Purlin question

[Patters1978]

Hi

Wonder if someone can help.
We have a little roof section on the house that is approx 3 x 2 meters it's like a little loft section downstairs in the kitchen.
The missus wants it vaulted with maybe a velux in it.
Having a look up it's got a massive purlin in the middle of it.

With the size of the roof does it need that? Could it be made smaller?
What are my options?

Cheers

 

[Wayners]

Contact a building structural engineer

 

[cdbe]

Possibly as above.

Although if you want it open you'll need to insulate the sloping roof to a considerable depth - probably almost as deep as the purlin so it'll be hidden anyway.

You may need to consider the loss of bracing caused by removing the ceiling joists.*

If the purlin is slap bang in the middle of where you want the velux then you'll need deeper rafters (sized via online span tables).

* In my case the rafters were fixed at the top with heavy duty angle brackets.

 

[catlad]

Larger rafters would be the sensible way to go for insulation and skylights.

 

[Patters1978]

Right sorry for not replying sooner I have been measuring the roof and putting it into SketchUp.

So first picture is the roof structure right now, oddly the second picture show that the ceiling support is away from the wall? unsure why.
None of the rafter have birdsmouth at all.

My idea going on the rafter span table is couldn't I double up the rafters as shown in picture 3/4?
The span from support to support is 212cm and in the picture I have just used 150 rafter

 

[catlad]

Use 400 centres and only double the rafters by the skylight, 150mm rafters will be plenty at 2.12m span.