ᐅ Slab foundation with concrete core activation. What are your thoughts?
Created on: 19 Dec 2017 12:37
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Peter L
Hello everyone,
If everything goes well, we plan to start building our own home next year, in 2018. We want to contract the trades independently and also carry out some parts ourselves. Here are some key details:
Approximately 200m² (2,150 sq ft) of living space without a basement. Underfloor heating with hardwood floors and an air-source heat pump. Ideally, a photovoltaic system will be installed on the roof and an energy storage unit in the utility room (KFW40+ standard). We are planning to use calcium silicate bricks with an external insulation system made of Multipor (cost considerations). This is just for your information and not meant to be part of the discussion.
I have spent quite some time researching ground slabs and have read a lot. It puzzles me that there are so few experience reports on Swedish slabs or similar systems. There are only one or two threads on this topic in this forum. It might be due to the tendency to report online mainly when one is dissatisfied, or perhaps people don’t realize when they are building a prefabricated house. Either way, most of the posts I found are five years or older. Often, people are unfamiliar with the Swedish slab, and what is not well known or regarded as proven tends to be viewed negatively. I was able to clarify many criticisms with some research and therefore we are still leaning towards the Swedish slab, although we are not completely certain, as I have never read a clear recommendation.
1. Costs
A frequently mentioned concern is the cost, so I will keep it brief. If you include the underfloor heating and screed in a conventional slab, the cost difference becomes less significant. The Swedish slab, however, offers significantly better insulation and thus saves money over time.
2. Speed
There was a criticism in this forum that the Futura ground slab reacts very slowly. In a building with Futura on the ground floor and a conventional underfloor heating with screed on the upper floor, the upper floor warms up within about 30 minutes, while it takes around 6 hours on the ground floor. Well, concrete is much more inert and it naturally takes longer for the heat to be noticeable. The advantage, however, is that concrete retains heat longer. Each person must decide how important it is to be able to adjust the temperature quickly. I wouldn’t necessarily consider this a disadvantage.
3. Impact noise
I read briefly that impact sound insulation might be worse. How significant is this on the ground floor? Is this really the case and are there current solutions to reduce it?
4. Maintenance
I keep reading that if something breaks, it’s hopeless. I can imagine it’s easier to break open screed than concrete, but to be honest – why would you want to do that? Isn’t it more of a theoretical problem? Suppose a pipe breaks for some unknown reason, water will continue to flow and the concrete won’t dissolve or degrade because of that, right? I don’t fully understand this criticism.
5. Time savings
No criticism here, but a Swedish slab doesn’t require drying time, which speeds up the construction process and eliminates moisture in the house.
So far, I don’t see any significant negatives, though I am not an expert and can only judge based on the information I have. I would therefore appreciate an expert opinion. Are there any mistakes one can make when pouring a Swedish slab, and are there other disadvantages I might not have considered?
What would be the advantages of a conventional slab? I imagine it can also be insulated to achieve similar benefits in that respect. Then the main difference would be the drying time for the screed. Perhaps there are other considerations when building with calcium silicate bricks plus external insulation.
I look forward to your opinions.
Peter L
If everything goes well, we plan to start building our own home next year, in 2018. We want to contract the trades independently and also carry out some parts ourselves. Here are some key details:
Approximately 200m² (2,150 sq ft) of living space without a basement. Underfloor heating with hardwood floors and an air-source heat pump. Ideally, a photovoltaic system will be installed on the roof and an energy storage unit in the utility room (KFW40+ standard). We are planning to use calcium silicate bricks with an external insulation system made of Multipor (cost considerations). This is just for your information and not meant to be part of the discussion.
I have spent quite some time researching ground slabs and have read a lot. It puzzles me that there are so few experience reports on Swedish slabs or similar systems. There are only one or two threads on this topic in this forum. It might be due to the tendency to report online mainly when one is dissatisfied, or perhaps people don’t realize when they are building a prefabricated house. Either way, most of the posts I found are five years or older. Often, people are unfamiliar with the Swedish slab, and what is not well known or regarded as proven tends to be viewed negatively. I was able to clarify many criticisms with some research and therefore we are still leaning towards the Swedish slab, although we are not completely certain, as I have never read a clear recommendation.
1. Costs
A frequently mentioned concern is the cost, so I will keep it brief. If you include the underfloor heating and screed in a conventional slab, the cost difference becomes less significant. The Swedish slab, however, offers significantly better insulation and thus saves money over time.
2. Speed
There was a criticism in this forum that the Futura ground slab reacts very slowly. In a building with Futura on the ground floor and a conventional underfloor heating with screed on the upper floor, the upper floor warms up within about 30 minutes, while it takes around 6 hours on the ground floor. Well, concrete is much more inert and it naturally takes longer for the heat to be noticeable. The advantage, however, is that concrete retains heat longer. Each person must decide how important it is to be able to adjust the temperature quickly. I wouldn’t necessarily consider this a disadvantage.
3. Impact noise
I read briefly that impact sound insulation might be worse. How significant is this on the ground floor? Is this really the case and are there current solutions to reduce it?
4. Maintenance
I keep reading that if something breaks, it’s hopeless. I can imagine it’s easier to break open screed than concrete, but to be honest – why would you want to do that? Isn’t it more of a theoretical problem? Suppose a pipe breaks for some unknown reason, water will continue to flow and the concrete won’t dissolve or degrade because of that, right? I don’t fully understand this criticism.
5. Time savings
No criticism here, but a Swedish slab doesn’t require drying time, which speeds up the construction process and eliminates moisture in the house.
So far, I don’t see any significant negatives, though I am not an expert and can only judge based on the information I have. I would therefore appreciate an expert opinion. Are there any mistakes one can make when pouring a Swedish slab, and are there other disadvantages I might not have considered?
What would be the advantages of a conventional slab? I imagine it can also be insulated to achieve similar benefits in that respect. Then the main difference would be the drying time for the screed. Perhaps there are other considerations when building with calcium silicate bricks plus external insulation.
I look forward to your opinions.
Peter L
T
toxicmolotof21 Dec 2017 08:31The term “concrete core activation” sounds impressive, but in my opinion, it is mostly a marketing term.
Of course, with underfloor heating in concrete, it is the concrete itself that is heated.
For any other underfloor heating embedded in screed, you could just as well call it “screed core activation,” or for a wall heating system in the bathroom, “sand-lime brick, plaster, and tile core activation.”
It just doesn’t sound as good and hasn’t caught on. Why it is called that for the slab foundation is something to think about.
Of course, with underfloor heating in concrete, it is the concrete itself that is heated.
For any other underfloor heating embedded in screed, you could just as well call it “screed core activation,” or for a wall heating system in the bathroom, “sand-lime brick, plaster, and tile core activation.”
It just doesn’t sound as good and hasn’t caught on. Why it is called that for the slab foundation is something to think about.
Bieber0815 schrieb:
Interesting thread. I've been wondering whether the term "concrete core activation" here refers to a traditional underfloor heating system embedded directly into the slab (instead of, as is usually the case, in the screed above). Or if it means thermally "activating" the structural elements of a single-family house (compare concrete core activation on Wikipedia).
So, what exactly is this about? I used the term because I believe that the Schwedenplatte and Futura systems apply this concept. I did not want to refer to a specific supplier, so I used the term concrete core activation.
However, I also find it difficult to separate the term as you just did. I understand that it’s not simply about placing the underfloor heating pipes in the concrete instead of the screed, but also using the concrete itself as a thermal storage medium. In addition to concrete core activation in the slab, walls can also be used, but here I am focusing on the slab and possibly the ceiling (cooling ceiling).
Does that answer your question, or how do you understand it?
Alex85 schrieb:
I'm not quite sure what you're getting at [emoji4]
You need as much insulation as the energy performance certificate requires for this building component. Whether it's placed on top of the slab or underneath doesn't really matter in principle, as long as the thermal insulation value is achieved.
Traditionally, insulation is applied mainly on top of the slab, below the heated screed. This is cost-effective because it can be made from EPS and the heat from the underfloor heating goes upwards rather than downwards. Insulation is also installed beneath the upper floor screed (typically around 6-8cm (2.5-3 inches), I believe) so that the underfloor heating there warms the upper floor instead of overheating the ground floor through the intermediate ceiling.Yes, I understand that [emoji23]But good insulation in the floor is crucial because
1. you will NEVER be able to access it again later
2. better materials are not that much more expensive and
3. heat losses are higher here since the underfloor heating operates at a higher temperature level.
I did a rough calculation with a U-value calculator.
Using 2cm (0.8 inches) EPS (impact sound insulation, I didn’t know better) and 8cm (3 inches) aluminum-faced PIR, I got a value of 0.25.
The Swedish structural board performs better here.
I'm not trying to prove anything; I just find the discussion interesting.
I still don’t understand.
2cm plus 8cm is worse than what exactly? The Swedish slab is insulated with XPS, WLG 035. If, for example, they use 20cm of that material, the insulation value is naturally better than with equivalent material (although PUR is better) at half the thickness. The question is: at what cost?
I just checked our thermal insulation certificate. According to that, heat loss through the slab accounts for about 8% of the total building heat loss. The U-value of the component is 0.164.
The U-value is intentionally this low because the client’s requirement was to get as close as possible to KfW 55 standard. For the last decimal place, insulating the floor slab is a convenient method since increasing insulation there is relatively inexpensive. Increasing the exterior wall insulation by 2cm (1 inch) or upgrading to better glazing for the windows would have a significantly greater impact on the building’s transmission heat loss, but would also be more costly.
Limit for transmission heat loss (H‘T) for KfW 55 in W/(m²K) = 0.292. Planned is 0.291, thanks to the somewhat over-insulated floor slab.
2cm plus 8cm is worse than what exactly? The Swedish slab is insulated with XPS, WLG 035. If, for example, they use 20cm of that material, the insulation value is naturally better than with equivalent material (although PUR is better) at half the thickness. The question is: at what cost?
I just checked our thermal insulation certificate. According to that, heat loss through the slab accounts for about 8% of the total building heat loss. The U-value of the component is 0.164.
The U-value is intentionally this low because the client’s requirement was to get as close as possible to KfW 55 standard. For the last decimal place, insulating the floor slab is a convenient method since increasing insulation there is relatively inexpensive. Increasing the exterior wall insulation by 2cm (1 inch) or upgrading to better glazing for the windows would have a significantly greater impact on the building’s transmission heat loss, but would also be more costly.
Limit for transmission heat loss (H‘T) for KfW 55 in W/(m²K) = 0.292. Planned is 0.291, thanks to the somewhat over-insulated floor slab.
Hello,
I have worked on about 60 to 70 single-family homes with "Sweden slabs" and installed one myself in my own house as a DIY project.
Here are some impressions and experiences.
Of all the houses built, I can only recall one with significant issues regarding the flatness of the surface. My own is not perfect, but even without flooring, it is acceptable.
Impact noise has not been a problem in any of the houses.
My own house has a footprint of 250m² (2700 sq ft), including the garage. I would not do it the same way again.
When using a floor jack or if a hammer falls on the floor, noises are transmitted.
The insulation can only be compared based on specific examples. I appreciate that there is no direct connection to the ground on the building side.
Also, insulation thicknesses of 10 to 20 cm (4 to 8 inches) are not the limit.
Lumpi’s statements about the “Sweden slab” and solid construction are incorrect. Heavy structures are also possible; it all depends on the compressive strength of the slabs.
Precise planning, workmanship, and measuring are important.
I am not aware of any damage to underfloor heating systems. I do not install couplings in the concrete.
The interface between the heating installer and the slab manufacturer is completely trouble-free.
If there are concerns about the drinking water installation, it is best to lay it in empty conduits.
Olli
I have worked on about 60 to 70 single-family homes with "Sweden slabs" and installed one myself in my own house as a DIY project.
Here are some impressions and experiences.
Of all the houses built, I can only recall one with significant issues regarding the flatness of the surface. My own is not perfect, but even without flooring, it is acceptable.
Impact noise has not been a problem in any of the houses.
My own house has a footprint of 250m² (2700 sq ft), including the garage. I would not do it the same way again.
When using a floor jack or if a hammer falls on the floor, noises are transmitted.
The insulation can only be compared based on specific examples. I appreciate that there is no direct connection to the ground on the building side.
Also, insulation thicknesses of 10 to 20 cm (4 to 8 inches) are not the limit.
Lumpi’s statements about the “Sweden slab” and solid construction are incorrect. Heavy structures are also possible; it all depends on the compressive strength of the slabs.
Precise planning, workmanship, and measuring are important.
I am not aware of any damage to underfloor heating systems. I do not install couplings in the concrete.
The interface between the heating installer and the slab manufacturer is completely trouble-free.
If there are concerns about the drinking water installation, it is best to lay it in empty conduits.
Olli
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