ᐅ Construction costs for terraces and similar elements in cost estimates according to DIN 276

First of all, hello to everyone in this great forum!

We are also future homeowners and currently have some questions about construction costs during the conceptual planning phase.

The plan is for a Bauhaus-style house with about 200 sqm (2,150 sq ft) over two floors. We now have initial designs including a cost estimate based on DIN 276.

We have generally liked the idea of having roof overhangs on the south side with covered terraces on the ground floor and balconies on the upper floor underneath. One of the concepts includes exactly this, while the other does not.

However, with the concept that includes covered outdoor areas, the costs according to the DIN 276 estimate skyrocket. The architect explained that the covered terraces and balconies are fully included in the cost estimate, specifically in the parameters of usable floor area (UFA), gross volume (GV), and gross floor area (GFA).

This means that the concept with 200 sqm (2,150 sq ft) of “indoor” space without any overhangs, terraces, or balconies is cheaper than the concept with 180 sqm (1,940 sq ft) of indoor space plus 40 sqm (430 sq ft) of covered balcony/terrace area. The UFA of the first building is 200 sqm (2,150 sq ft), while the second is 220 sqm (2,370 sq ft). Multiplied by the same construction cost index (CCI) values, the second building is more expensive even though it offers less indoor space.

My question is this: Is it really true that the cost estimate does not distinguish between fully enclosed living space and a terrace covered by a projecting roof? The latter should be significantly cheaper to build than true living space, right? Even if it is structurally connected to the main building as a cantilevered roof extension...

I would greatly appreciate your advice here.

DIN or not... the answers probably won’t help you much. These remain estimates. If your architect told you that the gross floor area (GFA) including roof overhangs and cantilevers was used for the cost estimate, then that’s likely how it was done.
I’m not sure it makes sense to compare two different projects based on cost estimates.
Are both designs from the same architect?
What is clear is that every cantilever, every overhang, etc., costs money. Your architect should have experience with this. Does he say that the actual costs for the design with canopies and so forth will be lower, while the costs for the design without overhangs more closely match the final costs?

From a distance or blindly, it is difficult to assess. Based on your description, I can hardly believe it either. Actual enclosed space—that is, with walls, windows, underfloor heating, electrical installation, floor and wall coverings, and so on—inevitably has to be more expensive.

You can only properly evaluate it if you provide plans.

Just from reading the forum, cost estimates from independent architects and actual construction quotes often differ significantly. The real offers are always more expensive. I've even heard of a factor of 2 (!).

But in general, it is true that any deviation from a "straight" wall increases costs. Our originally planned balcony (cantilever slab 2.5 x 1.2m (8.2 x 3.9 ft)) would have cost around 8,000... with the cheapest possible railing.

Edit: Do yourselves a favor and give your plans to a building company to get a quote, so you know where you really stand.

Obstlerbaum schrieb:
From a distance or without detailed information, it’s hard to judge. Based on your description, I also find it hard to believe. Fully enclosed space, meaning with walls, windows, underfloor heating, electrical installation, floor and wall coverings, etc., must inevitably be more expensive.

That sounds logical at first... but I would be cautious. As mentioned, this is an estimate based on volume, which is never the definitive answer. Besides that, one should not underestimate the additional effort involved. Every corner increases manufacturing costs. Regardless of the construction method, this affects both materials and labor time, as well as different requirements for insulation, structural engineering, waterproofing, and so on.

Mottenhausen schrieb:
From just reading the forum, cost estimates from independent architects and actual construction bids can differ significantly. The real bids are always more expensive. I've even heard of a factor of 2 (!).

A factor of 2? You mean double?? I would quickly dismiss such an architect... Variations are understandable, but a factor of 2 means something went completely wrong.

Mottenhausen schrieb:
Edit: Do yourselves a favor and give the plans to a homebuilding company and ask for a quote, so you at least know where you stand.

If you don’t trust the architect, that’s understandable... but normally, you shouldn’t have to turn to a homebuilding company first just to find out whether the architect’s cost estimate is reliable.