Dave Page wrote:
wrote:
Lets review the options.
1. Lay new joists on old at 90 degrees This will leave you with a
very weak floor, as well as being a pain to insulate.
Hmm, why would this lead to a weak floor? I figured that laying the new
joists at 90 degrees to the old ones would spread load across the old
joists, and laying the new floorboards across the
you'd have exactly the same wood supporting as you have now, and 3" is
marginal. Spreading a roomful of load out over a room makes little
difference, it only helps with high point loads, not with total load,
deflection or rigidity.
This method has the advantage that I can space my new joists at 400mm
(the pre-cut width of the insulation roll) rather than having to deal
with the existing 350mm joist spacing, and means that I can do the loft
in fewer "strips" of insulation (three or four as opposed to a dozen).
minor in comparison to leaving yourself with a borderline floor support
structure.
Other people have commented that insulation roll is "supposed" to be
laid *across* the joists. I have to assume that this precludes flooring
the loft space,
thats how its done when theres no flooring. With flooring, the goods
themselves will trap air, if packed in cardboard boxes, and so will
insulate some more. You can roll insulation out on any unused floored
areas if you wish.
3. Add new 4x2 joists to the top of the old ones, inline, attaching
with glue and screws.
Yeah, this was my original plan, and looks like being what I'll end up
doing after all, possibly using the poly vapour barrier mentioned by
Doctor Drivel in
yes
NT