ᐅ Realistic Cost Estimate for a Basement?

Hello Forum,

We are currently planning a basement for our single-family home. In addition to the building services room and a laundry room (washing machine + dryer), there will also be a gym and a study.

The four rooms will cover an area of about 65sqm (700 sq ft). The ground is suitable for this (from approximately 2.5m (8 feet) of medium-density gravel layer according to soil report – load class 2 according to waterproof concrete guidelines). The basement will have perimeter insulation (exterior walls, floor slab, basement ceiling) – the design is currently based on KfW 40 standards, which require thicker insulation according to advice from the forum 😉 The study and gym will have underfloor heating. The study will also have a light well. The gym and laundry room will have light shafts. The building services room will have no windows. The floor will be continuously laid with anhydrite screed, followed by a floor covering. Electrical installations will be surface-mounted on the walls.

The additional construction costs (especially setting out the building grid and excavation of the foundation pit) are not included in the costs. I am currently budgeting about €1250 per sqm (approximately $130 per sq ft), which is about €81,000 for the basement. However, everyone looks at this price as if it were a car and says that €35,000 more than enough? What is your assessment?

Best regards,
Andy

Andi3579 schrieb:

Hello Forum,

We are currently planning a basement for our single-family home. Besides the building services room, laundry room (washer + dryer), it will also include a gym and a home office.

These four rooms are spread over an area of about 65sqm (700 sq ft). The ground is suitable for this (approximately 2.5m (8 feet) of medium-density gravel layer according to the soil report – load class 2 according to the waterproof concrete guideline). The basement will have perimeter insulation (on the outside, the floor slab, and the basement ceiling) – the current plan (and based on advice from the forum 😉 ) is for KFW 40 standard, which requires thicker insulation. The home office and gym will have underfloor heating. The home office will also have a light well. The gym and laundry room will have light shafts. The building services room will have no window. The floors will be finished with anhydrite screed that is poured continuously, followed by a floor covering. Electrical installations will be surface mounted on the walls.

Additional construction costs (especially for staking out and excavation) are not included in these costs. I am currently planning a price of 1250€ per sqm (approximately $139 per sq ft), which means about 81,000€ (about $90,000) for the basement. When I present this price, everyone looks at me like I’m crazy and says that 35,000€ (about $39,000) would be more than enough. What is your assessment?

Regards
Andy

Although we are building without a basement, it has often been mentioned in the forum that the costs for a finished basement are about the same as for normal living area.

Andi3579 schrieb:



The additional construction costs (especially setting out the building lines and excavation of the foundation pit) are not included in the costs. I am currently planning with a price of €1250 per m2 (approximately €81,000) for the basement. Now, everyone looks at this price like it’s a car and says that it’s way too expensive and that about €35,000 more would be sufficient?

If a basement is planned, I would definitely recommend obtaining a soil report for the cost estimate.
Potential issues:
- partly rocky ground conditions
- groundwater depth
- contamination (asbestos, WWII remnants)?

If there is a basement, I would definitely plan for it to be over 2.0m (6.6 feet) high.

Andi3579 schrieb:

Now with this price, everyone looks at you like you’re crazy and says that 35,000€ (about $38,000) more than that is more than enough?

These "everyone" probably haven’t dealt with construction costs for at least 5 years. Or is there even one among them who has built recently?

I think your assessment is much more realistic.

And even if it were that cheap (which it won’t be) – what’s better? Having an extra 45,000€ (about $49,000) left over or needing to refinance 45,000€ (about $49,000)?
😉

What do you think is missing from a square meter created above ground? So why should the groundwork, which is generally more expensive than the structural build (due to factors like reinforcement, waterproofing, extensive reinforced concrete instead of cheaper bricks, and excavation disposal), be cheaper? Because of the slightly missing exterior plaster and surface-mounted installations? By the way, simple windows cost roughly the same as masonry.

Ten years ago, for 35,000 euros, you might have gotten a nicely calculated, unfinished brick root cellar, with the excavated soil spread around the garden for landscaping – your acquaintances are probably comparing that to this.

Although we are building without a basement, it has often been mentioned in the forum that the costs for a residential basement are the same as for regular living space.

I have read that too, but I just can’t make the numbers add up. For our basement, that would mean construction costs of €162,000. Could someone maybe explain where these costs are supposed to come from? Are wet rooms, etc. being included in the calculation?

konibar schrieb:

If a basement is planned, I would definitely get a soil report for cost estimation.
Potential issues:
- partly rocky ground
- groundwater depth
- contamination (asbestos, World War II remnants)?

If it’s a basement, I would definitely calculate a height of more than 2.0 m (6.6 ft).

This was already examined by a geotechnical report. The subsoil is mainly sandy and gravelly with some silty layers near the surface and medium to dense gravel layers starting at about 2.5 m (8.2 ft) depth. Groundwater occurs at a depth of around 5 m (16.4 ft); above that, there is water from about 1.1 m (3.6 ft) depth which has been classified as stagnant and seepage water. No other contamination was found because the entire site was excavated to a depth of about 1.5 m (4.9 ft) due to a suspected archaeological site (which was not confirmed in writing).