Workshop roof

Discussion in 'Carpenters' Talk' started by mcubbin, Apr 26, 2017.

  1. mcubbin

    mcubbin New Member

    I am building a workshop at the moment timber frame 6x2" osb sheathing on walls and roof timber cladding with steel profile sheets. It will be 4.8 x 6m, 3m at the eaves and 4m at the ridge. I have had a quote for roof trusses, but if possible I would prefer a cut roof if possible. What size of joists and rafters would I need.
     
  2. vivaro man

    vivaro man Active Member

    Mac, by cut roof do you mean hand made or pieced in situ? You can make a jig on the floor or on stools and use ply webs to make some trusses. Very easy and simple. I'm assuming you have some 6x2 and so you want to use that, that's OK for your bottom chord. Your rafters can be made of 4x2 but you'll need a kingpost. Personally, if it was me I would go for home made trusses and use lighter sections, it's not a particularly big building. Is it being done under inspection? Have you any drawings?
    One tip unless the building is just for a store you'll have some heat in there and box profile steel sweats and drips terribly in cold weather. Have you got enough osb to cover the roof and then add the box profile? Can you source some insulated panels as an alternative?
    Good luck anyhow.
     
  3. mcubbin

    mcubbin New Member

    Thanks for the reply, yes I mean hand made, and I thought a king post would be needed, I was planning on using 6x2 for the whole lot. There will be no inspection, it does not need planning and within 30 sq metres so no building warrant. I was going to use the osb on the rafters with a layer of insulation then battens and steel profile leaving a gap between the insulation and the steel. No drawings its really just a box 4.8x6.0x3.0 made out of 6x2's sheathed in 11mm osb, waterproof membrane and cladding, and insulation in the stud wall. I had looked up the span tables, I put new roof joists in my house a 4.5 m span and they were massive, obviously alot more weight, but have not been able to find info on whats needed for steel profile at that span. So you reckon a 6x2 with 4x2 rafters and a king post will span 4.8m, slightly less 4.5m taking account of the stud walls? couple of drawings below, is that what you mean for the simple truss. shed1.jpg rafter.jpg
     
  4. mcubbin

    mcubbin New Member

    Forgot to ask, would that be at 600 centers or 400.
     
  5. vivaro man

    vivaro man Active Member

    Hi Mac, thinking about your design over tea and I think I would use a queen post and 2 members dividing the rafters in 2. The members will meet the queen upright post at the centre of the bottom chord and from there will touch the rafter and divide it in 2 so that you have in effect got 2 triangles (very strong shape). The 4x2 rafter is not then supporting the whole weight of the steel and osb roof but some load is being transferred down to the meatier bottom chord. It also allows for snow loading as well. No doubt you will, like all of us, chuck stuff up into the space and load it with junk. I keep all my hard wood in such a space.
    All trusses on 600mm centres, usually walls are made on 400mm centres that's generally because of sheet material sizes. I would be happy to see your walls being on 600mm centres because I would advise you to make the walls up in osb panels and screw together once completed. It will go up in a morning with 2 of you. The roof trusses will take a bit longer but cut 2 sticks for getting the surface to surface measurement about 550mm. Skew the screws and when you've got 2 up join the underside of the top chords with a bit of scrap but get them 100% upright and square.
    Load the wall plates with the trusses and 2 of you working opposite one another slide them in place with your cut sticks guiding your spacing.
    Use the rest of the osb on the roof and the inside, carefully cut out doors and windows. You could even router them out with a bearing cutter.
    I would place all my power cables in plastic trunking, it's a lot easier to add cables to in the future rather than burying it in the wall panels. You can first fix it and then get the sparky to commission it and away you go.
     
  6. KIAB

    KIAB Super Member

    This a great video for shed roof, Shannon makes the mathes easy, as is the layout,etc.

     
    vivaro man likes this.
  7. mcubbin

    mcubbin New Member

    Hi, yes I have seen that thanks, its very clear. Thanks Vivaro for that comprehensive advice , see below what the truss company came up with, for £36+vat, if I was to use this sort of thing, either bought or made, other than the osb sarking would it need any other bracing or purlins. photo.jpg
     
  8. vivaro man

    vivaro man Active Member

    Hi Mac, no purlins needed or other members. Purlins are traditionally used in a cut roof and act as beams to support the rafter or top chord. That is a queen post truss and it was the one I was suggesting as being best for your job. £36 isn't too bad.
     
  9. mcubbin

    mcubbin New Member

    Hi, I may go down again and have a word with them, I had hoped to have a more open structure, but from what you have said I will need this kind of truss anyway, I was
    quoted £1.60+vat per metre by my local timber merchant for 6x2's so not going to see much change out of £20 for the timber.
     
    vivaro man likes this.
  10. vivaro man

    vivaro man Active Member

    Mac, at least you'll have some peace of mind and they do look OK when raised. I know what you mean about an "open structure" but it only gets piled up with rubbish.
     
  11. mcubbin

    mcubbin New Member

    The main purpose of the building is as a painting studio, I am a professional artist, I was also going to have a framing workshop in it. The front elevation will face north so
    good opportunity to have north facing light, which is best coming from the top, so rather than windows in the sides I intend having a row of rooflights, probably velux type. So a complex truss system is not ideal, but I supposed an advantage of bought trusses is their small section timber.
     
  12. vivaro man

    vivaro man Active Member

    Mac, I can't help you on that. I thought northern light was supposed to be superior but I don't know why.
    If I were you I would be looking at good quality insulation especially insulated box section roof sheets. Installing a woodburner and a sink will help tremendously. A good easy chair is always a good thing to have. Plenty of bench space but put them on 100mm wheels so that they can be moved around.
    As for lighting the area I would look around for some help from a sparkie. There are some really good lights available now that apparently are very easy to work under.
    By heck it could be a brilliant work space.
     
  13. mcubbin

    mcubbin New Member

    It is because is does not change too much,in the northern hemisphere the sun moves across the southern sky so windows facing south will have the sun moving east to west causing the direction of light and shadows to change, the light from a north facing window is reflected diffused light from the sun in the south so does not change as much. Yes I will insulate have been looking at secondsandco for kingspan and yes a woodburner is also on the list. Thanks again for your advice, what part of the country do live in?
     
  14. Dr Bodgit

    Dr Bodgit Super Member

    There was mention of this on Grand Designs recently, light from the north is very consistent as its diffuse light so its what Artists like. Kevin McCloud visited an old artists studio I think on the North Circular which had a lovely large north facing window on the top floor. It gave the paintings inside a lovely almost eerie quality.
     
  15. mcubbin

    mcubbin New Member

    Thats right, the idea originated from the days when artists had no choice but to work with natural light.
     

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