Sir,
According to Section 65 B (54) "works contract" means a contract wherein transfer of property in goods involved in the execution of such contract is leviable to tax as sale of goods and such contract is for the purpose of carrying out construction, erection, commissioning, installation, completion, fitting out, repair, maintenance, renovation, alteration of any moveable or immovable property or for carrying out any other similar activity or a part thereof in relation to such property.
According to rule 2 A (i) of Service Tax (Determination of Value) Rules, 2006 "Value of service portion in the execution of a works contract shall be equivalent to the gross amount charged for the works contract less the value of property in goods transferred in the execution of the said works contract.
However, gross amount charged for the works contract shall not include value added tax or sales tax, as the case may be, paid or payable, if any, on transfer of property in goods involved in the execution of the said works contract. OR
Where the value has not been determined under clause (i), the person liable to pay tax on the service portion involved in the execution of the works contract shall determine the service tax payable in the following manner, namely:-
(A) in case of works contracts entered into for execution of original works, service tax shall be payable on forty per cent. of the total amount charged for the works contract;
2[(B) in case of works contract, not covered under sub-clause (A), including works contract entered into for,-
(i) maintenance or repair or reconditioning or restoration or servicing of any goods; or
(ii) maintenance or repair or completion and finishing services such as glazing or plastering or floor and wall tiling or installation of electrical fittings of immovable property,
service tax shall be payable on seventy per cent. of the total amount charged for the works contract.
Therefore, in my opinion, if the service provider issues a combined bill for supply of material and service provided and since you are constructing a new duct for passing of smoke you are liable to pay service tax on 40% of the total amount charged for the works contract.
If the contractor issues separate bills for material and service provided then you have to service tax @14% on the value of service provided.