# Overspanned Roof Joist?



## paul81 (Nov 20, 2013)

I have a two-car garage measuring 20'x20' with cinderblock walls and a gable-end roof. The roof joists are 2x10s 16"OC, split perpendicular from a triple-2x10 center beam spanning the whole 20' with no support column. There's a half inch or more of plywood covering the joists with a staircase up to this storage area. 

Looks like (d) here, but 16" joist spacing.









Isn't the support beam overloaded? Walking around in the attic area feels very solid, but I don't want to store stuff up there if it is going to collapse. This is definitely outside my experience.

As there's no trusses, the roof itself isn't being supported by these joists but it is still a long span.


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## griz (Nov 26, 2009)

You list your trade as "General".

General what? Just what exactly is your trade?

Your terminology sounds like you watch too many Saturday morning shows. 

Why is this so far out of your experience?


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## CarpenterSFO (Dec 12, 2012)

paul81 said:


> I have a two-car garage measuring 20'x20' with cinderblock walls and a gable-end roof. The roof joists are 2x10s 16"OC, split perpendicular from a triple-2x10 center beam spanning the whole 20' with no support column. There's a half inch or more of plywood covering the joists with a staircase up to this storage area.
> 
> Looks like (d) here, but 16" joist spacing.
> 
> ...


Paul, you're asking for engineering advice (is this structure strong enough?). If you look around C.T., you'll find that we don't give out engineering advice even to fellow contractors.

Often the moderators send DIYers off to DIYChatRoom.COM, but it's hard to see how it would be responsible for anyone there to give you structural advice, either.

If you have any concerns about the structure, or if you have any question in your mind about whether that space was built to be used for storage, you should hire a good contractor to help you sort it out.

As Griz says, your post marks you as an amateur.


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## fourcornerhome (Feb 19, 2008)

Your roof joists are fine...the problem is with the floor rafters.


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## CarpenterSFO (Dec 12, 2012)

fourcornerhome said:


> Your roof joists are fine...the problem is with the floor rafters.


You beat me to it!:laughing::laughing:


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## greg24k (May 19, 2007)

You have an attic with a staircase so it must be treated as Habitable attic which is served with fixed stairs per R301.5 MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS which calls for 30LB LL PSF. 30LB is the same as the requirement for the second floor bedrooms.

Therefore triple 2x10 beam supporting one floor can have a Maximum span:

6'7" if Northern Species (No. 1 and No. 2 Grades)
7'6" if its Douglas Fir or Larch (No. 1 and No. 2 Grades) 
7'11" if if its Hemlock and Fir (No. 1 and No. 2 Grades)


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## CarpenterSFO (Dec 12, 2012)

greg24k said:


> You have an attic with a staircase so it must be treated as Habitable attic which is served with fixed stairs per R301.5 MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS which calls for 30LB LL PSF. 30LB is the same as the requirement for the second floor bedrooms.
> 
> Therefore triple 2x10 beam supporting one floor can have a Maximum span:
> 
> ...


Of course it's not a legal space. If you're going to meet code, you'll put in something that will contribute to the value of the home.


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## Morning Wood (Jan 12, 2008)

Sounds like you need a whole new garage to me. You should give me a call.


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## rjconstructs (Apr 26, 2009)

It might have worked better to have gone with a minimum 2x12 16oc with no beam in the middle and no significant storage above. Engineered joists are the way to go anymore. An engineer can give you the best fix to apply here.


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## mk5065 (May 25, 2009)

fourcornerhome said:


> Your roof joists are fine...the problem is with the floor rafters.


What the heck is a floor rafter???


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## greg24k (May 19, 2007)

CarpenterSFO said:


> Of course it's not a legal space. If you're going to meet code, you'll put in something that will contribute to the value of the home.


What ever he is making there or has already in place its considered to be a Habitable Attic.

He obviously don't know s*^t what he is doing, or maybe someone did it for him and since I'm having a wonderful morning as I usually do, I gave him a min code requirement...
He can call himself lucky this thing he is building or already build it, will not cave in on him or someone else if he be smart enough and break up the span to a minimum requirement... Not to mention when I see post like this, they keep me stay sharp with the codes (That is when I'm in a good mood :laughing


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## CarpenterSFO (Dec 12, 2012)

mk5065 said:


> What the heck is a floor rafter???


Was funny; the original poster doesn't know what a roof joist is.


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## ScipioAfricanus (Sep 13, 2008)

CarpenterSFO said:


> Was funny; the original poster doesn't know what a roof joist is.



I don't know what a roof joist is either.


I think MK5065 doesn't know what irony is. :whistling

Andy.


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## Willin (Aug 20, 2012)

What I think was described is an attic floor structure, all 2x10 dimensional lumber frame, 20' total reach in two spans, two equal simple spans supported at center by a flush beam of (3) 2x10s.

Using 30 psf live and 10 psf dead as the floor load, his joists are way more than plenty, _even if spaced at 24"._

His problem, as he suspects, is the flush beam at center, the triple 2x10. It _barely_ passes if I plug in a uniform live load of only 7.5 psf and the same for dead. I use Weyerhaeuser's _Forte_ software for analysis.

So, can he walk around up there safely? Sure. A whole lot of roofs in Texas and Florida are built lighter than that, and get walked on.

Can he store anything up there? Yes, as long as he is careful. You could load the entire floor with 24 x 24-inch book cartons, and as long as you only put 30 pounds in each, you would be fine.


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## fourcornerhome (Feb 19, 2008)

mk5065 said:


> What the heck is a floor rafter???


It's the opposite of a roof joist


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## CarpenterSFO (Dec 12, 2012)

ScipioAfricanus said:


> I don't know what a roof joist is either.
> 
> 
> I think MK5065 doesn't know what irony is. :whistling
> ...


Roof joist = rafter, for some engineers. First set of plans from one of them, I called him to ask, "What the heck is an 'R.J. (Typ)'?" Maybe it's a regional thing.


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## paul81 (Nov 20, 2013)

Willin said:


> What I think was described is an attic floor structure, all 2x10 dimensional lumber frame, 20' total reach in two spans, two equal simple spans supported at center by a flush beam of (3) 2x10s.
> 
> Using 30 psf live and 10 psf dead as the floor load, his joists are way more than plenty, _even if spaced at 24"._
> 
> ...



This is exactly what I meant. 

This is my own garage on a 60yr old house, not something I built. I do small tiling, flooring, and remodeling work under a friend who is a pro. I wasn't sure what to put there. Sorry if I'm not qualified to be here, but appreciate the responses.

I'm concerned that the center beam is overloaded as it is spanning 20'. Searching various forums, the suggestions I've seen for a center beam spanning this distance are *far* larger than a triple 2x10. The code inspector didn't mention it when I bought the place nearly a decade ago, but I hadn't thought about it much until I needed a storage area.


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## hdavis (Feb 14, 2012)

Good decyphering, Willin:thumbsup:

To figure out what it will really do, you'll need to inspect that beam, and also see how much deflection and where it has occurred over the years. Span tables and calculators use a grade of lumber, and you have to verify that the way the beam was built (at least to the extent it can be observed) it should be classified as #1, #2, or whatever grade of lumber AS USED.

Not something easily done by someone who is inexperienced.


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## procrpntr (Nov 17, 2013)

Paul I am frequently asked to convert unused attic space into bedrooms, storage, hobby room,etc. The problem is helping ho understand a ceiling is not a floor.I can certainly turn it into one, but cost often rears her ugly head up, and interferes. That said, I would ask if u can locate a post practically, under the beam without over interfering with the flow of your garage.that's the easy way. The u start looking at other beam options, do have headroom in garage for new beam? Do have enough height to add more to the floor if u distorted your existing joists with I joists and added locks to the beam?is it cheaper to remove ceiling and rebuild floor? Also just for kicks find ever 7 feet is off finished floor would be in attic and then measure between this is your actual usable space. One thing is certain, if you get a permit you will need engineering.


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