How to build pergola ceiling joist and rafters?

[jasonlee]

I'm trying to build a 6x3.5m pergola, the span of the rafter will be roughly 3.5m at 600mm spacing.

The idea is trying to create a level enclosed ceiling underneath and a pitched roof between 1 and 5 degree towards the front of the gutter. The whaling plate will be fixed to the existing house structure. 

My question is can I use one rafter for both ceiling joist and roof rafter to support metal sheeting, I'm thinking to use 140mmx45mm H2 MGP10. Is it possible to rip the top of the timber at a small angle from one end to the other to create that slope but at the same time to keep the bottom straight use for ceiling joist? I attached a drawing for your reference, green part to keep. 

Thanks

Jason

[jasonlee]

Hi Dave,

thanks for your input. Can you explain what exactly you mean by having two beams side by side ? I have attached a picture of the structure I’m trying to build. I have no problems in terms of the height, it’s just that the pergola is a free standing one, if I need to raise the height for the rafter to get a pitch what is the best way to frame it on the structure I attached below ?

 

[MitchellMc]

As mentioned previously @jasonlee, you can use the same timber to act as the ceiling joist and rafter. However, it needs to be of a suitable calibre to support both the load of the roofing sheets and the internal lining. 140 x 45mm is not of a suitable calibre to span your 3500mm distance, let alone support those loads. As @Dave-1 mentioned, you can have two timbers side-by-side to carry heavier loads but the 140mm is not capable of those spans.

I think what you'll need to two is separate the 6000mm length with a large beam in the middle running the 3500mm direction. From that, you can divide the 3500mm length in two with beams that run perpendicular to it. That way when you use the 140mm timber it only has to span half the 3500mm distance.

Mitchell

[Dave-1]

Morning @jasonlee 

So next question.

Is this a pre-bought pergola or one you are building from scratch?

If its from scratch, have you drawn up any plans? And do you have a photo of the area you wantto build it in? It may help with a solution to the probelm.

As to the side by side question. I am talking about the rafters across  the width of the pergolla you are designing. The ones you wantto champhor down from 140mm to 90mm. I was suggestion that you can bolt/connect two of the lengths together side by side (long flat side to long flat side) to form a stronger beam. Tho after @MitchellMc's suggestion I am starting to think that a 3.6m span may cause some bending even in that.

If you have a plan drawn up we can see what your proposed dimensions are. 

Dave

[jasonlee]

Hi @Dave-1,

This is a pergola I need to build from scratch. 

I don't have a plan for this project but I tried my best to put something together below hope you can understand. There will be some roof extenda brackets on the existing roof and those 3 blue posts to support the main beams. On top of the beams are the ceiling joist/rafters which I want to use one timber for both ideally spanning across 3500mm at 600mm spacing. If I'm going with this option, what's the best size timber for the main beam and rafter to use? I can double them up side by side as you mentioned to make it a stronger rafter. 

Another option is to build something like a dwarf wall (picture attached) at the back of the pergola roof above those ceiling joist (running just flat and straight now), then have separate rafters going from the dwarf wall down to the front of the beam where those posts are to create any pitch that is reasonable. I'm not sure if this is the proper way to do it as the pergola has nothing to fix to at the back, only the roof extenda is holding the main beam.

Please advise your thoughts on this.

Jason

Option 1

Option 2

[Dave-1]

Morning @jasonlee 

I like your sketch and drawing. The drawing would be solid for sure and the beams I would be using 110mm by 45mm ish. I just hesitate impacting the roof for waterproff reasoning. I do like the 600mm spacing as well.

I prefer freestanding pergollas. As in not attached to a roof, mainly becuase a structure should be able to stand on its own and also not to add stresses to an existing structure. 

I am not sure if your post that ends up in the middle of the driveway is just an example of the layout or you are planing on covering part of the driveway   If you are planing on covering part of the driveway I would consider twisting the whole pergolla so there are no legs on the driveway and connect it to the house with a shorter width roof? Or I could be jumping the gun

Dave

[jasonlee]

Hi Dave,

yes that’s just an illustration what I’m planning to do, it’s the same situation at the backyard. The 110mm beam you mentioned, is that for the pergola main beam that supported by posts? 

[Dave-1]

Morning @jasonlee 

I am just going off what I used for my pergolla to span about the same distance. (you can find the project in here Pool deck stage 1 and Pool deck stage 2 )

As to your question, yes it is. The way I figure it, you want whatever you use to be able to hold teh stuff over your head / car/ boat, whatever so over engineered is better then not. It may cost more but guarentee the first time you have a strong wind/rain come through you will be thinking "oh man, glad"

Dave