Project: 3m by 6m weekend house, roof 3m high, walls 20cm insulation.
Question: I want build it from lighter/thinner materials, and i want to calculate from how thick materials i can build this I Joist (Picture One) So it would be same strength as 200mm by 50mm timber stud. I Joist will be 3m high.
Is there way to calculate thickness of materials for OSB and four Timber studs and how much load it can handle.
This is a bad idea to try and build your own I joists. Often the building codes will defer to the manufacturers specifications for engineered materials like I joists, engineered beams and also engineered OSB board. This is done because every manufacturer is different and because these manufacturers generally have actual accredited engineers that are certified and vetted who test these things in a methodical and proper way.
A small shed, on a residential property, is still considered a seperate structure, and as such is subject to your municipalities building codes, zoning requirements, by-laws and building permits. A review of your plan or an inspection likely will not pass and code enforcement may require you to tear down the structure if they feel it is unsafe. Inability to comply with code enforcement can result in loss of your occupancy permit for the residence.
Code aside, I think even using engineered I joists for studs wouldn't be the best idea. While I joists are okay for hanging drywall on a ceiling, a wall tends to have a lot more nails, screws and anchors run into it for everything from pictures, TV's hanging on lags, etc... With drywall, the screws will be run into the sides of the I joist where they will not damage the OSB in the middle. Running a nail or screw into the middle of an I joist greatly damages the integrity of the joist, and there would always be the possibility that somebody would attempt this and damage the stud. For a shed I am thinking about possibly trying to hang pegboard on the wall as an example.
Furthermore I can't even imagine how one can safely frame for a window or door with I joists. What is the proper way to nail the jack and king stud together? What if the wall is load bearing? Engineered I joists are tested when they are laid out on a span, not supporting load vertically.
Just use dimensional lumber, or purchase pre fabricated engineered I joists for supporting the load on a floor per the manufacturers specifications.
I am not familiar with metric tables or codes in the UK, however there are lots of free online span/size reference tables for timber/type of wood, LAMS, and fabricated I-beams. I do urge caution if you are considering making your own I-beams. Fabricated beams have to meet specific standards for the type of woods, glues and fasteners. There are often made with a process of epoxies, pressure and metal inserts. We never try to fabricate our own beams for joists or trusses. I guess the application would be an important factor as to whether self made beams would be safe and strong enough.
If I understand correctly, you are trying to fill i-joist bays with insulation. If that's so, then you should do a simple 2x4 stick frame 24" OC (this will be your structure), sheathe with 1/2" (or 5/8) plywood, air barrier, then on the outside attach your i-joists vertically to be filled with insulation. Your joist will then be similar to a larsen truss (google it).
If you are dead set on using your trusses as such, then you should replace the two 2x4 on the bottom with a single piece (2x6) perpendicular to the OSB/plywood and with a cutout similar to the commercial i-joists.
Take a look here at this Building Science article for an example similar to what you're suggesting. In this case, the 2x4 interior wall is the load bearing structure. The 2x3 and plywood/OSB joiners are only in place to hold the insulation.
I am not seeing these caveats at all. There is a Canadian company that makes a product called a T-Stud which consist of two 2x3's and dowels. If this can be done to replace a 2x6 and is four times stronger I don't see why a I-Joist system couldn't be used to build a stud the same way without the complication of drilling and doweling all these holes for the dowel rods.
Trus-Joist Corporation has an informative .pdf that addresses some of these problems. It's here: www.woodbywy.com/document/tb-821/ (I found this link by Googling the phrase 'I-joists as wall studs'.) One of the main problems I noticed in the document is securely attaching the studs to the floor. What they describe is to add stiffeners to the OSB web at the bottom end, then use metal connectors to attach that combination to the floor. If I were doing your project, I'd have no problem doing that, but for a commercial builder, it's some extra materials expense, and quite a lot of extra labor. So I guess builders who are concerned -- as you and I are -- with decreasing the amount of timber used in building, while obtaining the most effective wall insulation, will want to do a cost trade-off between the extra cost of the structure, and the energy cost savings over its lifetime.
When my wife and I built our straw-bale house in southern Oregon, we used conventional 8-inch stud construction for the gables, insulating them with 8" R-30 fiberglass batts. We love the house, which took us 2 years to build.
Hope this has been some help -- Jerry Brown
I have used TJI's as studs in a commercial building supporting 60' trusses. I like the tiny 'I' beam profile that reduces thermal bridging and substantially increases the overall performance of the wall. A TJI is designed to efficiently hold tremendous loads in a horizontal plane: Forces are forces and horizontal or vertical will make little difference. I use 7/16" OSB for the exterior wall and prefer to load the exterior edge of the wall. I used a structural engineer with a sense of humor but It is a highly efficient system. (I'm an Architect in PA)
