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
11ant schrieb:
If the risk or costs were assessed as high, the issue would probably have been dismissed in commercial construction by now. I hadn’t seen it that way before. Good point.
According to reports, the prefabricated concrete slab (Swedish slab) doesn’t require impact sound insulation because the mass of the concrete prevents or greatly reduces impact noise. That sounds reasonable, and these slabs have been used for several years now. If this were a problem, it would likely be better known or something would have been done to address it, right?
If I build conventionally, I would have the same insulation values, and possibly even higher costs. The downside would be moisture issues and longer drying time of the screed. Are there any other advantages or disadvantages?
I also looked into this and discussed it with the architect. He thinks they are too expensive, and the slab manufacturer wants to install their underfloor heating, which the heating contractor does not agree with. By the time you reach the upper floor, the question arises who will do it, potentially leading to mixed systems (although I believe this can be resolved). Otherwise, the insulation of the slab is nothing special. You save on formwork thanks to continuous XPS insulation around the edges. You can also make this yourself if you consider it a good system. There are also "kits" available for this, for example Jackudur Atlas, if I remember correctly. Ultimately, to meet the energy saving regulation or a KfW standard, you need insulation with a target U-value specified by the energy consultant (or whoever did the calculations). Let’s say, overall, you need 20 cm (8 inches) of insulation “below.” Then you can consider whether to place it under the slab, above it, or both. The problem with putting it “underneath” is that XPS is significantly more expensive than EPS. In our own plans, in consultation with the engineers, we aim to use the thinnest possible XPS and the rest as EPS under the screed.
Multipor because of cost? Good luck with the tender.
If you want a low-cost option, go with EPS. Mineral wool already comes with a significant price increase (panels are more expensive, fastening is necessary). Multipor is even more expensive and has the disadvantage of a lower insulation value (EPS/neopor has a thermal conductivity of WLG 035 or 032, mineral wool similar, Multipor 045), which results in thicker wall construction.
Regarding thermal mass, thanks to calcium silicate bricks, you already have more than enough in the house, so in my opinion, that is not a valid argument.
*ETICS = External Thermal Insulation Composite System (also called external thermal insulation or external wall insulation)
Peter L. schrieb:
As building material we are planning calcium silicate brick with an ETICS* made of Multipor (cost issue)
Multipor because of cost? Good luck with the tender.
If you want a low-cost option, go with EPS. Mineral wool already comes with a significant price increase (panels are more expensive, fastening is necessary). Multipor is even more expensive and has the disadvantage of a lower insulation value (EPS/neopor has a thermal conductivity of WLG 035 or 032, mineral wool similar, Multipor 045), which results in thicker wall construction.
Regarding thermal mass, thanks to calcium silicate bricks, you already have more than enough in the house, so in my opinion, that is not a valid argument.
*ETICS = External Thermal Insulation Composite System (also called external thermal insulation or external wall insulation)
Lumpi_LE schrieb:
A prefabricated wood foundation slab basically only works with a timber frame house. Since that is not the case here, the topic is irrelevant.The manufacturer’s information suggests otherwise.
Where does that statement come from?
The purpose of the panel is to eliminate the need for an additional floor structure by integrating everything that would normally go on top directly into the panel.
The tolerance requirements for screed are significantly higher than those for a concrete slab, but these stricter standards would also need to apply to the concrete slab.
Manufacturing can only be done once these higher requirements are contractually agreed upon.
However, if a solid masonry house is built on such a concrete slab, preferably with two reinforced concrete ceilings, the "thin panel" will deform so much that screed will have to be applied again to achieve a level floor. This will not happen with a timber frame house. Without knowing the full background, it is likely that the “Sweden panel” originates from Sweden, where this construction method is more common.
The tolerance requirements for screed are significantly higher than those for a concrete slab, but these stricter standards would also need to apply to the concrete slab.
Manufacturing can only be done once these higher requirements are contractually agreed upon.
However, if a solid masonry house is built on such a concrete slab, preferably with two reinforced concrete ceilings, the "thin panel" will deform so much that screed will have to be applied again to achieve a level floor. This will not happen with a timber frame house. Without knowing the full background, it is likely that the “Sweden panel” originates from Sweden, where this construction method is more common.
Alex85 schrieb:
I also looked into this and discussed it with the architect. He says they are too expensive, and the slab manufacturer wants to install their underfloor heating, which the heating engineer does not agree with. By the time we get to the upper floor, the question arises who will do it, potentially leading to mixed systems (although I believe this can be resolved). I don’t have any concrete quotes yet, but based on my research, the cost difference between conventional and thermally activated concrete slabs is not very significant. For the upper floor, a conventional construction method is planned.
Alex85 schrieb:
Otherwise, the insulation for the slab is nothing special. You save on formwork by using continuous XPS insulation around the edges. You can also build this yourself if you consider it a good system. There are also "kits" available, for example Jackudur Atlas, if I remember correctly.
Ultimately, to meet the energy saving regulations or a KfW standard, you need insulation with a target U-value specified by the energy consultant (or whoever did the calculations). Let’s say you need a total of 20cm (8 inches) of insulation “below.” Then you can decide whether to position it under the slab, above, or a combination of both. The issue with placing it "below": XPS is significantly more expensive than EPS.
We ourselves plan, in consultation with the engineers, to use the thinnest possible XPS and the rest as EPS beneath the screed. We are not completely set on the Swedish slab or similar systems and are open to alternatives. I quickly checked, and XPS is either twice or even five times as expensive as EPS. But... the price for XPS (500kPa) is approximately 7.60€/m² (about 0.72 USD/ft²) [1]. EPS currently costs around 1.60€ per square meter (about 0.15 USD/ft²), and for a slab of 120m² (1,292 ft²), that makes a difference of about 200€ to 1,000€. Of course, that is significantly more, but given the total cost of building a house, I find it still reasonable. The price difference in bricks is usually much higher. Or am I calculating this wrong?
Alex85 schrieb:
We are planning, in consultation with the engineers, to use the thinnest possible XPS and the rest as EPS under the screed. What is your exact construction setup and what cost per square meter do you expect? The Swedish slab has a similar system[2].
Lumpi_LE schrieb:
The purpose of the slab is to eliminate the need for an additional floor build-up by integrating everything usually installed on top into the slab itself.
The tolerance requirements for the screed are significantly higher than those for a foundation slab but should also apply to the slab.
You can produce this only if the stricter requirements are contractually agreed upon.
If a solid house is built on such a slab, ideally with two reinforced concrete ceilings, the “thin layer” will deform so much that a screed will have to be applied again to create an even floor. This will not happen with a timber frame house. Not knowing the background, the Swedish slab probably comes from Sweden, where this type of construction is common. No, the Swedish slab is made by a German company based in Berlin that builds a foundation slab according to the Swedish principle. But it is not exactly the same. Futura builds a similar slab and just calls it Futura in my opinion.
I am reading your objection for the first time now. According to the manufacturer’s website, the slab is suitable for all house types, and I have also read multiple times that solid houses have been built on a Swedish slab without any issues. Do you have sources for your claim, or is this your assumption?
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