securitynewbie, unfortunately as there are structural issues when it comes to use of loft space in a mega way, it would not be a good idea that I or anyone could give advice on these public forums, what if someone else whose situation may look very similar but altogether different, and starts using this thread as a reference and starts adding timber beams to his loft to strengthen it and not knowing full well about loads spreading, beam sizes and load bearing capacities, maximum deflection allowed, dead weights, live weights, many many other factors too which even BR don't bring into consideration, things can go disasterly wrong, house insurance can become invalidated, so due to these issues a specific advice on how you can strengthen your loft floor cannot be given, though we can discuss in general what is really needed, and how some owners did theirs, possibly using proper plans and builders, and inspected by BC, its not about safety of your own family but those of neighbours, take for instant, someone took his chimney breast out, and did not support the upper stack adequately, it collapsed breaking through his bedroom floor, and also damaging his neighbor's property, luckily no one was killed but it could have been fatal.
If you PM me your email, I could email you some links and sketches and give you some general direction, but end of the day you are responsible for safety of yourself and those around you, and answerable to your insurance company, what i am doing in my loft is my responsibility, and I don't do any guess work, I always double check figures, sizes, find out more about things , ask builders, go to places where they are carrying out jobs and watch them see how they do these things, fortunately lots of my friends had their lofts converted, they asked me to come and have a look whilst work was going on, so I managed to see how steel girders are inserted, and supported, all to BR and BC standards.
we have already discussed what size joist should be, now a days 7"x2" is what is required, even though it looks overkill, but this is one way your insurance company will not be able to dispute a claim should there be a collapse, but if you used 4x2 or 6x2, then they could refuse a claim. So I hope you see my point some things on these forums cannot be taken at face value, but as a general guide.
Currently, I have laid 15mm chip boards from disused wardrobes, someone next door to me was throwing away 4 of them, I asked if I can take them, and so I made use of them as the floor boards, they serve my purpose very well, cost me nothing, and allows me to walk in gently and put stuff away, evenly distributed, I can't see any problems, as long as you use your common sense, don't put heavy duty floor boards weighing tons, and don't store very heavy items, like lead acid batteries! reams of paper or books, just light bulky household things, like your beds, they are ok, they are large and so weight is evenly distributed over a larger area, remove wheels if you can, same for cupboards and wardrobes, lay them flat, and empty. you may not even need reinforcing, and it may be just adequate as is.
But you need to measure deflection, using a piece of string held at each end of the ceiling about 10 to 15mm below, from each wall, stretch it straight, and then measure the mid point of thread to ceiling gap, after storing stuff does this gap close up? that is your deflection.
Currently another friends is looking for a builder to have his loft converted to a dormer. I will be watching that construction with an eagle eye, and take lots of pictures, and measurements)
