Help planning to build a pergola on an old Concrete slab

[AriG]

Hi all, long time reader first time poster. Just after some assistance with planning out to build a pergola over my existing concrete slab (see attached picture, not a great shot but will be taking more tomorrow).

A bit of background info, the concrete slab. The slab has had some movement over the years particularly the part closest to the yard. The step out of the house is something like 90mm and once you get to the end of the slab its well over 100mm (can't recall the exact variation I will need to remeasure). I do plan to build a deck over the slab in the future but I though it would be best to sort out the pergola first.

The are itself is quite large the slab measures 6400mm (W) x 3760mm (L) this also includes the area under the eaves.

I had planned to use the roof extenda system rather than connecting the pergola directly to the facia of the house to provide a bit more head room as the eaves are quite low (appox 2000mm - 2200mm (H)) and I figured it would be a bit more simpler and secure from a DIY perspective.

The biggest concern I had was how to connect the posts of the pergola to the concreate slab as I did not want the posts to encroach on the pathway. I figured using stirrups would be a solution however its the fact the slab is uneven that I'm not sure if it is even viable in the first instance.

Any advice around timber to use for this project and specifics around fasteners and timber spacings for would be greatly appreciated! I have watched the how to build a pergola videos so will be applying what I have learnt to this summer project of mine.

Thanks in advanced for all your help 😊

[Jason]

@AriG,

Let me extend a very warm welcome to the Bunnings Workshop community. We're thrilled to have you join us and trust you will get loads of help and inspiration from our clever and creative members. 

Apologies for the slow reply, we are missing one of our resident Bunnings D.I.Y. experts on the site at the moment as Mitch is taking a well-earned break. I'm sure @EricL will be happy to assist as soon as possible. 

Let me also tag @DIYgals, @sandy_d, @raymao268, @Brad and @tom_builds to see if they might like to kick off the discussion in the meantime.

Jason

[DIYgals]

Hey @AriG,

we completed a similar project about a year ago. Initially we thought about using the roof extenda brackets but decided to have our pergola separate to give it more height. The roof itself flys over the existing roof and has its own gutter. 

If you have access to a laser level it would probably be a good start to check what all the different heights are and start to mark it out. I think stirrups would still work well on your cement and you could adjust the heights of each post according to the levels. Let me know if you have any other questions. 
Good luck!

[EricL]

Hello @AriG

My apologies for the late reply. It's great that you've received fantastic advice from @DIYgals. I agree with the recommendation of using a Laser Level in the area. This will let you see at what height the Stirrups need to be placed. However, if you want a more substantial base, you'll have to cut into the surface of the concrete slab and build a new concrete footing. 

Timber size will depend on the plan that you've drawn up. However, you'll need to use exterior-rated timber like H3 or LOSP primed pine. I recommend using M12 sized bolt and nut combination where appropriate. 

Below are some possible options.

• Posts LOSP Structural Primed Radiata Pine 112mm x 112mm
• Beams LOSP Primed Radiata Pine 280mm x 42mm
• Rafters LOSP Structural Primed Radiata Pine 185mm x 42mm
• Batons LOSP FJ Primed Radiata Pine 42mm x 42mm.

Since you've already seen the Pergola tutorial, I've placed links to some of the amazing Pergola projects that our Workshop members have shared. 

• Pergola over low-level deck by @DIYgals
• Barbecue entertaining area with pergola by @sandy_d
• 3 x 4m gable pergola by @Jimi

Please keep us updated with your progress, we look forward to seeing the start of your project.

If you need further assistance, please let us know.

Eric

[tom_builds]

Hi @AriG,

When building my pergola I ended up using fascia brackets that attach in to the roofs rafters. Like the roof extenda system they provide a more secure attachment then just attaching on to the fascia itself, however they are quite a bit cheaper than the roof extenda and it doesn't involve making permanent holes in your roof (just a bit of tile lifting and replacing to get access to the rafters). 

To solve the problem of low clearance you could build your pergola with a reverse skillion roof, meaning the lowest part of the patio roof will  be where the eavess already are and then it will rise up away from the house, as in the below image.

 

@DIYgals suggestion of using stirrups and cutting the posts to fit is a great plan for fixing into the slab.

Let us know which option you go with, and best of luck with your project!