Steve wrote:
Ian G wrote:
18mm ply glued and screwed to the top of the joists (instead of
unglued chipboard) , forming a T beam was a solution proposed by a
structural engineer and adopted by me when I did a loft conversion
some years ago. We didn't put a piano up there, but the purchasers of
the house did install a water bed and there have been no adverse
reports from neighbours whom I have remained in contact with. The
increase in strength over the unglued floor was impressive, confirming
in practice what the Moment of Inertia calculations indicated. We
were able to jump up and down on the floor and detect very little spring.

Our joists were 6x2 inches, at 16inch spacing and spanned 12 feet, to
give you an idea of our configuration. The resulting stiffness was, if
I remember correctly better than what would have been achieved with
recommended joist depth for that span. Sorry I can't remember if 8
inch joists would have been sufficient for that span. I remember that
the addition of the ply to form a T beam gave lots more improvement
over doubling up the beams. Where our span increased to 14 ft . the
solution was to double up on the 6x2 beams

I'll try to find my own calculations which I did to "prove to myself"
the efficacy of the scheme, and perhaps substitute your 4x2 beams.

regards
Ian

Thanks very much Ian, that is very encouraging.

If you do come across the calculations, I would be very interested indeed.

My email address is not valid so try g8izy_ @ _ blueyonder.co.uk,
obviously minus the underscores.

Thanks again

Steve

Reading your post again, I wonder did you put the ply on top of the
joists to form a T beam or did you sandwich them between joists as I
proposed to form a T beam.

Just that I cannot afford the extra floor height.

Steve