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Corrugated Metal Roof - how did you ventilate your panels


Tom's Barn

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Hi All

 

I am in the process of specifying the details for our new corrugated roof (dictated by the conservation officer). The main issue I am coming across is how to ventilate the roof panels because the foam closure strips have no ventilation holes in them. One supplier has sent me a foam closure for the panels which has holes drilled in it and mesh infils. This seems like a great solution but it is 20mm higher than the normal strips. Before I fully commit to this product (the only one I have seen so far), how did you ventilate your corrugated roof?

 

Many thanks for sharing your experience with this matter

 

Tom

Edited by Tom's Barn
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I have a building that faces south west and into most of the incoming storms, I  left my tin open at the bottom and open at the top, I then put a vented ridge on and used the foam closures between the tin and where the ridge flashing met the tin to stop rain driving up under the flashing and onto the roof membrane. Air is free to travel up the roof  below the tin and out the ride at either end, also I did not seal the joints of the ridge flashings as they have a good overlap and this will allow some further ventilation. Then just for good measure I left a vented gap below the timber sarking / sheeting and vented this out the gables. It’s a glorified shed so probably well over the top but living in an extremely wet environment I wanted to go overboard on ventilation.

 

I have a tin roof on another house but this faces East with the gables facing north to south and never gets driving rain from anywhere but the gable ends so I did not use any closure strips and it works great. 

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I've steel as with @Cpd and have the foam closures at the top between the corrugated and the ridge cap.

 

The bottom is left open to allow for ventilation, and I should note that they descend into a hidden gutter, so wind can't get driven up.

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Nothing in there for mice to be interested in, if anything the foam closures would be there “go to” on the menu. Spiders and a few other bugs might make a home In there but that’s not a concern to me as they won’t do any damage. My reasoning  is that I wanted as much ventilation as possible to prevent possible condensation build up and if and when there was any condensation it would dry out as quickly as possible. 

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13 hours ago, Cpd said:

Nothing in there for mice to be interested in, if anything the foam closures would be there “go to” on the menu. Spiders and a few other bugs might make a home In there but that’s not a concern to me as they won’t do any damage. My reasoning  is that I wanted as much ventilation as possible to prevent possible condensation build up and if and when there was any condensation it would dry out as quickly as possible. 

thanks for all the replies so far. With the open venting option and your push for maximum airflow I presume your tin has a batten and counter batten underneath? I am surprise to hear it has been left open. I would have thought the wasps would have loved the space under the roof. Mind you it may get a little too hot for them...

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We've battented and counter battented with standard treated battens, 38 by 25mm.

 

I guess you could place instect or rodent mesh along with the first line of counter battens to your structure, with your foam filler stapled against the counter batten and topped with mastic tape, ready for when you install the corrugated on top...

 

It'd probably be only a little bit of extra effort, but I can imagine installing the sheets on top of that will get quite faffy.

 

Win and rain has been the main concern for us, the insect and rodent issue hasn't been. Our roofers, architect and building control haven't said a thing about it either

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3 hours ago, jamieled said:

I start our roofing tommorow. We have mesh to install as per @Visti describes, although I have no eaves foam fillers, just a closure piece to allow a ventilation gap.

good luck with the roof @jamieled. If you can take a picture of your install that would really helpful to fully understand your approach. Many thanks

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My roof design is different as it’s vented on both sides of the sarking. I just put the tin directly onto the sarking board. battens and counter battens are the way to go though. My roof is on a glorified shed so not trying to meet any specific standard, more aiming to prevent water getting in and if any condensation does get in then making sure it is well vented.  It’s blowing a gale outside right now with the water blowing up the 45 degree roof..... if the closer strips were not in place between the ridge flashing and the tin then the water would blow right up under the ridge flashing and onto the roof membrane and then have to travel all the way down the roof under the tin  and out into the gutters !!!!! The closures at the top are essential to prevent this. The bottom of the tin is within the gutter so rain can not get in  and wind is minimal but load if ventilation as no closer strips. 

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  • 3 months later...
On 10/10/2019 at 17:24, Visti said:

We've battented and counter battented with standard treated battens, 38 by 25mm.

 

I guess you could place instect or rodent mesh along with the first line of counter battens to your structure, with your foam filler stapled against the counter batten and topped with mastic tape, ready for when you install the corrugated on top...

 

It'd probably be only a little bit of extra effort, but I can imagine installing the sheets on top of that will get quite faffy.

 

Win and rain has been the main concern for us, the insect and rodent issue hasn't been. Our roofers, architect and building control haven't said a thing about it either

Hi @Visti

 

I hope the roof installation went well....any lessons learnt? 

 

Also I cannot find any guidance re batten size. How did you choose the 38 X 25 battens?

Surely in a strong wind the uplift on the screws for the horizontal batten at 25mm is too much. I would have thought a 50mm horizontal batten at the very least. Any guidance appreciated.

 

Do you have a spec sheet for fitting the sheets. I am struggling to find a capable person to fit. I know in the end it will be me that ends up fitting it which I don't really have time.

 

Thanks oh and any photos?

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On 09/10/2019 at 15:18, Cpd said:

I have a building that faces south west and into most of the incoming storms, I  left my tin open at the bottom and open at the top, I then put a vented ridge on and used the foam closures between the tin and where the ridge flashing met the tin to stop rain driving up under the flashing and onto the roof membrane. Air is free to travel up the roof  below the tin and out the ride at either end, also I did not seal the joints of the ridge flashings as they have a good overlap and this will allow some further ventilation. Then just for good measure I left a vented gap below the timber sarking / sheeting and vented this out the gables. It’s a glorified shed so probably well over the top but living in an extremely wet environment I wanted to go overboard on ventilation.

 

I have a tin roof on another house but this faces East with the gables facing north to south and never gets driving rain from anywhere but the gable ends so I did not use any closure strips and it works great. 

Hi @Cpd

 

Thanks again for the previous info. Question if I may.....what batten sizes have you used on your roofs?

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1 hour ago, Tom's Barn said:

Thanks again for the previous info. Question if I may.....what batten sizes have you used on your roofs?

My roof is treated sarking board 150x22mm onto 400mm roof joists with membrane on top of the sarking, it’s vented below the sarking with a 50mm gap between sarking and inserted and fully sealed / taped calotex the gap is vented at the soffit with vents at each bay and up to a fully vented ridge....  so I decided to not use battens and fixed directly to the sarking and through the  roof membrane, I observed this for about 3 years before I got round to closing it all in from the inside and everything was bone dry with a really good draught up each of the Joist bays, It’s probably NOT the correct way but in my very windy location (a few hundred yards from the sea and prevailing ocean breeze) its worked really well, any condensation that may form will dry out pretty quickly. The lack of space under the tin will also provide very little space for interested wildlife looking for a new home. Was I doing it again and knowing what I know now I would probable batten the roof out just as good practice and to increase ventilation even more. However I don’t loose and sleep over what I have done. 

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9 hours ago, Cpd said:

My roof is treated sarking board 150x22mm onto 400mm roof joists with membrane on top of the sarking, it’s vented below the sarking with a 50mm gap between sarking and inserted and fully sealed / taped calotex the gap is vented at the soffit with vents at each bay and up to a fully vented ridge....  so I decided to not use battens and fixed directly to the sarking and through the  roof membrane, I observed this for about 3 years before I got round to closing it all in from the inside and everything was bone dry with a really good draught up each of the Joist bays, It’s probably NOT the correct way but in my very windy location (a few hundred yards from the sea and prevailing ocean breeze) its worked really well, any condensation that may form will dry out pretty quickly. The lack of space under the tin will also provide very little space for interested wildlife looking for a new home. Was I doing it again and knowing what I know now I would probable batten the roof out just as good practice and to increase ventilation even more. However I don’t loose and sleep over what I have done. 

Many thanks for sharing this info. Are you saying you have now closed the ventilation gap within the roof space completely? I talked with proctor recently and they said as long as the roof space was completely filled with rockwool and a vapour membrane was attached inside then there was no need to ventilate due to the 75mm of ventilation above the membrane. Thank you

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No I have a vented area of 50mm above the insulation and below the sarking running up between each joist. 
my vcl is behind the plasterboard but all the insulation is fully fitted and foamed / taped at each layer. 
there is No where for air to move between the layers of insulation as there are no gaps. 
the vented area is open at the bottom of the roof with soffit vents and open at the top with roof vents as well as a 200mm  open vented triangle just below the ridge. 
air freely moves in this area, you will of course get air flowing up beneath the tin in each of the curves / profiles as they are open at the bottom and open at the top 

as I said probably not the text book roof but it seems to be working well, I expect if you did a condensation risk analysis then it would show potential problems with the joists but due to my windy location I am happy with how it works. I have also read that you can fully fill with the correct build up but I have always felt that should there be any issues with damp then I want it capable of drying out ASAP. My shed roof is far more basic and until I decide on whats going on in there I will keep my options open. 

B047F21E-FB38-46C7-8184-699CC5C5AD88.jpeg

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1 hour ago, Tom's Barn said:

Thank you. Just ordered some to see what they are like. Much appreciated.

I can't comment on the quality of this  one as I on purpose put a link from random ebay seller to not create a conflict of interest, but generally we use this kind of thing all the time on our roofs, corrugated and box profile, and it works perfect. 

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@Tom's Barn the battens were all fixed through the external timber marine board and external membrane down to the joists themselves, both vertical and cross battens. Any other way is asking for trouble.

 

That results in 50mm clearance between the sheet and the board which allows it to ventilate and try if you get any condensation on the underside. WeYou don't want to fully block the passage of air under the sheets for this reason. We got our sheets treated on the backside with an anti-condensation layer to help avoid that anyway. 

 

Cladco, the steel sheet supplier has some decent installation manuals on their website. Highly recommend.

 

See my post below in how not to install corrugated sheeting.

 

 

Very DIYable, wouldn't pay a roofer to do it next time when I do the car port. I'd recommend listening to @Cpd's posts as they are very helpful.

 

My own tips are:

 - get the domestic screws and caps, we didn't know there were options and the commercial ones are quite obvious, even with caps.

 - you only need to cut sheets down to length. Don't cut along the length of you can avoid it. For windows, one sheet each side and then shorter sheets above and below, don't cut out the corner for the sheet to wrap around. Looks horrid.

 - use the right tool to cut the sheets (nibbler) and it is a breeze. Don't be and idiot and try with a recip saw... Very very bad cuts.

 - plan the spacing of your fixings ahead of time. It is really obvious if they aren't aligned or regular 

 - don't trust trades when they claim they can do a job. Check their references, give them the supplier instructions, walk it through with them, check up on them, inspect the work as they go, get a paper trail via email... 

 - ... Or just DIY this. Low skilled job provided flashings are in place along the edges of the sheets

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