I have been trying to form an opinion about load-bearing capacity, deflection, collapse, etc. However, I feel that I can't come to a good conclusion, so I am trying to ask the question here, and it concerns "Risk" in construction.
Conditions:
House built in 1969, 2-story.
The floor structure consists of 70x195mm floor joists on centers 600mm apart. According to information, it was not built with the idea that there would be load-bearing walls, which can be suggested as, for example, the living room is 30 sqm without interior walls. Span between the walls is about 4.75m.
Unclear which grade the wood is, but as mentioned, built in 1969.
In 2010, a new bathroom was built on the upper floor by the previous owner, about 10 sqm. Approximately square.
Due to uneven floors, it was leveled with up to 8cm of self-leveling compound at the highest point and about 2-3cm at the lowest. The highest level is in the middle of the house (beams), the lowest level towards the outer wall. Then on top of that there were tiles and a corner bathtub 🙈.
Has been functioning since then, no visible cracks in either the tile or grout, etc. However, there is deflection in the beams and by measuring on the upper floor and ground floor, I manage to get it to about 1.5-2cm deflection in the middle of the house. But difficult to measure as these houses are relatively uneven everywhere.
Due to a damaged waterproofing in the drain, we have now, through the insurance company, renovated the entire bathroom, but no reinforcements to the beams have been made (not included in the insurance claim). They have once again leveled the entire area but now about 6cm at the highest (not 8 as before) and then around 2cm at the lowest.
My non-professional assessment is that we are at the same weight as before, maybe around 2 tons distributed over 10 sqm (not entirely even load distribution). This is supported by a total of 6 floor joists, two of which are partially supported in the middle by a wall on the lower floor.
I understand that according to today's regulations for new constructions this is far too weak (floor joists) but the question I want to get answered is... How big is the risk that the floor structure will collapse? Hasn't happened since 2010, but that doesn't say anything about how big the risk actually is. I would like to calm my nerves somewhat 😊
Conditions:
House built in 1969, 2-story.
The floor structure consists of 70x195mm floor joists on centers 600mm apart. According to information, it was not built with the idea that there would be load-bearing walls, which can be suggested as, for example, the living room is 30 sqm without interior walls. Span between the walls is about 4.75m.
Unclear which grade the wood is, but as mentioned, built in 1969.
In 2010, a new bathroom was built on the upper floor by the previous owner, about 10 sqm. Approximately square.
Due to uneven floors, it was leveled with up to 8cm of self-leveling compound at the highest point and about 2-3cm at the lowest. The highest level is in the middle of the house (beams), the lowest level towards the outer wall. Then on top of that there were tiles and a corner bathtub 🙈.
Has been functioning since then, no visible cracks in either the tile or grout, etc. However, there is deflection in the beams and by measuring on the upper floor and ground floor, I manage to get it to about 1.5-2cm deflection in the middle of the house. But difficult to measure as these houses are relatively uneven everywhere.
Due to a damaged waterproofing in the drain, we have now, through the insurance company, renovated the entire bathroom, but no reinforcements to the beams have been made (not included in the insurance claim). They have once again leveled the entire area but now about 6cm at the highest (not 8 as before) and then around 2cm at the lowest.
My non-professional assessment is that we are at the same weight as before, maybe around 2 tons distributed over 10 sqm (not entirely even load distribution). This is supported by a total of 6 floor joists, two of which are partially supported in the middle by a wall on the lower floor.
I understand that according to today's regulations for new constructions this is far too weak (floor joists) but the question I want to get answered is... How big is the risk that the floor structure will collapse? Hasn't happened since 2010, but that doesn't say anything about how big the risk actually is. I would like to calm my nerves somewhat 😊
Without being a constructor, it feels pretty unlikely that something will collapse. The size of the beams is well chosen and a deflection of 1-2cm should not be that dangerous. As you also said, if it hasn't moved and cracked at the joints, etc., it seems to remain rigid. There is probably someone here on the forum who can calculate it for you to get a clear answer.
Yes, I believe the deflection is okay, i.e., completely rigid and it doesn't move in that sense. However, it's a very heavy static load that wasn't calculated for in 1969, back then there was wet room carpet in the bathrooms.
I also understand that when calculating, you look at deflection, i.e., how much it can bend, and the tolerances are very small since you simply don't want slanted floors.
What I can't quite understand is how much force is needed before you start talking about collapse risk, beams breaking, etc. Obviously, it's not easy to say without knowing all the specific conditions, but maybe there is a reasonable estimate. For example, you can load 500kg per square meter without it collapsing, but the beams might bend down 5cm then… 🧐
I also understand that when calculating, you look at deflection, i.e., how much it can bend, and the tolerances are very small since you simply don't want slanted floors.
What I can't quite understand is how much force is needed before you start talking about collapse risk, beams breaking, etc. Obviously, it's not easy to say without knowing all the specific conditions, but maybe there is a reasonable estimate. For example, you can load 500kg per square meter without it collapsing, but the beams might bend down 5cm then… 🧐
I don't think you need to worry about the risk of collapse, but you don't want movements, especially when it's a wet room, due to the risk of leakage.
I don't know what the conditions are, but if you're concerned, perhaps a pillar/beam solution could be an option?
Otherwise, there is carbon fiber reinforcement which is convenient but relatively costly.
I don't know what the conditions are, but if you're concerned, perhaps a pillar/beam solution could be an option?
Otherwise, there is carbon fiber reinforcement which is convenient but relatively costly.
Pillars or beams underneath are unfortunately not possible without building new walls (rooms) on the ground floor.
It is built with glued floor chipboard over the entire area, followed by reinforcement and self-leveling compound.
There was no floor chipboard previously, only boards with a thin masonite board on top.
I'm not overly worried about movements since the old bathroom functioned without visible cracks in the tiles, tiles, or grout. However, it had a rolled waterproofing layer. The new bathroom is built more stably in terms of movement.
It's mostly the weight that I'm concerned about...
sure, there has been this weight or at least a similar weight for 13 years previously without anything breaking, but that's no guarantee, I think. The fear probably arises from looking at how things are dimensioned in today's houses, and everything below this is not approved... but since I'm not an engineer, it's easy to misinterpret things. Of course, there's a difference between standards for deflection and deflection before it breaks.
It is built with glued floor chipboard over the entire area, followed by reinforcement and self-leveling compound.
There was no floor chipboard previously, only boards with a thin masonite board on top.
I'm not overly worried about movements since the old bathroom functioned without visible cracks in the tiles, tiles, or grout. However, it had a rolled waterproofing layer. The new bathroom is built more stably in terms of movement.
It's mostly the weight that I'm concerned about...
sure, there has been this weight or at least a similar weight for 13 years previously without anything breaking, but that's no guarantee, I think. The fear probably arises from looking at how things are dimensioned in today's houses, and everything below this is not approved... but since I'm not an engineer, it's easy to misinterpret things. Of course, there's a difference between standards for deflection and deflection before it breaks.
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Wood deforms significantly before it breaks. You would have noticed a deflection of 5cm before there was any risk of collapse. Wood also starts to bend and sway long before there is any risk of collapse. In a tiled bathroom, you would have noticed very small movements as cracks would have formed.
I am an old designer but have too little information about your house to make any calculations. But based on what you tell, I can reassure you that it will hold.
What happens if it is too weak is that cracks form, it creaks, it sways, not that it collapses.
I am an old designer but have too little information about your house to make any calculations. But based on what you tell, I can reassure you that it will hold.
What happens if it is too weak is that cracks form, it creaks, it sways, not that it collapses.
Thanks for the response...
When it comes to deflection, it is incredibly difficult to measure. When I use a laser from the ground floor up toward the ceiling (upper floor), I get a difference of about 1-2cm, but it's worth noting that the ground floor is not level either, so it's not that simple.
If I place a level on the upper floor in the room adjacent to the bathroom, I get about 1-2cm of deflection. The lowest point is in the middle of the house/room relative to the exterior wall.
Regarding the self-leveling compound, the tiler estimated it to be 6cm at the highest point (middle of the house) and then 1.5-2cm at the drain. There is also an approved slope throughout the bathroom. So with that information, one might assume that the beams deflect 3-4cm minus the slope towards the drain.
I don't mind if there is 2, 3, or 4cm deflection in the middle. It doesn't noticeably affect the upper floor. The most important thing is that the beams don't break or fall away from the walls they rest on.
I find it so difficult to understand what, for example, 200kg/sqm means when talking about strength.
Does it mean that the beams deflect within tolerance, or does it mean that, for instance, 300kg/sqm would break the beams?
If it matters, there is a gypsum ceiling on the ground floor. Gypsum on tongue and groove. No cracks in the gypsum for 10 years. That should at least indicate it's not moving, right?
When it comes to deflection, it is incredibly difficult to measure. When I use a laser from the ground floor up toward the ceiling (upper floor), I get a difference of about 1-2cm, but it's worth noting that the ground floor is not level either, so it's not that simple.
If I place a level on the upper floor in the room adjacent to the bathroom, I get about 1-2cm of deflection. The lowest point is in the middle of the house/room relative to the exterior wall.
Regarding the self-leveling compound, the tiler estimated it to be 6cm at the highest point (middle of the house) and then 1.5-2cm at the drain. There is also an approved slope throughout the bathroom. So with that information, one might assume that the beams deflect 3-4cm minus the slope towards the drain.
I don't mind if there is 2, 3, or 4cm deflection in the middle. It doesn't noticeably affect the upper floor. The most important thing is that the beams don't break or fall away from the walls they rest on.
I find it so difficult to understand what, for example, 200kg/sqm means when talking about strength.
Does it mean that the beams deflect within tolerance, or does it mean that, for instance, 300kg/sqm would break the beams?
If it matters, there is a gypsum ceiling on the ground floor. Gypsum on tongue and groove. No cracks in the gypsum for 10 years. That should at least indicate it's not moving, right?
What I usually suggest when people have difficulty sizing the beams for a porch or similar structure, or just want an idea of what holds or how wood behaves at the breaking point, is to take a beam and place it between two supports and stand on it. See how long between the supports it takes before it bends. See how much longer is needed before it breaks, or how much more weight. Preferably have a few different sizes, or compare between having the beam lying down or standing up.
Smart trick even if it might not provide an answer to my concern. But I understand that you get an idea of how much is required before a beam actually breaks.
I have now measured everywhere with a laser, both up and downstairs, and the largest difference I get is 1.7cm directly under the bathroom.
Did the same exercise in the living room and there I can get up to 0.5-0.8cm deflection (with a bedroom above).
So, summarized regarding how much the beams bend is 2cm if you allow for some tolerance.
Then whether this even provides any guarantee, I have a hard time judging. What I know is that the bathroom most likely weighs 2 tons (3 walls rest on the joists). This is too much according to current rules/norms, but it's unclear if it means low, medium, or high risk of damage to the structure.
We will not be installing a corner bathtub again, but rather a washing machine and dryer that will likely add 100kg of static load.
I have now measured everywhere with a laser, both up and downstairs, and the largest difference I get is 1.7cm directly under the bathroom.
Did the same exercise in the living room and there I can get up to 0.5-0.8cm deflection (with a bedroom above).
So, summarized regarding how much the beams bend is 2cm if you allow for some tolerance.
Then whether this even provides any guarantee, I have a hard time judging. What I know is that the bathroom most likely weighs 2 tons (3 walls rest on the joists). This is too much according to current rules/norms, but it's unclear if it means low, medium, or high risk of damage to the structure.
We will not be installing a corner bathtub again, but rather a washing machine and dryer that will likely add 100kg of static load.
Everything you need to know is in Säkert Vattens' publication "Bjälklagets uppbyggnad i våtrumskonstruktioner": https://www.sakervatten.se/download...lagets-uppbyggnad-i-vatrumskonstruktioner.pdf, where a type-approved construction is presented.
After being involved in a renovation project where the floor did not meet these criteria, I have been surprised by the lack of knowledge about this among wet room certified construction companies and their subcontractors with BKR-cert. There were at least 5 well-reputed companies involved, all of which said there were no issues. Since we already had an engineer in the project, he eventually had to spell it out for them.
After being involved in a renovation project where the floor did not meet these criteria, I have been surprised by the lack of knowledge about this among wet room certified construction companies and their subcontractors with BKR-cert. There were at least 5 well-reputed companies involved, all of which said there were no issues. Since we already had an engineer in the project, he eventually had to spell it out for them.
I understand that, and according to this, my floor joists are not the right dimension for the span of the house according to the current requirements. This is regardless of whether it involves a bathroom or not. But my interpretation of it all is that they primarily look at bending stiffness in all requirements, which is important in bathrooms considering the waterproofing. I don't think there is any problem with glued floor particleboard and up to 6 cm reinforced self-leveling compound.
What I'm wondering about is the weight, i.e., the total weight. It's often said to be 200kg/sqm. But I can't understand what it means if you exceed this. Yes, the deflection becomes greater on the beams and falls outside the current requirements/tolerances, which are narrow. But beyond that, how much is needed before one starts to talk about potential risks of beams breaking from the weight and thereby causing something like a collapse. I cannot find any example of this.
What I'm wondering about is the weight, i.e., the total weight. It's often said to be 200kg/sqm. But I can't understand what it means if you exceed this. Yes, the deflection becomes greater on the beams and falls outside the current requirements/tolerances, which are narrow. But beyond that, how much is needed before one starts to talk about potential risks of beams breaking from the weight and thereby causing something like a collapse. I cannot find any example of this.
It will not collapse. If it were close to that, you would have already noticed. Think of all the old houses with roofs that haven't caved in yet despite over 1 meter of wet snow on them.
There is talk of static/bound and mobile/free/dynamic loads. On a floor in a house, the bound load is considered to be 2-2.5 kN/m2. The free load is calculated to be of similar size. A force of 1 kN is approximately the same as a load of 100 kg. Bound load includes, for example, furniture, but also floor coverings. Free loads are mostly people loads.
It is a reassuring answer
so should I interpret it as that approximately 200kg/sqm refers to fixed loads, such as a bathroom, and that it is then (usually) accounted for at least 100kg more per sqm for temporary loads, e.g. people?A AG A said:
What happens if you e.g. run static/bound load at 300kg/sqm?