Building my first Deck

Discussion in 'Landscaping and Outdoors' started by gzuz1990, Jun 14, 2021.

  1. gzuz1990

    gzuz1990 New Member

    Hi,

    I am about to start building my first deck in my garden and had hoped that someone could offer some advice.

    The deck size is 6.5m x 4.5m. It will be installed about 100mm AFFL.

    The outer joists on each side are spaced at 357mm and all others are at 400mm centres. (Have spaced outer 2 left and right at 357 for uniformity instead of having one side at 307 and the other at 400).

    I have put together a cad layout of my interpretation of the suggested post and joist locations. Could someone confirm if this looks about right:
    upload_2021-6-14_13-43-37.png

    I have also seen suggestions that every joist should have a support in the centre and the front and back should be supported at every second joist.

    My plan for the deck has changed a little since i finished the layout and the back of the deck will now be supported from an existing wall.

    Thanks,
    Graeme
     

    Attached Files:

  2. Jord86

    Jord86 Screwfix Select

    That amount of noggins and their positioning is a waste of timber and pointless, and the post arrangement doesn't make sense as at least half of the joists would be unsupported. What depth of joist are you opting for? Two rows of noggins at one and two thirds of the span along the 4.5m run would be fine.
     
  3. Severntrent

    Severntrent Screwfix Select

    Without knowledge of joist size any comment on structural adequacy cannot be made except as Jord states you need supports to all joists unless you have got sky hooks.
     
  4. gzuz1990

    gzuz1990 New Member

    Thanks for the feedback.

    I have ordered 45 x 95mm c16.

    Does the below make more sense?
    upload_2021-6-14_15-39-11.png

    Thanks,
    Graeme
     
  5. Jord86

    Jord86 Screwfix Select

    Yes, however you don't need as many support posts at the perimeter, one every six foot would do, and if you run the posts underneath the joists or notch the posts to house the joists then you won't need coach bolts and will save yourself a couple of hundred quid.
     
  6. gzuz1990

    gzuz1990 New Member

    Thanks for your reply.

    With reference to notching the posts, is a central channel in the post best to have material either side of the joist or is it fine to notch 45mm out of one side and butt the joist up tight to the notched face?

    If notching would you use coach screws instead of coach bolts?

    I take it if using coach bolts the recommended fixing is an m12?

    Thanks,
    Graeme
     
  7. warcs

    warcs Member

    45x95 may prove a little bouncy at those spans
     
  8. Jord86

    Jord86 Screwfix Select

    Notch half the material out one side is fine, yes to coach screws and yes to m12. 4x2 will span 2m, yours is 2250 approx (half of 4.5m), unless you're planning on having parties then it should be fine, otherwise add more posts or 4x2 legs.
     
  9. gzuz1990

    gzuz1990 New Member

    Thanks, would the additional legs need postcreting in or could they rest on slabs?

    Really the deck will be low enough that a slab under the joists would probably touch the ground.
     
  10. Severntrent

    Severntrent Screwfix Select

    15 spacings at 400mm = 6m ?

    Based on floor loadings used in residential dwellings for building regs of 150kg/m2 your joists spans fail in strength and deflection. However if you accept a lesser loading of 100kg/m2 the joists would pass strength and deflection requirements.

    Building regs do not require noggins on joist spans of less than 2.5m so the noggins provided are not really required
     
  11. gzuz1990

    gzuz1990 New Member

    So if I added bearing members horizontally on the drawing view at 1.5m from the back and 1.5m from the front then laid the joists on top of those would that help? I could then reconfigure for 5 x posts at 1.5m including 2 outer posts for each of those 2 bearing joists and then retain the existing amount of posts along the front edge of the deck, would that work?
     
    Last edited: Jun 14, 2021
  12. Severntrent

    Severntrent Screwfix Select

    Yes, and the same number of posts on the along the front ( whats happening at the back - do a final proposal sketch)
     
  13. gzuz1990

    gzuz1990 New Member

    The back will be supported on the same size timber, fixed to a wall, 15 x m10 threaded rod inserted into the brick with chemfix, joist hangers for each joist supported by that beam.

    I'll do a final sketch tonight when I get in.

    Thanks,
    Graeme
     
  14. gzuz1990

    gzuz1990 New Member

    Hi,

    Please see below as discussed:
    upload_2021-6-14_23-21-32.png
    I really appreciate all of the advice you both have given me on this.

    Thanks,
    Graeme
     

    Attached Files:

  15. Severntrent

    Severntrent Screwfix Select

    Thats more like it, only problem is the 2 bearing joists fail in deflection and strength (using standard 150kg/m2), suggest supporting them at every 3rd joist i.e 1.2m spacing or doubling up bearing joists and putting another run on other side of support posts
     
  16. gzuz1990

    gzuz1990 New Member

    Thanks,

    Something like this?
    upload_2021-6-15_10-23-2.png
     
  17. Severntrent

    Severntrent Screwfix Select

    Spot on, now all you have to do is think about the posts foundations
     
  18. gzuz1990

    gzuz1990 New Member

    Ive got 15 bags of postcrete on their way, 15 posts cut to lengths of 600mm, 400mm under soil level, horizontal support members raised above ground level by 10mm, joists resting on top of the horizontals, finished deck level of approx 225mm. Should that be sufficient? I have a number of breeze blocks that i did plan to break in half and use as a footing under the post to take me below the frost line.

    I have seen suggestions that i should fill the post holes half way with type1 or similar and then fill with postcrete, would you say there is any merit in that or just postcrete the whole way?
     
    Last edited: Jun 15, 2021
  19. Severntrent

    Severntrent Screwfix Select

    No merit whatsoever except for a bit of cost saving, don't get to hung upon frost line its a bit of decking not a house
     

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