ᐅ Slab foundation with concrete core activation. What are your thoughts?
Created on: 19 Dec 2017 12:37
P
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
The supply temperature needs to be calculated precisely. However, low supply temperatures are naturally no problem for screed.
Installing it additionally in the intermediate ceiling would also be an option.
You have accessed even more storage mass with the Swedish plank. And hopefully a top U-value.
I haven’t checked yet.
Installing it additionally in the intermediate ceiling would also be an option.
You have accessed even more storage mass with the Swedish plank. And hopefully a top U-value.
I haven’t checked yet.
Peter L. schrieb:
According to some statements, the Swedish slab does not require impact sound insulation, I consider that to be marketing talk.
Joedreck schrieb:
Leak test. Oh, I see. But I think the original poster is more concerned about sharp stones in the concrete.
Lumpi_LE schrieb:
The Swedish slab basically only works with a timber frame house. I first came across the term (not specifically the Swedish slab, but concrete core activation) several years before residential construction—in structural engineering projects. That’s where reinforced concrete skeleton construction is still common, even though many non-firewalls are lightweight partition walls and facades are often hung on the outside.
Peter L. schrieb:
Is it more of a note to be aware that some sanding might be necessary, or is it really a bigger problem when it happens? You’ll more likely smooth concrete by adding layers rather than grinding it down. I wouldn’t skip the screed, also because of impact sound: it affects not only rooms below but also adjacent ones—and that’s why it’s recommended that the floor covering can float.
By the way, a moderator will probably complain soon, external links are not allowed here.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
I just did some browsing and came across their website. The slab is apparently leveled using a laser, which is supposed to ensure it’s ready for flooring installation.
The small stones in the concrete… well, no idea. That’s their business, and they should know what they’re doing.
I have to admit, I don’t really understand the impact on impact sound insulation (impact noise). Experienced homeowners would really need to weigh in on that.
By the way, I noticed they only use 10cm (4 inches) of concrete. So it doesn’t have as much thermal mass as I originally thought.
But the U-value of 0.17 is quite good.
The small stones in the concrete… well, no idea. That’s their business, and they should know what they’re doing.
I have to admit, I don’t really understand the impact on impact sound insulation (impact noise). Experienced homeowners would really need to weigh in on that.
By the way, I noticed they only use 10cm (4 inches) of concrete. So it doesn’t have as much thermal mass as I originally thought.
But the U-value of 0.17 is quite good.
The tip about JACKODUR was quite helpful. I did some research and came across the Thermo slab from IfU (Institute for Environmental Energy). Just search “thermobodenplatte ifu” on Google. It should be the sixth result. Very short domain name.
I had a few nice phone conversations and so far I am quite convinced. Actually, I was only looking for comparable U-values, but they couldn’t provide those. JACKODUR only specifies the thermal conductivity, and the exact U-value has to be calculated. Since Jackodur is certified for passive houses, the U-value should be very low. On the website, there is a note from >012.
The costs were roughly within range as well, since the materials are usually purchased directly from the manufacturer and you only pay for the labor if you need it. For example, 40€/m² (40 €/ft² approx.) for JACKODUR, about 15€/m² (15 €/ft² approx.) for glass foam granulate, 25€/m² (25 €/ft² approx.) for heating, etc.
I also found it interesting that it is not compliant, for example, to use two different rigid foam boards together. Now I wonder how the Swedish slab solves this since it uses both EPS and XPS. I looked into this more closely and found that the EPS boards are not placed where the walls will later be positioned. Interesting…
I also found the information about concrete as an energy storage medium interesting. In one project, it was found that in winter it was enough to activate the heating only every few days (for example, when the sun is shining). Due to the insulation and the concrete, the interior temperature remained constant. Of course, not all details are known, but you get the figures on how much energy concrete can store. For the upper floor, it is still recommended to use traditional screed and underfloor heating, mainly because of impact sound insulation. On the ground floor, impact noise is less of a problem. An additional luxury would be a concrete ceiling which can also cool in summer, but it is not necessary.
I just wanted to share this information here with everyone. Not everything may be fully questioned yet, but so far it looks promising, reliable, and of good quality.
I had a few nice phone conversations and so far I am quite convinced. Actually, I was only looking for comparable U-values, but they couldn’t provide those. JACKODUR only specifies the thermal conductivity, and the exact U-value has to be calculated. Since Jackodur is certified for passive houses, the U-value should be very low. On the website, there is a note from >012.
The costs were roughly within range as well, since the materials are usually purchased directly from the manufacturer and you only pay for the labor if you need it. For example, 40€/m² (40 €/ft² approx.) for JACKODUR, about 15€/m² (15 €/ft² approx.) for glass foam granulate, 25€/m² (25 €/ft² approx.) for heating, etc.
I also found it interesting that it is not compliant, for example, to use two different rigid foam boards together. Now I wonder how the Swedish slab solves this since it uses both EPS and XPS. I looked into this more closely and found that the EPS boards are not placed where the walls will later be positioned. Interesting…
I also found the information about concrete as an energy storage medium interesting. In one project, it was found that in winter it was enough to activate the heating only every few days (for example, when the sun is shining). Due to the insulation and the concrete, the interior temperature remained constant. Of course, not all details are known, but you get the figures on how much energy concrete can store. For the upper floor, it is still recommended to use traditional screed and underfloor heating, mainly because of impact sound insulation. On the ground floor, impact noise is less of a problem. An additional luxury would be a concrete ceiling which can also cool in summer, but it is not necessary.
I just wanted to share this information here with everyone. Not everything may be fully questioned yet, but so far it looks promising, reliable, and of good quality.
This is XPS, probably with a thermal conductivity value (WLG) of 035. You can enter this into any U-value calculator. The desired U-value of 0.17 is achieved with 20 cm (8 inches) of material thickness.
I wouldn’t personally mess with the foundation. The principle and construction method are well known now. In principle, anyone can build it. Lay out the XPS, put the formwork on top (this is simple), and produce the slab as usual. The perimeter insulation on the side is either installed together with the formwork or added afterward. You don’t need a special kit from Jackodur for that.
But as mentioned, whether using this method or EPS under the screed, in terms of insulation performance, it’s the same. I would go for the cheaper option. Especially since with the screed and sand-lime brick walls, there is already substantial thermal mass inside the house.
I didn’t understand what you meant by mixing EPS and XPS.
Is a slab foundation even economically feasible on your site?
I wouldn’t personally mess with the foundation. The principle and construction method are well known now. In principle, anyone can build it. Lay out the XPS, put the formwork on top (this is simple), and produce the slab as usual. The perimeter insulation on the side is either installed together with the formwork or added afterward. You don’t need a special kit from Jackodur for that.
But as mentioned, whether using this method or EPS under the screed, in terms of insulation performance, it’s the same. I would go for the cheaper option. Especially since with the screed and sand-lime brick walls, there is already substantial thermal mass inside the house.
I didn’t understand what you meant by mixing EPS and XPS.
Is a slab foundation even economically feasible on your site?
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