Hello,
I would like to know if anyone has experience with insulating the concrete slab.
I am currently in the planning phase and considering pouring the concrete slab on top of 100mm (4 inch) insulation.
Can anyone provide information, experiences, or tips?
Regards, Stoffelm
I would like to know if anyone has experience with insulating the concrete slab.
I am currently in the planning phase and considering pouring the concrete slab on top of 100mm (4 inch) insulation.
Can anyone provide information, experiences, or tips?
Regards, Stoffelm
It works just like usual. Just be careful with the foundation grounding. A special solution is needed there. I’m not exactly sure if 100mm (4 inches) is sufficient. The material must be compressive resistant, for example, Styrodur or glass foam gravel.
Also, try searching on Google for the term "Sweden plate." There are also ready-made systems for slabs that can simply be poured.
Also, try searching on Google for the term "Sweden plate." There are also ready-made systems for slabs that can simply be poured.
Hello Stoffelm, hello Jörg,
in the latest issue of the German Engineers’ Journal, a new product from Jackon Insulation GmbH (33803 Steinhagen) was introduced:
Perimeter insulation system Jackodur Atlas.
I have not yet had any personal experience with it. However, from what I can see on the company’s website (jackon-insulation.com), it makes a very good impression. It is practically free of thermal bridges, easy to install, and also suitable for passive houses.
In contrast, I consider the Swedish panel system to be less straightforward.
I also have some concerns regarding structural stability when I look at this thin floor slab. In practice, it will probably be unavoidable to at least apply a screed layer.
in the latest issue of the German Engineers’ Journal, a new product from Jackon Insulation GmbH (33803 Steinhagen) was introduced:
Perimeter insulation system Jackodur Atlas.
I have not yet had any personal experience with it. However, from what I can see on the company’s website (jackon-insulation.com), it makes a very good impression. It is practically free of thermal bridges, easy to install, and also suitable for passive houses.
In contrast, I consider the Swedish panel system to be less straightforward.
I also have some concerns regarding structural stability when I look at this thin floor slab. In practice, it will probably be unavoidable to at least apply a screed layer.
Hello Hope
Why do you differentiate between a standard slab and one made of waterproof concrete (WU concrete) for the two insulation options?
Either there is a need for a waterproof basement (soil report?) or not! This has NOTHING to do with the choice of insulation material.
The insulation can be designed the same way for both materials, depending somewhat on the installation thickness. XPS will remain thinner. Cellular glass gravel must be installed in multiple layers depending on requirements, compacted—but not too hard, as it would crumble otherwise, which would defeat the purpose.
The advantage is that you basically do not need a drainage filter layer; it forms automatically. However, it must be laid over a geotextile membrane, as otherwise, when compacted, it would sink into any soft subsoil. Additionally, this prevents fines from spreading over time within the visible area.
It would be less suitable for cantilevered elements—such as under a protruding ground-floor slab for bay windows or non-basement areas.
Furthermore, it should extend at least 50 cm (20 inches) beyond the edge of the slab.
Since it is made from recycled glass, this is a good consideration in terms of embodied energy for insulation production. It is also highly load-bearing and shows no compression or shrinkage itself. It is rodent-proof as well, which other materials are not without additional protection.
As an alternative to gravel, there are also FOAM boards—defined rigid panels that can also be used for clean foundation insulation. Formwork for gravel edges should ideally be made of this material as well. This poses no structural issues; it just needs to be planned accordingly.
Why do you differentiate between a standard slab and one made of waterproof concrete (WU concrete) for the two insulation options?
Either there is a need for a waterproof basement (soil report?) or not! This has NOTHING to do with the choice of insulation material.
The insulation can be designed the same way for both materials, depending somewhat on the installation thickness. XPS will remain thinner. Cellular glass gravel must be installed in multiple layers depending on requirements, compacted—but not too hard, as it would crumble otherwise, which would defeat the purpose.
The advantage is that you basically do not need a drainage filter layer; it forms automatically. However, it must be laid over a geotextile membrane, as otherwise, when compacted, it would sink into any soft subsoil. Additionally, this prevents fines from spreading over time within the visible area.
It would be less suitable for cantilevered elements—such as under a protruding ground-floor slab for bay windows or non-basement areas.
Furthermore, it should extend at least 50 cm (20 inches) beyond the edge of the slab.
Since it is made from recycled glass, this is a good consideration in terms of embodied energy for insulation production. It is also highly load-bearing and shows no compression or shrinkage itself. It is rodent-proof as well, which other materials are not without additional protection.
As an alternative to gravel, there are also FOAM boards—defined rigid panels that can also be used for clean foundation insulation. Formwork for gravel edges should ideally be made of this material as well. This poses no structural issues; it just needs to be planned accordingly.
Thank you for the post.
The two mentioned options come from an old and a new building specification, and now we have the difficult choice to make.
The concrete will be the same in both cases, but thanks for the note. We still need to double-check that.
The first option is listed in our building specification, and we actually like this version (thanks also for the tip about the fleece). However, our builder is now only constructing according to the second option. The second option, however, lacks a frost barrier and/or drainage.
The frost barrier and drainage would be included in the gravel layer in option one.
Here is the structure of the second option:
- 5cm (2 inches) lean concrete layer (without gravel, directly on the soil)
- 12cm (5 inches) XPS insulation boards
- 25cm (10 inches) reinforced concrete slab
- possibly welding membranes will be used, but this is not yet decided
Now a few questions:
Where exactly do the welding membranes go, between which layers?
Is it acceptable to pour concrete (lean concrete layer) directly on the soil without gravel? Is this meant to replace the gravel?
And what is the benefit of all this if there is no frost barrier?
The more you read online, the more risks you find that you should watch out for.
Thanks and best regards
Hope
The two mentioned options come from an old and a new building specification, and now we have the difficult choice to make.
The concrete will be the same in both cases, but thanks for the note. We still need to double-check that.
The first option is listed in our building specification, and we actually like this version (thanks also for the tip about the fleece). However, our builder is now only constructing according to the second option. The second option, however, lacks a frost barrier and/or drainage.
The frost barrier and drainage would be included in the gravel layer in option one.
Here is the structure of the second option:
- 5cm (2 inches) lean concrete layer (without gravel, directly on the soil)
- 12cm (5 inches) XPS insulation boards
- 25cm (10 inches) reinforced concrete slab
- possibly welding membranes will be used, but this is not yet decided
Now a few questions:
Where exactly do the welding membranes go, between which layers?
Is it acceptable to pour concrete (lean concrete layer) directly on the soil without gravel? Is this meant to replace the gravel?
And what is the benefit of all this if there is no frost barrier?
The more you read online, the more risks you find that you should watch out for.
Thanks and best regards
Hope
Hello Hope
You only mention a construction company... don’t you have an architect handling the planning who can also advise you here?
The basement waterproofing largely depends on the specific requirements set by the local conditions… so, what is the soil like down there, and how well does it drain? From that, the need for a waterproof (WU) basement as a whole either arises or not.
A frost barrier (frost skirt) is needed only in areas where the slab might be exposed without soil cover, meaning the house or the basement, if there is one, wouldn’t be backfilled with earth down to the local frost depth, which is typically at least 80 cm (31 inches).
If that is not the case, you definitely need a frost barrier—without it, you would have a serious construction defect.
I would also not recommend using just a blinding layer beneath the insulation. If the insulation were installed directly on a blinding layer without a drainage layer underneath, it would likely cause problems.
The excavation won’t be perfectly even, and 5 cm (2 inches) might not be enough to create a flat surface for the insulation and thus the slab. On an uneven, rough blinding layer, the insulation material could break.
A better and safer solution is a drainage layer made of a filter or gravel mix, properly graded and compacted… with a fine layer of grit or sand spread and leveled on top. Then you can simply lay the insulation boards on this stable, even surface.
The waterproofing membrane would usually be installed on the concrete floor inside the basement rooms before further finishing, but this depends on the basement construction.
For masonry walls, whether basement or ground floor, a bitumen membrane would also be installed under the first and second courses of bricks or blocks. The lower membrane can later be connected with the floor membrane, providing continuous protection against rising moisture.
However, this has nothing to do with the requirements for a WU (waterproof) basement—you would have to clarify that separately if there actually is a basement.
If you don’t have a basement, you will need a continuous frost barrier around the building, either made of concrete or a mineral mixture that serves the same purpose.
You only mention a construction company... don’t you have an architect handling the planning who can also advise you here?
The basement waterproofing largely depends on the specific requirements set by the local conditions… so, what is the soil like down there, and how well does it drain? From that, the need for a waterproof (WU) basement as a whole either arises or not.
A frost barrier (frost skirt) is needed only in areas where the slab might be exposed without soil cover, meaning the house or the basement, if there is one, wouldn’t be backfilled with earth down to the local frost depth, which is typically at least 80 cm (31 inches).
If that is not the case, you definitely need a frost barrier—without it, you would have a serious construction defect.
I would also not recommend using just a blinding layer beneath the insulation. If the insulation were installed directly on a blinding layer without a drainage layer underneath, it would likely cause problems.
The excavation won’t be perfectly even, and 5 cm (2 inches) might not be enough to create a flat surface for the insulation and thus the slab. On an uneven, rough blinding layer, the insulation material could break.
A better and safer solution is a drainage layer made of a filter or gravel mix, properly graded and compacted… with a fine layer of grit or sand spread and leveled on top. Then you can simply lay the insulation boards on this stable, even surface.
The waterproofing membrane would usually be installed on the concrete floor inside the basement rooms before further finishing, but this depends on the basement construction.
For masonry walls, whether basement or ground floor, a bitumen membrane would also be installed under the first and second courses of bricks or blocks. The lower membrane can later be connected with the floor membrane, providing continuous protection against rising moisture.
However, this has nothing to do with the requirements for a WU (waterproof) basement—you would have to clarify that separately if there actually is a basement.
If you don’t have a basement, you will need a continuous frost barrier around the building, either made of concrete or a mineral mixture that serves the same purpose.
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