Garden room build, odd shape, roof ideas

Speedyrazor

Speedyrazor

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Hi, I am building a garden room which is not your 'standard' shape, using the space I have available. I have almost completed the foundations and basic floor base (see pics).
I am trying to keep within permitted development, under 30m2 and within 2.5m maximum height. The issue I'm having is in the roof design. I was planning on a flat ,cold roof, using rubber EPDM, but having trouble visualising the layout of the joists and fall. Thought I would post here to see if anyone has come up against this 'challenge' before?

Kind regards.

IMG_8216.JPG
 
Which way did you intend it to fall? In anycase it's not so complicated if you have access to some kind of cad programme? Even Sketchup would do, which is free to use.
 
Thanks for your replies.
House is to the left of the picture, Was planning for 2 windows to go on left side, and door to go at front of picture.
I was intending fall to go to the right, hedge side. I did try and use Sketchup in the beginning, but couldn't get my head around it. Any tips would be much appreciated on how to go about it.
Many thanks.
 
Speedyrazor said:
Any tips would be much appreciated on how to go about
Click to expand...

Put in the first firing from the central point on left to the back with a 1 in 40 fall
Then make all your other firings parallel.
That will set the fall towards the rear and the roof all in line on side view.
It will set the gutter at rear level

The front of the roof will fall, but your face is can be set level so you won't see that.
 
Hi Notch7, great suggestion, simple and effective, I didn't consider firings as I couldn't find them that long, as my longest joist in the middle is about 5.6m, if I could find them that long, I just then cut them down shorter and shorter as it goes along. Anyone know where can I get 5.6m firings please?

Kind regards.
 
Speedyrazor said:
Hi Notch7, great suggestion, simple and effective, I didn't consider firings as I couldn't find them that long, as my longest joist in the middle is about 5.6m, if I could find them that long, I just then cut them down shorter and shorter as it goes along. Anyone know where can I get 5.6m firings please?

Kind regards.
Click to expand...
you can use shorter firrings, just add a bit of say 50 x 25 to the underside to make up the height -obviously you would need to work out where to cut the firring to make up the height you need.

Ive always cut my own firrings so never had to worry about buying them

if you want a warm roof put the firrings under the insulation. Use enough firrings to support the insulation though.
 
get a polystyrene block the full size off the area but scaled down
cut the roof at the angle and direction you want then remove the odd shapes
iff done accurately will give you a good idea about how supporting walls that may have level tops in your head will indeed be on a slope
 
I am looking at the Spanning Tables for the roof joists (https://www.timberbeamcalculator.co.uk/span-table/flat-roof-joists?load=0.75&class=C24). Roof joists will run from left to right, same direction as floor joists, fall to the right, hedge side. There are 18 joists, 16" centres, all of varying lengths, so trying to work out what I can 'get away with' in terms of joist height, as I am using permitted development, overall roof height can't be anymore than 2.5m, so roof joist height is important, every mm counts. Could I get away with C24 47x170?
Here are the clear spans for my roof joists.
Workshop-v3.jpg
 
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they should be at 16" centres not 16" apart so iff its say 48mm its 14and 1/8th" apart
if its 51/2" its 14" apart
 
Speedyrazor said:
Yes, sorry, 16" centres, I corrected it above.
Click to expand...
not being picky just making sure we all are singing from the same hymn sheet :D
i should have said do you mean appart or centres
havent done the calculations but iff they are very very near you may get away with tight noggins right at the end from 485-491
or even doubling up on longest 4 timbers
also iff the point is the high side then perhaps a 4x2 flat side on from perhaps 442 to 452mm may help
just ideas as its a challenge
also worth noting in a structure its often easier to have a transition or short flat section so you can put change off angle on horizontal timber connecting to verticals rather than having to angle full length often on more than one face off a single timber making it impossible often overly weak
now in your drawing it seems to be allowed for but worth a mention
 
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Thanks big-all, although I'm not sure I understand some of your suggestions:

"also iff the point is the high side then perhaps a 4x2 flat side on from perhaps 442 to 452mm may help" - Could you explain what you mean by this please?

"also worth noting in a structure its often easier to have a transition or short flat section so you can put change off angle on horizontal timber connecting to verticals rather than having to angle full length often on more than one face off a single timber making it impossible often overly weak
now in your drawing it seems to be allowed for but worth a mention" - I don't understand, could you please explain?

Kind regards.
 
instead off the firings at that point you have a cross beam helping to support the joists to the wall sideways now it wont do a lot but iff your over span by say 10% it may bring it nearer to zero
 
Apologies, I'm not sure I still understand you. You mean like this (the fall is from left to right in direction of joists)?
Workshop-v4.jpg
 
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