Insulation under the floor slab - Is it sensible? Experiences

2019-10-14 12:02:20

Although I have no technical expertise, 045 would be too little for me personally; I would opt for the 035. In our case, the initial offer included 10 cm insulation under the floor slab, but the calculation showed that this was not necessary to comply with the energy saving ordinance. Therefore, we omitted it and saved 2.5k. Instead, I invested 1k extra in better insulation on the floor slab – from 14 cm 035 to 10 cm 022 plus the 3 cm 045 Rolljet, which our heating engineer insisted on. According to ubakus, this still improved the U-value from 0.24 to 0.187 and saved us 1.5k compared to the original plan.

That sounds interesting. Did you also take measures with the masonry? With sand-lime bricks, there are thermal insulation blocks that could be used for the bottom row of bricks... What about your other insulation? ETICS? How does the insulation run at the connection between wall and floor slab?

2019-10-14 13:31:54

We have Ytong. I would have to check the Lambda value they have in the calculation, but it will not be an exceptionally good value since it was built only according to the Energy Saving Ordinance.

We have a base slab with an 80 cm frost skirt and 10 cm perimeter insulation in the basement area (Knabe brick) then on the base slab 17.5 cm Ytong, 18 cm mineral wool, 2 cm air layer, and 11.5 cm facing bricks.

I don't know exactly what that is, since we did not use a KfW loan. It's something between the Energy Saving Ordinance and KFW 55.

2020-02-02 13:57:59

Our architect also said that insulation under the concrete slab is nonsense. Firstly, the insulation is applied on the slab, and secondly, the temperature of the soil under the house regulates itself. Whether inside in winter or summer, there are about 15 degrees in the soil directly beneath the slab. But everyone will probably have a different opinion on that.

2020-02-02 16:29:09

Is actually nonsense and costs money. We did it because of [KFW]. But it doesn't bring you a single euro in savings or anything else.

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Insulation under the floor slab - Is it sensible? Experiences

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