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Precast floors - block on flat

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  • 21-05-2008 11:12am
    #1
    rebellad
    Registered Users Posts: 227 ✭✭


    I am looking at putting in precast floors on the 1st floor in a new self build. The precast company has said that I only need block on flat where 2 of the precast slabs meet. My engineer is saying that I need block on flat on all the walls where the slabs are resting. Has anyone heard of (or had) problems with only having block on flat where two slabs meet??


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    #2
    De_man
    Registered Users Posts: 552 ✭✭✭De_man


    rebellad wrote: »
    I am looking at putting in precast floors on the 1st floor in a new self build. The precast company has said that I only need block on flat where 2 of the precast slabs meet. My engineer is saying that I need block on flat on all the walls where the slabs are resting. Has anyone heard of (or had) problems with only having block on flat where two slabs meet??


    yes they're needed where the precast slabs meet, all external openings
    internal door openings have to be double lentils etc, i reckon get your engineer to have a chat with the precast company about this.

    afterall he'll have to sign off on the job

    but in our job i used block on flat only where they meet,
    (which was nearly everywhere)


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    #3
    unclebill98
    Registered Users Posts: 3,816 ✭✭✭unclebill98


    WE use blocks on the flat for the entire basement to hold the slabs. Except for the one part which only had one story to go on top rather than 2. Engineer ok'd that.


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    #4
    bauderline
    Registered Users Posts: 898 ✭✭✭bauderline


    Same on mine, only at the point the slabs meet...


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    #5
    Slates
    Registered Users Posts: 336 ✭✭Slates


    rebellad wrote: »
    I am looking at putting in precast floors on the 1st floor in a new self build. The precast company has said that I only need block on flat where 2 of the precast slabs meet. My engineer is saying that I need block on flat on all the walls where the slabs are resting. Has anyone heard of (or had) problems with only having block on flat where two slabs meet??
    Block on the flat where 2 slabs meet, block on edge everywhere else

    Double lintels will not do over loadbearing ope's, you will need reinforced steel or reinforced conc lintels


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    #6
    sydthebeat
    Subscribers Posts: 41,093 ✭✭✭✭sydthebeat


    some manufacturers need 215 on external walls... generally the hollowcore type...

    other manufacturers only need 215 where slabs meet... generally the solid wide slab type....

    go with whatever the manufacturer specifys....


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    #7
    De_man
    Registered Users Posts: 552 ✭✭✭De_man


    Slates wrote: »
    Block on the flat where 2 slabs meet, block on edge everywhere else

    Double lintels will not do over loadbearing ope's, you will need reinforced steel or reinforced conc lintels

    yep that's correct we used reinforced con lintels

    can't remember how to use the edit function...
    (rushed the earlier post) don't forget the pads under the reinforced steel


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    #8
    Slig
    Registered Users Posts: 1,550 ✭✭✭Slig


    how do you reinforce steel?:D
    different manufacturers specify different criteria and most (if not all) will have in house engineers, some dont even require a structural screed. Get it in writing from the manufacturer though


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    #9
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    sydthebeat wrote: »
    some manufacturers need 215 on external walls... generally the hollowcore type...

    other manufacturers only need 215 where slabs meet... generally the solid wide slab type....

    go with whatever the manufacturer specifys....

    This is my experience too


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    #10
    Slates
    Registered Users Posts: 336 ✭✭Slates


    Slig wrote: »
    how do you reinforce steel?:D
    different manufacturers specify different criteria and most (if not all) will have in house engineers, some dont even require a structural screed. Get it in writing from the manufacturer though
    Heavy duty steel lintels have alot more "stuff" in them as the layman would say..........


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    #11
    rebellad
    Registered Users Posts: 227 ✭✭rebellad


    Anyone ever heard of any issues with having precast on block on edge?? My engineer is being really sticky about this and it looks like he won't change his mind - I am going to try to get him to contact the rep and see what he will say to him. I can kinda see where the engineer is coming from in that I am having underfloor heating and block partitions upstairs which will put a lot of extra weight on the walls so they would be more likely to crack if block on edge. But the cost of going with block on edge on all the loads bearing walls and the increase in the foundation seems to be a bit excessive!!!


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    #12
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    was this not answered already in the posts above ?


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    #13
    RKQ
    Registered Users Posts: 2,292 ✭✭✭RKQ


    Go with Manufacturers recommendations and specifications.
    Get your Engineer to talk to the Manufacturer. Get written confirmation from Manufacturer. Engineer won't have to sign off on the element designed by others- precast slab!.
    I assume its a two storey house, not a bunker! At the most, inner leaf of external walls would be increased to 150mm thick. Steel I beams may work over doorways.


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    #14
    Supertech
    Registered Users Posts: 597 ✭✭✭Supertech


    Engineer won't have to sign off on element designed by others ie the floor, but will have to sign off on structure holding it up - ie the walls. Talk to engineer and see his reasoning. Spans may be an issue, loads at first floor may be an issue - he's the project supervisor and has the final say not the floor manufacturer. 150mm thick gives you coursing problems where standard block meets non standard and they're pain to work with. If the eng says 215 and wont budge he's the boss.


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    #15
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    Supertech wrote: »
    Engineer won't have to sign off on element designed by others ie the floor, but will have to sign off on structure holding it up - ie the walls. Talk to engineer and see his reasoning. Spans may be an issue, loads at first floor may be an issue - he's the project supervisor and has the final say not the floor manufacturer. 150mm thick gives you coursing problems where standard block meets non standard and they're apin to worjk with. If the eng says 215 and wont budge he's the boss.

    100% agree


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    #16
    sydthebeat
    Subscribers Posts: 41,093 ✭✭✭✭sydthebeat


    why not get a second opinion.....

    after all, its the budget that shouts the loudest....


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    #17
    RKQ
    Registered Users Posts: 2,292 ✭✭✭RKQ


    If in doubt get a second opinion!
    If the Manufacturer certifies that the slab spans are adequately supported on "whatever size block", they know what they are certifying. Their Engineers are experienced and specialist in these calculations. The manufacturer has Irish Agg. Certificates etc, proving their systems strengths and appropiate spans, supports and uses.


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    #18
    Supertech
    Registered Users Posts: 597 ✭✭✭Supertech


    Doesn't matter what the floor manufacturer certifies RKQ - supervising engineer has final say on project, and he's entitled to be picky - it's his ass if there's a problem. Put yourself in his shoes - if your client arrived along with a second opinion from someone on one of your projects to force you to change your mind cos the floor supplier said everything would be OK what would you do ? Why not just let the floor guys do the supervision altogether .... understand where your advice is coming from but let's be fair to the guy who has supervised the thing so far ...


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    #19
    RKQ
    Registered Users Posts: 2,292 ✭✭✭RKQ


    I assume construction has not started yet! Otherwise this is a problem!
    The Supervising Engineer has last say if he / she has certified works to date.
    But if the foundation is in, why are we having this conversation?
    Why wasn't this sorted at the design stage?

    If no works have started on site and nothing has been certified / inspected, then get a second opinion and new Engineer if necessary. No point battling with your Engineer before the work starts! Its a long and difficult process, so don't start on the wrong foot.

    Whats the problem with the Manufacturer and their Indemnity Insurance covering the works?
    It relieves the Engineer of liability. Structural cracks in walls or slab would be the Manufacturers liability. Why would the Engineer continue to be so "sticky"?
    Has he had a "bad" experience with the Manufacturer?

    Will the Manufacturer certify their product? If they won't then move on.


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    #20
    construct06
    Registered Users Posts: 505 ✭✭✭construct06


    certyfing the product is fit for use will be easy for the precast manufacturer to do. they will not and cannot certify the walls supporting the slabs. i worked in a precast manufacturers for a time and i am familiar with the design software and extent of design for these type of projects.

    the design software assumes adequate supports and looks at the span/width/opes as the critical criteria to determine amount of einforcement, requirement for structural screed etc...

    you will probably find that the precast company will say that 100mm block supporting the precast is ok, and obviously to make their product more amenable to potential buyers they will want to omit the expense of having to put in wider foundations and block on flat at supporting walls.

    Also you'll probably find an engineer who will certify the 100mm blockwork but to be honest with anything structural there really is no point chancing it! And your engineer as well as covering his own ass is also covering yours! He sounds like he wants the job done right and to be honest guys like that are far and few between......

    If manufacturer is still insisting 100mm blockwork is ok, get them to supply calculations supporting their claim. Also ask the question who will indemnfy you against any cracking or failure of the walls....

    I doubt youd get all that supporting documentation from the precast manufacturer!...


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    #21
    rebellad
    Registered Users Posts: 227 ✭✭rebellad


    Have spent the last 3 days going back and forward with the engineer and manufacturers on this. We have been in contact with the precast manufacturer and basically they won't sign anything guaranteeing the structure of the walls, their answer to the question was " I can show you 500 houses where it is done block on edge". My engineer has always done block on flat and says he isn't going to change until the manufacturers can guarantee in writing the structure of the wall, he is the named engineer on the mortgage so if I decide to change I foresee some hassle with them over it. The foundations are being dug today so it looks as if it's out of my hands now anyway. The engineer recons it will cost 6k max more so I guess I will just have to grin and bear it. I guess at the end of the day he is the one signing it off and he is doing it to guarantee the structural soundness of the house so 6k now might be nothing compared to what I would have to pay if anything happened had I gone block on edge. Thanks for the help guys, I must go back to the blocklayer and renegotiate a new price - hopefully he will be feeling sympathetic towards me ;)


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    #22
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    timber frame ? :D


    ...... sorry could not resist that


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    #23
    d o'c
    Registered Users Posts: 129 ✭✭d o'c


    With regard to double lintels mentioned earlier over door openings etc.
    What size are these normally for say a standard internal door. heightXwidth

    block on edge I assumed 4" width, so what height is the norm.


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    #24
    muffler
    Registered Users Posts: 45,861 ✭✭✭✭muffler


    I think we need to state the obvious here. This is a discussion forum and not a design centre. Each case is different as there are varying factors that can affect the sizes so we cant allow any sizes to be specified.

    Theres no problem with debating any planning or construction matter here but I dont want to see this forum used for specifying something that is not standard. If it were allowed there is always the possibility that it could leave boards.ie responsible for the content of the posts here. Ongoing legal action against boards.ie has made us all take stock of what the risks are with the content of certain posts.

    d o'c you will need to get an engineer to specify the lintel sizes for you.


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    #25
    Slates
    Registered Users Posts: 336 ✭✭Slates


    d o'c wrote: »
    With regard to double lintels mentioned earlier over door openings etc.
    What size are these normally for say a standard internal door. heightXwidth

    block on edge I assumed 4" width, so what height is the norm.
    Send your drawings to Killeshal pre-cast in Offaly and they will size your lintels


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    #26
    Mellor
    Registered Users Posts: 39,101 ✭✭✭✭Mellor


    I have to agree with muffler, there are various factors affecting structural design, and I don't think we should be encouraging one way or another.

    People have posted saying they have seen both ways done, but at the end of the day, its your engineer that has the say.
    I have a similar situation here, where my engineer is specing 44x225 C24 timber, this is a huge job and this is overkill imo. But I have to run with it, as it is what he wants.


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    #27
    d o'c
    Registered Users Posts: 129 ✭✭d o'c


    ok, point taken, I can see where you're coming from.

    I will look into it.

    I have 4W X 6"H on at present, and have yet to build above this, so my options are still open for adding
    more strength above openings. It's a bungalow renovation and I'm using precast slabs for an attic conversion.

    So much work done, so much more to do :(


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    #28
    RKQ
    Registered Users Posts: 2,292 ✭✭✭RKQ


    rebellad wrote: »
    My engineer has always done block on flat and says he isn't going to change until the manufacturers can guarantee in writing the structure of the wall, ;)
    I agree fully with your Engineer. If the precast floor can't certify their product and the walls supporting it then forget them! Your Engineer has to sign off on the house and its his Professional Opinion that you should respect.
    There are advantages to precast floors but are they really worth the extra 6K? There are disadvantages too!:confused:


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    #29
    smashey
    Registered Users Posts: 21,676 ✭✭✭✭smashey


    rebellad wrote: »
    Anyone ever heard of any issues with having precast on block on edge?? My engineer is being really sticky about this and it looks like he won't change his mind - I am going to try to get him to contact the rep and see what he will say to him. I can kinda see where the engineer is coming from in that I am having underfloor heating and block partitions upstairs which will put a lot of extra weight on the walls so they would be more likely to crack if block on edge. But the cost of going with block on edge on all the loads bearing walls and the increase in the foundation seems to be a bit excessive!!!
    That's his job.

    /edit. I agree 100% with muffler's comment. This forum is for discussion, not design. Please remember that.


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