Calculation of construction costs for the basement

Hello everyone!

As is well known, the calculation of construction costs during planning is based on the gross volume (BRI) and/or the gross floor area (BGF). This is done for all floors of the house and thus also for a possible basement.

Considering a basement with exemplary, usual values, the following costs result:
- according to BRI: 90m² x 2.7m x 340EUR/m³ = 82620 EUR
- according to BGF: 90m² x 960 EUR/m² = 86400 EUR
- on average therefore 84510 EUR.

On the other hand, approximately 40000...55000 EUR are often stated as additional costs for a basement, depending on the equipment and sealing.

The sheer magnitude of the differences creates uncertainty.

Now there are three questions:
1) How do these values fit together?
2) And what is the experience of former homeowners who know the actual costs in retrospect?
3) A semi-open basement floor in a hillside location is considered a ground floor. Does the approach according to BRI/BGF then apply without exception, or is the distinction more between living and utility rooms?

Hello Yves,

Considering a basement with exemplary, typical values, the following costs result:
- according to BRI: 90m² x 2.7m x 340EUR/m³ = 82620 EUR
- according to BGF: 90m² x 960 EUR/m² = 86400 EUR
- on average thus 84510 EUR.

How do you come up with the values €340.00 and €960.00? The first one is set too low, the second – the utility basement – too high….

3) A semi-open basement floor on a hillside is considered a ground floor. Does the approach according to BRI/BGF then apply without exception, or is the distinction rather between living and utility rooms?

First of all – a basement remains a basement and does not suddenly turn into a ground floor overnight. At most, it can be a basement converted for residential purposes. And if this is the case, it will also be calculated as living space; your €960.00 won’t get you far there.

With Rhineland greetings

How do you come up with the values €340.00 or €960.00? The first is too low, the second – the utility basement – is set too high....

First of all – a basement remains a basement and does not become the ground floor overnight. It can at most be a basement converted for residential purposes. And if this is the case, it is also calculated as living space; with your €960.00 you won’t get far.

The value of €340 per cubic meter of enclosed space corresponds to the medium standard for a single-family house.
The value of €960 per square meter gross floor area accordingly refers to the external dimensions of the house multiplied by the number of floors.

As far as I know, this procedure is based on DIN 277; we received such a calculation from the architect. If the living or usable area were used, the latter value would of course be higher, e.g., at €1500/sqm.

Example for our current plan, house 7.88m x 10.88m with basement, upper and attic floors, 38-degree roof and 0.75m knee wall:

Cost GFA: 7.88m x 10.88m x 3 floors x €960/m² = €246,900
Cost GVA: 728m³ x €340/m² = €247,520

A correction factor of 0.925 is applied for our region, resulting on average in a rounded €233,000.

Here the issue I mentioned becomes apparent: the basement costs 1/3, about €80,000, while elsewhere about €55,000 is assumed?!

Our project involves a utility basement including garage (27m²), with entrance hall, laundry room and garage being heated. The house entrance is located on this basement floor due to the hillside location.

Here the issue I mentioned becomes apparent: Here the basement costs 1/3, so around 80,000 EUR, but elsewhere about 55,000 EUR is set?!

Sure, the basement then "costs more"... it has to carry the too low costs for the living space...

I find it quite strange to calculate living + basement space at the same value....

Our architect, for example, calculates 1,300€ for the living area and 800€ for the basement... gross!

Hello,

The value of 340 EUR per cubic meter of enclosed space corresponds to the medium standard for a single-family house.

Again - who says that? Your architect?

The value of 960 EUR per square meter gross floor area accordingly refers to the exterior dimensions of the house multiplied by the number of floors.

If the origin of the above value is subjective, how can this total figure be valid?

This procedure is based, to my knowledge, on DIN 277,

This DIN only explains how to determine the floor areas and volumes of buildings in structural engineering; nothing more and nothing less.

We received such a calculation from the architect ...
Example for our current planning, house 7.88m x 10.88m with basement, upper and attic floors, 38-degree roof as well as 0.75m knee wall:
Costs BGF: 7.88m x 10.88m x 3 floors x 960 EUR/m² = 246,900 EUR
Costs BRI: 728 m³ x 340 EUR/m² = 247,520 EUR
A correction factor of 0.925 is applied for our region and the rounded average results in 233,000 EUR.

I have always found it interesting what architects calculate. I do not believe that this amount will be sufficient for your construction project; especially not considering the description of the basement and also not in Jena.

Here the topic I addressed becomes apparent: The basement costs 1/3, about 80,000 EUR, while elsewhere around 55,000 EUR is assumed?!

Your architect is using a mixed calculation; since one value is too low and the other too high, the price is relatively correctly determined. So you cannot assume that one-third of the sum is allocated to the basement. With just under 8 x just under 11, I would estimate EUR 40,000 for the usable basement including external insulation/plaster in the hillside area (one-third of the area) plus another EUR 10,000 for lining the garage and heating of 3 certainly small rooms.

With Rhineland regards

OK, so I'll try again

In my posts above, I only spoke about the pure construction costs, meaning the cost groups 300 and 400 according to DIN 276. You are right, DIN 277 is of course only used for the calculation of room volume, etc.

If the origin of the upper value is subjective, how can this total figure have validity?

The values 340 EUR/m3 and 960 EUR/m2 are objective and come from the Construction Cost Index 2012, which should be familiar to you.

I have always found it interesting what architects calculate. I do not believe that this amount will be enough for your construction project; especially not according to the description of the basement and also not in Jena.

Of course, the above-mentioned 233,000 EUR are not enough for the construction project because these are only the pure construction costs and additional incidental construction costs (approx. 35,000 EUR) as well as other costs for the land, preparation, etc. (approx. 70,000 EUR) will be added. Our basement is to be built as brick masonry.

Jena is not far away, but we are building in a completely different area around Gera – yes, there are such drastic regional differences.

Therefore, the architect’s approach is understandable and also logical for me based on the realistically reflected construction costs of the BKI for the planning.

The Construction Cost Index captures, as the term suggests, only the pure construction costs (building construction and technical installations).

Your architect uses a mixed calculation; because one value is too low and the other too high, the price is relatively correctly determined. So you cannot assume that 1/3 of the total amount is attributable to the basement. With roughly 8 x roughly 11 I would estimate about 40,000 EUR for the pure usable basement including outer insulation/plaster in the hillside area (1/3 of the area) plus another 10,000 EUR for lining the garage and heating 3 certainly small rooms.

There again are about 50,000 EUR for the basement. That was exactly what I was concerned about in the beginning. The approach based on the usable area (in our case about 65 m2) leads to this result at 800 EUR/m2.

Applied to our example, this means for the living floors 130 m2 x 1300 EUR/m2 = 169,000 EUR and for the basement 65 m2 x 800 EUR/m2 = 52,000 EUR. This makes a total of 221,000 EUR for the pure construction costs.