Rebuilding old shed - roofing question

[alex robinson]

Hello,

I am looking to rebuild an old (quite large) shed. Given the amount of work that will be involved I thought it would make sense to make more work and replace the old rotten structure with an insulated one. I will be reusing the old dwarf walls to build the frames on, hence the slightly odd layout.

I was wondering about something like this for the roof (as viewed from the top of the first picture).

Firstly, does this seem vaguely plausible? The current structure has lasted over 40 years, and was made with very small section timbers, but I would like to play it safe as well as allowing for a stronger, insulated roof.

I know doors and windows will have to be worked out, but that can come later.

Second, what would people suggest for the roof? I dislike roofing felt as too flimsy and short lived. I have EPDM on my workshop and it is brilliant, but is the pitch of the roof too steep for this? What would people suggest for the layers? Inside skin of OSB, kingspan, air gap, OSB, then either vapour membrane and orduline/metal sheeting or just EPDM glued onto the OSB?

Thanks!

Alex

 

[Jameshow]

What about insulated steel roofing sheets. They would be my choice.

They are very self supporting so only need a few purlins to hold up.

 

[alex robinson]

What about insulated steel roofing sheets. They would be my choice.

They are very self supporting so only need a few purlins to hold up.

I have looked at them and they are tempting (if quite expensive). Do you need any of the vapour layers etc with them, or do you simply place them straight onto the rafters/purlins?

 

[Fitzroy]

I would happily copy a frame structure that has lasted 40yrs, additionally you know it works with the wall structure you have. Going to thicker timbers will place more load on the walls, perhaps unnecessarily. I'm a EPDM convert, no reason why it can't be used on a pitched roof.

I don't understand your build up, it should be internal lining, vapor BARRIER, insulation, ventilated air gap, roof deck, waterproof layer. In your case OSB, barrier membrane, kingspan, ventilated gap, OSB with EPDM adhered to it.

If you are using a waterproof layer that is not continuous, ie tile, onduline sheets, etc then it could be. internal lining, vapor BARRIER, insulation, air gap, roof battens, breathable membrane, tile/sheets.

The idea of the vapour barrier on the warm side is to keep the warm moist air from penetrating the ceiling and getting into the cold roof space, where the moisture can condense. If you do get some transmission of moisture then the ventilated air gap enables it to evaporate preventing damp.

 

[alex robinson]

I would happily copy a frame structure that has lasted 40yrs, additionally you know it works with the wall structure you have. Going to thicker timbers will place more load on the walls, perhaps unnecessarily. I'm a EPDM convert, no reason why it can't be used on a pitched roof.

I don't understand your build up, it should be internal lining, vapor BARRIER, insulation, ventilated air gap, roof deck, waterproof layer. In your case OSB, barrier membrane, kingspan, ventilated gap, OSB with EPDM adhered to it.

If you are using a waterproof layer that is not continuous, ie tile, onduline sheets, etc then it could be. internal lining, vapor BARRIER, insulation, air gap, roof battens, breathable membrane, tile/sheets.

The idea of the vapour barrier on the warm side is to keep the warm moist air from penetrating the ceiling and getting into the cold roof space, where the moisture can condense. If you do get some transmission of moisture then the ventilated air gap enables it to evaporate preventing damp.

The existing structure would never support any kind of insulation - uprights are 2x2 as are most of the roof components. This rotting through and causing the asbestos roof to collapse has caused the need for replacement!

Got the vapour barrier and breather membrane mixed up. Interesting to know that EPDM would work on a pitched roof. Never need to bother with felt again!

Done some more looking up about the insulated roofing sheets and they look amazing. Bit confused about the various bits needed. Some places seem to suggest water deflector flashing on top of the wall underneath the roof panel, others don't sell it and sounded confused when I asked on the phone! Has anyone got any pictures of an installation they have done that shows the barge boards / deflectors etc they used please?

 

[HOJ]

You say insulated, It is a shed, you are not likely to be sleeping, bathing, cooking in it etc. all these vapour barriers and layers aren't necessary, keep it simple.

What about insulated steel roofing sheets. They would be my choice.

And mine, worked on Barn conversion earlier this year and used this option on an extension.

 

[alex robinson]

You say insulated, It is a shed, you are not likely to be sleeping, bathing, cooking in it etc. all these vapour barriers and layers aren't necessary, keep it simple.


And mine, worked on Barn conversion earlier this year and used this option on an extension.

View attachment 166647

That looks great. Where did you get the panels from?

You may be right and keeping it simple is best. I was amazed what a difference insulating my workshop made to the condensation and dampness in there, and wanted to make sure I did a proper job! Sounds like the panels are pretty handy though.

 

[rob1693]

Mines only 4 2 by 4.0 m but its better insulated abd warmer than house WiFi sound system beer fridge and heating if i need it , I get relegated there when watching football

 

[alex robinson]

Mines only 4 2 by 4.0 m but its better insulated abd warmer than house WiFi sound system beer fridge and heating if i need it , I get relegated there when watching football

Heating! That really is luxury... Not sure how any speakers would cope with the amount of dust that seems to get everywhere for me though

 

[rob1693]

I'm mostly hand tool so mostly shavings

 

[mc281]

Hello,

I am looking to rebuild an old (quite large) shed. Given the amount of work that will be involved I thought it would make sense to make more work and replace the old rotten structure with an insulated one. I will be reusing the old dwarf walls to build the frames on, hence the slightly odd layout.

View attachment 166511
I was wondering about something like this for the roof (as viewed from the top of the first picture).

View attachment 166510

Firstly, does this seem vaguely plausible? The current structure has lasted over 40 years, and was made with very small section timbers, but I would like to play it safe as well as allowing for a stronger, insulated roof.

I know doors and windows will have to be worked out, but that can come later.

Second, what would people suggest for the roof? I dislike roofing felt as too flimsy and short lived. I have EPDM on my workshop and it is brilliant, but is the pitch of the roof too steep for this? What would people suggest for the layers? Inside skin of OSB, kingspan, air gap, OSB, then either vapour membrane and orduline/metal sheeting or just EPDM glued onto the OSB?

Thanks!

Alex

 

[mc281]

My shed has an almost flat roof and was a real PIA until I had heavy flame gun felt put on. The guy who did it owned a local well respected roofing company and told me to expect 20 years minimum! That was 15 years ago and it still looks as though it was put on yesterday. It gets full sun for 18 hours a day and hasn't changed even a tiny bit!

 

[TomGW]

A properly torched on felt roof will last for ages. Replacing it when the time comes is a pain though.
Regardless of what's underneath if your top layer is osb do consider flexible grp on T&G osb. I can thoroughly recommend Flexitech 2000. Absolutely DIYable and results in an amazing roof that is suitable for regular foot traffic - not that you'll need that but it demonstrates just how much more durable it is in comparison to felt or EPDM. Also much lighter than any other option.

 

[Fitzroy]

You say insulated, It is a shed, you are not likely to be sleeping, bathing, cooking in it etc. all these vapour barriers and layers aren't necessary, keep it simple.

Aren't necessary is related to current and future use. My workshop is also missing some of the elements of a 'belt and braces build' which I have reasoned unnecessary on the basis of occasional use, similar to what you propose. My shed would also make a great teenagers snug, yoga studio, or gym for a future owner so although I do not have a ventilated cavity behind the insulation I did install a vapour membrane as it was low cost and easy, and hopefully increase the longevity of the building in other use scenarios.

 

[HOJ]

Aren't necessary is related to current and future use.

I understand your points, my comment was based on the definition "Shed" if the intention long term would be for alternative use, then agreed elements could be incorporated now, along with other provisions, but then you would need to do far more detailing structurally and design to a different set of standards, with cost's and the amount of work increasing significantly.

 

[alex robinson]

I understand your points, my comment was based on the definition "Shed" if the intention long term would be for alternative use, then agreed elements could be incorporated now, along with other provisions, but then you would need to do far more detailing structurally and design to a different set of standards, with cost's and the amount of work increasing significantly.

I think having had a shed with retro fitted insulation for a workshop and seen the difference, I would never want one completely without. Cold I don't mine, everything going rusty is just such a pain.

Aren't necessary is related to current and future use. My workshop is also missing some of the elements of a 'belt and braces build' which I have reasoned unnecessary on the basis of occasional use, similar to what you propose. My shed would also make a great teenagers snug, yoga studio, or gym for a future owner so although I do not have a ventilated cavity behind the insulation I did install a vapour membrane as it was low cost and easy, and hopefully increase the longevity of the building in other use scenarios.

There is no plan for living in there or the like, bit I agree that future proofing as much as possible is a good plan. Making anything like this will be a major effort, so a bit more to get more flexibility seems a good investment.

 

[HOJ]

I think having had a shed with retro fitted insulation for a workshop and seen the difference, I would never want one completely without. Cold I don't mine, everything going rusty is just such a pain.

My full time joinery/woodwork workshop is an 18th century listed barn, with only limited roof insulation fitted as best I can, wood burner in the winter, never had a problem with rust, ventilates freely.