Architect cost breakdown for a 33 sqm extension in RLP

Hello dear forum,

We own a semi-detached house from 1988 that is 6 m x 11 m in size. Since the west side has no windows and the living room window faces north, we want to build an extension on the west side. This will be externally 3.4 m x 11 m, so about 33 sqm of living space or internally create 130 m^3 of additional living space. The plan is to place the single-story extension on a slab. The existing house has a basement. The extension should have a shed roof (with roof pitch towards the house wall). The architect swears that with this small roof surface there will be no problems with water.

To use the whole thing, some openings must of course be made in the load-bearing existing wall. The weight of the entire house resting on the outer wall must of course be supported by corresponding concrete beams. The structural calculations are currently running for this.

Our architect has now drawn up a cost estimate of about €126,000 excluding interior finishing. This includes architect / structural engineer / energy consulting / soil survey. The price seems very high to me. Although the cost estimate always includes 10% unforeseen costs per item, still...

Since we also want to renovate something in the old building, we wanted to borrow €150,000 from our friendly credit institution, but according to the institution this does not correspond to the achievable value in a possible sale.

That is the current state of affairs. The question now is, should we risk managing the extension with the €120,000 that the bank can provide us or should we cancel the whole project?

Of course, we also have some equity but we want to keep this for a higher quality kitchen, materials for the interior finishing, and for "a little security."

I would really be grateful for helpful hints. Do you think such a small extension can cost so much? Has anyone of you ever realized something similar? There are "extension calculators" on the internet, for such a project with higher quality fittings I do not get over €85,000. I have no idea whether the architect is completely off with his prices.

Thanks and best regards,
Brufi

Hello,

This will be 3.4 m x 11 m on the outside, so approx. 33 sqm of living space or 130 m^3 of additional living space inside. The plan is to place the single-story extension on a concrete slab.

I assume that the extension is approvable and that an extension does not violate setback distances?

The extension is to have a shed roof (with roof pitch towards the house wall). The architect swears there will be no problems with water on this small roof area.

Assuming careful execution, it will lead to no problems whatsoever.

To make use of everything, some openings will of course have to be made in the load-bearing existing wall. The weight of the entire house resting on the exterior wall must of course be supported by corresponding concrete beams. Structural calculations for this are currently in progress.

It "must" be founded on undisturbed ground; therefore, the extension must be supported down to the basement level of the existing building. At 11.00 m, that adds up to a nice sum; the required lintels will prove to be "peanuts" in comparison.

Our architect has now drawn up a cost estimate of about €126,000 without interior finishing. This includes architect / structural engineer / energy consulting / soil investigation. The price seems very high to me. Although the cost estimate always includes 10% unforeseen per item, still...

Provided the soil survey holds no surprises, the estimate is plausible. I just roughly calculated what it would cost if we realized the extension (we won't, RP is not our field). Then – assuming the ground offers no surprises – the bill would be around a good €120k.

That is the current status. The question now is, should we risk tackling the extension with the €120,000 that the bank can provide us, or should we cancel the whole project?

I would never take risks when building a house and do not recommend it to any builder. Then you might as well play Russian roulette.

You are already quite far along in your planning; therefore, from my point of view, it is only consistent to at least finalize planning and cost certainty. You have to pay the commissioned architect and structural engineer anyway as of today; then let the architect also initiate the tender. With the average calculated from the returned offers, you will get a good overview of the expected costs. If it lies beyond all reason, you can still decide against the extension. If you stop at this point, the question "what if...?" will always remain open.

Rhenish regards

It "must" be founded on natural ground, therefore the extension must be supported down to the basement level of the existing building. At 11.00 m, that adds up to a nice little sum; the required lintels will prove to be "peanuts" in comparison.

Maybe a bit off-topic, but out of curiosity: Why must an extension like this (even if it has no basement) be supported down to the basement level of the existing building?

Hello,

Maybe a bit off-topic, but out of interest: Why does an extension like this (even if it has no basement) have to be supported down to the basement level of the existing building?

It is not off-topic

"The" soil surrounding the semi-detached house (workrooms) was also altered with the construction in 1988; so it is no longer naturally formed terrain. However, foundations may only be placed on grown (naturally formed + load-bearing) soil.

Best regards from the Rhineland

Hello and thank you very much for the prompt responses,

unfortunately, these are not very good news for me at the moment – I had rather hoped for answers like, for example, "the price is calculated way too high."

Indeed, we will obtain offers from various shell construction companies and hope that we come in somewhat lower than calculated here. I have the impression that the price-performance ratio of such a "small" extension is – for whatever reason – significantly worse compared to a complete new build...

Best regards,
Brufi

Good evening,

Indeed, we will obtain offers from various shell construction companies and hope that we come in somewhat lower than calculated.

Hoping, believing you should "only" do in church

I have the impression that the price-performance ratio of such a "small" extension is – for whatever reason – significantly worse compared to a complete new build...

I don't know what "bargain" you purchased the semi-detached house for? The price calculated by your architect is market-appropriate; surprisingly so. For you, it will get more expensive solely due to additional foundation costs than a simple new build usually requires

Rhenish regards