Beagle Appreciator wrote:My assumption is that at this scale outward horizontal forces should not be that large also considering its only 9 and a half feet between the front and back wall. Do you have any calculations or tables that show how much force would be imparted on the walls outwardly? I might add a tension cable between the edge of the second/higher step area to the top of the wall if during the build or otherwise concerns in that direction materialize. 5 degrees of slope is not necessarily enough to shed water and even higher angles is the roof is dusty or dirty and I just do not wanna deal with flat roofs.
https://www.mathscinotes.com/2010/11/th ... llar-ties/You can calculate the net tension at the rafter tie line (top of walls) using basic statics. Your model does not, at this time, offer any structural member to take up tension loads in the horizontal projection at the midspan rafters. The doorway rafter is well trussed and the opening into the over cab area is supported by columns in the wall structure, once sheathed would provide tension resistance at those two locations. You can approach supporting the midspans in a variety of ways. You can add relatively small plywood or metal gussets at the roof peak that will act as tension members as a collar tie would. You can use upper cabinetry at the wall to rafter interface to act as a combination of purlins and chords in tension along the diagonal between the wall and the inboard rafter tie point of the cabinetry above the doors/openings at each rafter. All loads can be calculated, but you must offer tension resistance in the horizontal projection of the peaked roof or it will bow outward with any, and all, loadings.
For the bed over cab area, the information you are looking for is how to create the appropriate free body diagram to calculate the static forces for a cantilever, or overhang. This is not simple, but it is straight forward, albeit time consuming. You calculate the load of tributory area of the floor, in your drawing example the joists/beams send the floor load to the front edge and the interface. As your solid wood members by themselves are not large enough to contribute meaningful load resistance to the moments that will likely be exerted here, you'll need to distribute the loads through other means of making a trussed beam, sandwich core construction of horizontal decking uses stressed skins to take the loads as an I-beam would and is applicable here, much like in boats that use clear spans with thin section deck spans, they normally use a structural foam and FRP sandwich with the strength required to prevent excess deflection and resulting dynamic loads. Your steel cables at the edges produce a reaction in the angled wall section behind the cab, but those walls are out pf plane with the cable vector, and so there is also a twisting force at the end tie point, very tricky. The cables in the roof terminate at a rafter midspan without anything to support the reaction other than what little the beam profile can withstand, which is not much - this load would rely nearly entirely on skin to support as drawn.
Glen-L uses the side walls of the cabover with plywood to act as the two main stressed members supporting the entire cabover structurally, with the floor section sending the loads side-to-side, rather than front-to-rear as yours does. Some images here:
https://www.glen-l.com/cabover-camper-framing/ Your build has no strictly vertical wall segments that project back over the truck bed portion, that would normally act as a tall, engineered beam to take the bending moments produced. Yours will be a very, very difficult design to distribute loads by comparison as it is currently drawn.
Learn enough about free body diagrams and how to make them so you can at least understand the load paths in your build, this will help you locate the force concentrations - then you can calculate the static loads, bending moments, reaction force at each interface, or in each plane.