Help with hanging joists in loft

9 Nov 2010
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United Kingdom
I have a loft conversion that was done eons ago and the upshot is that the joists need to be larger and supported adequatly.

I have what I think is called a cut roof so the rafters hang over beams down to the outside wall of the house and the joists for the loft are nailed to the rafters about three or so feet up each rafter from the outside wall and then span to an interior supporting wall. Currently, in the loft at each side of the house is a small false wall that is attached to one of the roof supporting beams (which is in effect supporting the loft joists). The joists are at these points 425mm below the bottom of these beams.

The idea that I have is to put in new larger joists adjacent to the current joists and suspend these from the roof beams. Is there a method of doing this? Does anyone have a better idea?
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shen i did mine buildingregs wanted 8X3 Joistsputting in , adjacent to ceiling joists and with a gap of 25mm between bottom of new and ceiling( to prevent ceiling bounce downstairs. these rested on the wallplate on the inner wall of house wall and rested on supporting walls halfway acroos loft. i believe but dont quote me, that you cannot suspend them of the roof. as this may want to in effect push your house walls away from each other as roof takes the strain.
You can't generally hang floors off rafters especially in loft conversions, if you want to do this by the book youy'll need to employ a structural engineer anyway! Often rafters in older houses barely have the strength to support the roof finish let alone hanging a floor off them.
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