ᐅ Demolition and New Construction on Existing Basement – Structural Stability OK?

Hello everyone,

We recently inherited a house (a prefabricated timber frame house from 1971) for which renovation is no longer worthwhile. Therefore, we have decided to demolish the house down to the basement and build a solid, masonry house on top. The basement is already built with masonry and should be able to remain intact.

We also found a construction company that offers everything from one source: demolition, renovation of the basement, and construction of the masonry house, all turnkey.

My concerns are about the structural stability of the basement. It was originally designed to support a lighter timber frame house. However, the construction company preferred to first create the plans and provide us with a quote before clarifying whether the basement can support the new structure.

Is it usual for structural calculations to be done only afterward? (After the plans are made by an architect and the quote is prepared)

Shouldn’t a reputable construction company clarify this in advance? Our offer to provide the structural calculations for the basement from 1971 was ignored. They said it is currently not necessary. (Possibly after signing the contract?) Should we stay away from this provider, or is this indeed common practice?

Many thanks in advance

sharky72 schrieb:

Is it common practice to have the structural calculations done only afterwards? (After the architect has completed the plans and the quote has been prepared)

For a "real" new build, the structural engineering is usually commissioned after the building permit / planning permission has been approved without conditions.

sharky72 schrieb:

Shouldn't a reputable construction company clarify this in advance? Our request to provide the structural calculations for the basement from 1971 was ignored. The company said it is currently not necessary. (Possibly only after contract signing??) Should we avoid this provider or is this indeed standard practice?

Whenever I read something like this, it always raises my hackles...

In your situation, your preferred general contractor (who exactly are they?) should first and foremost address the existing basement; the existing structural calculations are crucial for this.

Regardless of which provider it is, to me it sounds like some parties might already be rubbing their hands together. If the basement cannot support a new, solid masonry structure to be built, you will inevitably face substantial additional costs. Once you have signed the construction contract, you will have to accept whatever consequences arise.

On the other hand, I don’t understand your approach either. As a layperson, you depend on what the general contractor or others tell you being truthful. Didn’t it occur to you at any point that it would be more sensible to know to what extent the existing basement can be used, or what the worst-case scenario could be, before you even look for a contractor for the new build?

You can find an expert in existing buildings of almost any age through, for example, consumer advice centers in your country or professional associations of independent experts. They won’t work for free, of course; but if I were you, I would sleep much better having a report in hand that evaluates your basement, explains the necessary renovation work, and above all confirms or denies its load-bearing capacity.

With that in hand, no contractor can pull the wool over your eyes—at least not concerning the basement.

Kind regards

Hello and thank you very much for your 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 planned to demolish and rebuild the basement. An architect and two independent home builders (one specializing in prefabricated houses and one in solid construction) examined the basement and pointed out that we could save the money for demolishing the basement and building a new one. But you are definitely right; I will get this confirmed in writing by a structural engineer before signing anything.

Regarding your question about disability insurance (BU), I am not sure (since this is my first post) whether it is appropriate to discuss that publicly here. But if you are interested, I can send you a private message.

Another question: The basement has a load-bearing central wall running through it. Shouldn't the load-bearing walls on the ground floor be located directly above this? The plans we received now show some load-bearing walls on the ground floor where none exist below in the basement. I have attached the plans here.

Kind regards

Hello,

sharky72 schrieb:

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

Very good!

sharky72 schrieb:

Originally, we wanted to demolish the basement and rebuild it. An architect and two independent house suppliers (one prefabricated house provider and one traditional masonry house provider) have inspected the basement and pointed out that we could save the cost of demolishing the basement and building a new one.

I have been doing this job for several years and could probably give a preliminary opinion based on a visual inspection. However, since the condition of the basement is very important in your specific case, I would rely only on statements that are documented on paper and signed by the management.

sharky72 schrieb:

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

Yes, I am interested... partly for professional reasons; I also prepare evaluations of building documents.

sharky72 schrieb:

Another question: The basement has a load-bearing central wall that runs continuously. Shouldn’t the load-bearing walls on the ground floor be located directly above this? The plans we have now received show some load-bearing walls on the ground floor where there are none in the basement. I’ve attached the plans here.

Not necessarily; a beam could be used in this case. As you can see, I’m again using words like "could." So a specialist is needed to provide written confirmation that this is possible or not—in this case, the structural engineer. The structural engineer, in turn, needs to be sure that building on the existing basement is feasible, that the masonry can support a solid single-family house, or whether additional structural measures need to be taken afterward, and so on… everything is interconnected.

Kind regards