ᐅ Extension of the ground floor concrete slab with a cantilevered section
Created on: 5 Dec 2025 14:25
T
trissedpHello everyone,
A single-family house consists of a basement, the ground floor, and the first floor.
The concrete ceiling on top of the basement walls has the layout shown in image 1.
It can be seen that there is an opening on one of the long sides of the concrete ceiling.
From the inside, it looks like image 2 shows (a loggia with a glass front).
This loggia (and thus the opening in the concrete ceiling) is approximately 1m (3 feet) wide and 4m (13 feet) long.
Attached to that opening from the outside is a kind of balcony (wooden deck on a steel structure).
The goal is to regain the living space lost due to the loggia (opening in the concrete ceiling).
The glass front would be removed, as well as the attached balcony.
I have researched how this could be approached and am now interested in your opinions.
Feel free to be critical, but please try to stay constructive.
There is no need at this point to mention that this should be professionally executed with proper structural calculations by an appropriate company.
I want to find out whether the sketched approach is generally correct or if I am making major mistakes here.
The concrete ceiling would be cut away at a 45° angle on all three sides, and reinforcement connections would be added to these contact surfaces afterwards.
Formwork would be created, and the reinforcement connected to the existing structure would be installed.
The concrete contact surfaces would be treated with a product designed for concrete bonding.
Then, concrete would be poured into the formwork and compacted.
So far, I can imagine this procedure well, but I wonder if the large connecting slab will really be load-bearing.
Will this newly poured section have the same load capacity as if the concrete ceiling had been cast as one piece originally?
A large window front will be installed on this concrete section later.
The concrete piece would have to carry this load, but it is essentially cantilevered.
There is no support underneath it, and on one of the long sides, the new section does not rest on anything.
I considered, see image 3, installing a beam under the newly poured section on the left and right into the masonry.
This beam should catch the "cantilevered" load.
Do you think this will be necessary, or do you find the beam overkill?
(I know this is a sensitive topic, since it involves structural matters, but I’m just looking for opinions.)
I am looking forward to hearing your thoughts!
Best regards,
Tristan
A single-family house consists of a basement, the ground floor, and the first floor.
The concrete ceiling on top of the basement walls has the layout shown in image 1.
It can be seen that there is an opening on one of the long sides of the concrete ceiling.
From the inside, it looks like image 2 shows (a loggia with a glass front).
This loggia (and thus the opening in the concrete ceiling) is approximately 1m (3 feet) wide and 4m (13 feet) long.
Attached to that opening from the outside is a kind of balcony (wooden deck on a steel structure).
The goal is to regain the living space lost due to the loggia (opening in the concrete ceiling).
The glass front would be removed, as well as the attached balcony.
I have researched how this could be approached and am now interested in your opinions.
Feel free to be critical, but please try to stay constructive.
There is no need at this point to mention that this should be professionally executed with proper structural calculations by an appropriate company.
I want to find out whether the sketched approach is generally correct or if I am making major mistakes here.
The concrete ceiling would be cut away at a 45° angle on all three sides, and reinforcement connections would be added to these contact surfaces afterwards.
Formwork would be created, and the reinforcement connected to the existing structure would be installed.
The concrete contact surfaces would be treated with a product designed for concrete bonding.
Then, concrete would be poured into the formwork and compacted.
So far, I can imagine this procedure well, but I wonder if the large connecting slab will really be load-bearing.
Will this newly poured section have the same load capacity as if the concrete ceiling had been cast as one piece originally?
A large window front will be installed on this concrete section later.
The concrete piece would have to carry this load, but it is essentially cantilevered.
There is no support underneath it, and on one of the long sides, the new section does not rest on anything.
I considered, see image 3, installing a beam under the newly poured section on the left and right into the masonry.
This beam should catch the "cantilevered" load.
Do you think this will be necessary, or do you find the beam overkill?
(I know this is a sensitive topic, since it involves structural matters, but I’m just looking for opinions.)
I am looking forward to hearing your thoughts!
Best regards,
Tristan
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