3m flat roof span with 44 × 95 joists


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Thankyou everyone for the advice. I have decided to redo the roof with 6x2 joists (just took delivery today) and take the roof up an extra 2 inches (this will take me 50mm over my planning permission but i doubt anyone will notice).

My plan:

  • Install 6x2 joists, 400mm spacing
  • Double up the 6x2 joists at 1/3 and 2/3 of the roof length to give extra reinforcement.
  • Take down the current 4x2 joists and save the timber for other projects.
  • Joist hangers will be cut open to get the joists out and then cut off leaving the bottom section nailed in the wall framing.
  • Right angle brackets will be used to give extra fixing between the joists and the top plate. I probably won't do every joist as its overkill, every other joist is more likely.

"....would mean i'd go over my planning permission height by 2 inches..." Seriously, nobody's going to enforce against that - really!
Looking around at some other outbuildings i think you are probably right, I see some big monstrous sheds and storage units and no one seems to care.
Im going to take it 2 inches above and cross my fingers. I don't think anyone will care like you say.
You don’t need any joist hangars, brackets, straps etc on your roof. Save your money. The only metal you need is your nails.
Where this shed sits the fence panel was blown off last year due to storms. Just in the last few weeks with the recent storms, 4 of my neighbours fence panel blew off (they were in bad condition to be fair) but we do get some pretty high winds here.
Umm, I'd disagree. Am Essex based and had open fields both front and rear and the house front faces west - so the wind is either blowing front to back or the vice-a-versa. When we have storms blowing stepping outside via a side door and mug of tea usually results in half the tea being lost in the wind. When I questioned my BC as to why a pitched roof EDPM covering my rear extension required 95 x 150 x 6mm thick I-beams over 2 picture windows he replied wind loading...
During one storm a neighbour lost 4-5 concrete ridge tiles 2 of which ended up in my front garden... they weigh approx 6.6kg each ignoring any attached mortar....
Agree, neighbour lost some roof tiles too last week from the storm. To be honest the joists hangers and brackets cost £1 each so its worth it just for piece of mind when I'm sleeping at night and can hear some high winds outside 😄
Build the ground up 2” around it as it’s measured from the highest ground level and just go with 6x2 then !!
👍 ill be repaving the area around the shed when its done so will remember to do this
And then a few tonne of roof tiles or slates to help prevent lift, screw nailing is the old way of attaching joists to the wall plate, but then the joists where bird mouthed to the wall plate and a much thicker section.

To the OP the clue is in the name joist hanger the right angle plates you have shown above are correct tor that application, but don't forget the herringbone cross braces, very important, joist fail by twisting first they do not shear straight through.
Thanks, ill pick up some of those right angle brackets for when I redo this roof. Im using screws solely on this build no nails, but have been cross bracing them.
just to bung in another tuppence worth, how about cutting off one side of the hanger only leaving the other side to hold the timber down and adding stepped 6x2 alongside the 4x2. i have tried to picture what i mean ie cut away the red bits and add 6x2 timber shaped like the black bit alongside the 4x2 where the red bits of hanger have been removed. no nails need to be removed and in fact if you just cut the bottom of the marked triangle and fold it back the new joist will sit alongside happily

View attachment 174865
Thankyou for this tip, very good idea, I'm going to be taking these 4x2 joist out as I'll reuse the wood for the door and window framing on the walls but I might keep 1 or 2 in there and use this method to double up the joists for extra rigidity
Could you not sit a 47 x 50 or 75 down to 0mm firring piece on top of the existing rafters?
Possible but i'd rather not cut firing strips, limited tools
Hi I would grind down each side of bracket and move new joist to new positions (no nail removal) if you go with 6x2 I would not cut bottom out of it because it could split. Could you'd save 4x2 timber for bench making and future projects, I would not space new joists to far apart false economy.
Do the job once do it right 👍 hope you get it sorted
Good idea, problem is i spaced these out by 500mm as i run out of wood so the hangers are in the wrong position if i want to do 400mm on centers.