Shop framing question

[ejb]

Hi guys.

Looking for a answer to a quick framing question:

I have a 32x26 one story shop/out building with an almost flat roof (2/12 pitch).

I want to change the roof to a regular pitched roof like 8/12 and add some storage space as a second floor.

There are no internal posts currently and I'd prefer not to add any, so my plan is to remove the old roof which will leave essentially a 26x32 "box" with no top and then purchase some 26' long IJoists that are rated to cover that span and cover them with 3/4 TG plywood which will become the floor of the 2nd floor.

For the new roof I figure conventional framing, 16"OC joists 2x10's or whatever is called for....

Question is, by my rough estimating in order to put an 8/12 pitch over a 26' span it means each side will end up being almost 17' long. Seems to me, with a 17' span on the rafters, a knee-wall(or other support) will be called for...so, can a knee wall put put on a framed floor if there is no support directly under that knee wall? in other words, the knee wall will transfer some of the weight of the roof to the floor joists, but not directly to earth...is that common? safe? likely to be code compliant?

Thanks all!

(Yes, I'll ultimately get a building permit but need to design my solution first)

 

[randy41]

you could use ijoists for your rafters too maybe eliminating a bearing kneewall.

 

[Erik_in_Hoyt]

8/12 pitch won't leave you much standing room up there.
26'' clear span will take a pretty thick I-joist for the floor. (maybe a 16" deep one?)
10" I-joist for the rafters should work well, though, instead of conventional lumber -- may cost less than using 2 by lumber - and you wouldn't need a knee wall to support it, unless you get frightful snow/wind loads in your area.

If you build a short wall (3'-4') above the floor joists, you could flatten that roof to a 4/12 or 6/12 pitch and make it a lot easier to work on while roofing -- or doing future repairs, while expanding your usable floor space. (4/12 with 4' sidewall would give you the same overall peak height as your proposed 8/12, as well)

good luck - and I look forward to updates as it gets built!

 

[6sunset6]

I don't think you can put a knee wall on an unsupported floor. I like the idea of short side walls and a lower pitch roof. Or trusses with a big square hole in the middle.

 

[WVBill]

I'm building a 24' x 24' workshop building.

Clear span on the first floor with a 12/12 pitch roof to provide space in the "attic" for storage, etc.

Original plan was to use 14" TJI360 wood I joists 16" OC for the ceiling/second floor joists. This would give a 40 psf LL at L/480 for a good solid floor. Then I was going to use 2X10 16" OC for the rafters.
I would use a non-structural 4' high knee wall down each side to form an attic room 16' x 24'

I priced out the TJIs plus the 2X10s at around $2750 delivered.

Then I contacted a Truss company and gave them my specs. They came up with trusses made up of a 2x10 bottom chord, 2x6 top chord and 2x4 structural webs forming the side "knee walls" - spaced at 24" OC giving the same 40psf LL at L/480 for the 14' 3" x 24' attic floor. These priced out at around $2000 delivered and are going to save one heck of a lot of work building the roof rafters!

Check out trusses. Don't go to one of the box stores/lumber yards - go directly to a truss company and save the markup.

WVBill

 

[ejb]

Did you get a 12/12 pitch on your trusses? If so, did they come in more than one piece? I vaguely remember being told that the steep pitch trusses aren't available because they are too hard to truck because of the size...I prefer steep roof's.

Do you have pictures you can post of yours going up so I can picture it better?

 

[MrJimi]

Here are my wooden I beams, 24 feet long for second floor like your gonna be doing

 

[WVBill]

ejb

Yes, they're two-part trusses. There's about a 2' "piggyback truss" that forms the peak of each one. You're right, steep-pitch trusses need to come in two parts so they can be trucked. That issue didn't phase the truss company I went with at all.

They're being delivered next Friday (July 27) hope to have them going up that weekend or the next. I'll post pictures.

What are you going to use for roofing? I'm going with metal ribbed roofing same as I used on my barn. Real easy to install

Bill

 

[schmism]

I don't think you can put a knee wall on an unsupported floor. I like the idea of short side walls and a lower pitch roof. Or trusses with a big square hole in the middle.

you can, the floor just has to be designed to take any load from that wall.

NDS allows you to put non-bearing partion walls anywere on a floor with 40plf live load design with no addtional analysis required.

im looking at a 26' attic truss with no overhang (can be added in the feild) with a 10/12 pitch 2x10 over 2x8 2/ OC with proper load that works with #2 SP on my computer at this moment.

shipping height of 11-7-11, room dimention of 8x14

Most truss fabracators can build up to 12' on there tables easly. The largest table we sell is a 14' table but those are rare.

Most large span trusses are indead piggybacked. Although im offten called upon to supply a feild spliced truss which is shipped in 2 halfs and assembled in the feild with either a feild press or a connection called out by an engineer that consists of plywood and scabs.

 

[ejb]

ejb


What are you going to use for roofing? I'm going with metal ribbed roofing same as I used on my barn. Real easy to install

Bill

No final decision on the roofing, but leaning towards metal. I've installed a bit in the past and its pretty easy and quick. Second choice would be asphalt.

Look forward to the pictures.

 

[RPK]

Ejb;

I assume your building is 26 ft wide? If so, 2x8 rafters 16" .o.c with 2x6 collar ties should work fine. Rafter sizing is based on the "span" If a building with a gable style roof is 26 ft wide the "rafter span" is 13 ft. This is what you would be referring to when using rafter span tables in building code books. Depending on the snow load for your area 2x8's should be o.k

You may want to consider engineered " attic storage trusses". They usually have a 2x6 bottom chord. They can be installed 24" o.c. and can be designed to support a 40lb/sq ft load. Which is the same rating as a house floor.

RPK

 

[EddieWalker]

I have a 32x26 one story shop/out building with an almost flat roof (2/12 pitch).

I want to change the roof to a regular pitched roof like 8/12 and add some storage space as a second floor.

There are no internal posts currently and I'd prefer not to add any, so my plan is to remove the old roof which will leave essentially a 26x32 "box" with no top and then purchase some 26' long IJoists that are rated to cover that span and cover them with 3/4 TG plywood which will become the floor of the 2nd floor.

For the new roof I figure conventional framing, 16"OC joists 2x10's or whatever is called for....

Question is, by my rough estimating in order to put an 8/12 pitch over a 26' span it means each side will end up being almost 17' long. Seems to me, with a 17' span on the rafters, a knee-wall(or other support) will be called for...so, can a knee wall put put on a framed floor if there is no support directly under that knee wall? in other words, the knee wall will transfer some of the weight of the roof to the floor joists, but not directly to earth...is that common? safe? likely to be code compliant?

Thanks all!

(Yes, I'll ultimately get a building permit but need to design my solution first)

Your plan is pretty good and should work without any complicated engineering.

Just to be sure, are your walls stick build with studs on 16 inch centers with double top plates. Do you have any windows or walls on the side walls, and do they have proper sized headers? If so, this is good. If you have pole construction, then that will need some engineering to know what the poles will support based on there size and spacing. Then the purlines need to be sized according to the load you will be putting on them. This is beyond my skills with what information you've given.

The I joists will rest on top of the walls and tie the walls together. They will suport your second story loads and become the bottom chords of your new roof. This is extreme over build, but for your purposes, an ideal way to do this.

The 8:12 pitch will give you an inside roof height at the peak well over 8 feet, so that's plenty for storage. Going with a steeper pitch will give you more height, but I can't imagine why that would be important.

You'll need 16 foot long 2x6's for your rafters and cut them down to size.

You mention a hip wall, but I wasn't clear on where you planned on placing this hip wall. My first thought was above the exterior walls to raise the entire roof. This is possible, but tying it all together is VERY involved and would be the expensive way to go. VERY EXPENSIVE.

Placing your rafter tails above the exterior walls will be the easiest, cheapest and strongest way to go. Just tie them into the I joists and exterior walls with whatever overhang that you desire. Then build the hip wall at the one third point of your rafters.

With a 26 foot span, your half way point is at 13 feet, so your hip wall should be around 4 to 4 1/2 feet in from the exterior walls. This will give your rafters the support of bracing that a truss has because of the strength of your I joists. You will literally be resting the weight of the rafters on the I joists.

Eddie