Advice on vaulted ceiling for garage

Discussion in 'Builders' Talk' started by Adrian72, Apr 1, 2024.

  1. Adrian72

    Adrian72 New Member


    Hoping someone can advise me.

    I’m starting working on building a timber frame garage/workshop. Size is 9m x 3.5m. I really want to have a vaulted ceiling to maximise head/storage space but am unsure of what material to use for the ridge beam. It seems impossible to find a timber beam in that length, is that because the maximum for timber beam is 6m? If that’s the case can I opt for Glulam, wooden I-beam or do I need to go for steel. It’s a DIY project so trying to keep costs down but want it structurally sound.
    Thanks for the advice.
  2. Astramax

    Astramax Super Member

    Steel appears to be the preferred route these days.
    Adrian72 likes this.
  3. arrow

    arrow Screwfix Select

    Scarf the ridge beam.
  4. stevie22

    stevie22 Screwfix Select

    If you're going full vault you'll need steel to get the strength. or a seriously big Glulam
  5. Adrian72

    Adrian72 New Member

    Thanks all for the quick response. Scarfing a timber beam is intriguing so will explore that. I’ll also get some advice and quotes on the steel option.

    I’ve not even laid my slab yet so have plenty of time to research the roof.

    Thanks again.
  6. Jord86

    Jord86 Screwfix Select

    3.5m on a span is bugger all really with the run of the rafters being 1.75m or thereabouts, especially if the roof covering is to be lightweight, but will need 4x2 collar ties in to be safe.
    Adrian72 likes this.
  7. stevie22

    stevie22 Screwfix Select

    It's a 9m long beam Jord, so if he wants a vault that is going to be a big beam.

    Personally I would go with a king truss or a pair and then everything could be timber without too much difficulty.
  8. BuildingMad

    BuildingMad Screwfix Select

    Surely whats needed is a joined ridge 'board' for leaning & counterbalancing rafters on, not a 'beam', as used in normal built up roofs.
    Needs some form of ties to avoid spread though, not necessarily at joist level to give the additional height. Could have occasional joists at normal level though.
    No need for purlins on that small span.
    Last edited: Apr 2, 2024
  9. stevie22

    stevie22 Screwfix Select

    The OP needs to decide what he wants.

    A full vault needs to be top supported so the beam is either mahoosive or is itself supported (hence the king truss comment).

    An elevated tie can work but the rafters needs to be sized accordingly and there is a limit how far this can be made to work. The roof itself might be lightweight but there is a need to think about the dreaded white stuff and make a decision about what to allow. It's a shed so no building regs to worry about and if a shed roof deflects a bit more than code allows so what.
  10. BuildingMad

    BuildingMad Screwfix Select

    My choice would be
    9" x 1 1/2" ridge board
    6" x 2" rafters.
    9" x 2" ceiling joists bolted to rafters at 2.7m & 5.4m
    6" x 1 1/2" collar ties on all the rafters in the top third.
  11. Severntrent

    Severntrent Screwfix Select

    Interesting, is that a finger in the air design or is there some sort of analytical basis involved. Why 2.7 and 5.4 and not 3.0 and 6.0, rafter spacing to be??
  12. Jord86

    Jord86 Screwfix Select

    No I understand that Steve (not trying to undermine you, I know your credentials) but it’s only a small span with presumably little weight, the OP would have to stick some form of timber collar in underneath a ridge in order to fit lighting and what have you anyway (strip light or a few spots) if he wants overhead storage then he’d have to put joists in, so to me it just makes sense to fit collar ties if he wants it vaulted, or ceiling joists for some of the area if he wants storage.

    My carpentry college books from ages ago (Peter Brett, Nelson Thornes Publishing) state that a collar tie roof (slate covering, I assume) would span up to 4.5m and that would just be sized on most likely 4x2 rafters with a 6x1 ridge board, by contrast a couple roof which is vaulted with no ties whatsoever spanned ( might be wrong, it’s been years since I read it) approx 3m, maybe 3.5m.

    I don’t see how what the OP is proposing could be any different?
    arrow likes this.
  13. Adrian72

    Adrian72 New Member

    Hi again

    I really appreciate you all taking the time to reply to my post. Thank you. All good advice for me to go away and research. A bit daunting for a DIYer but I’m confident I can sort it.
    Thanks again.
    ginger tuffs likes this.
  14. Adrian72

    Adrian72 New Member

    Just to clarify what I want, think my original post was a bit unclear:

    Definitely want a vaulted ceiling, not flat with a loft space. I want the height to make the space feel bigger but also, if I’m honest like the idea of learning and pushing my DIY skills. I might be out my depth though so might revert to a more straightforward design.

    I’ll keep working on improving my understanding of the maths involved and keep you updated with my progress.
  15. Mr Rusty

    Mr Rusty Screwfix Select

    I would ask yourself exactly why you want the vaulting. You can still use the loft space for storage. This is identical in size to the garage I built in lockdown, and I just used an online truss supplier. King post trusses at 450 centres cost me about £600 at the time. Mine was clad single skin block with piers.

    If you want full vaulting I would do what @stevie22 suggested and divide it up in to 2 or 3 bays with king trusses and use a smaller ridge beam. IMHO you won't span 9m without mega sized beam which will cost £££
    stevie22 likes this.
  16. Adrian72

    Adrian72 New Member

    Thanks Mr Rusty, good advice. Thanks for the link to your post too

    I think common sense needs to prevail here on my part. I've always thought a vaulted ceiling would be good and was up for the challenge but I'm not going to make it harder (or more expensive) than it needs to be. On reflection a loft is a probably a better use of the space anyway.

    Appreciate all the advice, I'll pop back in from time to time with photos of my progress. :)

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