Less than 25cm for Load-bearing and Insulating floor structure. Is it possible?
I have a construction dilemma and hope someone can answer a couple of questions regarding roof terraces.
The new extension will consist of a bedroom whose roof will function as a roof terrace.
To access the roof terrace, one of the windows in the existing building will be converted into a door.
The floor structure in the existing building is about 25cm with a ceiling height on the ground floor of about 220cm. I was thinking of maintaining the same ceiling height in the extension, and this results in having < 25cm to build a load-bearing and insulating roof terrace. Is it possible?
The new extension will consist of a bedroom whose roof will function as a roof terrace.
To access the roof terrace, one of the windows in the existing building will be converted into a door.
The floor structure in the existing building is about 25cm with a ceiling height on the ground floor of about 220cm. I was thinking of maintaining the same ceiling height in the extension, and this results in having < 25cm to build a load-bearing and insulating roof terrace. Is it possible?
Can you imagine considering concrete as a material?
What is the span?
Maybe it can work with steel beams embedded in a wooden joist.
Maybe it can work with steel beams embedded in a wooden joist.
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You're getting a bit stingy with insulation...
A wooden joist floor is usually made with 195 or 220-planks with c150-300 mm. Then it's probably appropriate to lay, for example, anti-mold treated plywood that you then cover with the waterproofing layer (felt+metal?). After that, you should be able to lay decking on blocks without ruining the height... Or well, it's going to be tight...
A wooden joist floor is usually made with 195 or 220-planks with c150-300 mm. Then it's probably appropriate to lay, for example, anti-mold treated plywood that you then cover with the waterproofing layer (felt+metal?). After that, you should be able to lay decking on blocks without ruining the height... Or well, it's going to be tight...
I can very well imagine concrete. Previously considered using about 8-9 cm of concrete (reinforced with 8150), then a waterproofing layer and 10 cm of styrofoam + some suitable cladding material (possibly tiles), but I wonder if 10 cm of styrofoam is enough as insulation?
The span is 360 cm or 350 cm (internal measurement), depending on which direction the joists are laid. The extension consists of three new walls and one existing. It is probably easiest to lay the joists on the new walls instead of trying to attach them to the existing house, right?
If using 195 plank, should you use cc30 or cc60? What does s150-300 mean? Stringfellow Hawke, can you describe a bit more in detail? Feel free to include an example.
When it comes to material choice, I am completely open to suggestions. The construction is 20 cm lightweight concrete on the outer and 15 cm on the inner walls. The outer walls will be insulated with 7-10 cm of styrofoam at a later stage...
The span is 360 cm or 350 cm (internal measurement), depending on which direction the joists are laid. The extension consists of three new walls and one existing. It is probably easiest to lay the joists on the new walls instead of trying to attach them to the existing house, right?
If using 195 plank, should you use cc30 or cc60? What does s150-300 mean? Stringfellow Hawke, can you describe a bit more in detail? Feel free to include an example.
When it comes to material choice, I am completely open to suggestions. The construction is 20 cm lightweight concrete on the outer and 15 cm on the inner walls. The outer walls will be insulated with 7-10 cm of styrofoam at a later stage...
Hello,
To make it all more understandable, I would need to arrange a detailed drawing. I request to get back to you later in the week.
But briefly summarized, we solved this with Kerto beams of dimension 45x195 (I'll double-check later) placed c/c 450. The ceiling in the room below had to be lowered by 100mm. On top of the Kerto beams, we used Masonite. Then wedges (cut from 45x94) were used to create a slope away from the house. These wedges were placed exactly on each Kerto beam. At the outermost point, where the wedges are thinnest, they were 25mm (if I recall correctly) and innermost, closest to the house wall, they were about 90mm (again, need to double-check). On top of the wedges was placed 22mm tongue-and-groove boards which were finally covered with Derbigum. The mat's direction was laid in the same direction as the slope, to avoid standing water in the seams' elevations (hope you understand what I mean). Afterwards, it was once again wedges but of pressure-treated wood. This time the thin end was placed nearest the house, to restore a horizontal surface. These wedges were, of course, placed in the exact same spots where the Kerto beams and the first wedges lie. I glued standard roofing felt to the underside of each wedge to reduce friction against the Derbigum (the waterproofing layer). In a few (three-four) places per wedge, I placed a dab of glue (some roof-related glue, need to check it) so that the wedges would stay in place. On the wedges, I screwed down decking made of larch and was very careful that the screws did not penetrate the wedges, as I didn't want to puncture the waterproofing layer. Once the entire decking was completed, I erected railings that are screwed into the house walls and the decking, thereby holding the entire package in place.
There are some steps that are also important to mention, hopefully, it becomes clear what I mean. At the back, closest to the house, the waterproofing layer folds up about 350mm. This fold is attached to the tongue-and-groove boards. The tongue-and-groove boards sit on 45x120 studs. The studs are attached to the house. Between the studs, I have EPS (100mm) which is attached to the house (stone house). In this way, the wall has been insulated. The outside of the studs has been clad with horizontal paneling. Between the paneling and the EPS, there is a 20mm gap. The paneling has been painted lead-gray and faces south. When the sun shines on it, the paneling becomes warm, as does the air behind it. The air thus begins to rise and thereby draws the air located between the Masonite and the tongue-and-groove boards (the terrace). Thus, I have arranged air circulation under the terrace's waterproofing layer.
I understand that it might be tricky to understand what I mean, even if it's crystal clear to me, but I will arrange drawings and 3D images later in the week when I have access to Google Sketch-Up. Then it will definitely be clearer.
I have some tips that describe how to make good and straight wedges. It took many studs before I figured out how to do it. When I made our second balcony a couple of years ago, it turned out right from the beginning, so I would gladly share the wedge-making technique if there is interest.
By the way, the Kerto beams protrude from the house. Thus, the entire terrace does, ending with some sheet metal and a gutter to direct away water.
Btw, the terrace is the favorite spot, recommended, despite the construction complexity!
PS: https://www.byggahus.se/forum/threads/isolering-och-taetning-av-tak-terrass.83207/#post-1617337
To make it all more understandable, I would need to arrange a detailed drawing. I request to get back to you later in the week.
But briefly summarized, we solved this with Kerto beams of dimension 45x195 (I'll double-check later) placed c/c 450. The ceiling in the room below had to be lowered by 100mm. On top of the Kerto beams, we used Masonite. Then wedges (cut from 45x94) were used to create a slope away from the house. These wedges were placed exactly on each Kerto beam. At the outermost point, where the wedges are thinnest, they were 25mm (if I recall correctly) and innermost, closest to the house wall, they were about 90mm (again, need to double-check). On top of the wedges was placed 22mm tongue-and-groove boards which were finally covered with Derbigum. The mat's direction was laid in the same direction as the slope, to avoid standing water in the seams' elevations (hope you understand what I mean). Afterwards, it was once again wedges but of pressure-treated wood. This time the thin end was placed nearest the house, to restore a horizontal surface. These wedges were, of course, placed in the exact same spots where the Kerto beams and the first wedges lie. I glued standard roofing felt to the underside of each wedge to reduce friction against the Derbigum (the waterproofing layer). In a few (three-four) places per wedge, I placed a dab of glue (some roof-related glue, need to check it) so that the wedges would stay in place. On the wedges, I screwed down decking made of larch and was very careful that the screws did not penetrate the wedges, as I didn't want to puncture the waterproofing layer. Once the entire decking was completed, I erected railings that are screwed into the house walls and the decking, thereby holding the entire package in place.
There are some steps that are also important to mention, hopefully, it becomes clear what I mean. At the back, closest to the house, the waterproofing layer folds up about 350mm. This fold is attached to the tongue-and-groove boards. The tongue-and-groove boards sit on 45x120 studs. The studs are attached to the house. Between the studs, I have EPS (100mm) which is attached to the house (stone house). In this way, the wall has been insulated. The outside of the studs has been clad with horizontal paneling. Between the paneling and the EPS, there is a 20mm gap. The paneling has been painted lead-gray and faces south. When the sun shines on it, the paneling becomes warm, as does the air behind it. The air thus begins to rise and thereby draws the air located between the Masonite and the tongue-and-groove boards (the terrace). Thus, I have arranged air circulation under the terrace's waterproofing layer.
I understand that it might be tricky to understand what I mean, even if it's crystal clear to me, but I will arrange drawings and 3D images later in the week when I have access to Google Sketch-Up. Then it will definitely be clearer.
I have some tips that describe how to make good and straight wedges. It took many studs before I figured out how to do it. When I made our second balcony a couple of years ago, it turned out right from the beginning, so I would gladly share the wedge-making technique if there is interest.
By the way, the Kerto beams protrude from the house. Thus, the entire terrace does, ending with some sheet metal and a gutter to direct away water.
Btw, the terrace is the favorite spot, recommended, despite the construction complexity!
PS: https://www.byggahus.se/forum/threads/isolering-och-taetning-av-tak-terrass.83207/#post-1617337
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@eestere Incredibly grateful for your response! This helps me figure out a construction and motivates me even more by showing that it's possible to build and that the roof terrace is appreciated 
If you find your sketchup files, I would be even more thankful!
As I mentioned, I have a very similar issue, ~25cm joists and an extension with a roof terrace. However, I have a slightly longer span, 4.5m, so I probably need to reinforce a bit more.
You've had this for about ~10 years or so? Have you noticed any problems with the solution?
Thanks once again!
If you find your sketchup files, I would be even more thankful!As I mentioned, I have a very similar issue, ~25cm joists and an extension with a roof terrace. However, I have a slightly longer span, 4.5m, so I probably need to reinforce a bit more.
You've had this for about ~10 years or so? Have you noticed any problems with the solution?
Thanks once again!
This thing with the upstand is something I now see will become complicated for me. Since the ceiling height in the upper floor is minimal (215 at the highest point and 27-degree slope) and I want to have a patio door out, there is very little margin. If I calculate with a narrow 70 cm door, I have approximately 197 cm left to the door.
Based on your construction, I get the total thickness of the joists including the decking to about 38 cm. If I set the terrace decking level with the floor of the upper floor, I can have a 7x180 door and use ~17 cm (197-180) for the "upstand." Not very much, in other words, and it means that the ceiling of the extension is then about 13 cm (38-25) lower than in the rest of the ground floor.
If I reduce the patio door to 6x170 (child-sized ♂️), then I have 215-15-170=30 cm left. If I still allocate 17 cm to the upstand, I can have the ceiling of the extension level with the old part of the ground floor.
That is, it requires significant compromises in one or more directions...
Based on your construction, I get the total thickness of the joists including the decking to about 38 cm. If I set the terrace decking level with the floor of the upper floor, I can have a 7x180 door and use ~17 cm (197-180) for the "upstand." Not very much, in other words, and it means that the ceiling of the extension is then about 13 cm (38-25) lower than in the rest of the ground floor.
If I reduce the patio door to 6x170 (child-sized ♂️), then I have 215-15-170=30 cm left. If I still allocate 17 cm to the upstand, I can have the ceiling of the extension level with the old part of the ground floor.
That is, it requires significant compromises in one or more directions...
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