RSJs - Ridge beams

[RonnyRaygun]

Been told I would be looking at
250x150 Purlins.

So I assume the Ridge would be a similar size, if not smaller.

Well...you'll need one purlin, which will probably be taking a lot less load than the ridge beam, as the ridge beam also has to support the new dormer roof.
And your span is 7.4m according to your sketch, so I would say that a 250x150 purlin would be woefully inadequate too. A 254x146 UB would be nearer the mark. Large sections I know, but you've got a huge roof. Now if you are planning to support the purlin and ridge beam somewhere near the middle, these sizes reduce massively. Then you need larger steels in the floor...

 

[ibby]

When I spoke to the SC

He said I will need 3 new steels.

1 Ridge Beam
2 RSJs @ 250x150

Now he told me, one of the new RSJs would replace the bottom purlin.

The other would be at the top of the dormer height.

 

[RonnyRaygun]

When I spoke to the SC

He said I will need 3 new steels.

1 Ridge Beam
2 RSJs @ 250x150

Now he told me, one of the new RSJs would replace the bottom purlin.

The other would be at the top of the dormer height.

Ah right, so a 250x150 steel beam...I thought you meant timber! There you go then, a 254x146 purlin, and another 254x146 at the top of the dormer...is this because the dormer will be lower than the ridge?
If so then the ridge beam will probably be a 254x146 as well.

 

[tim00]

woody,

Thank you for your reply. In my limited experience, i've never supported an in-situ ridge with a beam. In my dormer case above, as it's new work, it would be a case of beam or board from the get-go.

 

[tim00]

RonnyRaygun,
Thank you for your post. I did wonder what was being referred to. I should be more alert.

 

[ibby]

When I spoke to the SC

He said I will need 3 new steels.

1 Ridge Beam
2 RSJs @ 250x150

Now he told me, one of the new RSJs would replace the bottom purlin.

The other would be at the top of the dormer height.

Ah right, so a 250x150 steel beam...I thought you meant timber! There you go then, a 254x146 purlin, and another 254x146 at the top of the dormer...is this because the dormer will be lower than the ridge?
If so then the ridge beam will probably be a 254x146 as well.

correct.


The dormer will be lower than the ridge height.

My Ridge sits at 3.2 Meters, Its very big you see!

 

[noseall]

How do you mean? In another thread - you might not have seen it - Ibby says he wants a full width dormer, so how do joists help

Read more: http://www.diynot.com/forums/building/rsjs-ridge-beams.311952/page-2#ixzz1mNTaJBGY[/QUOTE]

noseall wrote:
Joists perhaps...?


That may be a slight possibility if all the rafters and joists form a neat triangle, but when one or both sides of the roof are cut to form the dormer, the loadings change (triangle is broken) and the ridge needs support
__________________
Instant message me! I'm trying it out for a bit ... addy in my profile comments

Read more: http://www.diynot.com/forums/building/rsjs-ridge-beams.311952/page-2#ixzz1mNTvQKds[/QUOTE]

I suppose i have to read the WHOLE post in future!

I'll go sit on the naughty step now.

 

[RonnyRaygun]

I suppose i have to read the WHOLE post in future!

I'll go sit on the naughty step now.

I think Freddy said it best

Where's your crystal ball?