Kelvin Posted February 5, 2023 Share Posted February 5, 2023 Our architectural specification roof build up states 18mm ‘WBP Plywood’ for the standing seam metal roof. The timber kit doesn’t include it as the build up is OSB, breather membrane, and battens to create a ventilation space. The Greencoat PLX roof supplier also states WBP Plywood. My question is which class is WBP Plywood. The WBP just refers to the glue not the wood. Class 2 can be for exterior use with some weather exposure during construction. Class 3 is weatherproof. I assume class 2 is fine. See below for the class details. I’ll ask the roofing company and architect to be more specific. https://elliotts.uk/ideas-and-advice/plywood-classes-explained Link to comment Share on other sites More sharing options...
Mike Posted February 5, 2023 Share Posted February 5, 2023 The page you linked to suggests the fail-safe answer - If you have previously specified or purchased WBP (weather and boil-proof) or Exterior quality plywood for construction purposes, you should now purchase plywood to comply with EN636, Class 3. If you're using a vented cold roof construction then Class 2 could be used, but personally I'd stick with Class 3 for the extra margin, especially if there's a risk that it could be exposed to the weather for a while during construction. Link to comment Share on other sites More sharing options...
Kelvin Posted February 5, 2023 Author Share Posted February 5, 2023 Yes vented cold roof. The aim would be to have the roof follow on quickly after the deck is on but best laid plans and all that. Link to comment Share on other sites More sharing options...
Kelvin Posted February 5, 2023 Author Share Posted February 5, 2023 I’ve found this. Class 2 can be used and optionally protected with the VMZINC membrane. https://www.associatedlead.co.uk/wp-content/uploads/2019/10/VMZINC-Standing-Seam-Reprint-April-2019-R5.pdf Link to comment Share on other sites More sharing options...
Iceverge Posted February 5, 2023 Share Posted February 5, 2023 I think it was @SimonDand @Patricksuggested/used 4x1 timbers closely spaced in preference to plywood. I prefer this idea as the risk of moisture that condenses on the back of the metal roof can much more easily dry to the ventilated cavity. Link to comment Share on other sites More sharing options...
SimonD Posted February 5, 2023 Share Posted February 5, 2023 Yes, sarking boards are the preferred method according to the Federation of Traditional Metal Roofing Contractors UK Guide to Good Practice. However, plywood is extremely common as it's much easier, quicker and cheaper to install so contractors naturally tend to go for this. It's also okay to use OSB but screw pull out is much reduced and therefore care should be taken especially in exposed areas where uplift could pose a problem. If using plywood, I'd suggest definitely using a membrane between plywood and metal roof - some installers are known to omit this. 1 Link to comment Share on other sites More sharing options...
Kelvin Posted February 5, 2023 Author Share Posted February 5, 2023 (edited) The two quotes i have so far include a membrane and assume 18mm plywood deck. If you fit class 3 plywood it become really dear. Class 2 can be had for less than half the cost. Treated sarking boards are less than half the cost of class 2 but probably take twice as long to fit Edited February 5, 2023 by Kelvin Link to comment Share on other sites More sharing options...
Patrick Posted February 5, 2023 Share Posted February 5, 2023 2 hours ago, Iceverge said: I think it was @SimonDand @Patricksuggested/used 4x1 timbers closely spaced in preference to plywood. I prefer this idea as the risk of moisture that condenses on the back of the metal roof can much more easily dry to the ventilated cavity. Officially : everything that @SimonDa Said. Unofficially: Sarking boards all day every day and if you rather use something else- use another roofing system . 1 Link to comment Share on other sites More sharing options...
markharro Posted February 5, 2023 Share Posted February 5, 2023 This is interesting as I will be boarding our roof myself prior to the zinc roofers taking over. I was planning to use ply and have bought a nail gun to fit it. I was guessing that this would be fine using 50mm ring shank nails but this is just an assumption. I need to find out the correct method or methods and also the correct number of nails per full sheet. I'm assuming our SE could provide this detail but it would be interesting to hear the thoughts of people on the forum. I'm in Edinburgh in case its relevant. Link to comment Share on other sites More sharing options...
markharro Posted February 5, 2023 Share Posted February 5, 2023 I also previously wondered about sarking boards. We have a curved apex and I think that would be easier to form in sarking boards also. Its def interesting if these are half the cost of the cheapest ply! My other issue though is time. I have allocated 1 week to boarding the roof with ply with my partner's assistance as labourer but I won't be able work 9-5 on it. I have my day job to juggle as well so its probably more realistic to allow maybe 3 hours of roofing per day over 5 days with a bit more over 2 weekend days. With ply and a nail gun I was banking on that being more than enough time for what must be around a 120 - 130m2 roof surface. Will it suffice if I use sarking boards? thanks. Link to comment Share on other sites More sharing options...
Kelvin Posted February 5, 2023 Author Share Posted February 5, 2023 Class 2 plywood isn’t the cheapest plywood. It’s in the middle. You can probably work out how long it’ll take you. Ply is something like 2.4mx1.2m in the biggest sheets. The sarking boards are 150mm x 4.8m Link to comment Share on other sites More sharing options...
SimonD Posted February 6, 2023 Share Posted February 6, 2023 20 hours ago, markharro said: This is interesting as I will be boarding our roof myself prior to the zinc roofers taking over. I was planning to use ply and have bought a nail gun to fit it. I was guessing that this would be fine using 50mm ring shank nails but this is just an assumption. I need to find out the correct method or methods and also the correct number of nails per full sheet. I'm assuming our SE could provide this detail but it would be interesting to hear the thoughts of people on the forum. I'm in Edinburgh in case its relevant. If using 18mm plywood, then 50mm galvanised ring shanks are fine. I'd nail at 150mm along edges and 300mm otherwise. If you want more reassurance then 150mm all over wil do the job. 20 hours ago, Kelvin said: If you fit class 3 plywood it become really dear. Class 2 can be had for less than half the cost. Treated sarking boards are less than half the cost of class 2 but probably take twice as long to fit Not necessarily, there are several suppliers where I can get class 3 plywood at the same price as class 2 as it tends to depend on the origin and species of the timber. I think that even B&Q and Wickes, for example, sell class 3 ply for about £45/sheet. I'd be surprised if sarking boards were cheaper per m2. However, the most important thing here is what you're using it for and putting it all into perspective. We're talking about probably a few hundred quid and a few hours of labour on a roof that costs thousands and thousands and products like Greencoat PLX come with a 50 year guarantee with a lileky life of 70+ years. This is the substrate for this wonderful covering material. Link to comment Share on other sites More sharing options...
Kelvin Posted February 6, 2023 Author Share Posted February 6, 2023 Can you link the suppliers as I can’t find any that are selling it at class 2 prices. B&Q quality is shocking. Wickes do have class 3 for about £15/m2 which is £2200 plus fitting for my roof albeit I’m doing it myself. Link to comment Share on other sites More sharing options...
saveasteading Posted February 6, 2023 Share Posted February 6, 2023 21 hours ago, markharro said: if these are half the cost of the cheapest ply! Perhaps. but will be slow. If done by a builder they will charge a lot more. The gaps are great for allowing venting, but don't stiffen the structure as such as sheets. Your design may need the large sheets, so ask. You could use them for the curved bit though. I think the price of OSB is better than plywood again. OSB generally provides enough structural stiffness, so ask your SE if you can use OSB, if you want to. Always put a vapour barrier on it, whether ply or OSB. Ply is made from hardwood from exotic forests. Whether we can trust certification that no orangutans or macaws died is a matter of opinion. Find out the costs, tell your professional, and ask them if you can use your chosen material. They don't always know the costs or practicalities, and it isn't their money. They might even thank you for the current best value information. Link to comment Share on other sites More sharing options...
SimonD Posted February 6, 2023 Share Posted February 6, 2023 3 hours ago, saveasteading said: Ply is made from hardwood from exotic forests. Only some of it. There's good reason to question the origin of some hardwood ply from Asia and Brazil, but plenty of other choices such as spruce or pine either from Scandinavia or even Chile. 4 hours ago, Kelvin said: Can you link the suppliers as I can’t find any that are selling it at class 2 prices. I can't link to the products as they're local suppliers to me who are a bit old school as it's mostly dog & bone or the odd email (see below), but at the end of the day, class 2 will suffice as it's under cover. Sometimes you've just got to go with what you can get, I had to do a lot of that as I was trying to build right through Covid19. 4 hours ago, Kelvin said: B&Q quality is shocking. I disagree. Granted, you've got to make your selection but I recently made my son a desk using B/BB pine plywood from B & Q and being a B face it has come out really nice. I wouldn't buy bulk as I'd do that with a trusted local timber merchant instead. My choice supplier for my build has been Robbins timber in Bristol. Link to comment Share on other sites More sharing options...
markharro Posted February 10, 2023 Share Posted February 10, 2023 On 06/02/2023 at 18:42, saveasteading said: Always put a vapour barrier on it, whether ply or OSB. Hi @saveasteadingdo you have a link to a specific vapour barrier product? thanks Link to comment Share on other sites More sharing options...
Kelvin Posted February 10, 2023 Author Share Posted February 10, 2023 17 minutes ago, markharro said: Hi @saveasteadingdo you have a link to a specific vapour barrier product? thanks If it’s VM Zinc for example they have their own membrane Link to comment Share on other sites More sharing options...
saveasteading Posted February 10, 2023 Share Posted February 10, 2023 Cromar Vent 3. But any good brand should be fine. Just avoid any that are sheets of plastic with holes punched in them. 1 Link to comment Share on other sites More sharing options...
Patrick Posted February 10, 2023 Share Posted February 10, 2023 5 hours ago, Kelvin said: If it’s VM Zinc for example they have their own membrane Aludex it's called Link to comment Share on other sites More sharing options...
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