One for the builders

[Tropey]

I've got a question for the builders out there.
I'm putting a pergola up at home. Where I am putting it is over a concrete slap (stencil design) The slab is about 200mm is thickness.
I am going to secure the anchors for the upright posts straight onto the concrete slab as there isn't enough room to sink them in the ground next to the fence.
My question is how close to the edge can I safely drill the holes into the conrete for the dynabolts to go through without risking the concrete cracking or breaking away. I was thinking about 30mm from the edge should be enough or do I need more or can I get away with less ?
Thanks for the help.

[JarrardB]

I'm no builder, but it's probably worth mentioning how heavy the pergola will be... ie is it going to have a shade cloth roof, maybe colourbond? Also how far apart are the posts? (further apart means more load i reckon).

[Tropey]

thanks for that JarrardB.
It's going to have timber posts and laserlite sheeting for the roof. The whole structure will be about 12m long and 3m wide and there will be 3 posts supporting it on the one side (the other side will be secured to the house)

[Chad_TJ]

Dont take my advice as the bible, i work for a builder, but personally i think i would make it more like 60-100mm from the edge, as sometimes with just decrative slabs the rio (steel) inside the slab might only be about 30mm from the edge. And you want to try and get the bolts on the side of some rio as it will reduce the chance of the edge of ya slab braking away. Just some advice mate.

[murray]

dont use dyna bolt use chemi set anchors
they dont spread the hole side loading the concreate

[carvesdodo]

If you don't allready have the post "feet", you could use 5mm thick angle on the house side of the post as the mount, to get away from slab edge.

Brace top of post to bearer well - reduces post wobble which reduces strain on slab / post mount

Chem Set sounds good - never used it - Lots of good "techo" glues out there for building.

[Chad_TJ]

yeah defiantely use Chem set, its a brilliant invention, you can even just chem set threaded rod in the holes that will hold pretty well. Just make sure you blow out the hole well.