roofing question

[gmsextension]

Hi all,
I am having a single storey, flat roof extension with a skylight. I was planning on having the skylight positioned as close to the existing back wall as possible, and possibly resting on the steel that will support the opening leading into the new extension. One of the builders said in order to get a good seal on the roof I would be better advised to set it about a foot or so away from the steel and have the skylight supported independently by its own 4 steels. Is this correct? As someone has told me this has been advised to make the roofing job easier for the roofer! Confused Would really appreciate any advice, comments and suggestions. Thanks

 

[tony1851]

You need space around the skylight to enable the roofer to get access to make proper seals.

And why would the skylight itself need 4 steels to support it? Unless spans are large, timber trimmers usually suffice.

 

[gmsextension]

Thanks for reply,
Would you say then about a foot is enough. The skylight (dome) is 2.4mx1.2m and the architect has indicated steels in the drawings.

 

[tony1851]

Thanks for reply,
Would you say then about a foot is enough. The skylight (dome) is.4mx1.2m and the architect has indicated steels in the drawings.

A foot should be enough - you need it as near to the wall as practicable to get light further in, but sufficient to allow working access.

I still don't know why the architect has used 4 steels - can you post the part of the drawing which shows this?

 

[gmsextension]

Will have a go, but not sure how to.

 

[gmsextension]

Hi Tony1851,
I'm still working on trying to get the plans for you to view. Two problems basically. Firstly, Im not good at technical stuff on the computer (probably basic stuff to you) and secondly, my son has put sooo many restrictions on this computer I'm even more limited!
Will try again tomorrow. Thanks for your patience.

 

[tony1851]

Difficult to explain but easy to do!
If you go to the Forum Index, there is a General section at the top, which has 'Forum Information'.
Click on that and there is a section showing how to upload a pic.

 

[gmsextension]

Hi Tony1851,
I think I may have done it. I took pictures of the plans as the PDF file wouldn't download for me. The pictures are a bit blurred but hopefully good enough to get the general idea.

 

[tony1851]

The two 8"x4" steels going side-to-side (across the extension) are OK (though I would have used 7"x4"s to reduce the depth a little). But the two 6"x3 1/2" steels bridging them are unnecessary. Paired timber joists would be more than adequate on that span, and a lot easier to fit into the main steel beams.
Ask the designer if he has detailed how the smaller steel beams are connected to the main beams. If he wants bolted connections, they should be detailed; and they will cost more. Much cheaper and easier with timber, and more practical.

 

[gmsextension]

Thanks. Have you got some idea of the size the paired timber joists should ideally be?

 

[tony1851]

A span of 1.2m, supporting only the end of the lantern would only require double roof joists - whatever they are - 7x2, 8x2 ??

 

[gmsextension]

Thanks for all the help and advice but it's leading on to more questions!
(if you don't mind)
If that part of my plan is already passed (the steels for supporting the dome), can I just ask the BC man if they can be changed to smaller steels and the paired timber joists that you have suggested or do I have to submit more plans? The architect is getting really fed up with me now and I'm still waiting for him to finalise the main steel calculation for the existing opening and remove the central post. There must be a formula to calculate this, is this something you know about too?
Really grateful

 

[tony1851]

Thanks for all the help and advice but it's leading on to more questions!
(if you don't mind)
If that part of my plan is already passed (the steels for supporting the dome), can I just ask the BC man if they can be changed to smaller steels and the paired timber joists that you have suggested or do I have to submit more plans? The architect is getting really fed up with me now and I'm still waiting for him to finalise the main steel calculation for the existing opening and remove the central post. There must be a formula to calculate this, is this something you know about too?
Really grateful

As far a building control is concerned, the plans are not cast in stone. You can make changes as you go along, as long as the changed work still complies.

In this case, whatever beams you use to trim the lantern, you will almost certainly be asked by b/c for structural calculations to prove adequacy.

There is no straightforward 'formula' for this, if your architect cannot do this you need to engage a SE.

 

[gmsextension]

He is an SE / architect, he says. When I ask him to make changes he alters other things too that I don't want altered. If he explained that changing this will affect that before he made a change I could let him know if I want to go ahead with the change. I have been trying to get my plans drawn and approved for almost a year now. I've never done this before and am worried about what to expect if this is the easy part!
So many thanks for your help, I really appreciate it. At least I can be more assertive and appear confident when discussing these changes.[/i]