sarah barrows Posted May 12, 2017 Share Posted May 12, 2017 Hi, I was wondering if there is a 'calculator' that will give the correct number of joists/firrings/fillets/wall plates that I need to order? Is this an easy calculation or do I need to get someone structural to do it ? I am doing a small flat roof extension with a roof lantern - on a tight budget but I'm getting there !! Link to comment Share on other sites More sharing options...
PeterW Posted May 12, 2017 Share Posted May 12, 2017 How much does that lantern weigh ..?? That will affect the loading and the span as will if there is access to the roof. Link to comment Share on other sites More sharing options...
sarah barrows Posted May 12, 2017 Author Share Posted May 12, 2017 (edited) 1 hour ago, PeterW said: How much does that lantern weigh ..?? That will affect the loading and the span as will if there is access to the roof. Thanks again for the reply - yes its 145 Kg. No roof access is required. Edited May 12, 2017 by sarah barrows Link to comment Share on other sites More sharing options...
PeterW Posted May 12, 2017 Share Posted May 12, 2017 2 hours ago, sarah barrows said: Hi, I was wondering if there is a 'calculator' that will give the correct number of joists/firrings/fillets/wall plates that I need to order? Is this an easy calculation or do I need to get someone structural to do it ? I am doing a small flat roof extension with a roof lantern - on a tight budget but I'm getting there !! So it's 4m x 5m ..?? Assuming you can get a wall plate securely rawl bolted to the existing house then you should be ok with C16 195x44 @400mm centres running in the direction of the house to the garden. I would double up the ones under the edges of the lantern and use proper timber hangers for the ones running under the long sides. Don't forget to leave a 15mm recess all around the inside of your kerb to allow for plasterboard when you're measuring for your lantern. Link to comment Share on other sites More sharing options...
jamiehamy Posted May 12, 2017 Share Posted May 12, 2017 That seems slightly light? Our 900x2400 (plus upstand dims) weighed 138kgs, although it's triple glazed. If double glazed should be right but still seems on the light side. Is it being build in situ? 1 Link to comment Share on other sites More sharing options...
sarah barrows Posted May 12, 2017 Author Share Posted May 12, 2017 28 minutes ago, PeterW said: So it's 4m x 5m ..?? Assuming you can get a wall plate securely rawl bolted to the existing house then you should be ok with C16 195x44 @400mm centres running in the direction of the house to the garden. I would double up the ones under the edges of the lantern and use proper timber hangers for the ones running under the long sides. Don't forget to leave a 15mm recess all around the inside of your kerb to allow for plasterboard when you're measuring for your lantern. great, will do. Thanks so much. Link to comment Share on other sites More sharing options...
bassanclan Posted May 12, 2017 Share Posted May 12, 2017 Google "trada tables" and you will be able to see the options available with a given load & span 1 Link to comment Share on other sites More sharing options...
sarah barrows Posted May 13, 2017 Author Share Posted May 13, 2017 21 hours ago, jamiehamy said: That seems slightly light? Our 900x2400 (plus upstand dims) weighed 138kgs, although it's triple glazed. If double glazed should be right but still seems on the light side. Is it being build in situ? I got that from the supplier but I'll double check - thanks. Link to comment Share on other sites More sharing options...
sarah barrows Posted May 13, 2017 Author Share Posted May 13, 2017 18 hours ago, bassanclan said: Google "trada tables" and you will be able to see the options available with a given load & span thanks - good information there. Link to comment Share on other sites More sharing options...
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