Hi I am intending to lay some flooring in our loft, as I am fed up with hopping from joist to joist when putting things in there for storage (I know, if I threw them away there'd be no need to go up there but ...).
It's a 1930's house with joists 100 mm x 50 mm, about 4.2 metres long at 350 mm centres, lath & plaster ceilings. I don't think these will strong enough to take the load without deflecting enough to crack the ceiling underneath, even though the local Council (Building Regs office) say they are OK for the static load. So I want to strengthen the joists before laying the flooring (V313 chipboard T&G four sides). However I am not sure how to do it. I initially thought about screwing some 50 mm x 50 mm on top of the joists, then thought I should make it 50 mm x 75 mm (or even 50 mm x 100 mm) so that I can have a nice depth to upgrade the insulation. But I'll need some really long screws to get through 100 mm and bite into the joist underneath, and will probably wear out the cordless drill doing it! Anyone able to suggest some alternatives?
Also - before putting starting I intend to coat the existing joists with wood preservative, just in case condensation under the floor becomes a problem. However, I am worried that any preservative which gets on to the plaster will cause staining underneath. Anyone with any experience of doing this? The new timbers will be pre-treated.
Many thanks
LS