corrugated roof design

[carlos]

hi iam  trying to reroof an old stone shed with corrugated tin, i have leveled off the walls with a sort of concrete ring beam with a 2x4 wall plate bolted on.

iam going to use 6x2 to make "a" frames. the span is 3.8m (12 ft)  so iam  a bit unsure how far apart to put the "A"s?

i was going to put 3x4 purlins on top of the "A" but as i have raise the roof up a bit already iam faced with a fair bit of stone work to biuld the walls up, iam crap at stone work so iam now wondering if i could use lighter 2x4 purlins set inbetween the "A"s maybe on hangers, i will put in 3 per side along the length of the roof.

i havent actually finished the "A" and the bit of green 4x2 was just to aid the set up.

any input appreciated

thanks carl

[donnk]

4 x 2 be plenty. We get 3x2 trusses that take 4 ton of pantiles no problem.

[drinksloe]

On shed roofs the 'trusses'/steel are usually 5m centres, but would depend on wot size of purlins u decide on.

It also might depend wot size of purlins u can actually buy, i have heard in short supply/high demand, 

U would be easier using hangers and screwing the purlins in too too keep hieght down.

 

I take it u dont have much snow?

Looks quite a shallow roof pitch from the photos, but obviously be fine in the past since stone work is at a similar angle ( unless u've raised the wall heads)

[carlos]

i have lowered the pitch angle a bit mainly just so theres not so much stone work to do on the gables, but it does look a bit shallow??!!

we dont get much snow normally but it is a seriously windy spot in the winter.

is there a typical pitch for this type of roof?

not really done any roofing and stuff online seemed to mainly related to slate or epic farm buildings.

thanks

[daveatdave]

looks like you want to lift it up at least a foot to bring it in line with the gable rake i would use 6x2 for them you might get 6inch of snow on the roof one day by the time you have built the gables you will be a expert go for it 

[muttley9050]

Pitch is fine for a sheet roof. I would pitch it in 5x2. Thec use 4 batons instead of purlins.

As stated above 3x2 trusses are available but these are computer designed and factory built so completely different loading to a hand cut roof. 5x2 is fine at 1.9m run. If you want to use less timber use 4x2 the wrong way up as battens and keep the trusses 1.2m apart.

This would give you a height of 5.5 to 6" above plate

 

 

 

 

 

[carlos]

cool thanks for the replies,

i think i will raise the pitch a bit as i havent really started cutting the timbers yet.

ive got 6x2 so iam still going to use them for the trusses and i recon i will space them at 1.6m intervals then infill with 4x2 purlins top and bottom and one in the middle, i hope that will be butch enough!!

the original roof had about a quarter of that timber but despite being rotten and old the closeness and strength of the grain was incredible, maybe scots pine or something certainly not what one gets at the builders supplies today.

thanks again for the replies they have really helped.

carl

[carlos]

update !  now thinking of 6x2 rafters  at 1.6 m apart with 3x2 on end running length ways as purlins ( ontop of the rafters) there will be three per side at just over 1m spacings,

any thoughts ? 

thanks

[scbk]

I've seen some old sheds with barely any timber in them, somehow still standing. I'm still learning, and usuaully just do what looks "ok" or whatever timber I have to hand.

 

 

According to planwell roofing: . "Unsupported purlins must have a depth of at least 1/ 20 of their span."

So 3x2 on edge is good for 1.5m span.

[carlos]

cool, good info, iam not too far out then with 1.6m rafter spacing, could always move them closer since i have only got two up,

thanks carl