Attach pergola to balcony

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Old 03-06-17, 06:44 PM
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Attach pergola to balcony

Attach pergola roof to balcony
I would like to add a pergola style roof outside measuring something like 12x10'
I thought that one side of it could be attached to the existing concrete balcony. The other side would be fence posts in concrete bases.
What sort of attachment will be strong enough for the balcony side. Can I put a horizontal 2x4 into the concrete and then rest the pergola roof wood pieces on that and screw them in?






 
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Old 03-06-17, 11:13 PM
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A concrete deck is not the norm I'd say this might be a good question for a structural engineer/architect.

We dont know the size of the structure you are proposing but typ nothing would use something as small as a 2x4 for as a Ledger.
 
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Old 03-07-17, 05:56 AM
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What do you mean by "pergola"? Are you creating an open, mostly cosmetic wood framework or do you want to build a full roof that must withstand wind and snow loads?

I am not sure how you were planning to attach to your porch roof since the railing is completely covering the outer perimeter. It's impossible to say what your existing concrete porch floor can handle without knowing how it's constructed. I'm assuming an Engineer will get expensive as they won't be able to see what reinforcing is inside the concrete which probably means expensive testing or just a simple "no". Whatever you are considering I think it would end up being cheaper and easier (if you do it properly) to make your new structure totally free standing and not supported by your existing porch.
 
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Old 03-07-17, 06:38 AM
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It's just to provide a shade area like a gazebo. There will be no heavy load on the roof of the pergola.
Kind of like this:


The concrete is reinforced so it just needs to support some of the individual pergola rafters.
 
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Old 03-07-17, 09:37 AM
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The "gotcha" is that you have no idea how and where the concrete is reinforced so you're pretty much guessing.
 
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Old 03-07-17, 09:57 AM
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But there's hardly any weight on that pergola roof and with a lattice effect, wind will go mostly through it. Can't I just drill holes in the concrete and anchor a beam to that then secure the pergola rafters to it? Metal brackets maybe?
 
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Old 03-07-17, 10:00 AM
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I think the free standing idea is a winner, the decking is supporting a railing but even 10 2x8/10's have some heft too them. Assuming the plan is to use the same attachments, who knows what they will hold.

Don't want it to come crashing down!
 
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Old 03-07-17, 10:05 AM
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If I use free standing as there will then be 2 additional posts in the way, which probably won't look great in front of the concrete balcony.
Can remove the existing railing bottom and attach a beam to the concrete with new anchors.

What's your concern, the weight?
http://web.archive.org/web/20100601233921/http://www.magnetmart.com.au/media/magnet_mart/startsmart/build/make_pergola.pdf
This guide uses framing anchors / hangers with a ledger plate/stringer.




 

Last edited by qwertyjjj; 03-07-17 at 11:13 AM.
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Old 03-07-17, 11:39 AM
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The concern is basically everything. You've got a relatively thin cantilevered cast concrete deck. There is nothing "standard" about it's construction. Do you have access to the engineering or drawings for its construction? If you have them you could have an Engineer take a look at it.
 
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Old 03-07-17, 02:20 PM
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It's about 8 inches thick. Is that thin?
Unfortunately, no plans exist that I'm aware of.

I think you're saying 2 upright posts carrying load vertically will be stronger than an 8 inch thick reinforced concrete carrying load.
A 2x6x12 rafter weighs about 10kg.
Multiplied by 20 = 200kg.
The pergola rafters won't weigh much more than that, which is around 2 people standing on the same area of balcony+ half the weight will be held by 2 posts at the other end of the pergola away from balcony.
Granted there are some extra forces from wind and sideways but still...

Here's an example where it guess through the house wood structure.

www.ronhazelton.com/projects/how_to_build_a_pergola_over_a_patio
 

Last edited by qwertyjjj; 03-07-17 at 02:44 PM.
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Old 03-07-17, 06:33 PM
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I think you're saying 2 upright posts carrying load vertically will be stronger than an 8 inch thick reinforced concrete carrying load.
I vote for freestanding. An engineer might say it's OK to lay a ledger on the patio deck, but I doubt it. I also highly doubt they would let you drill into the edge of the concrete to use anchors or rebar.
All the plans you posted show the ledger board attached to the house, which is the norm and needs to be very strong.
To me the beauty of a pergola is having 4 large 6x6 posts that are obviously larger than needed to hold up the top.

The posts look nice wrapped with brick or some other base extending 3 to 4' up.
 
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Old 03-07-17, 06:43 PM
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I'll have a think about how I can get 2 extra posts for freestanding in there without it looking odd.
I'm interested though, why does drilling holes for 2.5"x0.5" expansion anchors cause a problem. Does it weaken the concrete?

People seem to put them in brick walls all the time and also concrete grade for decking.
 

Last edited by qwertyjjj; 03-07-17 at 07:02 PM.
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Old 03-08-17, 06:10 AM
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I believe the frost line around here is 6ft.
What's the best way to secure the posts that deep? I've seen these big screw in type post attachments at the store. Concrete would be cheaper I think but digging 6ft with a shovel is going to be a big job. I think there are also rocks underneath meaning a screw post might run into trouble.
Does the screw in post have to go below the frost line also?
 

Last edited by qwertyjjj; 03-08-17 at 06:37 AM.
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