Advice on new flat roof, joists? will this sag- roof company

Discussion in 'Builders' Talk' started by sean oc, Jul 25, 2020.

  1. sean oc

    sean oc Member

    Hi

    Posted after some insulation advice and noticed people commenting about the roof joists c24 timber being way to small, they are smaller than existing joists in the other roof its joined to but i thought maybe they are better timber. I have left this up to roofing company to do

    I had few people round who said they would do the same one brick pier and frame up, some people said leave windows on course of block down and just frame up off the top no need for a brick pier.

    Are these joists going to fail? this is my worry as i have paid alot of cash out for a job that i wanted to be hassle free for as many years as possible.

    Could i add some extra Joists in now to try help hold the weight?

    Any advice would be ideal

    Thanks
     

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  2. Severntrent

    Severntrent Screwfix Select

    Advise you to give size,span and centres
     
  3. sean oc

    sean oc Member

    Span is 2.8m ish

    Timber is 95mm x 45mm C24 and spaced approx 430mm apart

    Thanks
     
  4. Abrickie

    Abrickie Screwfix Select

    Timbers are undersized, when you say roofing company do you mean flat roofers who normally just cover the roof or a firm that does all roofing works, it’s looking a little clueless diy imho
     
    Deleted member 11267 likes this.
  5. sean oc

    sean oc Member

    They had good reviews and seem to do alot of roofs flat and pitched etc

    Is it worth me kicking up and asking more questions hes had half the cash already as i presumed it was correct. me being no roofer i trusted their judgement
     
  6. Severntrent

    Severntrent Screwfix Select

    Yes just tell him building regs specify 47x120 size for that span and that is for other materials actually used in the roof construction i.e. plaster board, insulation ,boarding,felt etc not exceeding 50 kg/m2 and see what he says. Extra joists can be added to make it structurally sound
     
  7. sean oc

    sean oc Member

    Just spoke to him about he, they did decide to use this size and will add noggins to brace it all rather than 6x2 to try keep overall weight down on top of windows. as rubber roof is quite light compared to felt anyway.
    He said it wont sag with the pier, and support from house and brick wall helping support the middle as its two separate rooms with one roof across the lot.

    I maybe worth sticking 2 or 3 larger joists in to help support? and work out were to stick them best to fit large plaster board?
     
  8. stevie22

    stevie22 Screwfix Select

    Severntrent says 5x2 not 6. Noggins will have a miniscule effect on the roof deflection which is why joists are sized and not guessed and they won't affect the loading on the window which it is not designed to take. As Abrickie says your man sounds a bit clueless

    Anybody can write reviews: I always go by recommendation.
     
  9. Jord86

    Jord86 Screwfix Select


    There's not another room going in underneath those joists surely? Noggins don't prevent sag or bounce if the span is undersized, the OSB sheet covering acts as a brace as it ties all the joists together, however for your situation really speaking it should be a tongued and groove type to allow for a small expansion gap.
     
    Deleted member 11267 likes this.
  10. Abrickie

    Abrickie Screwfix Select

    “ keep the weight down over the windows “ kick him off site and get someone who knows what they are doing to put it right and finish it off.:rolleyes:
     
    gadget man and Jord86 like this.
  11. The joists are too small and the single trimmer they are hanging off is not correct either.
    Either get him to do it properly or get someone who can, he can nogging all he wants but they will not help undersized timbers.
    He is just giving you a load of flannel and sweet talk, to try and convince you his dodgy work is fine.
     
  12. Frutbunn

    Frutbunn Active Member

    Which tables are you using, they're certainly not Eurocode 5?
     
  13. sean oc

    sean oc Member

    No sorry meant if you see in image 2. its one single roof over two rooms. existing brick built utility room which is being replaced like for like and one of this conservatory

    He said he used this sized timber on a few jobs and garages etc and not had any problem, said the works guaranteed and he will come back to fix any issues if any occur which he says wont happen
     
  14. sean oc

    sean oc Member

    Think my best is to add some large joists like 145x45 next to some of the existing ones and use these large ones to fit my plasterboard to when i do the ceiling? i could add a 145x45 every 2nd joist approx and could use this to fit 1.2 x 900 plastboards is that makes sense?

    Them extra every 2 joists may help? :S

    Not sure what to do, hate getting work done i cant do myself as you are always guessing if they are doing it right, and get conflicting info. Cheers for all the input so far
     
    Last edited: Jul 25, 2020
  15. Jord86

    Jord86 Screwfix Select


    How long has his company been trading? Guarantees are all well and good but useless if he's got a breadcrumb trail of various companies that have gone under in the last few years.
     
  16. No good hanging off the single trimmer. You are as well biting the bullet, take it down and start from scratch, doule trimmer properly sized and supported and properly sized joists.
     
    Abrickie likes this.
  17. Frutbunn

    Frutbunn Active Member

    He may very well have, but how long is a piece of string? There's finite limit on any size timber, simply stating he has used that size before is meaningless.
     
  18. sean oc

    sean oc Member

    hmm he has had my cash and insists it will be fine.

    Problem i have now if i kick him off site, I don't have no were near the cash to start over and it will be left with a open shell. took me long enough to save for this and it looks like its no were near up to standard :l took me ages to decide on a compnay as well as had so many other things cocked up in the past by 'professionals'

    he has had half the cash for materials etc
     
  19. Severntrent

    Severntrent Screwfix Select

    Old TRADA tables, are they that much different? But we're coming out the EU soon so we can forget the Eurocodes :)
     
    stevie22 likes this.
  20. Severntrent

    Severntrent Screwfix Select

    To be fair he probably has not encountered any problems as until there is a snow loading of 75kg/m2 on his structures (plus someone up there doing some maintenance work) they will not have been subjected to the maximum loads they are supposed to be designed for, just hope global warming keeps the snow away
     

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