Thanks a bunch for your response.

Looks like I was indeed under insured. The new proposal from my current insurance broker values the building as per today's market value (say 450, 000 euro, although sale value per apartment would total  more than 600, 000 euro). The premium becomes close to 600 euro in this case.

The property is indeed "copropriété" with a single roof. If what you state above is 100% true as per law,  we will continue with a single building insurance, making sure we are not under-insured

If yes you are probably fully under insured...

I pay more than 500€ for a big house, (not divided, empty, that I rent out), 70 km away from Brussels...

Moreover there is no choice for the ABEX index, it is enforced, just like the "health" index on which the rent adaptation may be calculated by the landlords.

For November 2012, the ABEX index = 729

Just have a look HERE

In parellel, I visited KBC and they suggested separate building insurance for each apartment:

As often, bankers don't know how to be professional insurers;

Since this is now a "copropriété" having a single roof, as Syndic, you are obliged to take take a single insurance to cover the whole building block.

I am a honorary syndic for a small "maison d'maitre" converted to three apartments way back in 70s. I own two apartments and my quotie part is, unfortunately, 80%.WE are only two owners.

[color=#004BE0] Current insurance :   Incendie risques simples ABEX 690, conditional-risk [/couleur]
Currently, we have one single insurance for the whole building (including three apartments) with AXA ,"'Police: Incendie risques simples(HABITATIOn L'INDICE ABEX 690)"  which costs us around 300 euro

On my request to verify if we have sufficient covergae, the agent visited and proposed me to upgrade our insuarnce to a  New capital of 450, 000 euro ( ABEX 711), resulting in double the premium

[color=#004BE0] Another Proposal :   Incendie risques all-risk ABEX 711 [/couleur]

In parellel, I visited KBC and they suggested separate building insurance for each apartment:

As a owner with 80% quotiate part, I am interested in taking building insurance per apartment. Being the syndic, I intend to do by officially calling the second owner for a meeting and recording it in "process verballe" that, effective this date, each owner is responsible for insuring their building on their own.

Although, the second owner is living out of the country, tried to sell his/her apartment 6 months ago through an agent but stuck at "compromise de vente", as the building plan doesn't comply with 'communale/urbanisme' town plan for that apartment.

Do not known if/how/when the sale will happen but apparently, second owner doesn't pay any charges
Meantime, through a lawyer, new buyer is chasing II owner to sell at a rock bottom price .

(1) Any suggestions what kind of of insurance we keep for a "maison de maitre" with three apartments from 1970s?  ABEX 690 or ABEX 711?

(2) What is the practice? Do you recommend keeping a "single building insurance" for three apartments or breaking it into individual building insurance per apartment?

With only two owners, given the circumstances that II owner doesn't respond to letters or email or don't pay , I want to send registered letters inviting him/her for a 'assemble generale'  meeting for changing from "single building insurance" to "each owner takes his/her building insurance model". After the second invitation, as I know she won't attend, as the syndic, we will make a 'process verbale' confirming change of building insurance to per apartment from so and so date.

(3) Making a regulation change for the apartment -on the second 'assemble generale' , if second owner misses both meeting despite informing in all official channels-ageIs this approach *Legally right*?