# 4x6 Rafter spacing



## Abandoned Barns

How far apart can rafters made of 4x6s need to be? 

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## TnAndy

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Depends on a whole variety of factors:

1. Expected load

2. Roof pitch

3. Clear span

4. Sheathing type and thickness


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## Harry Chickpea

Yep, TnAndy is right. You also want to include wind load in that list as well as static and snow load.

If you don't need the attic space this:

....../\.
...../..\.
..../\../\.
.../..\/..\.
tie beam or cable
wall ctr wall

is MUCH stronger. Halving the span effectively quadruples the load capacity. (more or less)


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## Abandoned Barns

Do all those factors fit into some "Rafter spacing formula" that spits our a Rafter distance or is it more of an experience and good judgement thing? 

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## Harry Chickpea

It (load bearing capacity) used to be something calculated using the "modulus of elasticity" of the material and a handful of formulas. Mostly that has been superseded by building code requirements. Rafters are typically 16" or 24" OC due to sheathing/decking dimensions, so the dimensions of the rafters become the variable.


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## TNHermit

4ft..


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## Abandoned Barns

Thanks Fellas. For all your good help. I ended up hiring a carpenter buddy of mine to help out as I didn't want to be literally hanging my pride over my family's heads. 

The rafters (4x6 Cyprus) ended up being a little over 3' apart. 







can I just say; eyow! Those were heavy! The roof is 1x6 rough cut Cyprus (Cyprus mill next town over) and will be asphalt on top. My wife really loves it, but we've had some bowing in the band, so we got some more 4x6 Cyprus and are in the process of putting in drop down headers to better support the rafters between the piles. 

I do road construction by trade and am a little bit wanting in the carpentry experience department so I really appreciate the help. 

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## Harry Chickpea

I hate to mention it, but you do know you that by installing them flat instead of upright you cut their resistance to bending by about half? You may have problems with snow load if you get a heavy wet snowstorm. Consider a standing seam metal roof that you can wax before winter to allow for easy snow removal.


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## Abandoned Barns

Oh we're in the southern part of South Carolina, so we only see snow once every 3 or 4 years. It's usually less than an inch and is already gone by supper (not that it prevents the whole state from going into full on "it's the end of the world" mode). So I'm not as worked about the snow as I am about tropical storm Karen which is supposed to be looming around here somewhere. 

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## jwal10

What I don't see, are any tie joists from wall to wall to keep the walls from spreading, hope this is not what you are seeing....James


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## Abandoned Barns

Rafter joists are next, but my question is this; do they (joists) need to be between the actual rafters or can be from plate to plate? 

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## Abandoned Barns

Sorry, duplicate post.


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## Abandoned Barns

Sorry, duplicate post.


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## haypoint

Since 4 x 6 rafters are stronger when set upright, not laid down as you have, why did you elect to lay them down?


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## Abandoned Barns

I didn't. The carpenter we hired did. We've had a couple of problem like that now, but there's no going back w/o taking off the roof. 

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## jwal10

They need tied to the plate to keep them from spreading, on top or ?, just tie it in well. Now do they need to be tied together like trusses? Depends on if rafters are strong enough to not sag between the plate and peak. Trussing makes a rafter very strong....James


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## farmgal

Abandoned Barns said:


> I didn't. The carpenter we hired did. We've had a couple of problem like that now, but there's no going back w/o taking off the roof.
> 
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I would make him redo it all. there is absolutely no strength when laid flat. And they are too far apart for my liking. He isnt a carpenter. 

there is so much information on the net, I m surprised more research wasnt done before this went forward. 
[ame]http://www.youtube.com/watch?v=qOKHH1CzwSM[/ame]

My home is set up as ridge beam set up. No collar ties needed.


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## jwal10

How wide is the building? No ceiling, just the roof underlayment? Trussing ties Ridge beams need to be big timbers to hold the weight to keep walls from spreading and the roof from developing a sag....James


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## BarbadosSheep

I am not sure I am seeing it right, but in the bottom right corner of the photo, it looks like those roof rafters are sitting on a single 2x4? If I am seeing that right, that is going to be big problems.


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## Abandoned Barns

The porch deck itself is 18' wide. 

The rafters are currently set on top of a 2x4, however this week end there will be 4x6 put up underneath them like drop down headers between the piles.

I have no idea why he thought to do it that way rather than to use the 4x6 as the top and cut bird mouths into the rafters, but I hate it. 


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## wharton

Are you saying that you have these rafters, laid flat, at 3' O.C spanning 18' ? If so, you better find some help and gently remove everything before it ends up on your head!


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## Harry Chickpea

Wharton, the more I think about this, the more I agree and the more I get angry. There are times that I try to be polite and not come off as overbearing know-it-all and let people do what they will, and I often regret it. This is one of those times.

My opinion of that "job", spoken in the vernacular, is unprintable. 4" cypress is better than 2" pine, but it is STILL totally unacceptable. _No way_ would I have accepted it. "deck" wouldn't refer to the roof substrate, if you catch my drift.


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## BarbadosSheep

OK I gotta be a little blunt here. I am really shocked that your "builder" put the entire weight of that roof on top of a single 2x4 band. And now that it's starting to sag, you are going back and putting in some structure to hold it up. You went about this whole thing totallly backwards. You build the supports FIRST, then load it up. And now you are spanning 18' with boards that were installed the weakest way possible. In all honesty, you have no business building anything without understanding the principles of construction first. This porch roof could all just suddenly collapse some day. Tear it off and do it right while you still can. And don't let that so-called builder do it because he has no clue how to build anything. Dang....I would be SOOOO mad if he messed my porch up that bad.


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## ErinP

I keep looking at this thinking, "You're paying this guy _money_?!?!"

I mean, if we're going to have these kinds of screw-ups, I want to be making them myself for free.


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## farmgal

Im sorry if I came off a bit harsh, just upsetting that people pretend they know what they are doing at the home owners expense. It is your friend so it hard to get mad. Maybe, if its just a porch roof, you can just build a strong frame structure underneath, enough to keep the sag out.


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## RWDitto

He was probably low bidder, and the price was right....(When you live and learn, it is called experience).


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## KMA1

I will just put my 2 cents in here to say that I agree that this mess needs to be taken down and rebuilt. But not by the same person doing the building this time. Set the rafters upright. Personally in my log house my rafters are 4x8 and are spaced at 3.5 feet but my ceiling/decking is 2X6 tounge and groove. I could have gone to well over 4 feet spacing with the 2x6 t&G, but chose not to. In your case, the controlling factor is your use of what appears to be 1x8 rough sawn cypress, which may not be dry, resulting on warping. I would recommend 16 inch 0n center for your rafters as log as you use 1x decking on the roof. It is the only way you will a straight roof. With 6 inch log walls, I had no problems with supporting the weight and went with collar beams on several rafters pairs to keep the walls from spreading at the top. For your application, I would recommend at a minimum double 2x4 on top of the wall studs and the rafters should rest squarely on top of the studs. Then you will need a ceiling joist attached to the rafter and top plate by each rafter.

Good Luck!


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