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Mansard Loft Conversion without raising floor height.

Discussion in 'Floors, Stairs and Lofts' started by Mmark, 21 Nov 2019.

  1. Mmark

    Mmark

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    We have a standard semi detached Victorian home. We are converting our existing loft with small dormer to a full size mansard.

    To do this we are being asked to put in 4 steels. 2 above the existing floor, 2 in the ceiling. Because the existing floor joists runs the wrong way, we are being told to put the beams on top of the existing floor. Which loses us about 220mm in height. Worse it means the existing bathroom,
    Which is on the eaves side is pushed up and becomes smaller than it is now.


    Is there a way to avoid raising the floor. Such as flitch plating the existing joists? I asked the architect, he said the only way was steel beams on top. I just want to make sure I’m getting accurate advice for peace of mind.
     
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  3. Ian H

    Ian H

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    Will the steels be under the loft room walls so not really affecting the floor height?
     
  4. Mmark

    Mmark

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    I've attached the two relevant parts, from the diagram the architect provided. The first shows the side profile and the four steels. The diagram shows the steels in the existing floor (not raising any height). The builders say the diagram is wrong, the existing joists go the wrong way, so the steels must be placed on top. So they simply moved the steels up, on top of the existing floor, significantly raising the floor height and reducing the space of the existing bathroom. The second shows the the above view of the two steels on the floor.

    I did ring the Architect and he said to do the same thing. A friend, who is not an architect, mentioned that we could have possible strengthened all the existing joists with fletch plates, rather than having steels and raising the floor. So I'm just looking to make sure we have done the right thing, and there really was no credible other alternative.
     

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  5. Ian H

    Ian H

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    SB1 could be 300mm tall and wouldn’t affect the floor if you used hangers for the joists.

    SB2 is the awkward one. Even if it were directly under the wall above it I guess it would pass through a doorway or 2 at some point.

    I’m no expert but looking at that the only thing I would be thinking was to move SB2 as far to the rear (left on pic) as possible. We had steels front and back then the joists were supported in the centre off a load bearing wall.
     
    Last edited: 24 Nov 2019
  6. First of all I would ask the architect to make sure the drawings show existing joists are shown spanning in the correct dimension and then consult a structural engineer on the proposed steelwork and structural aspects.
     
  7. Mmark

    Mmark

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    I wrote to the firm, asking them about the steels they placed in the existing floor. This was there answer:
    “The engineers design is based on finding a structure within the existing floor and checking it against what the engineer has shown. I assume that the builder did not find any steels there that could be used.”

    I think in essence what they are saying is, they thought steels may already be there - but they did not know. Our builder confirmed there is no steels, instead there are 2.5x7 inch joists running 13 apart, and some are doubled up. Running from the front wall to the back wall, with some resting on a wall half way between. We had a 30 year old loft conversion here from before, I guess they changed over the old loft joists to those 2.5x7 to support the new floor weight. Although I’m also now wondering what was wrong with the old floor, those timber beams look much bigger and stronger than the new ones put in. Just it uses a brick wall to lay on, instead of a steel.

    Anyway the builders steels cannot be placed there, as in the diagram, as those joists run front to back, instead of side to side. i.e. the steels would have to cut through all the existing joists. So instead the builder has had to place the steels on top of the old joists and I’m losing around 250mm in head height :(

    Whole thing has driven me a little insane, and I don’t feel I’m getting good advice. Not entirely happy my construction engineers diagrams were all based on “guessing” on what might be there.
     
  8. Possibly ask the engineer and architect - first of all, if it is already a loft floor ,and the proposed alterations are what you call a mansard , why is steelwork required to strengthen the loft floor, and if it really is necessary would it be better to position it under the loft floor joists as downstand beams to the first floor ceiling (I know some people don't like boxed out beams at ceiling level :!:) Also why are the proposed roof timbers at 300mm centres ,they are not usually spaced as close together as that :!:
     
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  9. tony1851

    tony1851

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    As per Leo., why are they putting a new floor in?? If the existing joists are 7x2.5 spanning external wall-to-internal wall-to front wall, surely they would be OK?
     
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  11. Mmark

    Mmark

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    I had two different engineer friends help me this weekend, they confirmed my suspicions that at most i’d just need to sister some boards as what is there is borderline acceptable for the span. I know very little about building work, it was only a suspicion and then frantic googling to see if I was close or wide to the mark - tbh I was really hoping I was wrong :(

    It started a week and a half ago. Builder goes to put in steels, says he can’t as floor boards are wrong way. he insists only way to do steels is if he goes above. I ring the structural engineer, he says the same, if there are no existing steels. It seems it did not occur to the builder that maybe to query with the structural engineer if the existing joists were suitable, nor did the structural engineer have any idea of what flooring I had prior, or think to ask us. I know very little, so I was in their hands.

    I personally had no idea at the time (I didn’t even have access to the loft area, all sealed off). I know almost nothing about building work, it was only after I went up there a week and a half later (once it was safe for me to access), I thought “hmm my old joists are even bigger than new ones”. I started to investigate, and basically had my suspicions casually confirmed by two other engineers who saw detailed photos and measurements.

    For about one day I was really ****ed and thought about insisting the builder rip out the new floor (I’d pay for it, as they blame me for providing incorrect diagrams). However plumbers and electricians come next week, they order the Juliette balcony on Monday. The stress it would cause to the builders, and probably the damage to the relationship, means I’m now stuck with it. Both engineers who visited also urged me not to rip it out, they said I was too far down now to do it in a manageable and sane way.

    Basically i got screwed and ended up putting in a new floor I never needed, losing around 250mm in head height, and no one will take responsibility, so I’m stuck with it.
     
  12. Ian H

    Ian H

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    How very strange. You would think he would have cancelled the steels as soon as he saw the existing joists were not 3x2’s.
     
  13. tony1851

    tony1851

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    If there was an existing conversion there, perhaps the architect should have picked up on this rather than just assuming.....?
     
  14. Mmark

    Mmark

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    “How very strange. You would think he would have cancelled the steels as soon as he saw the existing joists were not 3x2’.”
    “If there was an existing conversion there, perhaps the architect should have picked up on this rather than just assuming.....”

    I asked my architect friend, and he said “each person missed something, each step of the way”. So there was an opportunity for both to be a little more pro-active and probably the builders should have taken more time to speak to the structural engineer once they realized things where not quite correct. However he did say there was nothing contractual for them to have to do so, that it’s just the difference between good professionals that go the extra mile, and see opportunities to improve, and ones where you get the bog standard minimum. So there is no actual “fault”.

    All very frustrating, I was tempted to make the builders take out the unneeded floor. But the same architect advised me not to put myself through that stress, that we are too far gone down that path now.
     
  15. tony1851

    tony1851

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    “each person missed something, each step of the way”.

    That's a little bit of a get-out whereby the architect is trying to deflect at least some of the blame rather than admitting that
    he didn't consider whether the existing floor might have been OK - or even to suggest getting it checked beforehand.

    If there has to be an apportionment of blame, it might be more on the architect's side than the builder's; the builder can't technically be
    expected to know whether or not the 7x2.5s would be OK. Also, the builder would not take kindly to a delay in his schedule while everyone else faffs about deciding where the blame lies and what to do next.

    But - as you say - you have to take the long view; principles don't pay the rent.
    Commiserations :cry:
     
  16. o_O - That is b u l l s h i t .
     
  17. catlad

    catlad

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    I think you should tell them all to fook off and don't pay any of them because it sounds like bull to me.
    How can you start ripping up a floor knowing the timber you are going to use for the new floor is smaller!!!
     
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