House demolition and new construction on existing basement - structural integrity OK?

Hello everyone,

We recently inherited a house (prefabricated house in timber frame construction from 1971) for which a renovation is no longer worthwhile. Therefore, we decided to demolish the house down to the basement and build a solid house on top of it. The basement is already built solidly and should thus be able to remain.
We have also found a construction company that offers everything from a single source: demolition, renovation of the basement, as well as construction of the solid house, all turnkey.

My doubts concern the statics of the basement. It was originally built for a lighter timber frame house. However, the construction company preferred to first create the plans and make us an offer before even clarifying whether the basement can support this or not.

Is it common practice for the structural calculations to be done only afterward? (After creating the plans by an architect and preparing the offer)

Shouldn't a reputable construction company clarify this in advance? Our offer to provide the structural calculations for the basement from 1971 was not accepted. It was said by the construction company that this is currently not necessary. (Possibly after signing the contract??) Should we steer clear of this provider or is this indeed the standard procedure?

Many thanks in advance

Is it common practice that the structural calculations are only done afterwards? (After the plans have been created by an architect and the offer has been made)

In a "real" new build, the structural engineering is generally commissioned after the approval-free building permit has been submitted.

Shouldn't a reputable construction company clarify this in advance? Our request to provide the structural calculations for the basement from 1971 was not addressed. They said it is currently not necessary. (Possibly after the contract is signed??) Should we stay away from this provider, or is this indeed the usual procedure?

When I read something like this, my hair stands on end...

In your case, your preferred general contractor (who is it?) should primarily take care of the existing basement; the existing structural engineering is very important here.

Regardless of not knowing which provider this is about, it reads (to me) as if someone is already rubbing their hands in your case. Because if the basement cannot support a still-to-be-built, solid masonry, inevitably additional costs in the multiple thousands will arise for you. Once you have signed the contract, you have to swallow the bitter pill that may be presented to you.

On the other hand, I also don’t understand your approach? You are a layperson and thus reliant on what the general contractor or someone else tells you being true. Did it never occur to you that it would be more sensible to know to what extent the existing basement can be used or what the worst case could be for you before you look for a general contractor for the new build?

For example, via the consumer advice centers across the country as well as through the Association of Independent Experts, you can find an expert for existing properties of almost any age. They do not work for free – of course; but in your position, I could sleep much better if I had a report in my hands assessing my basement, explaining the necessary renovation measures and above all confirming or denying its load-bearing capacity.

Equipped this way, no general contractor can sell you a pig in a poke; at least not for the basement.

Kind regards

Hello and thank you very much for the honest words.

Under no circumstances will we sign such a contract. We will definitely involve an expert as well as an independent construction supervisor. Originally, we also wanted to demolish the basement and rebuild it. An architect and two independent house providers (one prefabricated house provider and one solid house provider) have looked at the basement and pointed out to us that we could save the money for the basement demolition and the new basement. But you are definitely right, I will have this confirmed in writing by a structural engineer before we sign anything. Regarding your question about BU, I don’t know (since this is my first entry) if one is allowed to simply write that publicly here. But if you are interested, I can gladly send you a private message.

Another question: The basement has a load-bearing central wall that runs all the way through. Shouldn’t the load-bearing walls on the ground floor also run exactly above this? The plans we have now received partly show load-bearing walls on the ground floor where there are none below in the basement. I have attached the plans here.

Kind regards

Hello,

Under no circumstances will we sign such a contract. We will definitely involve an expert as well as an independent construction supervisor.

Very good!

Originally, we also wanted to demolish the basement and rebuild it. An architect and two independent house providers (one prefab house and one solid house provider) examined the basement and pointed out that we could save the money for the basement demolition and the new basement.

I have been doing this job for several years and "could" probably - "by sight" - also make a statement. But since in your specific case the condition of the basement is very important, I would only rely on statements that also make it onto paper along with the signature of management.

But if you are interested, I can gladly send you a private message.

Yes, I am interested ... if only for professional reasons; I also prepare evaluations of construction documents.

Another question: The basement has a load-bearing central wall that runs all the way through. Shouldn't the load-bearing walls in the ground floor also run exactly above this? The plans we have now received show load-bearing walls on the ground floor in places where there are none in the basement below. I have attached the plans here.

Not necessarily; a beam could also be used here. As you can see, I write "could" again. So a specialist must be hired who confirms in writing that this is possible or not; in this case, the structural engineer. The structural engineer, in turn, needs the certainty that construction can be built on the existing basement at all, that the masonry can carry a solid single-family house, or whether additional structural measures need to be taken afterward (can be taken), etc. ... one thing depends on another.

Best regards