Following on my previous thread, I am wondering whether my project will come to fruition:
I have a flat roof with 7" x 2" joists at 16" c/c spanning 12ft with no intermediate support. They appear to have two layers of Strawboard (Stramit?) which are then finished in felt.
The project is/was to build access to this roof for a roof garden, so putting down decking over this area using 3" x 2" on edge with the decking screwed to them. The 3" x 2" would be down the slight slope, i.e. in line with the roof joists. (Would this count towards load-spreading, perhaps?)
It seems from the Building Regs in the table for "Maximum clear span of flat roof joists; Access not limited to the purpose of cleaning and maintenance" that the permitted dead load excluding the self weight of the joist is "Not more than 0.5 kN/m2".
If the Stramit boards have a density of 380kg/m3 then at 4" thickness I make that a loading of 38kg/m2 which only leaves around 12.6kg/m2 for imposed load.
Am I reading the situation correctly? It seems that without extra support mid-joist I would not get Building Control permission for what I want. Unfortunately, due to the location an rsj could not be inserted without removing the roof!
Any bright ideas out there?
I have a flat roof with 7" x 2" joists at 16" c/c spanning 12ft with no intermediate support. They appear to have two layers of Strawboard (Stramit?) which are then finished in felt.
The project is/was to build access to this roof for a roof garden, so putting down decking over this area using 3" x 2" on edge with the decking screwed to them. The 3" x 2" would be down the slight slope, i.e. in line with the roof joists. (Would this count towards load-spreading, perhaps?)
It seems from the Building Regs in the table for "Maximum clear span of flat roof joists; Access not limited to the purpose of cleaning and maintenance" that the permitted dead load excluding the self weight of the joist is "Not more than 0.5 kN/m2".
If the Stramit boards have a density of 380kg/m3 then at 4" thickness I make that a loading of 38kg/m2 which only leaves around 12.6kg/m2 for imposed load.
Am I reading the situation correctly? It seems that without extra support mid-joist I would not get Building Control permission for what I want. Unfortunately, due to the location an rsj could not be inserted without removing the roof!
Any bright ideas out there?
