecaption 01-08-2013 09:58 PM

The bad part is using 2 X 4's your not going to be able to have an over hang.
With an over hang it keeps the water from running down the siding which can cause all kinds of issue later on.
I personaly will not build any building without over hangs on all side.

Gary in WA 01-08-2013 10:02 PM

http://publicecodes.cyberregs.com/ic...?bu2=undefined

Gary

cleveman 01-08-2013 10:06 PM

I agree that it is best to have a soffit and a hip roof.

But I think you can still do this with 2x4's. The span is just from the ridge to the wall, then the 2' overhang has nothing to do with the strength of the roof. You can attach a 2x6 fascia to the tails the same as you would to truss tails.

You can use some "look-outs" to tie the rafters and fascia back to the building. These are just some ca. 2' 2x pieces which are sistered alongside the tails and go back into the building. Go to a book and look them up if you need to.

funfool 01-08-2013 10:21 PM

Toss in my 2 cents. I would not do it!
My reasons are, Once you add a 4/12 pitch to it, it is longer then 8'
Then you need a over hang and notch the rafter to sit on the top plate, just not much you can notch out of a 2x4 safely.

Then add, that a 16x24 shop is a very nice tool or toy.
Maybe down the road, you may want to insulate that ceiling to keep that hot GA sun from baking you..

I would simply prefer to build the bones of the structure solid, skimp on other things that can be replaced later.
You can always build it right, dry it in .... add shingles later.
Once you build it with crap 2x4, you cant go back and replace those later.

joecaption 01-08-2013 10:29 PM

How many post have we seen on here with cracked rafters when they used 2 X 4's?
There's sure been quite a few.

cleveman 01-08-2013 10:51 PM

Those codes that GBR posted show that you can easily span 8' 16" oc, with all but the worst lumber.

As for notching out at the top plate, you don't need too much of a notch. You could even build some trusses for the 24' run if you like, so you'll have no notches at the top plate. Not even a real truss. Just attach your ceiling joist alongside the rafter and nail everything together. You can do this on your other end as well.

You'll have an 8' long run for a rafter (the longest) and you can put some ceiling joists in alongside it.

funfool 01-08-2013 10:54 PM

I dunno Joe .... even if we could calculate it and make the load rate come out in our favour.
So many reasons not to do it..

Just going to be a place to store your hay and keep it dry ... maybe.

GBrackins 01-08-2013 11:18 PM

are there ceiling joists being installed? if not your 2x6 beam will not be sufficient to hold the roof up I'm afraid (if it's running in the 24' direction).

cleveman 01-08-2013 11:27 PM

He doesn't need a stinking beam, he just needs a ridge board.

And the ridge board isn't holding anything up, it's just holding the rafters apart and giving something to nail into.

GBrackins 01-09-2013 12:05 AM

if there are no ceiling joists then a structural ridge beam or rafter ties located in the lower 1/3 of the attic space (between top plate & ridge) is needed or the rafter thrust will push out the tops of the load bearing walls, which in turn will cause the ridge to saddle (bow). A ceiling joist is a type of rafter tie. Don't take my word for it ..... from the 2009 International Residential Code, basis for most local building codes:

R802.3.1 Ceiling joist and rafter connections. Ceiling joists and rafters shall be nailed to each other in accordance with Table R802.5.1(9), and the rafter shall be nailed to the top wall plate in accordance with Table R602.3(1). Ceiling joists shall be continuous or securely joined in accordance with Table R802.5.1(9) where they meet over interior partitions and are nailed to adjacent rafters to provide a continuous tie across the building when such joists are parallel to the rafters.

Where ceiling joists are not connected to the rafters at the top wall plate, joists connected higher in the attic shall be installed as rafter ties, or rafter ties shall be installed to provide a continuous tie.
Where ceiling joists are not parallel to rafters, rafter ties shall be installed. Rafter ties shall be a minimum of 2-inch by 4-inch (51 mm by 102 mm) (nominal), installed in accordance with the connection requirements in Table R802.5.1(9), or connections of equivalent capacities shall be provided. Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice.

Collar ties or ridge straps to resist wind uplift shall be connected in the upper third of the
attic space in accordance with Table R602.3(1).

Collar ties shall be a minimum of 1-inch by 4-inch (25 mm by 102 mm) (nominal), spaced not more than 4 feet (1219 mm) on center.


cleverman you are correct when ceiling joists/rafter ties are installed you only need a nominal 1" ridge board who's height must equal the ends of the rafter cut as tension and compression forces are balanced eliminating rafter trust. Same as in an engineered truss roof.

Lupus71 01-09-2013 05:49 AM

Man you guys are up too early! Thanks for all the replies. Looks like I need to bite the bullet and pay for trusses. It's actually cheaper to buy them than build them myself. Rafters would have been half the cost but oh well. Thanks again.


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