The boards I’m suggesting is ply. A full ply sheet measures 2.44 x 1.22m. The roof slopes front to back and is 3m long. This would mean if you put a ply sheet on lengthways front to back you’ld be left with a 56cm cut. The piece of board you have left you cut off a 56cm rip and start the next row with this. You’ll get 4 56cm wide strips out of a full sheets of ply.
Over a 3m span I’d normally use 6x2s @ 407mm centers but you’ve already 4x2s forming the ring so I’d span the 3m with 4x2s but bring the centers down to 305mm.
Put noggins in to prevent twisting.

Edit..we’re typing at the same time again..over the 3m span I’d definitely go 305 centers..on the shed bit you have a supporting wall so 407 centers will be fine.
Don’t go to travis for your ply. I’m trade and buy my ply from wickes at normal prices as it’s cheaper than TP.
Wbp ply if you can get it if not Hardwood ply from wickes..

thanks mate. just looked at wickes and cant see any 15mm hardwood ply there at 2.44 X 1.22.

google shows Travis Perkins do sell them. ive had all my wood from there so far and have been haggling on price and knocking price down so have a decent relationship with them.

how much would you be happy to pay for 15mm sheets if i give em a ring and say i wont pay any more?

i finished my roof last week, used EDPM instead of felt – cost more, but was pretty easy to lay, and given the amount I’d spent on the rest of the shed, I figured a longer lasting, more waterproof solution was best

wickes 18mm ply

Last time I asked TP for this they wanted £50

i saw that mate but noticed its softwood. TP is hardwood. is softwood still ok?

It says it’s rated for external use so yes..

What about OSB3? Cheaper than ply.

wickes 18mm ply

Last time I asked TP for this they wanted £50
so that works out if i buy 9 boards at £24 each, £216 if my maths is correct. just rang TP and asked them for their price, i asked for WBP and was quoted £226 inc vat, so not tooo much difference.
the quote from them is shows it being…. ‘529899 SELEX B/C STRUCTURAL RADIATA PINE
PLYWOOD 2440X1220X18MM E1′

do you know from that description whether that is indeed WBP and if its any better or worse than the wickes stuff?

What about OSB3? Cheaper than ply.

yes itll be cheaper, but wont look as nice sat inside looking up at it.

thanks

EDIT: just done a proper measure, with a bit of overhang at the back, its 6.7m X 3.4m.

change of plan for the roof. ive already got two 18mm OSB boards for the shed floor, 8ft X 4t and it takes 2 of us to lift one, theyre heavy!

i really was getting quite worried about a dozen+ big 4be2 joists plus 9 of them boards, thats some weight!
i started questioning why i need that weight (i dont think i do), i only want a cover, and the lighter the better.
i started looking at onduline again, got a quote from a place online, realised wickes were cheaper, realised my mate has a 20% discount at wickes and on impulse rushed through a purchase before he goes abroad tonight for a couple of weeks.

so, im having 16 green sheets delivered tomorrow. should have ordered the screws too but didnt want to p1ss my mate about with too many things when he should be packing 🙂

did it all quickly, hope my sums are right. each sheet is 950 by 2m (950 becomes 850 after overlaps). i figure 2 of them per 850 width will give me the depth i need with plenty to spare. and 8 of those comes out at 6.8m, i need 6.7m. think im ok. now have to work out how to fit these things, may need less actual joists and more thinner wood going across, not sure yet……

EDIT: oh, and at £179 for 16 sheets im happy with that.

Wouldn’t of been my choice of material for a pent roof but hey ho.

yeah dont know if ive made a booboo or not, as i say it was a snap decision driven by my fear of overloading the roof ring with too much weight.

the dynamics of fitting it tho and all the accessories may make it dearer in the end :-/

ok, this really is ‘make it up as you go along’….. 😀

ive cancelled the onduline. looked at how you fit it (on purlins which are mounted on top of joists) and realised ill struggle to stop the wind getting underneath it, and to dress it well enough afterwards without more wood on the ring beam. im stumped now.

ive mentioned i want the roof to be as light as possible as i dont particularly trust the weight of a dozen 4be2 joists plus 9 sheets of 18mm ply on just screws. i was awake half the night thinking bout this, its not doing me any favours 😀 i considered last night that its probably an even worse idea than i thought before. rather than the whole ring taking that weight, really all the weight of that wood is just on the front and rear beams, as each beam is individually screwed to the posts, theyre not connected to each other.

my gut feeling now is to go back to the ply option but as thin as poss, 5mm or something. im pretty sure youll advise its a bad idea but why? if its supported well enough i cant see half metre sections sagging for instance.

could i have your thoughts on that please?

thanks a lot, we’ll get there in the end, all part of the journey 🙂

Firstly if the strength of the screws is bothering you whack a coach bolt or a bit of studding through the joint. Easy to retro fit and will significantly strengthen the joint.

Thin ply isn’t a great idea. It’ll take its own weight to start with but over time will sag. I’d say 15mm minimum but 18mm is often cheaper as its more readily available.

Once you’ve got a solid deck any number of waterproof top layers will do. Felt roll (or shingles if you have a pitch), epdm or fibreglass for a tougher but more expensive finish.

I wouldn’t worry about the weight of the ply. A foot of snow however…

Firstly if the strength of the screws is bothering you whack a coach bolt or a bit of studding through the joint. Easy to retro fit and will significantly strengthen the joint.

good idea, ill do that.

been googling again….. what about polycarbonate sheets? they say theyre for shed/garage roofs etc, would they take a foot of snow/not look sh1t? think they do opaque as well.

i picture it looking a bit like this from inside the gazebo which seems acceptable. even better if opaque.

I’ve just used twinwall 10mm polycarbonate sheet on a greenhouse. Light weight and easy to work with. The sheets have a male/female edge so you can butt join them. Have a look at polycarbonate button fixings to attach them with.

It’s the size, spacing and pitch of the timber that will give you the strength rather than the roofing material.

finished the decking last night, theres nothing else i can do to it now til i sort out more wood for the roof and cladding. spent this morning digging up grass and replacing with gravel so it gives it its own ‘area’.

that pic maybe shows the end nearest the field a bit better too, with the 3.4m span ive got for the roof beams. looking at it now it just seems ive maybe made it a bit wider than i should ‘just cos i could’.

It’s the size, spacing and pitch of the timber that will give you the strength rather than the roofing material.

which i spose is what im talking about above. gut feeling is ill still use ply, 12mm compromise, but ill look into polycarbonate. had a quick look on youtube and it does seem a bit of a faff with all the edge and joining beads, tapes etc. and they wont come cheap either.

That’s looking great.

thanks mate, yep, im pleased with how its going.

next question….. after talking it over with my mate, ive decided to stick with ply for the roof, but thin ply first (4mm) topped with 8mm OSB, and staggered for strength and then that topped with felt.
got a quote for all the ply, plus some decent felt (38kg mineral if that means anything to anyone?) but im unsure about the felt adhesive. i thought id just be tacking it down with clout screws, and then using adhesive on overlaps. reading up on it suggests i should use underlay too??
is this just belt and braces, ive never seen felt plus underlay on any other sheds, so can i get away with my original plan, or do i really need to splash out another £100 or so on underlay? :-/

thanks

oh and also, do i have to spread bitumen/adhesive over the whole roof first or just the overlaps?

clout nails directly into felt through to the joists, or do i use wooden battens to hold the felt down?

thanks

just popped into builders yard on way home from work this morning to look at shiplap and ply. disappointed to see they dont do treated shiplap, id always thought they did, but ill just use another yard for that then.

also a bit dismayed to see just how flimsy 4mm ply is. it was warped and bowing all over the place on their pallets, so thats making me think i should just stick with 12mm ply rather than 4mm ply/8mm OSB and risk a warped inner lining at some point.

would appreciate thoughts on that as its your opinions and invaluable advice thats helping me out on this bad boy 🙂
also answers to above questions re underlay/bitumen/adhesive etc much appreciated.

thanks a lot

When I’ve done sheds with felt I’ve never used underlay and just used that black sticky stuff on the overlaps, IANAR 🙂

The thinnest ply I’ve uses is 9mm, but… It’s the wood you screw the ply to that gives it the rigidity. 4mm will be fine if you’ve got the noggins.

ahhhh balls, forgot bout the noggins. thats more timber needed then 🙂

i assume my only option for noggins is offsetting them to get the screws in yep as i did with the floor? and would i get away with just one set of noggins going across or will i need a couple of rows at a 3.4m span. i feel the answer is going to be 2 rows 🙂

Forgot to check back with this… looking good!

On the polycarbonate subject – are you still planning on using it? If so I can take some pics of the canopy I completed last year – looks similar to that pic on the last page – using 25mm poly. In fact my entire build is spookily similar to yours in essence.

Pics if you want them – I can just send them in a email to save cluttering up your thread. I think I took a few of the build itself showing some fancy cross halving joins.

i assume my only option for noggins is offsetting them to get the screws in yep as i did with the floor? and would i get away with just one set of noggins going across or will i need a couple of rows at a 3.4m span. i feel the answer is going to be 2 rows

You can offset them or skew the screws in at 45 degrees on half of them if you want them in line.

Noggins at the end of each sheet and one in the middle would be how I’d do it.

You can get a torch on felt called tecnatorch. Goes on very easy. Used it a few times and had no problems.
Or you could use a edpm rubber roof.

On the polycarbonate subject – are you still planning on using it? If so I can take some pics of the canopy I completed last year – looks similar to that pic on the last page – using 25mm poly. In fact my entire build is spookily similar to yours in essence.

Pics if you want them – I can just send them in a email to save cluttering up your thread. I think I took a few of the build itself showing some fancy cross halving joins.
thanks mate. id have liked to use that from a weight and looks perspective, but when i started pricing it up the cost started running away, so basically….. i just cant afford it :-/
id certainly like to see pics tho purely out of interest.

You can offset them or skew the screws in at 45 degrees on half of them if you want them in line.

ah ok, yep, 45 degrees may look better to keep em in line. i was going to say that surely all the screws would have to be 45 degrees wouldnt they, but then thought you probably mean to screw in every other noggin first, then 45 degrees for intermediate noggins, yep?

Noggins at the end of each sheet and one in the middle would be how I’d do it.

thanks

You can get a torch on felt called tecnatorch. Goes on very easy. Used it a few times and had no problems.
Or you could use a edpm rubber roof.

looked at epdm and ruled it out on cost and i think the torch on stuff is also more expensive isnt it? budgets being stretched so far so need cost effective materials. thanks tho.

google google googling as usual and had another idea from stuff i saw for sale…… i assume instead of felt i cant use this flashing tape on all the ply joins, and then paint this waterproof coating paint over all the roof too? as i say, it doesnt matter too much what the top of the roof looks like, it slopes away from view and only the inside is visible. viable alternative or should i really just stick with the felt?

ah ok, yep, 45 degrees may look better to keep em in line. i was going to say that surely all the screws would have to be 45 degrees wouldnt they, but then thought you probably mean to screw in every other noggin first, then 45 degrees for intermediate noggins, yep?

Yeah, that would do it.

Don’t use the paint. The wood will have a certain amount of movement in all weathers and I doubt the paint will move with it and would probably crack over time. Don’t hold the felt overlap down with batons as this will just hold moisture and rot.
Do use 12mm external ply or above. Do use noggins but I’d space every 1.22m staggered.

Don’t use the paint. The wood will have a certain amount of movement in all weathers and I doubt the paint will move with it and would probably crack over time. Don’t hold the felt overlap down with batons as this will just hold moisture and rot.

advice noted and taken, thats why this thread exists 🙂 must admit i was kind of hoping someone would say yep, good idea if you cant see the finish but im not going to ask for advice and then not take it, ill use felt.
i wont use the batons then either.

Do use 12mm external ply or above.

im certainly not going to have my overall thickness any less than 12mm now, 12 is the figure ive come up with as a good compromise of strength and weight. can i just ask whether you mean use 12mm ply only or its ok to use 4mm ply and 8mm OSB please?
my mate has suggested that the ply/OSB combo would actually be stronger than just ply if all the edges of the two layers were staggered and overlapped, so top layer starting halfway along bottom layer. would you agree with that?

also i have 2 X 4.8m length bits of 2X2 left over so far so was looking at utilising them somewhere. my thoughts at present are to use 2X2 as noggins, save the cost of more 4X2 (joists will be 4X2). ok it means the noggins wont be flush with the joists but as long as they all look the same then am i right in thinking its no big deal? they are only there to stop the joists from bending arent they, which 2X2 will do fine?

Do use noggins but I’d space every 1.22m staggered.

ok, so thats noggins halfway along each 2.44 length, thanks, so 2 rows of noggins. can i ask why you state staggered please? yes staggered will be easier to screw in, but less aesthetically pleasing as theyll be on view. spose its no biggie but just wondering if theres a strength advantage.

thank you very much.

Personally I’d stagger at 1m intervals and not worry about the join. Structural above asthaetics..
Staggered over 3 rafters so that you land on the join of the ply if your that bothered about looks but people will only look up once when they first visit and will tell you what a brilliant job you’ve done. After that they’ll just get on with doing whatever under it..
Space your rafters at 305 centers over the large span if using 4×2. Put the crown upwards.
The noggins will be to stop the rafters twisting..2×2 won’t cut it here
If you want to use the 2×2 up cut at 45deg and put in strategically placed braces in to resist side-loading from the wind.

Space your rafters at 305 centers over the large span if using 4×2.

see this is where i may have to ignore advice unless theres a very good reason. 4 joists per width of ply, over 6 widths of ply, is an awful lot of wood/weight. im trying to get an acceptable compromise of strength to weight, as i mentioned before, im not totally happy about the weight of all that wood resting on basically the front and rear beams which are just screwed into the posts. the weight doesnt go down the big 4X4 posts, its on the ring beam itself.
i was thinking of 2 joists per 1220 width as a compromise, so centred every 610.

sorry, i dont understand the rest of your post as i cant imagine in my head what you mean.
staggered over 3 rafters and at 1m intervals? and i also dont know what the crown is. i apologise, youre being very helpful but i just dont understand 😳

EDIT: im also not sure what the diagonal bracing would bring to the party as im thinking the noggins would be resisting wind from the side? i dont spose you could find any google images of what you mean by any of the above could you so i can see it in my head?
thanks a lot 🙂

If you were going to have 3 rafters per board the 1.22m ply joint would span 3 rafters.

Re Diagonal bracing..forget these if you’re happy with how far you’ve sunk the corner posts. What size are they and how deep did you go?

How wide is the opening on the open part..you might need a knee-brace to help support the weight of the roof here..

If you’re worried about weight on the ring put coach-bolts through.

crown up

Re side-/front-loading…sustained loading WILL cause movement…and although the noggins are in place you’ve only screwed into the end grain of the noggin which is the weakest connection you could make..don’t think it will be as strong as a pegged tendon a la ‘ timber-frame ‘..overtime the structure could weaken. Any diagonal bracing reduces any movement significantly..
I must admit though I do tend to over-build..

How wide is the opening on the open part..you might need a knee-brace to help support the weight of the roof here.

the open end facing the field is 3.3m wide between posts. the full front of the gazebo facing the garden is 4.6m with the intermediate support post 2.3m so exactly halfway.
just googled knee brace and i can see how thatd work. i may well try and saw some 45 degree angles into a few bits of wood and do that. ive just started on the joists (2 rafters per 1.22m ply width so 610 spacing). and as you can see from below pic, i made a few support bits of wood that i thought would set the front off nicely. i reckon your knee brace suggestion may look better now tho 🙂 havent got any coach bolts right now so plopped some 4″ screws in, but i plan on swapping for coach bolts, whether thats my chocks or your knee braces.

Re Diagonal bracing..forget these if you’re happy with how far you’ve sunk the corner posts. What size are they and how deep did you go?

theyre 4×4 posts, the holes were around 18″ for them but i probs used a couple of those inches with gravel for drainage. the 2 end posts (that would take the brunt of the winds from the field and cliff) i did with postcrete.

If you’re worried about weight on the ring put coach-bolts through.

yup, thats my plan now.

re diagonal bracing, i dont really want any wood to go from corner to corner as that removes the access to it doesnt it? i just want it to look nice and open.

crown up

gotcha, thanks. id do that naturally anyway, but as it stands these joists seem pretty straight.

thanks a lot mate

By diagonal bracing I didn’t mean corner to corner I meant knee-braces..my fault..
Good luck

thanks.

roof joists completed today. as mentioned before, theyre at 610 spacing so will support each end and halfway along each ply sheet too.
oh and colins guarding it protectively 🙂

need to do the noggins next, just need to know how to stagger them if you have any advice. at 3.3m depth, and joists halving each ply sheet, i was thinking first side do on the join and halfway, so from the front, set noggins at 4ft and 8ft (easier to work with imperial now as thats how the sheets are measured), then next joist do either just offset by the width of a 4×2, or….. do 4ft and 8ft from the rear as thats probably where the next sheet would be started from to stagger the sheets. that makes the noggins look a bit haphazard tho.

thoughts please?

EDIT: youll notice i also had to stagger the joists on the shed part, thats cos of the framework in the way of a full run, so i decided to do the front joists ‘on the join’ (as thats on view), and then inside the shed just off the join but i can muck about with extra noggins and whatnot for support in there, it doesnt matter how that looks.

Space the noggins at 610 also for a nice symmetrical pattern..start on the join ..
You should have a ply overhang front and back..

As for the shed part you can sister the rafters where they’re staggerd..

Space the noggins at 610 also for a nice symmetrical pattern..start on the join ..

yup, can do that on the join on the first row (and third, fifth, seventh etc), but what about the 2nd/4th/6th etc where they need to be staggered in some way, so cant be on the join?

You should have a ply overhang front and back..

ooh wasnt planing overhanging the front, thought itd need to be flush for the felt to fold over neatly, and maybe a board of some sort screwed to front to finish off. i get the overhang at back, but why the front?

As for the shed part you can sister the rafters where they’re staggerd..

had to google that, but yes, that makes sense, should have thought of that meself 🙂

thanks