Another roofing question.

[500e]

@gaz1 idea with 80 or 120mm insulation wont require so much wood have a finish sheet on bottom so nothing else required fit & forget
That's if you can source that sheet at present Kingspan are 5 miles a week short on material / production we were told

 

[julianf]

@gaz1 idea with 80 or 120mm insulation wont require so much wood have a finish sheet on bottom so nothing else required fit & forget
That's if you can source that sheet at present Kingspan are 5 miles a week short on material / production we were told

was that at me or gaz?

I have the insulation - its one more thing "in the way" currently!

 

[gaz1]

the wood is only there as pure strength and support even if you turned it sideways and bolted to the frame

fitted osb board to the top of it and felted the outside it would make no difference

 

[julianf]

your roof is easy

3x2 or 3x1s bolted to the frame dont forget to sort your rust and paint it first
9mm or 11mm osb to support the felt

use either latts run as rafter woods and then cross wood them using 2x1, 3x1, or 4x1s

then fit your roof panels

as ive used 3x2s meant i could insulate between the 3x2s and then finish off using 1" insulation

I have 120mm insulation currently.

where's that go? im not trying to be stupid, but nothing seems to match up! : (

 

[gaz1]

you too busy thinking about the problem

buy 4x2s and your osb boards

fit the 4x2s stood on there ends and bolt through them to the original framing thats 100mm there before you fit the osb board onto the roof and felt it up

fit a latt internal this will give you a total space of 125mm or more

if your worried about weight fit 4mm plyboard internal with screws and a washer to hold the plyboard up due to the bigger space in gripping

 

[julianf]

you too busy thinking about the problem

fit the 4x2s stood on there ends and bolt through them to the original framing thats 100mm there before you fit the osb board onto the roof and felt it up

fit a latt internal this will give you a total space of 125mm or more

Again, im not trying to be stupid, but if i use a 4x2 (100mm) then board over it, and lathe under it, the internal space is still going to be 100mm, right? And my insulation is 120mm.

Its discrepancies like this that make me feel like what people are saying, and what i hearing are two different things.


It seems, basically, after all this, you are saying to use 6x2 pulins and board over the top of them, but just in different words?

 

[500e]

A ridge and 1 perlin then that tile sheet, with insulation and finishing sheet (all one peice) job finished, of to the pub before lunch
Sell the 125 you have

 

[julianf]

A ridge and 1 perlin then that tile sheet, with insulation and finishing sheet (all one peice) job finished, of to the pub before lunch
Sell the 125 you have

Its not the insulation that's the problem - it was just that Gaz's example did not fit with the data given, so either my understanding of his description was inaccurate, or his understanding of the job inaccurate.

He seemed to offer a different solution to the "fit purlins and board over the top" which seemed to turn into "fit purlins and board over the top" - and i just feel that im missing some bit of information that would make it make sense to me!

I appreciate everyone's help, im not trying to be awkward, i just dont get it. Like i say, what im being told, and what is in front of me doesnt seem to match half the time.

 

[gaz1]

Again, im not trying to be stupid, but if i use a 4x2 (100mm) then board over it, and lathe under it, the internal space is still going to be 100mm, right? And my insulation is 120mm.

Its discrepancies like this that make me feel like what people are saying, and what i hearing are two different things.


It seems, basically, after all this, you are saying to use 6x2 pulins and board over the top of them, but just in different words?

no too much weight and too high its bad enough with 4x2s turned on its side 6x2s would be worse

your insulation is 120mm the space inbetween the woods with the latt on is 125mm

what your looking for is not having to cut the insulation so many times

this is built on the same principle



looking at it

its roof material then felt then wood rafters and woods with space inbetween to fill with insulation

yours would be built the same way but instead of rafters your using perlins your rafter beams are below your perlins

 

[julianf]

no too much weight and too high its bad enough with 4x2s turned on its side 6x2s would be worse

your insulation is 120mm the space inbetween the woods with the latt on is 125mm

what your looking for is not having to cut the insulation so many times

this is built on the same principle

View attachment 292704

looking at it

its roof material then felt then wood rafters and woods with space inbetween to fill with insulation

yours would be built the same way but instead of rafters your using perlins your rafter beams are below your perlins

In your photo, whats to stop me membrane sagging into the voids?
I mean i know the insulation is in there, but wouldnt it still sag over the purlins and pool if there ever was an issue?

Are you talking of using 4x2 and then a 1" baton to, effectively, make 5x2? If so, cant i just buy 5x2 (assuming it exists)?

 

[gaz1]

in the photo he didnt use boarding I would have done as i know it sags with heat and he got warned

if you want to fit just the insulation straight onto the metal do so but your woods need to be under the framing otherwise you have nothing to pull your roof down to make it solid

that means cutting slots into the wood at the angle iron points

ive drawn it in red for you



and then this way

its for either slate or metal roofs makes no difference

but if you want to fasten the felt to the insulation just nail it shove your roof on it and bolt it down to the perlins it will hold it in place

 

[julianf]

Right, so there is the first point of confusion -

I was always talking about putting the pulins on top of the aframes, as per my poor image below.

Then putting the insulation between them.

There would be no need to notch them to the metal a-frames. They could just screw on from underneath using the original holes. This is how the roof originally was, with the aesbestos.

 

[gaz1]

yours are not like mine as yours have a cross member leg on them mine are built like an apex frame



just fitting 4x2s onto your apex structure you are strengthening them

the cross member is your tier of the apex

yours is known as a raised tie truss done in angle iron

you will see by this

How much stronger is a triangle-shaped vs. A-shaped truss? Max snow load comparison?

I'm on a property in which there is a garden shed and its roof collapsed yesterday because of heavier than normal snow that accumulated on it over the past few months and it looks like yesterday was

diy.stackexchange.com

Raised Tie Truss - MBC Timber Frame

The MBC Passive Roof system delivers a U-Value of 0.10W/m2K. 400mm deep, high performance insulation forms part of the continuous thermal envelope.

www.mbctimberframe.co.uk

which is like this using 1" apex wood without the cross member



whilst this one uses 2" apex wood


the pic above has a lower cross wood to tie the apex and make it into a king

because the 4x2 sits on top of your metal tie truss your wood sits on top of the walls

like in these pics

Raised Tie Truss - MBC Timber Frame

The MBC Passive Roof system delivers a U-Value of 0.10W/m2K. 400mm deep, high performance insulation forms part of the continuous thermal envelope.

www.mbctimberframe.co.uk

used perfectly well on many old buildings

 

[Gareth J]

Right, so there is the first point of confusion -

I was always talking about putting the pulins on top of the aframes, as per my poor image below.

Then putting the insulation between them.

There would be no need to notch them to the metal a-frames. They could just screw on from underneath using the original holes. This is how the roof originally was, with the aesbestos.

View attachment 292739

If that's your plan of attack, what's wrong with going with the pic I sent previously (all stained black wood).

Steel rafters,
Purlins
Vertical Battons
Membrane
Counter battons
Tin.

Insulation sits between purlins and held in with whatever you decide is appropriate for the spacing/how you want the inside to look...

 

[gaz1]

for start off you have strengthened the roof truss with the 4x2

the red is your 4x2s that fasten to your apex metal and also sit on the outside wall whilst the yellow is the 3x2s or 4x2s makes no difference



so can fit 3x2s inside of them so the frame looks like this

same principle a 4x2 apex frame with 4x2 internals



then fit your osb board felt it and roof it fit the insulation on the inside of the structure

or insulate it then felt it and fit the roof on top

only difference is the length of bolts used

industrial bolts

Heavy Duty Composite Sheet to Steel Roofing Screws - Fixings & Fastenings | Forgefix

One of the UK’s leading distributors of fixings and fastenings with over 30 years of experience, we supply in excess of 2000 different product lines to builder’s merchants, plumbing merchants, DIY outlets, hardware stores

www.forgefix.co.uk

unknown if you can find the bolts to screw through the insulation too wood as normally its screwed onto metal z purlins

 

[Gareth J]

for start off you have strengthened the roof truss with the 4x2

the red is your 4x2s that sit on the outside wall whilst the yellow is the 3x2s or 4x2s makes no difference

View attachment 292768

so can fit 3x2s inside of them so the frame looks like this

View attachment 292767

then fit your osb board felt it and roof it fit the insulation on the inside of the structure

or insulation it then felt it and fit the roof on top

only difference is the length of bolts used

That's a neater, lower profile way. Probably better suited if it's going to end up less as a shed, more of a habitable space.

 

[julianf]

for start off you have strengthened the roof truss with the 4x2

the red is your 4x2s that fasten to your apex metal and also sit on the outside wall whilst the yellow is the 3x2s or 4x2s makes no difference

View attachment 292768

so can fit 3x2s inside of them so the frame looks like this

same principle a 4x2 apex frame with 4x2 internals

Thats what i was initially going to do, but i asked on another thread for the timber sizing for the purlins, and was told 4x2 or 6x2. Indeed, and, again, im not trying to be clever, as i appreciate your help, but i want to highlight where my confusion is comming from - i think you personally said 6x2, but now as low as 3x2.

So then i was going to use 6x2 where youve got the red, and notch them for 6x2 purlins, but that didnt seem the best plan.

 

[julianf]

If that's your plan of attack, what's wrong with going with the pic I sent previously (all stained black wood).

Steel rafters,
Purlins
Vertical Battons
Membrane
Counter battons
Tin.

Insulation sits between purlins and held in with whatever you decide is appropriate for the spacing/how you want the inside to look...

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.

 

[gaz1]

there was a difference on that one as we was talking about purlin spans

roofing calculations - purlin dimensions

Using this corrugated sheet material - https://www.cladco.co.uk/32-1000-box-profile-0-7-pvc-plastisol-coated-roof-sheet With a maximum unsupported purlin distance of 1.6m, how do i know the strength of the purlins to use? The datasheet gives the purlin spacing of 1.2m, but, so far as i can...

www.mig-welding.co.uk

this one you have made it alot clearer and its not the perlins with strength like a beam thats needed its basically strengthening your roof frames and using internal perlins

a big difference

the point of your rafters and your internal perlins is so you can fasten your roof sheets to it across the perlins

and these sheets do exactly that, there is an apex ridge board 4x2 along the top from one to the other you can see this on the internal above



if you want to use the lift and cross batten reference you would need to add rafters into the build as your changing the roof original build structure only works on new builds not old builds



each downward wood has a rafter underneath it and then is cross battened

yours would not have a rafter in the middle and would cause roof to be lifting in the middle not a good thing the only way to stop this is to make another 2 apex tie frames and some how tie these to the concrete wall you have

the latt batton fixed to the 4x2s is below the roofs natural level used more in something to screw your internal plyboard too really its there only to hold up the insulation in the roof nothing else

this will drop your internal roof gap instead of being inline giving you more space for your already bought insulation to be fitted internally

 

[gaz1]

all i would do is buy the

4x2s needed
osb board sheets
breathable felt
4-5 latts for inside spacings
and plyboard 4mm sheets

bolt 4x2s to the metal frame you have now as they sit on your walls and the top is fastened too a 4x2 ridge board
use 4x2s for the internal purlins
fit osb ontop of the frames
fit the breathable felt running length ways
and just fit the metal roof to this

then fit your insulation and screw the plyboard up to it

if i was building an internal frame then id fit in the extra rafters knowing id tie them down to the wall framing