ᐅ Is Insulation Under the Concrete Slab Beneficial? Experiences and Insights
Created on: 7 May 2019 17:18
L
lesmue79
Hello everyone,
I am currently considering leaving out the insulation under the concrete slab. The house itself will be a bungalow with a floor area of 102 m² (1,098 sq ft), featuring an air source heat pump, underfloor heating, controlled mechanical ventilation, and in terms of plumbing, a circulation line in a timber frame house.
In principle, we ordered a KfW 55 house, but since we have not applied for any KfW 55 subsidies from the banks or government, it would theoretically not matter to me whether the house meets the 2016 Energy Saving Ordinance (EnEV 2016) standards or KfW 55 standards. Because we are not receiving any subsidies, we also do not require a blower door test.
From initial discussions, I have learned that for KfW 55 certification, about 80 mm (3 inches) of Styrodur/Jakodur insulation would need to be installed beneath the slab.
Honestly, I don’t mind if the concrete slab has a U-value of 0.20 W/m²·K (values are estimated) due to insulation, or 0.22 W/m²·K without insulation (also estimated values).
What is more important to me right now is whether I should spend the estimated 2,000 € on the insulation and installation in the ground, which would basically pay off after 20 years by saving around 20 € per year in heating costs.
Or if I should rather invest the 2,000 € in something else for the house that I can use more effectively or benefit from, such as upgrading fixtures or investing in a photovoltaic system (and yes, I know that €2,000 is not enough to cover a full PV system).
Or is every millimeter of insulation really crucial when using an air source heat pump and underfloor heating? (I understand electricity costs won’t get cheaper, so that’s why I’m also considering the photovoltaic system…)
I am currently considering leaving out the insulation under the concrete slab. The house itself will be a bungalow with a floor area of 102 m² (1,098 sq ft), featuring an air source heat pump, underfloor heating, controlled mechanical ventilation, and in terms of plumbing, a circulation line in a timber frame house.
In principle, we ordered a KfW 55 house, but since we have not applied for any KfW 55 subsidies from the banks or government, it would theoretically not matter to me whether the house meets the 2016 Energy Saving Ordinance (EnEV 2016) standards or KfW 55 standards. Because we are not receiving any subsidies, we also do not require a blower door test.
From initial discussions, I have learned that for KfW 55 certification, about 80 mm (3 inches) of Styrodur/Jakodur insulation would need to be installed beneath the slab.
Honestly, I don’t mind if the concrete slab has a U-value of 0.20 W/m²·K (values are estimated) due to insulation, or 0.22 W/m²·K without insulation (also estimated values).
What is more important to me right now is whether I should spend the estimated 2,000 € on the insulation and installation in the ground, which would basically pay off after 20 years by saving around 20 € per year in heating costs.
Or if I should rather invest the 2,000 € in something else for the house that I can use more effectively or benefit from, such as upgrading fixtures or investing in a photovoltaic system (and yes, I know that €2,000 is not enough to cover a full PV system).
Or is every millimeter of insulation really crucial when using an air source heat pump and underfloor heating? (I understand electricity costs won’t get cheaper, so that’s why I’m also considering the photovoltaic system…)
I completely agree with you. It depends on the overall concept; ultimately, the goal is to achieve the desired insulation values with the least possible capital investment. Insulating beneath the slab avoids additional thermal bridges that cannot be prevented with insulation on top of the slab. Of course, these heat losses can be compensated by other measures to reach the desired insulation level... again, the overall concept is the key term here.
The question of what is economically sensible is philosophical, and each side can present calculations that say otherwise. It simply depends too much on all the assumptions about the future price development of the house and energy costs.
The question of what is economically sensible is philosophical, and each side can present calculations that say otherwise. It simply depends too much on all the assumptions about the future price development of the house and energy costs.
I received the thermal insulation certificate today... As mentioned, we ordered and requested KFW 55 on our side.
With the 80 mm (3 inch) Styrodur recommended by the builder underneath the slab, we are now achieving KFW 40.
Option A:
I now have the following choices: completely omit the Styrodur, receive a discount of almost €2200 for removing the originally offered 100 mm (4 inch) Styrodur beneath the slab, and possibly reach KFW 55 or slightly worse, accepting the resulting heating costs.
Option B:
I am happy with KFW 40 and correspondingly lower heating costs, as well as the price reduction for 80 mm (3 inch) Styrodur compared to 100 mm (4 inch) Styrodur – although I do not yet know the exact amount, which probably won’t be very impressive.
Option C:
I keep everything as originally planned with the 100 mm (4 inch) Styrodur, which will perform better than KFW 40, but I will never know exactly by how much (because a new thermal insulation certificate would need to be created, which nobody does for free), and I likely won’t notice any savings in heating costs since there is no comparison...
With the 80 mm (3 inch) Styrodur recommended by the builder underneath the slab, we are now achieving KFW 40.
Option A:
I now have the following choices: completely omit the Styrodur, receive a discount of almost €2200 for removing the originally offered 100 mm (4 inch) Styrodur beneath the slab, and possibly reach KFW 55 or slightly worse, accepting the resulting heating costs.
Option B:
I am happy with KFW 40 and correspondingly lower heating costs, as well as the price reduction for 80 mm (3 inch) Styrodur compared to 100 mm (4 inch) Styrodur – although I do not yet know the exact amount, which probably won’t be very impressive.
Option C:
I keep everything as originally planned with the 100 mm (4 inch) Styrodur, which will perform better than KFW 40, but I will never know exactly by how much (because a new thermal insulation certificate would need to be created, which nobody does for free), and I likely won’t notice any savings in heating costs since there is no comparison...
I would also lean towards KfW40. Are you using the KfW program for financing? Then you would already have a €5000 (about $5350) higher repayment subsidy compared to KfW55. If a photovoltaic system is planned, it’s also worth considering KfW40+, which offers another €5000 (about $5350) extra, and the battery storage, which otherwise might not be very cost-effective, is almost paid for. Photovoltaics are generally worthwhile anyway.
N
nordanney13 Jun 2019 07:30Chasqui schrieb:
We have insulation under the slab. Without underfloor heating. On top, there is parquet flooring.
Often, it still feels too "cold underfoot" for us.Without underfloor heating, it will always feel "cold underfoot," no matter how much insulation you add.Similar topics