Corrugated Metal Roof - how did you ventilate your panels

[Tom's Barn]

On 21/01/2020 at 19:22, Patrick said:

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. 

thanks Patrick. It has arrived and looks good. I will use that on the first and last row of purlins.

[Tom's Barn]

On 21/01/2020 at 19:56, Visti said:

@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

Hi @Visti

 

Thanks for your note and guidance. I have this evening received the notes from the structural engineer re battens and screw sizes. He has confirmed your idea of 20x50mm vertical battens, and the 25x50mm counter battens that hold the sheets and provide a drainage plane below. He has also confirmed the need to penetrate into the rafters when the counter battens cross the verticals which makes perfect sense. The only you mentioned that he has not provided information for is the screws holding the tin. You mention domestic screws and caps. Is there any chance you can send me a link to a type you are referring to. 

 

Thanks again for your points. They all serve to confirm the way forward. I did look at the fitting instructions online at the cladco and there are some good points on there.

 

T

[Tom's Barn]

On 21/01/2020 at 18:17, Cpd said:

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. 

Hi Col

An interesting approach, thank you for sharing and providing a graphic, it is very clear now. I don't think your tin is coming off any time soon.

Question....what screws did you use through your tin? I have been recommended to use timberlok screws but with 50x25mm counter battens they seem a little chunky.

 

Tom

[Tom's Barn]

On 22/01/2020 at 07:40, Russell griffiths said:

Is this any help. 

Stainless mesh over counter batten gap. 

then 100x25treated batten to take the sheets. 

Not corregated but it is metal. 

Hi Russ, what metal are you going with? I assume based on the support structure you are creating it is standing seam? Nice edge detail...

I have looked online for 25x100 and the sites say 22 x100. Is that what you have?

Tom

[Cpd]

https://www.cladco.co.uk/fixings-and-accessories/screws-to-wood-with-a-19mm-bonded-washer-pack-of-100
 

take your pick, depends how far you can go in. They are very good but you need to be carful not to over tighten them as you will distort the tin. If you over tighten one then back it of but check the washer as often it will have been distorted and you will need to replace the whole fixing to get a good seal. 

[Russell griffiths]

@Tom's Barn treated sawn 25x100 got it in BPS IN CIRENCESTER, really nice lads, the branch manager Wayne has been to site a couple of times, he’s keen on new business. 

Raised seam roof. 

In the pic of the stainless mesh I also covered the edges with sikaflex to stick it down because of the gaps created by staples. 

 

You could have come and had a look a week ago, but it’s all covered now. 

[Tom's Barn]

On 25/01/2020 at 07:05, Cpd said:

https://www.cladco.co.uk/fixings-and-accessories/screws-to-wood-with-a-19mm-bonded-washer-pack-of-100
 

take your pick, depends how far you can go in. They are very good but you need to be carful not to over tighten them as you will distort the tin. If you over tighten one then back it of but check the washer as often it will have been distorted and you will need to replace the whole fixing to get a good seal. 

thanks Col; much appreciated

[Tom's Barn]

On 25/01/2020 at 08:59, Russell griffiths said:

@Tom's Barn treated sawn 25x100 got it in BPS IN CIRENCESTER, really nice lads, the branch manager Wayne has been to site a couple of times, he’s keen on new business. 

Raised seam roof. 

In the pic of the stainless mesh I also covered the edges with sikaflex to stick it down because of the gaps created by staples. 

 

You could have come and had a look a week ago, but it’s all covered now. 

BPS - I am using them as well. I will drop in and take a look. Any chance I can pop over and see how you are getting on. Have you gone with the TATA steel standing seam?

 

thanks Russ; I hope to see you soon. You are very welcome to drop in and see the new build - just drop in when you are passing. We are the site (Ewen Barn) on the way out of the village towards Coates - the road that takes you under the old railway.

 

I always thought that with a raised seam / standing steam roof you needed to have a flat deck. I like what you have done because that ensures ventilation all the way through and under parts of the metal.

 

Talk soon

Tom

[Visti]

On 25/01/2020 at 07:05, Cpd said:

https://www.cladco.co.uk/fixings-and-accessories/screws-to-wood-with-a-19mm-bonded-washer-pack-of-100
 

take your pick, depends how far you can go in. They are very good but you need to be carful not to over tighten them as you will distort the tin. If you over tighten one then back it of but check the washer as often it will have been distorted and you will need to replace the whole fixing to get a good seal. 

 

We got the BAZ washers without realising, and they are quite large compared. Wish we'd known before hand, but it is all installed now and god knows I ain't going back and revisiting that!

[Cpd]

9 hours ago, Visti said:

We got the BAZ washers without realising, and they are quite large compared. Wish we'd known before hand, but it is all installed now and god knows I ain't going back and revisiting that!

I feel for you man, what a saga. But hay next time you will be a pro. We all make mistakes and Ive made plenty. I have the upmost respect for people when they come  on this forum and say “” I messed  up” how do I fix it and we all get to see how to fix it and how not to do it in the future. These fixings are great but as I said you need to get it just right otherwise the fabric / rubber on the washer gets over compressed and it does not re expand. 

[Patrick]

14 hours ago, Tom's Barn said:

I always thought that with a raised seam / standing steam roof you needed to have a flat deck. I like what you have done because that ensures ventilation all the way through and under parts of the metal.

Metal roofs, wether standing seam or corrugated, all condensate. Unless they are fully insulated foam panels. They do all need an air gap behind them.  As standing seam is a fairly flat sheet, this specially needs some kind of gap behind it. There are a few options, battens and counterbattens being one, a special, thick membrane that gives an airgap being another.

 

[A_L]

32 minutes ago, Patrick said:

As standing seam is a fairly flat sheet, this specially needs some kind of gap behind it.

 

Not according to the BBA cert for possibly the leading brand

BBA Certificate for Colorcoat Urban Roof panel.pdf

[Visti]

5 hours ago, Patrick said:

Metal roofs, wether standing seam or corrugated, all condensate. Unless they are fully insulated foam panels. They do all need an air gap behind them.  As standing seam is a fairly flat sheet, this specially needs some kind of gap behind it. There are a few options, battens and counterbattens being one, a special, thick membrane that gives an airgap being another.

 

 

The cladco ones come with an anti condensation coating on the back for an extra £2/m or so. Can't speak for how effective it is, but given how cheap the material is in the first place relative to other options I'd rather be safe than sorry...

 

Only downside is all the waste I have cannot be recycled as pure steel.

[Cpd]

19 minutes ago, Visti said:

Only downside is all the waste I have cannot be recycled as pure stee

Hmm burn it and cause pollution but get to recycle it... dump it in landfill and no recycling.... it’s a no win situation ......or be a complete optimist and put it in the shed and assume there WILL be a use for it at some point..... I was very pleased when I got to use some of my long kept off cuts to roof my water treatment plant ! ....not so mad now I thought .....

[Patrick]

9 hours ago, A_L said:

 

Not according to the BBA cert for possibly the leading brand

BBA Certificate for Colorcoat Urban Roof panel.pdf 1.05 MB · 4 downloads

?

Quote from the BBA cert you quoted :

 

"9 Condensation risk
9.1 In common with all metal roof constructions, there is a risk of condensation. This can arise as either
interstitial condensation within the roof construction or surface condensation at thermal bridges."

 

A breather membrane (a high quality one) is a kind of ventilation gap (for condensation purpose at least)

 

 

[Richflew]

Hi, I have read this thread with interest and joined the forum to participate (looking forward to seeing what else is on here ?)
We are in the initial stages of a barn conversion as in photo. One single storey wing has corrugated roof at present. The whole structure needs replacing but, as it is Grade II listed we would like to use black plastisol coated corrugated sheets to keep the feel as it is now (it's also considerably cheaper than other metal roofing).  We have to keep to the same height so insulation will go between rafters then over-boarded with insulated board to get to building regs.
Although common in other parts of the world it is uncommon to use corrugated sheets in the UK for domestic roofing. 
I have 2 questions... particularly for @Cpd  @Russell griffiths as it looks like you have done similar projects.
1) With the insulation as suggested is sound likely to be a problem when it rains?
2) Do you know if insurers and mortgage providers will have a problem with this type of roofing?

thanks

[Cpd]

3 hours ago, Richflew said:

1) With the insulation as suggested is sound likely to be a problem when it rains?

Despite rigid insulation’s poor acoustics properties it’s not as bad as I thought, I went to great lengths to make sure my insulation was all foamed and taped at multiple levels and I think this probably helps. I have then got osb on the inside and am still not at the point of plasterboard but when I do I will use an acoustic one, see what it’s like with one layer and double up if required... but having spent time in the building  without I am thinking one layer will be fine. When it rains your aware of the noice but it’s more a nice comforting sound as your happily inside ! Others with finished houses may have more info but for me I am happy. 

[Russell griffiths]

I have vaulted ceilings in every room, when it rains heavily you can definitely hear it, is it unpleasant, no

at the moment I do not have ceilings fitted just insulation on show, I intend fitting 15mm acoustic plasterboard on the ceilings which I think will take the sound down even lower. 

 

Is it silent ? no. is it annoying ? Not really I think with the telly on or just background talking I think it will just blend in, you certainly get a fair bit of noise from the rain on the windows. 

[Richflew]

thanks to both of you @cpd and @Russell griffiths This is comforting - I've had the OK from the building inspector too so I'm excited to get on with it now!!

[Richflew]

@Cpd after months of delays for various reasons we are now getting round to doing this. 

Looking at your drawing, can you explain to me why the sauring board is necessary rather than just using horizontal timber 3x2 lats to support the corrugated sheets.
Also, we have to build the timber truss structure.  My joiner says it's a waste of time having rafters every 400mm - do you have an opinion on this?

 

thanks

Richard

[Cpd]

Have sent you a pm. 
is your roof open / vaulted in the inside or is it a cold roof  with insulation on the flat ceilings ? If it’s a cold roof then you can probably get away with a lot less timber but if it’s a vaulted ceiling then you need to think about all the additional weight such as insulation and plasterboard as well as the extra work / wood around the windows. 
I needed sarking as my location is very exposed and it was part of what made the whole roof more rigid, also due to the serious exposure I wanted the roof membrane to be sitting on a solid deck rather than draped between rafters. 
 

[saveasteading]

I will not join this discussion unless needed. Have designed and manage a lot of steel cladding. Let me know if anything is still in need of input.

[Iceverge]

On 07/10/2021 at 13:51, Richflew said:

My joiner says it's a waste of time having rafters every 400mm - do you have an opinion on this?

 

Don’t disregard your joiners advice but run it by your SE before making any such changes. Metal roofs are quite light so it will probably be fine to increase to 600mm or greater. 

 

For my garage I fully taped a breather membrane pulled taut, battened and counterbattened with 25*50mm. 

 

If i was to do it again i would increase to 25*75 counterbattens i think as they would be less likely to split with the broad roofing screws.

 

FWIW I’ve always loved the sound of rain on a tin roof. 

[saveasteading]

23 minutes ago, Iceverge said:

Don’t disregard your joiners advice but run it by your SE

Yes. Usually joiners are aware of what works and doesn't, but by experience not calculation skills. . But not all do, and there may be other circumstances. At 600cc the timbers will be heavier, so the SE must decide, and you certainly can't use frames designed for 400 and place them at 600.

[GeGe]

Hi All,

 

I have just found this thread on the web, I might be late to the party, but hopefully some of you might be able to help? I am building an office above garage with a corrugated metal roof finish. I have a similar roof make up to @Cpd see my pic below. My main problem is, I have an air gap in rafter space above insulation which I will vent via soffit vents but how do I vent it through at ridge? There doesn't seem to be much in the UK market for that. There is only foam fillers to put under ridge to close the gaps, so water doesn't blow up there, but they are they are not breathable. Whereas in the US market where they use metal roofs a lot for residential spaces they have breathable ridge strips, (see pic). Any ideas if I can get anything like this in the UK (although would be hard to match sheet profile exactly). recommendations and comments would be appreciated. Thank you in advance.