Basement insulation under the footing or under the screed?

Hello,

we are approaching the final discussions with our builder regarding the specification of the house and have a question.

The single-family house will be built with a WU basement according to the 2009 Energy Saving Ordinance (no further energy efficiency 70 or 55 planned). The basement area is 70 m2. To meet the requirements of the Energy Saving Ordinance, the basement walls will be insulated with 100mm perimeter insulation 040.

The basement is actually planned as a storage cellar, but I do not want to forgo the option of later using it for residential-like purposes (guest room, study, or hobby room).

For energy reasons and to avoid cold floors, I would like to have the floor insulated as a special request; I requested a sub-slab insulation from the builder.

The estimated price is 3809 EUR (type of insulation not specified in detail, I expect lower standard).

Since I find the price quite high, I am now considering insulation under the screed. What do you think about this?

My view

Sub-slab insulation:
+ no thermal bridges, probably the best solution energy-wise
- high price

Insulation under screed:
+ floor heats up faster (I don’t always have to warm the entire slab if I only heat the basement for a few hours)
+ cheaper (however, I don’t know by how much)
- thermal bridges (but reduced by cove stones as the first row)
- lower ceiling height (or higher floor construction)

What is your opinion on this? Thanks for your advice

Aila

For the money, you can easily get the screed in the basement including 10 cm insulation, don't forget the floor height increase, adjust the stair rise and door openings.