Clear span front to back of the shed is 3m 300mm.
Looking at
TIA
Dave R
Only if your roofing material would object to someone standing on it mid span at 600mm...
Depends on what you may want to do on the roof. I beefed up our bought shed's roof with old fence posts and rafters, cos I like to put a ladder on it to get up the side of the house on occasion. The extras are also handy for hanging things on inside.
S
for the sake of an extra 3 lengths of timber, I would go with the 400mm spacings, also, I wouldn't put a flat roof on it neither. Built one about 6 years ago and it had a fall of 12 inches (300mm) over 3m and it is still like like new. 'flat' rooves tend to hold the water in puddles which creates weak spots, which the sun and the frost then make worse in summer and winter respectively.
If you go down this road, it's a matter of bituminised OSB boards and either torch-on mineral felt or a boiler and mineral felt etc, we used torch-on, one layer and it's still like new with no moss, bubbles or anything else.
Must admit to being a big fan of torch on felts, they seem to do a very good job with little or no fuss.
When I say 'flat' I mean 'flat with enough slope to chuck off the water'.
As stated previously (keep up at the back ;-) ) it has to be non-inflammable so I can't go for torch on felt on a wood deck.
I plan to use firings (SP?) to put a minimum slope on the roof.
Well yes - a flat roof isn't a problem; a horizontal[1] one is. Most roofs are (near enough) flat, as are walls.
I can't see any point in having a horizontal roof. Surely, in most cases, there's some way of getting a slope.
[1] Yes, a horizontal roof isn't flat - especially a big one.
I thought the phrase about combustibility and proximity to boundaries etc was something like "of substantially non combustible materials". Hence I would have thought that a block built shed with wood roof would meet that requirement?
If the contents of the shed go up in flames then would it matter if the roof is metal or wood? Or is that requirement to stop a fire from getting to the neighbours property?
Back to the original question, at a span of 3.3 metres that table suggests 50x170 would be suitable and somewhat cheaper. Assuming you are paying for the merchant to deliver its worth going along to select the timber for your project so you can discard anything that looks warped. They may think you are odd but otherwise you will get whatever the storesman loads onto the truck - which may not be perfect for a flat roof.
Dave.
Dave.
Talked to the planners/BCOs locally and they said tile or tin were O.K. but wooden deck was considered inflammable.
*If the contents of the shed go up in flames then would it matter if *the roof is metal or wood? Or is that requirement to stop a fire from *getting to the neighbours property?
Only applies within 2 metres of a boundary so presumably to protect neighbours.
*Back to the original question, at a span of 3.3 metres that table *suggests 50x170 would be suitable and somewhat cheaper.Fairly close to maximum loading, though, so 50*195 looks a better bet. I don't know what margin is allowed for in the calculations. I may want to walk on the roof. I may want to hang things (bicycles, tools, irritating neighbours) from the joists. I may want to put in a swing to go with my play pen ;-) Who knows? Seems bettter to slightly over-engineer now than have to retro-fit more strength later.
I appreciate its flammable, but was the question was "does it matter" since the bulk of the building is not?
One could go back to that calc I did the other day and plug in the actual spans etc.
Say we go for 3.3m span, 400mm spacing, and a roofing material weighing in at 15kg/m^2. Allow the typical additional 75kg/m^2 for snow and access etc, we get a roof joist with a:
3.3 x 0.4 x (15+75) x 10 = 1.2 kN total load per joist.That is a relatively light 1.2 / 3.3 = 0.36 kN/m UDL on each joist.
If you go play with superbeam it becomes apparent fairly quickly that even 50x175 is well in excess of what is required - even if you apply the same stringent requirement that one would use for a floor in a building (i.e. deflection at the centre of the joist shall not exceed
0.003 x the length - which gives you nearly 1cm to play with).50x175 of ordinary C16 timber would give you under 5mm deflection,
50x150 would still be under 7.5, and hence still be in spec.The only factor you may want to include is treating yourself as a short term point load during construction should you feel the need to stand on a single joist mid span and you happen to be a particularly FB! Then you might want to at least make sure there are some noggings in place before you start bouncing too much! ;-)
(note you get a little extra strength from the firings as well, which has not been included in the above)
Yes.
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