What rafters to use for pergola design?

[diy_hausdesigns]

Hi all 

Just seeking some advice. I'm planning to building a simple pergola (none covered with no purlins). I am unsure whether to use 90x45mm or 140x45mm for the rafters over a 3.8m span

Sketch of plan 

Sketch of the connection

The 90mm looks good and makes the whole project easier to build and manage. Here is a sample with some leftover 90x35.

But I suspect the 140mm may look better despite it taking a bit more time and effort to build.

Would love any input !!?

[Dave-1]

Afternoon @diy_hausdesigns 

Id definently go with the 140mm, mainly to stop any potential sagging down the track. Are you going to replace the house attachment points or cut the timber to suit?

I think it will bring the corner together nicely, It will provide a bit of shade and just make it feel more contained. Just having a second look at the way you have extended the posts up from the fenceline has me wondering if it may be better spreading the weight down the whole wall instead of just that top section? I know the open pergolla may not appear to be weighty but as soon as it gets wet and windy it will be heavier then what you may think.

Dave

[diy_hausdesigns]

Hi @Dave-1 

Thanks for the speedy response.

Appreciate your insights ! 140mm it is 😁

Planning to cut the timber to size for the house side and use the brackets which are attached to the ledger behind (already painted same as fascia).

I'll add a other support along the fence as well as you recommended - think that's a great idea to share the load.

Hugely Appreciate your help !

[Dave-1]

Howdy @diy_hausdesigns 

lol I was just procrastinating and staring at the screen instead of going out and finishing my bench for my deck hahahaha Yeah I really should go do a little more

Dave

[MitchellMc]

Hi @diy_hausdesigns,

@Dave-1 is on the money here. Although 90 x 45mm will physically span the distance, once it gets wet it will sag noticeably. Also, I think 140mm will look more aesthetically pleasing overall.

Mitchell

[diy_hausdesigns]

Hi @MitchellMc 

Thanks for further validating that. I will definitely got with the 140mm. I'll update you all once I get it started 😃

[jonced3]

Hi @MitchellMc 
I'm also working on a project to cover a dead space down the side of the house. Purely to prevent any water from coming into the garage. 
What are your thoughts on the following materials? 

• Wailing plate to fascia, beams = 140 x 45
• Rafters = 90 x 45. It will be spanning max 1.8m 

I've been told 140x45 might be an overkill for a basic/small structure like this.  Been also suggested we can span the rafters to 1200mm but I would probably rather see it at 900mm.

Thanks in advance

 

[MitchellMc]

Hi @jonced3,

From what you’ve outlined, 140x45mm for your beam and waling plate sounds perfectly fine and definitely isn’t overkill for a small pergola like this. For your rafters, 90x45mm should work well, and I agree with keeping the spacing at 900mm rather than increasing to 1200mm.

The next size down for beams would typically be 120x45mm or 90x45mm, but I wouldn’t recommend going as low as 90x45mm for a beam. That 140x45mm choice is solid and will give you some peace of mind. I can’t quite see the span for your rafters in the plan you’ve shared, so if you can confirm how far they’re spanning from the waling plate to the beam, that’ll give a more accurate idea. From what I can see, if the span is no more than 1.5m, 90x45mm rafters will be fine.

One important note: wailing plates cannot be attached to the fascia itself. Fascia boards aren’t structural, so you need to connect your wailing plate to the structural timbers behind the fascia, such as the ends of roof beams or rafters. Make sure the screws go into those structural members for a safe, stable connection. 

Please let me know if you have any questions.

Mitchell

[jonced3]

Thanks @MitchellMc for the prompt response. The span of rafter from wailing plate to beam should be around 1.7m, no more than 1.8-2m.  Once wailing plate is fixed to fascia (structural timbers) the actual internal span dimension will be close to the 1.5m. 

[MitchellMc]

That would be fine, @jonced3. However, if you find it's closer to 1.8m, I'd be inclined to consider upping the rafters to 120x 45mm.

Mitchell