Catnic for Bifold installation?

Discussion in 'Building' started by House7000, 28 Jun 2020.

  1. House7000

    House7000

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    Looking to join together existing sliding doors and separate door with a set of 3.5m bi folds. This means taking out a 300mm width wall between them.

    I assumed an RSJ would have to go in but have had one quote who said they could install a catnic to this as they have standard calcs for what they could take etc. My question is, is this ok?

    Also, assume I should ensure building regs are done for this?
     
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  3. 23vc

    23vc

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    Yes, a catnic type lintel can be used assuming no abnormal loadings and they come in standard lengths
    Yeah the work would be notifiable
     
  4. House7000

    House7000

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    Thanks. What is the difference between a catnic and an RSJ?

    This is the first time I'll have building regs involved in anything. Do I have to do this before the work is started? Or should any decent company offer to include this for me? Appreciate the cost will be added to quote.
     
  5. 23vc

    23vc

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    RSJ = generic term for a steel I beam. Catnic is a brand name but refers to off the shelf cavity lintels. Because they have precalculated loads, building regs don’t require calcs for them, and you also don’t normally need padstones, so no requirement for a structural engineer to design it like you would for a steel beam/RSJ.
    Speak to the builder and ensure they put a building regs application in. Or if they’re more a window installer they may have it covered under FENSA
     
  6. tony1851

    tony1851

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    A Catnic is a patented, specially-shaped lintel fabricated out of thin steel sheet; an RSJ is a hot-rolled steel 'I'-shaped beam (though RSJ is a misnomer as they are rarely used today - the modern equivalent is a UB = Universal Beam).
    Your proposal needs Building Regs approval, partly because it is a structural alteration, and also because you are increasing the area of glazing.
     
  7. House7000

    House7000

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    Thanks both. Very helpful and glad to hear it's an ok way to do it. They are FENSA registered but for completeness I should insist that they do building regs too? Then im completely covered?
     
  8. freddiemercurystwin

    freddiemercurystwin

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    A key factor is to determine if the bifold is top hung or floor supported.
     
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  9. Alastairreid

    Alastairreid

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    Keep in mind, building regs are the home owners responsibility.
     
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  11. ^woody^

    ^woody^

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    A catnic or similar steel lintel relies on the masonry immediately above it to form the 'beam' that takes the load above it. This makes it inherently less tolerant of loading from below, moving loads and vibrations or even fixing to it.

    So it can be a bad choice as whilst it may pass building regulations, the key considerations are about design and use, not just a single factor of loading.
     
  12. House7000

    House7000

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    Which is better in this scenario?

    Do I need to contact council then before getting this done / giving them the go ahead?


    So how do I know if what they are proposing is a good option then?
     
  13. tony1851

    tony1851

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    You need to establish whether or not the bifolds are top hung. Particularly if top-hung, you then need to find the tolerance they will allow for deflection of the beam.

    If using a Catnic, you would need to find out from them what the maximum deflection of the beam will be. To tell you this, they will need to know what load the catnic is suppporting; is it supporting just a roof, or the main back wall of the house plus the bedroom floor? - all this makes a difference to the deflection.

    If using a steel beam instead of a Catnic, you would need to tell the SE who calculates the beam what maximum deflection your doors can tollerate - s/he will then work back the figures to give the optimum size of beam.

    Unfortunately in life, some things are never simple :<(
     
  14. House7000

    House7000

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    It is going to just be supporting the roof for an extension part of the house so no floor above it (not yet anyway but thats for a good few years yet if at all).

    If this fitter is correct they should already have considered what you said above though right?

    I will ask about the hanging of them. I think its bottom hung but not 100%.
     
  15. frutbunn

    frutbunn

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    FENSA certification does not cover structural alterations or lowering the cill height for some reason. You will need B Regs
     
  16. ^woody^

    ^woody^

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    Yes if his day job is a structural engineer, and he has additional insurance for structural design and installation.

    How many window firms are Phoenix companies that shutdown and void the warranty and then start back up with a new name but same people. Don't answer it's rhetorical.
     
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