Workshop shed roof ventilation

[mp1981]

Hi, I am currently building a 4.6x3.2m workshop and I am at the roofing stage. I am planning on using an eave to ridge ventilation system. Above the rafters I have 11mm OSB on top of which I have breather paper. Onto this I wanted to put battening before attaching corrugated steel sheets. My question is that if I look at the fixing sheets for say onduline or coroline it says to fasten cross battens as opposed to battens going from eave to ridge. Now the air can still ventilate with the cross battens, however any moisture on the breather paper would surely be prevented from moving downwards due to the cross battening? The only way around this I can see is to fix battens and then counter battens on top but then there is a huge area under the sheets which might cause wind to get underneath and rip the sheets up? I'd be very grateful to any help or suggestions

Thanks
Matt

 

[carlb40]

The battens as per the instructions are the standard way to batten a roof out prior to tiling/ slating and in this case corrugated sheets. There should be minimal moisture with that amount of air flow. The only time it may cause an issue is with a hole in the sheet and allowing rain in.

 

[MMUK]

Fit dry verges on the ends of the gables and you'll have constant airflow along under the bitumen sheets.

 

[mp1981]

Thanks both for your response. I will be using the proper tek fixings so hopefully there won't be any leaks coming through the fixing holes. The other thing I was thinking was actually not to have the OSB on the outside of the rafters so I could put the breather paper directly onto rafters although fixed with a little bit of sag and then put counter battens on. I was hoping not to use dry verges as the ones i've seen on the market look ugly and I would like to have nice detailed wooden gable ends

 

[carlb40]

Thanks both for your response. I will be using the proper tek fixings so hopefully there won't be any leaks coming through the fixing holes. The other thing I was thinking was actually not to have the OSB on the outside of the rafters so I could put the breather paper directly onto rafters although fixed with a little bit of sag and then put counter battens on. I was hoping not to use dry verges as the ones i've seen on the market look ugly and I would like to have nice detailed wooden gable ends

If you leave the boarding off the little sag you will get og the breather paper will be minimal. The reason underfelt sagged between rafters was the weight. There is no weight to these breather papers/membranes

 

[MMUK]

Thanks both for your response. I will be using the proper tek fixings so hopefully there won't be any leaks coming through the fixing holes. The other thing I was thinking was actually not to have the OSB on the outside of the rafters so I could put the breather paper directly onto rafters although fixed with a little bit of sag and then put counter battens on. I was hoping not to use dry verges as the ones i've seen on the market look ugly and I would like to have nice detailed wooden gable ends

If you leave the boarding off the little sag you will get og the breather paper will be minimal. The reason underfelt sagged between rafters was the weight. There is no weight to these breather papers/membranes

Also, because they are woven fabric rather than bitumen tar, they don't stretch

 

[mp1981]

happy days, thanks guys

 

[blackrodd]

Hi, I am currently building a 4.6x3.2m workshop and I am at the roofing stage. I am planning on using an eave to ridge ventilation system. Above the rafters I have 11mm OSB on top of which I have breather paper. Onto this I wanted to put battening before attaching corrugated steel sheets. My question is that if I look at the fixing sheets for say onduline or coroline it says to fasten cross battens as opposed to battens going from eave to ridge. Now the air can still ventilate with the cross battens, however any moisture on the breather paper would surely be prevented from moving downwards due to the cross battening? The only way around this I can see is to fix battens and then counter battens on top but then there is a huge area under the sheets which might cause wind to get underneath and rip the sheets up? I'd be very grateful to any help or suggestions

Thanks
Matt

Surely, The ventilation requirement is for the roof space, and not the battens above the osb.
The profile will vent the osb space
The main reason for using the osb is for adding ridgidity to the roof structure, particularly in areas prone to high winds, as well as an excellent base for the tyvec.
Roofing batten has to be gauged now and not the product of an offcut.
I would keep the osb and ensure the galvanise rafter/truss ties were fixed as per building regs and hopefully, keep the roof on, and in place.
I have actually seen a complete roof blown off in high winds, and not a tie to be seen,
Not sure what the dreaded insurance assesor said about that!
Regards Rodders