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…)
G
Grantlhaua7 Oct 2019 09:16Tego12 schrieb:
There is no need to worry about XPS compressing. It is absolutely standard to insulate under the slab, and I am not aware of any cases where this has caused problems.We do not have insulation under the basement slab but instead have 10cm (4 inches) PIR insulation with a thermal conductivity of 0.022 W/(m·K) on top of the slab. In the single-story extension, however, we have 12cm (5 inches) insulation under the slab. According to our energy consultant, thermal bridges in the basement are so minimal when underfloor heating is installed that they can basically be neglected. Furthermore, there are now initial reports of inverted roofs with XPS insulation where the panels, despite proper specifications, became fully saturated with water, which in my opinion effectively nullifies the insulation properties of the boards. Therefore, with high groundwater pressure, I would recommend insulating on top of the slab rather than underneath.
R
readytorumble7 Oct 2019 10:14Tom_Säuer schrieb:
In my opinion, a masonry stove is not necessary in a timber-frame passive house. On the contrary, the single-story house tends to overheat quickly with one. Therefore, I don’t need any thermal mass in the wood stove. And besides: How many masonry stoves could I buy with the money saved by not installing a heat pump? And how much extra did you pay for the passive house standard?
We built minimally according to the 2016 Energy Saving Ordinance (insulation ON the concrete slab).
Ground source heat pump with horizontal collectors, entirely self-installed (cost about 12,000 euros for the heat pump, collectors, underfloor heating on 160m² (1,722 sq ft) including thermostats/distributor etc.).
Heating costs about 40 euros per month = 480 euros per year.
G
Grantlhaua7 Oct 2019 10:21readytorumble schrieb:
Ground source heat pump with horizontal ground collectors fully installed by myself (costs approximately 12,000 euros for heat pump, collectors, underfloor heating for 160m² (1,722 sq ft) including thermostats/manifolds, etc.).
Heating costs about 40 euros per month = 480 euros per year. Great price and respect for the work
N
nordanney7 Oct 2019 10:39Tom_Säuer schrieb:
Oh, from October to March you don’t get any sun? Where do you live? I live in Germany, which is cold and generally cloudy during autumn and winter. And you?
R
readytorumble7 Oct 2019 10:40Grantlhaua schrieb:
Great price and respect for the work Of course, this only works if you have a professional who works for you free of charge (family). Otherwise, you should fairly add the labor costs.
By the way: I don’t think I have seen the sun at all in the past 7 days.
N
nordanney7 Oct 2019 10:44A few years ago, we built a single-family house – as of today, it is slightly below the energy efficiency standard.
Heating costs with geothermal energy are max 40€ per month, including hot water for 5 people and 300 sqm (3,229 sq ft) of living space.
And that without insulation under the floor slab.
The heating system, including underfloor heating, cost around €25,000 (about 5-6 years ago).
That’s why I am skeptical about the benefits of additional insulation.
Heating costs with geothermal energy are max 40€ per month, including hot water for 5 people and 300 sqm (3,229 sq ft) of living space.
And that without insulation under the floor slab.
The heating system, including underfloor heating, cost around €25,000 (about 5-6 years ago).
That’s why I am skeptical about the benefits of additional insulation.
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