250kg aquarium in loft

Discussion in 'Engineers' Talk' started by Stripedfish, Dec 11, 2020.

  1. Stripedfish

    Stripedfish New Member


    I was wondering if I am being crazy not to get a structural engineer to look at this:

    I live in a 2004 built end of terrace that has a 'pre-built' converted loft.
    I want to put in a 150l aquarium that I estimate will weigh 230-250KG including the glass/rocks/cabinet etc.
    The footprint of the cabinet will be 60x55cm and it would sit across 2 8"x2" joists. Due to it being a loft space, I can't get it up against a supporting wall, so would be about 1m away from where I think the joists end.

    My question is - does this community think this is risky?

    I'd add I am NOT an engineer!

  2. Severntrent

    Severntrent Screwfix Select

    Depends on the span of the joists
  3. Stripedfish

    Stripedfish New Member

    They are about 5 metres in span, and the tank would be about 1.5m from one end. As I said it will be straddling 2 joists that are 45cm apart.
  4. Stripedfish

    Stripedfish New Member

    one other thing I just thought of is that I'm working from home sitting in a chair that rests over the same joists, about 2m further into the room, so that's another 85kg on the joists for 10 hrs a day..:(
  5. Madeofale

    Madeofale Active Member

    is there anything you can do to spread the weight over more joists

    before we moved into this house we lived in a large flat and that was one floor up, the place was built in 1922 and i had a 4x2x2 marine setup plus a 2x2x2 sump underneath, and that was full of liverock etc and that was alright, i doubt the joists in that place would have been 8x2 or even 7x2 probably 4x2 id imagine, but it was up against a wall, the joists would have gone into the wall too
  6. Severntrent

    Severntrent Screwfix Select

    Do not know what you mean by pre built converted loft but your existing beams wouldn't comply with building regs if the standard floor loading of 1.5kn/m2 is adopted, whilst strength wise they are OK (assuming 400 spacing and C24 Grade) they just fail on deflection but if your floor joists are above 2nd floor ceiling height this may not be a big issue. Basically you are at the limit of what is acceptable and unless you go down the line of specifying exactly what loads are to be imposed on the floor, putting in some control procedures to ensure your assumptions are not exceeded and then do definitive calcs to prove the adequacy of your joists its all a bit suck it and see. With 400 spacing and C24 In all probability it wouldn't collapse but the beams may bend a bit, best have a brolly in the bedroom.
  7. Stripedfish

    Stripedfish New Member

    Unfortunately I can't think of anything I can do other than put the tank on some marine ply to ensure the weight isn't on just the feet of the stand and evenly spread on the 2 joists (not sure that will make any difference though) I could get a bigger tank that goes over more joists, but that doesn't solve the problem :)
    I'm confident it won't fall through straight away, just concerned about the effect of the stress over time....
    The only space is up against the stud wall that divides the room from the side loft. The missus doesn't want it in the lounge, which is a) where I originally wanted it and b) has a concrete floor!!
  8. rogerk101

    rogerk101 Screwfix Select

    If they were 8x4s they would probably be OK, but they're 8x2s, so I wouldn't risk it ... especially since your insurance provider might not pay you out for any damage ... which could be substantial.
    The problem with 8x2s is that they tend to twist under load; unlike 8x4s which are much more stable. 8x2s tend to be used with preformed trusses and tend not to be installed with an abundance of noggins which would provide some resistance to twisting, but I certainly wouldn't want to be in the room underneath it when it fails.
  9. Stripedfish

    Stripedfish New Member

    Thanks. What I mean is the house was built new with stairs going into what would ordinarily be a loft space (i.e. there are 2 small rooms in between the sloping roof) I thought that may be relevant as didn't know whether there were different building regulations for that kind of loft as opposed to a house that is built and then has a loft conversion done later.

    I think either way I probably need to rethink the location or get it checked properly, as I definitely don't want a brolly in the bedroom ;)
  10. Severntrent

    Severntrent Screwfix Select

    So since it was "properly designed/constructed" it can be assumed design floor loads are 150 kg/m2 . If you can distribute the weight of the aquarium over a 2m2 area of floor with some bearers then the floor design load would not be exceeded and in reality unless you invite a load of mates up into your loft or pack it out with furniture there will be plenty of spare capacity in the overall design floor loading within the loft. At that span deflection is limiting criteria as opposed to strength so you will have plenty of indication if anything untoward is going to happen.
  11. stevie22

    stevie22 Screwfix Select

    I think you have attic trusses in which case the bottom chord doesn't act like a simple beam as it is part of a truss and is in tension as well as bending.

    The buckling that Roger referred to isn't much of an issue as the floor boards provide restraint to the top edge which is the one that tries to kick out.

    Timber "fails" by deflecting too far: it doesn't break I think in this instance you'd be fine. I would try to spread the load if possible and probably move my chair.
  12. Tilt

    Tilt Screwfix Select

    Any way of fitting extra beams to the existing ones, to help prevent movement etc.

    How far is it to the next supporting wall / structure underneath???

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