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
No sources, just straightforward engineering logic.
You can take the risk, but at the latest when the tiler says they cannot lay tiles here, you’ll have a problem.
I wouldn’t take that risk and would always plan for an additional screed layer.
That doesn’t cost anything significant, so why even waste a thought on it?
You yourself wrote at the beginning that you can hardly find anything, or have you found a construction blog showing slab-on-grade and solid construction?
You can take the risk, but at the latest when the tiler says they cannot lay tiles here, you’ll have a problem.
I wouldn’t take that risk and would always plan for an additional screed layer.
That doesn’t cost anything significant, so why even waste a thought on it?
You yourself wrote at the beginning that you can hardly find anything, or have you found a construction blog showing slab-on-grade and solid construction?
Honestly, I think that’s just a guess. Since it’s not well-known, it carries a high risk. I believe the panel would have disappeared from the market if there were frequent problems.
Otherwise, I would simply call and ask. In the end, I would try to have the company contractually commit to a tolerance.
If that’s refused, you can always redesign.
I like the concept. All the mass is within the thermal envelope. The concrete core activation especially helps to keep supply temperatures low, which saves a lot of money when using heat pumps.
Otherwise, I would simply call and ask. In the end, I would try to have the company contractually commit to a tolerance.
If that’s refused, you can always redesign.
I like the concept. All the mass is within the thermal envelope. The concrete core activation especially helps to keep supply temperatures low, which saves a lot of money when using heat pumps.
On the internet, one often reads as a downside that the surface isn’t always as level as needed for flooring. Then people sand or level it afterwards, but no one seems to account for that in advance. Whether that’s true, I don’t know. You always have to be cautious with statements like these online. For building materials, there are usually both very positive and very negative opinions depending on the author and their motivation.
Well, okay, but what’s the point here? Functionally, in my opinion, the thermally activated slab doesn’t really have any advantage, so it comes down to the price.
I haven’t checked if those numbers are accurate.
But I consider that difference significant.
Our calculation is about 110€ per m² (square meter) for the slab, including necessary insulation (KFW 55).
That means, for example, an 11 x 11 m (36 x 36 ft) “town villa” comes to 13,310€. Your mentioned 800€ price difference corresponds to a 6% higher cost.
If you stick with the attitude “it costs nothing,” you can calculate how much money that means for your overall project.
That’s probably one of the most impressive remote diagnoses I have ever read here. Where do you buy your crystal balls?
The structural engineer will calculate this.
Peter L. schrieb:
I don't have any concrete offers right now, but according to my research, the cost difference between a conventional slab and a thermally activated slab is not very large.
Well, okay, but what’s the point here? Functionally, in my opinion, the thermally activated slab doesn’t really have any advantage, so it comes down to the price.
Peter L. schrieb:
a difference of 200€ to 1,000€
I haven’t checked if those numbers are accurate.
But I consider that difference significant.
Our calculation is about 110€ per m² (square meter) for the slab, including necessary insulation (KFW 55).
That means, for example, an 11 x 11 m (36 x 36 ft) “town villa” comes to 13,310€. Your mentioned 800€ price difference corresponds to a 6% higher cost.
If you stick with the attitude “it costs nothing,” you can calculate how much money that means for your overall project.
Lumpi_LE schrieb:
No sources, just plain engineering sense.
That’s probably one of the most impressive remote diagnoses I have ever read here. Where do you buy your crystal balls?
The structural engineer will calculate this.
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