flat roof joists

[sarah barrows]

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 !!

 

[PeterW]

How much does that lantern weigh ..?? That will affect the loading and the span as will if there is access to the roof. 

[sarah barrows]

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

[PeterW]

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. 

[jamiehamy]

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? 

[sarah barrows]

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.

[bassanclan]

Google "trada tables" and you will be able to see the options available with a given load & span

 

[sarah barrows]

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.

[sarah barrows]

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.