Extend existing balcony. Need advice on how the joists should be placed

[randomkaka]

Hello!

We have a balcony today that measures 1.6x12m. We plan to extend it by 2x6m. Before I start building, I’d like to consult with you to ensure a stable construction. Tips and considerations are greatly appreciated!

Currently, there are joists with 60cm centers measuring 170x80mm, and the load-bearing beam is a steel beam. The idea is to splice the joists with new 170x45mm joists that are fastened with 2 through-bolts to the existing ones.
I’ll set 70cm support posts with 95x95mm posts at 2-meter intervals. The new load-bearing beam will be a 170x45mm joist. The decking is 2.44m above the ground.

I have 2 questions:
Should the joists rest on the new load-bearing beam, or should they be mounted with joist hangers to the new load-bearing beam for the most stable construction?
At the splice, how far should the new joists run parallel to the old joists? Is it enough for them to rest on the old load-bearing beam with the bolts about 5cm from the edge?
Is there a better solution for splicing the joists?

Thankful for a response,
Best regards

 

[justusandersson]

The load requirements for balconies are quite high. Therefore, 45x170 is not sufficient for the front support beam. Increase to 45x195 C 24. Joist hangers are usually a technically inferior solution. Here, it doesn't matter much if you use the right kind of screw (=acid-resistant). Note that the original beams are 80x170, which provides a better feel, even though it is an over-dimensioning. I have no comments on other details.

 

[Snickarkirre]

It sounds good that you are installing the new planks on the old beam and bolting them to the old ones about 50mm in. I wouldn't have placed the carriage bolt closer to the edge anyway. So extend the new ones by 100mm. Then I would use joist hangers, that way you should have the most stability with the least risk of twisting. If you place them on top, you'll probably need to insert blocking between the planks to prevent the timber from twisting and lock them laterally, so to speak (prevent shearing). Drive the carriage bolt through the beam that lies against the outermost pillars, and then it won't go anywhere.

 

[randomkaka]

The load requirements for balconies are quite high. Therefore, 45x170 is not enough for the front support beam. Increase to 45x195 C 24. Joist hangers are usually a technically inferior solution. It doesn't matter much here if you use the right type of screw (=acid-resistant). Note that the original beams are 80x170, which provides a better feel, even though it is over-dimensioned. I have no comments on the other details.

Thank you so much for your response.
I thought it would be convenient to keep the same height as the current joists since the decking is directly on top. I don't know how to solve the height difference if I go up to 45x195. Do you have any suggestions?

 

[randomkaka]

Sounds good that you're placing the new planks on the old bearer and bolting them to the old ones about 50mm in; I wouldn't place the carriage bolt closer to the end. So let the new ones extend by 100mm. Then I would use joist hangers to make it as stable as possible and minimize the risk of twisting. If you lay them on top, you might need to place blocking between the planks to prevent the wood from twisting and to lock them laterally, so to speak (prevent shearing). Drive the carriage bolt through the bearer that lies against the outermost pillars, and it won't go anywhere.

Thank you for your answer!

 

[justusandersson]

If you use joist hangers, install the floor joists level with the top of the carrying beam.

 

[randomkaka]

If you're using beam hangers, mount the floor joists level with the top of the load-bearing beam.

Sorry, I was unclear. I meant at the old load-bearing beam, where I intended to let the joists rest on the beam and attach them to the current joists.
Is it a good idea to notch 45x195 joists 25cm x about 10cm so they can rest on the old load-bearing beam according to the drawing? Would it be stronger than 45x170 joists?

 

[justusandersson]

I was probably unclear. 45x170 for the beams is OK. 45x195 is better even if you notch them a little. You mean 25 mm in height? However, a notch should go at a 45° angle to full height.

 

[Snickarkirre]

I understood that justusandersson meant that only the load-bearing beam that will be bolted to the glulam pillars you will install needs to be 45x195, and the others that will run parallel to those that are 80x170 can be 45x170. That's how I understood it but correct me if I'm wrong.

 

[randomkaka]

I understood that justusandersson meant that only the main beam that will be bolted to the laminated wood posts you will install needs to be 45x195, and the others that will lie parallel with those that are 80x170 can be 45x170. That's how I understood it, but correct me if I'm wrong.

Ok then I understand