Are my plan feasible - advice appreciated

Discussion in 'Engineers' Talk' started by PerthMan1, Feb 7, 2019.

  1. PerthMan1

    PerthMan1 New Member

    I would appreciate any views on a possible roadblock that my house extension plan seems to have hit. Someone may know whether there is a solution to this that is feasible at reasonable cost, or may have designed a solution to it in the past. Here's hoping.
    I have architect's drawing for a 2 storey extension to my bungalow that will convert it from a simple bungalow with a couple of rooms up in the converted attic space (completed many years ago) into an L shaped house. The upstairs, which was done more than 30 years ago, uses the current 6 x 2 roof beams (ceiling joists for the ground floor) as a floor - it would probably not pass if it was put to planning and building control today, as they might demand something thicker - 8 x 2 maybe. The way the roof is going to be changed is quite extensive and would require many of the existing roof structure to be cut away and replaced with new timber. Here is the problem: if I have to raise the existing floor upstairs, then the staircase needs replaced and I dont have space to put a new staircase in that would be legal in today's requirements, so I want to keep the upstairs floor at its current height on 6 x 2 beams at all costs. Is there a way to create a new roof, while using 6 inch beams, but somehow strengthen it (tensile stress presumably) enough to pass the building regs? I can probably manage the load bearing side of it by doubling up the number of ceiling joists, but a structural engineer I was getting a quote from has suggested that the existing beams in the ceiling would not be strong enough to stop the roof from stretching outwards.
    If there is not an easy solution, I dont want to go any further in terms of paying professional fees for a project that is probably unfeasible. Anyone been here before?
     
  2. AlvyChippy

    AlvyChippy Active Member

    Such "questions" are solved between architect and local planning authority. Those have different requirements and allowances. Of course, you can keep on drawing, specifying, negotiate ownself, I wouldnt hold my breath for such route to be eficeffic or successful.
    GTG, will try to see it in the evening
     
  3. MGW

    MGW Well-Known Member

    I have been house hunting, the number of houses with 5 bedrooms which are advertised as 3 and 2 bedroom because the stairs or floor does not meet standards is unreal. It seems daft, a pre-war house can have really narrow stairs, but post war not allowed, much seems to be if planning permission was granted when done, but it's not only the local authority, it's the mortgage and estate agents inspectors who highlight no planning given or not to regulations.

    Went to one bungalow with three bedrooms upstairs, but not to spec, so down as floored loft only, he had to rip out the stair case and fit a loft ladder although a very good loft ladder instead.
     
  4. kiaora

    kiaora Well-Known Member

    Hi
    First have a look at the span tables,
    https://www.bsw.co.uk/media/download/5

    If you have a local steel joist company, they do this sort of work every day,
    In my area, I would ask his opinion and advice, he most likely come up with straight forward answers, than just get Structual engineer to confirm calculations.

    It’s more of a building control issue that planning.

    Have you heard of a flech beam ? It’s steel plate bolted to joists to give more strength, I recently installed some to a purlin because the owner had knocked down a supporting wall that the purlin struts were on.
    Got the calcluations from a SE, job done !

    You can overcome any problem

    Regards
    Peter
     
  5. PerthMan1

    PerthMan1 New Member

     
  6. PerthMan1

    PerthMan1 New Member

    Hi, Thanks for these. I was aware that the structural engineer would be able to sort it out with the architect, but if the solution involved removing the whole of my roof and rebuilding it for tens of thousands, I would have gone with a simpler ground floor extension. So I was keen to know the likelihood of an easy solution before I submit these drawings and accept a structural engineer's quotation. Sounds like some steel beams will do the job. Just searched for a fletch beam. Looks like what I want. I may have to slide this under the existing floor alongside the existing 6 x 2 joists, but it is probably doable. I will go ahead with this, get the engineer to do the calcs and hope that the work on my roof doesn't amount to a complete rebuild. As mentioned by MGW it is a pain when something that was accepted years ago (like my staircase) would no longer be accepted, and forced you to avoid touching it for ever more in case they demand you undo the whole thing. Thanks again for the thoughts.
     
  7. kiaora

    kiaora Well-Known Member

    Hi
    If you going for fletch beam, when I did the purlin in the loft, 5m purlin, you can do it in 5 pieces .

    Obviously not 5 x 1m lenths, but 5 time 1.2 m to give overlap, SE will work it out.
    Then it’s a lot easier to install, must be accurate with the holes!
    upload_2019-2-8_12-43-13.jpeg
     
  8. kiaora

    kiaora Well-Known Member

    Btw, this was an empty house I was working in !
     
  9. Richard AJ

    Richard AJ New Member

    Sounds like you're in a quandry. I've re-read your post 3 times and get the impression you're going to form the second storey within the pitched roof area. The existing ceiling binders, which double as current floor joists will be carrying both bending stress and tensile stress (the first from you walking on it and putting furniture on it and the second from the outward thrust of the roof). The options are: 1) Install steels to support the existing floor joists, breaking up their spans- this'll impact on headroom at ground floor. 2) Install a ridge beam and support it from structural stud at the juncture to the L shape or a triangular support, fromed from steel with moment resisting connection at apex and at gables (assuming you have them). 3) Install plated connections at apex to each rafter to take out the bending moment at apex, box beam walls etc that these will take out thrust. 4) Install deeper timbers to form the first floor and tie new rafters to these at juncture over wall plate- although this will likely have an impact on the staircase.. I'd suggest attic trusses but you'll hit the issue of the staircase as BC will want it replacing.
     
  10. stevie22

    stevie22 Active Member

    I'm not clear where you are in the process: do yo have planning permission? If not them this is surely the first step as you might be stressing about something that won't happen.

    Building regs change with time but we don't have to go back and alter things so if you're not altering the stairs they can stay as can the floor.

    If you do need to strengthen the floor then simple sistering of some or all of the joists is probably going to be easies
     

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