Seamed metal roofing or catnic SSR2 advice required

[JamesP]

I fitted a warm / vented  roof using Tata - Catnic panels. Insulation above the rafters, breather membrane, batten and then panels.

Unconventionally I did not use a deck to fully support the panels.Air can circulate directly underneath which I hope also keeps excess heat away from the warm roof.

Zinc was not an option due to budget and a task beyond my abilities.

 

Edited March 17, 2021 by JamesP

[Dunny1234]

1 hour ago, Kevin J said:

@Dunny1234 A cold ventilated construction has been the method of construction for zinc roofing across Europe. Use 'penny gap' 25mm thick softwood boards as the deck supporting the zinc and you can't go far wrong. If there is condensation with in the roof build up the timber will be able to dry, the air will also protect the back (underside) of the zinc and allow a natural patination on the metal surface.

If you build using plywood you MUST isolate the zinc from the plywood using a structured underlay as ISO-Mat Metal. It has always been forbidden to lay zinc directly onto Plywood.

Warm roofs have become popular and IF installed correctly can offer some advantages. The Vapour Control Layer (VCL) must be specified in accordance with the level of humidity expected within the building and installed correctly to prevent moisture breaching into the roof construction - for the life of the building. 

DM Drawings if you need project specific advice or guidance?

Thanks Kevin, that’s exactly what the zinc guy is saying. The importance vapour barrier and the warm roof fixings, is why he wants to build up the warm roof. I’m trying to suggest, if I could install the insulation, and then hand over to him for the vapour barrier and zinc

[Bramco]

10 minutes ago, JamesP said:

I did not use a deck to fully support the panels

 

Interesting - everyone we've spoken to says you need the 18mm ply or OSB. From a lay persons perspective we couldn't really see why this was necessary - unless it is a way of trying to prevent 'oil canning'.  If so it's an expensive way of doing it!

 

Simon

[Dunny1234]

11 minutes ago, Bramco said:

 

Interesting - everyone we've spoken to says you need the 18mm ply or OSB. From a lay persons perspective we couldn't really see why this was necessary - unless it is a way of trying to prevent 'oil canning'.  If so it's an expensive way of doing it!

 

Simon

My guys suggesting no ply/osb on top of insulation. Just vapour barrier, zinc and a plastic thermal fixing down into the rafter. 

[JamesP]

25 minutes ago, Bramco said:

 

Interesting - everyone we've spoken to says you need the 18mm ply or OSB. From a lay persons perspective we couldn't really see why this was necessary - unless it is a way of trying to prevent 'oil canning'.  If so it's an expensive way of doing it!

 

Simon

The Tata / Catnic panels are fairly rigid, oil canning is inevitable but minimal in my experience. I did not want to  puncture a solid deck with yet more fixings.

The only downside to supporting the panels with just 3 battens is the noise when windy as the panels do ripple. I cannot confirm this but laying panels directly onto a solid structure even with matting must create condensation.

However Zinc roofs have been fitted and lasted for decades.

[LSB]

On 23/02/2021 at 06:26, Kevin J said:

Hi, you can purchase directly through the website.

should you decide the installation is too demanding, skill level for example, a training course is available. If you need tooling this is also available.

If other constraints such as time present an obstacle we provide details of competent Installers 

 

 

[SimonD]

5 hours ago, Bramco said:

 

Interesting - everyone we've spoken to says you need the 18mm ply or OSB. From a lay persons perspective we couldn't really see why this was necessary - unless it is a way of trying to prevent 'oil canning'.  If so it's an expensive way of doing it!

 

Not really, the osb for my roof at 126sqm cost me under £600. Would you really want to compromise a roof you're spending 1000s on for a fraction of the total cost?

 

The standing seam roof cover has little if any structural integrity as it's only about 0.7mm thick. On top of that a standing seam roof needs a defined number off fixed and sliding clips to prevent uplift, usually a maximum of 380mm apart and closer (perhaps 200-220mm) around eaves, ridges, and verges.

[Kevin J]

Oil Canning - has many factors to consider 

the substrate is one, if it's wrong how would your propose to fix the roof to it, the metal generally follows the shape. Also can the metal be fitted avoiding walking over it During installation - think Ridge - think rooflights.

the reflectiveness of the metal will draw you eye to any misshapen Panel. It's a function of the viewing distance, you move, your view changes along with the shape of the roof.

the installer makes a massive distance

width and length of panels, ease of handling to the roof, during transport etc.

Colour can impact

images are a Stainless steel roof installed by a professional, possible the least forgiving metal being hard, reflective (low reflective here Roofinox Classic) and sharp. Only 0.5mm thick! 

Finally off-site rolling. If you are using it then make suitable decisions on handling, loading the sheets to the roof and installation. Training is provided but may not give this much food for thought.

 

substrates: some are incompatible with the metal. Take guidance.

some substrates such as Hard Metal Board provide structural support with Insulation, a 2 in 1. 

 

Note: Roofinox Classic is uncoated. Pictures courtesy of Install Zinc, Chigwell

[Dunny1234]

Hi all, interesting stuff. Its funny how different metal roof providers give different types of guidance with they’re installation requirements. I think the only difference between to 2 types in the pics, are 1 has an additional layer of ply on top on the pir insulation which the clip are attached too (I can only assume that this reduces any thermal bridging problems with the insulation).
 

And with the other type of standing seam, the roof sheet goes directly onto the insulation, a warm roof plastic fitting go down through the insulation and screws into the ply way below. *obviously, a vapour barrier is installed on both under the metal sheets

 

is there advantages/disadvantages between these systems, or are both okay to use?

 

thanks 

[Russell griffiths]

@Dunny1234, you need to stick to your roof manufacturers approved method if you want a warranty. 

 

As to which is best, that’s up to you to decide. 

You need to do your own research and pick which you think is best. 

 

Every manufacturer will say his is the best. 

[Kevin J]

@Dunny1234 consider also the cost in your comarison. Clips that attach to a substrate are fixed £69.00 per 1000 and expansion £59.00 per 400 You use a specific arrangement to offer security (fixed) and thermal expansion of the roof. Thermoseam Clips which are supplied as clip with tube to go through the insulation are more expensive. Ball park on average you will use up to 10/m2, soon adds up!

You will also need the correct fixing to go down the tube appropriate to the anchoring material as well as a drive bit to insert in the tube.

Note: some distributors will charge for the tube and the stainless clip as separate items. 

 

The structural reliance of the rigid insulation is paramount for the life of the building. Someone else  may need access to the roof area after the metal is installed

[Simon R]

Ours is an HPS 200 (urban colourcoat)  warm roof. Three of us on the forum got together and ordered it directly from Blatcho Trapez. @Patrick did all the hard work with the manufacturers and now imports there products as a business. It worked out a heck of a lot cheaper that the TATA offering for what is essentially the same product

The roof make-up is all important as already pointed out other posts. Partick's incredibly helpful and worth contacting if your still looking for a solution. I know were not meant to do anything commercial on the buildhub, but the venture started here with self build self help.

 

[Dunny1234]

14 minutes ago, Simon R said:

Ours is an HPS 200 (urban colourcoat)  warm roof. Three of us on the forum got together and ordered it directly from Blatcho Trapez. @Patrick did all the hard work with the manufacturers and now imports there products as a business. It worked out a heck of a lot cheaper that the TATA offering for what is essentially the same product

The roof make-up is all important as already pointed out other posts. Partick's incredibly helpful and worth contacting if your still looking for a solution. I know were not meant to do anything commercial on the buildhub, but the venture started here with self build self help.

 

Thanks Simon, build looks great, great blog too. I don’t think I’m capable of doing the roof myself, but I’d be keen to build up the warm roof, prepped ready for the metal. The guy I’ve chatted to wants to install insulation and membrane him self, at a high cost. Surely, it not that hard??? What was your experience? How was your warm roof constructed? Any help would be much appreciated? Thanks 

 

[Simon R]

14 hours ago, Dunny1234 said:

but I’d be keen to build up the warm roof, prepped ready for the metal. The guy I’ve chatted to wants to install insulation and membrane him self, at a high cost. Surely, it not that hard??? What was your experience? How was your warm roof constructed? Any help would be much appreciated? Thanks 

 

Most of the work isn't that difficult, it comes down to attention to detail. Having said that, dealing with light materials in a windy environment is no fun, definitely a case of doing it when the weather is on your side.

Our roof from inside to out is made up of:

• VCL membrane stapled and taped (air tightness is all important as you don't want any vapour getting into the foam)
• Rafters are C24 225x40 wood at 400 centres.
• Spray foamed to a depth of 200.
• 18mm OSB board over the rafters.
• Moisture proof breathable membrane overlapped and tacked
• Battens running up the roof slope
• 18mm OSB in 400mm horizontal strips with 80mm gaps between the strips.
• HPS 200 roof covering.

The VCL and spray foam were done after the standing seam roof was complete.

 

No water should get under the standing seam, but there is always a risk of condensate, hence the dual layer of OSB which makes a natural chimney to give good ventilation. Interestingly Greg, one of the three who ordered our roof together did put another membrane under the standing seam roof. It was an expensive membrane not required by the manufacturer and we decided not to include it. Patrick will know what the membrane was.

[PeterTweeter]

SimonR

I believe I've hit the motherlode, cos your roof makeup appears to be the answer to my dilemma.

I'm 'designing' a TF extension to be topped by a 5m shed/skillion/monopitch standing seam roof. The constraints are that I want a pitch as great as possible (11deg) but I have little flexibility in how thick the roof can be without fowling on window openings above. So, unvented seemed to be the answer.

My current idea/plan follows the scheme you've detailed.

What you're describing is an unventilated ceiling. In the US & Canada, the use of closed-cell spray foam(ccSPF) is widespread & there are many examples of US & Canadian government guidance on good practice. All of this is in direct conflict with UK &, I assume, European practice ie warm/cold roof.

So, the questions I have are:

1. How was the sourcing of the spray foamers? Was it closed-cell? (I guess not since you included a VCL.)
   Over the pond, the feeling is that a VCL is counter productive. The foam forms the air barrier & keeps moisture away from the cold roof & any mosture that might be present can wick away back through the drywall. They also go for a vapour barrier paint - not too clear on this?
2. What was your thinking about the multi-layer sheathing/battening? This seems excessive.

By shear serendipity, I was in contact with Patrick last year re roofing & I beams. He is located not far from me, so I must set up a visit.

Ideally I would like zinc, but as others have stated, this is so hard to source - though & have a local lead @£200/m2(ouch!).

Any other advice/thoughts/guidance would be much appreciated.