Truss Design

[lojim]

Let me first say 'yes I know I could take some plans to an engineer to get them certified.' However, I'm attempting to keep costs down as much as possible AND it's NOT required for what I plan to build. I'm really looking for input from those that know construction.

So I'm in need of some help. I want to see if this is a good structure for a truss or not. If it matters, I am in the Poconos of PA. I have compared many different designs of trusses and combined them to make something that hopefully will work for me. First, the specs:

2x8x10 for 'lower' roof
2x8x12 for 'upper' roof
2x6x~6 for vertical 'hip roof' support
2x4x~5 for diagonal roof support
2x8 for vertical on lower section and overhang
2x8 for truss support and span (3 2x8x12 - 2 **** joints and 1 with 6' overlap on both boards which is not pictured)
Overall roof height is 14' with 24' span between posts (the black boxes at the bottom of the picture).That truss will span between both vertical 'hip roof' supports.
All joints will be reinforced with 1/2" plywood plates that are glued and screwed.

12' wide 'loft' will be left for storage that may or not be used that often.

Barns are constructed 4' on center for these style roofs - I figured that would work fine for my needs also or should they be closer? If I go with this design I would use 2x4 perlins 4' on center to attach metal roofing.

Sorry if my terminology is incorrect - it all makes sense to me.

Anyone know structure and will this work or how should it be modified?

 

[bczygan]

Let me first say 'yes I know I could take some plans to an engineer to get them certified.' However, I'm attempting to keep costs down as much as possible AND it's NOT required for what I plan to build. I'm really looking for input from those that know construction.

So I'm in need of some help. I want to see if this is a good structure for a truss or not. If it matters, I am in the Poconos of PA. I have compared many different designs of trusses and combined them to make something that hopefully will work for me. First, the specs:

2x8x10 for 'lower' roof
2x8x12 for 'upper' roof
2x6x~6 for vertical 'hip roof' support
2x4x~5 for diagonal roof support
2x8 for vertical on lower section and overhang
2x8 for truss support and span (3 2x8x12 - 2 **** joints and 1 with 6' overlap on both boards which is not pictured)
Overall roof height is 14' with 24' span between posts (the black boxes at the bottom of the picture).That truss will span between both vertical 'hip roof' supports.
All joints will be reinforced with 1/2" plywood plates that are glued and screwed.

12' wide 'loft' will be left for storage that may or not be used that often.

Barns are constructed 4' on center for these style roofs - I figured that would work fine for my needs also or should they be closer? If I go with this design I would use 2x4 perlins 4' on center to attach metal roofing.

Sorry if my terminology is incorrect - it all makes sense to me.

Anyone know structure and will this work or how should it be modified?

You have a modified gambrel roof there. It is one of the trickiest roof designs to engineer correctly. Do you know the zoning and building code requirements for snow and wind loads in the jurisdiction you are building in? Do you know how to engineer the connections for the members in that truss and to determine the species and grade of each component?......no? Do you even know if your jurisdiction requires engineered and sealed drawings for trusses? Did you know most truss companies make engineering calcs part of the truss package?

Bill
Builder and designer

 

[bgarrett]

I recommend a collar tie
Do you see how your design could split in two pieces right down the middle?
A tie is needed

 

[lojim]

You have a modified gambrel roof there. It is one of the trickiest roof designs to engineer correctly. Do you know the zoning and building code requirements for snow and wind loads in the jurisdiction you are building in? Do you know how to engineer the connections for the members in that truss and to determine the species and grade of each component?......no? Do you even know if your jurisdiction requires engineered and sealed drawings for trusses? Did you know most truss companies make engineering calcs part of the truss package?

Bill
Builder and designer

I know that any building under 1000 square feet does not require any form of building permit or inspection. I could build it out of stacked bails of hay and the township would not care. If I build it 1001 square feet or larger there are many many many requirements and inspections which is what I am hoping to avoid. That being said - I want to build a safe building as cost effective as possible.

I also did get a quote for trusses to be delivered. 11 trusses total with the same footprint as the one I laid out. What I am unsure of is the exact design because that is not 'released' from any of the companies I have checked with unless I buy their trusses. The CHEAPEST I have been quoted has been $2600 for those 11 trusses - which I figured is around $900 in material.


bgarrett - thanks for the suggestion for the collar tie. I will be sure to add that.

 

[nate379]

My Dad's shop which he built in 1990 has a gambrel roof see picture for how he did it. It's all 2x4 construction though he put them 16" O.C. I would have done 2x6 for the top chord and standard 24 OC instead.

Best thing to do is head to the lumber yard and have them draw you the plans. I did that for my shed and they didn't charge me anything, though I was ready to pay $100 or whatever.

5/8" ply on both sides and you should nail. Screws are not approved for structural use in just about all areas (snap off instead of bending)

What is the size of your shed, 12x20?

 

[Falcon67]

bgarrett - thanks for the suggestion for the collar tie. I will be sure to add that.

You best do some research on collar ties and their effect on rafter loading before you start sticking boards in there. That's why you pay for engineering. I have a design that moves the joist up 1 foot and makes it a glorified collar tie - This increases loading on the rafter depending on the roof load, plus it puts more pressure on the walls. Have no idea how that would change the member loading on your layout.

 

[lojim]

My problem is height.

Zoning says that the means of the roof can not exceed 15'. The township defines the 'means' as the distance from the top of the sidewall to the top of the roof divided by 2. Basically - the shorter my sidewall the taller my building. The goal is to have 12' high doors (for a camper) so I need 13' of ceiling height. With 13' high walls I would only have 4' of height for a 24' wide roof. However, by lowering the sidewall height and going with a gambrel I can keep the 12' door height but gain more height to the structure overall. 8' walls would give me a roof means of 7' above that. Overall height would be around 22'.

 

[srmofo]

You can buy truss designs from some builders, then construct them yourself. I can understand the need to save money but the integrity of the building needs to be safe.

 

[nate379]

That means thing can't be right? Top of sidewall to top of peak devided by 2 has to be 15 or less... so you can have a 30ft tall truss??

 

[lojim]

Yes. If I build an A frame with no sidewalls I can go 30' tall. I confirmed that with the township when I was asking about zoning regulations.

 

[GeorgiaHybrid]

That being said - I want to build a safe building as cost effective as possible. .................................

The CHEAPEST I have been quoted has been $2600 for those 11 trusses - which I figured is around $900 in material.

To get a safe building, have it engineered. You are not paying just for the materail, you are also paying for the knowledge, time and skill of an engineer. He is putting his license (and your life) on the line designing a truss. You can also check with a structural engineer in your area and have them design your trusses. You can then buy the material and build them yourself.

 

[rwhite692]

To get a safe building, have it engineered. You are not paying just for the materail, you are also paying for the knowledge, time and skill of an engineer. He is putting his license (and your life) on the line designing a truss. You can also check with a structural engineer in your area and have them design your trusses. You can then buy the material and build them yourself.

^^^^Agree 100%. In PA, you also have snow load considerations.

 

[nate379]

I would for sure get drawings done. I didn't see the 4ft OC, was thinking this was for a small shed.

It's worth paying a bit for it even just to be safe, and not to mention not have it come down after the first winter!

 

[CraigFL]

Trusses are designed by engineers because they are a very special structural member. In truss design you need to be sure all loads are transferred to the elements as tension or compression through the connections. This makes them VERY efficient load handling devices which is why they use the minimum of material and therefore are very light. Just because they are made of small members and have some x bracing doen't make them act like a truss.

Your inital drawing doesn't have these characteristics because some of the members are acting as beams where bending will be involved. Beams design requires depth to add strength which means larger sizes.

 

[shawnspeed]

you might want to spend some time looking around this site.. It's our tax dollars at work..so it is free..
http://www.ag.ndsu.edu/extension-aben/building plans/construction

 

[Stuart in MN]

Yes, the trusses need to be engineered, but the first thing to do is to talk to the local lumber yard - they buy their trusses from a local truss plant, and chances are that truss plant has a number of standard designs available. They may have something already engineered that will work for you.

 

[Red05GT]

The problem with the loft and the fact you are considering placing the trusses 4' O.C.
is, you will pack more stuff up there than you ever thought possible, and overload your
" in house" engineering. The result will not only be a sagging loft, but also a sagging roof
line, bowed walls, and possibly a collapsing structure.

 

[wfopete]

Or this one:

http://www.barnplans.com/index.html

 

[demographic]

As someone has already mentioned a few of your US agricultural sites give out free plans for this sort of thing HERE'S one site.
More HERE and HERE

 

[nate379]

That is true! The first year my Dad had his shop up he had to go back and add a steel beam across the ceiling because the floor had come done about 2" in the middle. He used 2x12s 12" OC. I want to say 22ft span, but I can't remember for sure.

The problem with the loft and the fact you are considering placing the trusses 4' O.C.
is, you will pack more stuff up there than you ever thought possible, and overload your
" in house" engineering. The result will not only be a sagging loft, but also a sagging roof
line, bowed walls, and possibly a collapsing structure.

 

[kbs2244]

These are free plans from N D State U

http://www.public.iastate.edu/~mwps_dis/mwps_web/tr_plans.html

 

[Racecarl]

you might want to spend some time looking around this site.. It's our tax dollars at work..so it is free..
http://www.ag.ndsu.edu/extension-aben/building plans/construction

These are the plans I used to build my gambrel roof rafters. The building inspector liked them and they are solid. I recommend these highly...

 

[Red05GT]

The elevated bottom chord in your drawing is the thing that would concern me the most.
What about using TJIs for the ceiling joist, sheath the loft floor deck, and then frame the
roof.

 

[bobbleheadhillbilly]

$2600 for 11 trusses of that nature is not too a bad price. Was this a quote from a lumber yard or directly from the manufacturer? I've seen cases where a lumber yard will put a 50% mark up on trusses when their only involvement was shuffling papers. What type of lumber did your base your $900 material price on? A couple things to consider in the price difference aside from the engineering. Truss plants will be using MSR lumber vs. the stud and No.2 they typically sell at places like Lowes or Home Depot. Steel gang nail plates will definitely cost more than plywood gussets, but offer greater holding power in a smaller/lighter package. Depending on your distance from the truss plant, $400 to $600 of that price could be the cost of delivery (fuel, oversize load permits). Personally, I'd try to deal directly with the manufacturer if at all possible, let them know in advance of site conditions(narrow approach or obstructions), and be polite to the truck driver. It's not as easy as some drivers make it look.
As far as the design goes I'd want to have the bottom chord splice positioned so that it is not directly under the peak joint. I'd be nervous about using it for any kind of storage considering the ends of the main bottom chord are not resting directly on a wall and the main means of joining chord members are gussets. Then add your snow load to the equation. If ceiling height is a concern, maybe consider a room-in-attic truss with a tray/coffer bottom chord. That way more of the load from the room is transferred to the bearing points.

 

[Falcon67]

you might want to spend some time looking around this site.. It's our tax dollars at work..so it is free..
http://www.ag.ndsu.edu/extension-aben/building plans/construction

Similar/same as the stuff at Iowa State. (MWPS). I bought the MWPS book, it's got lots of designs in it with full details and a wide span of loading and OC spacing.