ᐅ A single measurement can never be accurate.

Hello,

I hope someone here can help me.

We are currently renovating a house.

I have requested a quote from a plasterer because we want to have all the rooms plastered. An employee already came to take the measurements. In his quote, he states the wall area as 220m² (2,370 sq ft).

I took the time to measure everything myself. I simply multiplied each wall’s length by its height and always subtracted windows and doors. I came up with a total of 158m² (1,700 sq ft).

I spoke to the plasterer about this, and he said the 220m² figure is correct because doors and windows that are smaller than 2.5m² (27 sq ft) are included. Only windows larger than 2.5m² are deducted. He referenced the DIN 18350 regulation for this.

To me, this doesn’t make any sense, since I am paying for materials and labor based on the square meters.

The actual area should be 158m², not 220m².

It’s like buying 20 liters of fuel at a gas station but being charged for 40 liters at the register.

Does anyone understand this and could help me see it more clearly?

Thanks a lot.

Best regards,
Kristof

Mr.Aldi schrieb:

If I fill up 20 liters at a gas station, I don’t pay for 40 liters at the checkout.

Oversimplified calculation: I choose where I refuel. They all have different prices, sometimes even a 10% difference.

Mr.Aldi schrieb:

I spoke to my plasterer about this, and he says the 220m² (2,370 sq ft) figure is correct because doors and windows smaller than 2.5m² (27 sq ft) are included; only windows larger than 2.5m² (27 sq ft) are deducted. This is stated in the DIN 18350 regulation.

That’s exactly right! The “gaps,” meaning what you subtracted, remain in order to account for the edge work.

Mr.Aldi schrieb:

This makes absolutely no sense to me, since I pay material and labor costs per square meter.

You’re free to choose someone else. There’s nothing more to say on that. If you’re not satisfied with the price, you go to the next company or request a new quote.

220 sqm (2373 sq ft) measured with some allowance and 158 sqm (1701 sq ft) "billed down to the second decimal" are practically the same. Where there are openings, reveals are added – this doesn’t balance out exactly 1:1, but who would really want that if the quotation ends up being more expensive than the actual work?

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As mentioned before, this compensates for the extra effort required due to the windows. With fewer windows, it would probably be realistically cheaper because there would be more continuous surface area.

Be glad that he is taking the effort to prepare the quotation with measurements already taken.

What would have happened if you had requested 160 m2 (1,722 sq ft) yourself, and then, based on the DIN standard, the invoice was calculated using 220 m2 (2,368 sq ft).

I think if a quote is based on a measured survey, it should also be transparent and verifiable. From my experience, a measured survey always includes details like corners and reveals, not just rough estimates. If the relevant DIN standard allows for rough estimates (and the final invoice is then prepared in detail), that may be acceptable, but how many laypeople actually read a DIN standard? A note in advance or on the quote itself would be helpful.