An engineering problem

Dear engineers,

Perhaps you would be able to help me with a structural problem that is facing one of my projects. The proposal is for a loft room in a large house with a steep high roof. The space is ideal, but the structure is not. The existing loft floor, which will have to be strengthened, is supported near the centre of the house by the brick internal walls which reach up into the loft. At the outside edge of the house the roof drops down into the rooms below and the loft floor is fixed not to the walls, which are further out, but to the rafters. So the loft floor is smaller than the floor below. Imagine a shoe box with a lid that is smaller than the box –  the lid is supported at the centre, but the edges float (or rather are fixed to the roof in the real house). I want to strengthen the floor and support new walls and loads right to the edges. there must be many houses like this. What would your recommendation be?

Yours Sincerely,

Paul Snell RIBA, Kings Heath Architect

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One comment

  1. Tim Richardson · · Reply

    The standard (pretty destructive) solution is to put in a transverse steel in the room below, then put the new floor joists on top between the existing ceiling joists, of course you have to have two structural walls (and PW notices if its a Party Wall) and it messes up the room below. If you have enough height in the loft and space to do it put the steel on top of the existing ceiling joists and then cut the new floor joists to bear on it and again put them between the existing ceiling joists.

    A more creative and much more awkward solution is to turn the existing skeiling into a structural member using a flitch plate, of course this depends on the rafters being deep enough to take it and again messes up the ceiling below (but not as much and you can use the increased depth to insulate this but which is usually the cold spot). I like this one though because it feels better not to just stick in a load of steel wherever there is a structural issue.

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