Another roofing question.

[eLuSiVeMiTe]

If that was mine I'd be inclined to do away with the steel completely.

Internal 2x4 studwork all the way around. Insulated and boarded and will support the josts.
Joists across the short run and firrings for a fall

 

[Gareth J]

Not a lot wrong with that... : )

Initially i didnt understand how the end of the vertical batton would affix if i didnt have a ridge, but i realise now it will just overlap the top purlin and be fine.

In this plan, i assume the battons are just 2x1 or somthing, as theyre doing nothing other than holding up the membrane, and the sheet roof would still be screwing to the purlins themselves?

I wonder if all that will be a lot lighter than just board - i guess it must be. Thank you.

I defer to the more experienced advice here. My example is just a low stakes lean to single garage I wanted to replace cem fibre with tin for minimal hassle but include a membrane.

Regarding the ridge, obviously you won't want too much of an overhang. If your top purlins are not that close together, will probably make sense to put a board onto the ridge or tie both sides together somehow. You're sheets will be well tied together with capping tin and stitch screws anyway.

Have to say the concern over weight is a bit worrying. Is it really that close to the bone engineering that another sheet of board is going to make it dangerous? What about wind loading? Snow? Both of which could make a few sheets of board look insignificant!

PS, don't forget to tie it all down somehow

 

[julianf]

Have to say the concern over weight is a bit worrying. Is it really that close to the bone engineering that another sheet of board is going to make it dangerous? What about wind loading? Snow? Both of which could make a few sheets of board look insignificant!

Who knows. I have the original plans from 1971, but they offer nothing more than drawings. I just cant really see how it stays up anyway, but half of my house is like that (old stone and cob walls) and thats been up a couple of hundred years or so.

I just dont trust the garage construction, and dont want it to be the last straw that breaks the back.

 

[gaz1]

because yours has things missing on the frames

im not saying its not original as it could be but all of these have metal cross members on them even mine had it

I removed it as i have the apex frame type the first one

long width garages got the dual metal frame

up north we have the issue of weight of snow so something that wasnt really used was the tie truss

 

[julianf]

because yours has things missing on the frames

im not saying its not original as it could be but all of these have metal cross members on them even mine had it

I removed it as i have the apex frame type the first one

long width garages got the dual metal frame

up north we have the issue of weight of snow so something that wasnt really used was the tie truss

View attachment 292929View attachment 292930View attachment 292931View attachment 292932View attachment 292933View attachment 292936View attachment 292937

Mine was just like the photos youve posted.

The purlins, if thats what theyre still called, look like box in the photos, but really theyre just (aprox) 1" angle.

They dont even run the whole length of the roof, but in about 2m sections with overlap. The clips were just like those shown in the photos - little bent bits of galvanised metal.

Basically virtually identical to the photos posted.

 

[julianf]

Oh, i still have all the angle, but probably not the clips.

 

[julianf]

You can see in the photo below that ive tied in the sides with threaded bar set into the block work, and bolted to the section, to give greater stability (i took it down and reassembled it, hence the block work). You can see the grey angle with a bit of thread hanging out on the right hand side of the photo? Thats the top course one, but the others were put in whilst the blocks were being laid.

Ive also welded up and got dipped an overkill door frame so that will stop the walls "bending" in the middle. You can see a large bit of angle on the inner face that is bolted through the pre-fab sections. It didnt need to be that big, but it allows the right thickness for finishing 50mm cellotex and board on the inside.

The frame on the other side isnt done yet, but it will be the same - ive cut it all just not welded it yet.

 

[julianf]

I figured timbers over the walls would be good, as then the weight would go on the walls, rather than just a few bolts -

 

[gaz1]

yours is the older frame than mine as i have the 10ft garage type with a proper apex frame build and concrete corners

just to say you will be fine too build a 4x2 frame on your prefab shed and do a birdmouth over the wall

and frame it like this



a general query here you are putting metal box profile roof on ?
not the cheapfelt roof type

if you are then just fit a top and bottem wood like the older design

 

[julianf]

Am putting this stuff on -

 

[Miranda]

All this looks huge overkill to me!!! This shed.. 14’ wide has been here 40 plus years.

4x2 rafters. 3x3 purlins and twin 3x1 bracing in two places..

Our pre fab double garage has the same 1” angle roof structure shown on this thread vu Gaz …. Loads of it has rusted away but it’s still totally intact.

Why am I getting a security problem uploading a pic I took two mins ago?

 

[Miranda]

 

[julianf]

All this looks huge overkill to me!!! This shed..

[snip]

...has no insulation, no membrane, no inner skin, and is sat on block walls.

 

[julianf]

yours is the older frame than mine as i have the 10ft garage type with a proper apex frame build and concrete corners

just to say you will be fine too build a 4x2 frame on your prefab shed and do a birdmouth over the wall

and frame it like this

View attachment 292942View attachment 292943

a general query here you are putting metal box profile roof on ?
not the cheapfelt roof type

if you are then just fit a top and bottem wood like the older design

So my best, current plan, seems to be to get 5x2 and bolt them to the existing metal structures, notched over the walls to spread the weight.
Then get joist hangers and fix more 5x2 between them to act as purlins.
Then board (how thick, and is all osb the same grade? ie what do i buy?) and then membrane.

If i stack 4x2 purlins on top of 4x2 rafters (the bits bolted to the metal) then im 8" thick, and still dont have room for my 120mm insulation.
If i dont use joist hangers, but put whole purlins over the top of the rafters, then i have nothing to screw the inner board to.

Does that sound sensible?

If i cant get 5x2, i guess ill have to use 6x2.

 

[gaz1]

the latts are below the metal framework fastened to your wooding that your fitting

if you want to get 5x2s its fine that way all depends on how high you want to jack up your roof

then its sort the front edge out is how do you stop it liftng at the front only way i can think of is to fasten that perlin wood as close to the wall as you can get roughly an 1" away from the internal wall

 

[julianf]

the latts are below the metal framework fastened to your wooding that your fitting

if you want to get 5x2s its fine that way all depends on how high you want to jack up your roof

then its sort the front edge out is how do you stop it liftng at the front only way i can think of is to fasten that perlin wood as close to the wall as you can get roughly an 1" away from the internal wall

If I'm understanding you correctly, the metal is drilled for the old metal purlins.

I can screw up into the rafter wood from underneath.

That will stop any lift, right?

 

[gaz1]

the metal angle iron already has holes in it,
its fine to use them as i did do

just drill a hole right through the 4x2 drill a wider hole so the bolt sinks into it when it tightens it pulls the nut down into the hole

fit the 4x2s or 5x2s onto the metal angle iron and bolt tight

fit your high wood i think its 200mm from the top of the apex and same for the front edge as well

front edge id give it half an 1" or a full 1" out from the wall and cut your 4x2s level across all of them

fit your fascia board id buy plastic like we have it looks better or you would have to buy wood then metal facia board or thin plastic just better to buy the thicker fasia board



the angle on the above gave 5 1/2" so 6" fasia board was bought its cheap enough

then cut and fit insulation above your wall and felt across it

if you look at the above picture the only reason it has the extra wood is to support the felt but also support the roofing material as that material does sag in hot weather ive seen it so know it does it

if you want to do the same fair comment but if you dont just fit the felt and fit your roof metal onto the top of it then insulate it from the inside at your own leasure

 

[gaz1]

heres the video of how industrial buildings are done

but because your not lifting your roof like in the video alternatives have to be used

 

[Miranda]

[snip]

...has no insulation, no membrane, no inner skin, and is sat on block walls.

None of that weighs anything much.

Our covered yard has 27’ spans and 15’ bays. I agree the rafters are comparatively hefty at 12x3” but the purlins are 6”x2 over 15’ gaps with concrete big six roofing and are now completely covered with solar panels.

 

[addjunkie]

None of that weighs anything much.

Our covered yard has 27’ spans and 15’ bays. I agree the rafters are comparatively hefty at 12x3” but the purlins are 6”x2 over 15’ gaps with concrete big six roofing and are now completely covered with solar panels.

I agree, I think your over thinking this. Use self drilling steel fixing screws to fix wood to your trusses. Build the roof you want and block any gaps up with appropriate barge boards etc.
My farm shed has 6x2 purlings on 15ft bays with big 6 sheets too.

I hate concrete garages, if money isnt an issue, start from scratch.