A Home Information Pack is an assembly of important documents, relating to that property. see: A simple explanation of a HIP
It is envisaged that a Home Information Pack will reduce the transaction time, from receipt of an acceptable offer, to completion, because the important information required by the Purchaser is available "up front".
Generally, if the property is where you live then a Home Information Pack will be required before it is put on the open market.
The following are some instances where there will not be a requirement:
If the property is to be sold privately, to a known indivdual, and is not to be offered for sale on the open market.
Mixed use: residential/commercial: a property with combined living accomodation and a retail outlet.
Properties with sitting tenants.
Properties that are, or have a last use as a business premises.
A Farm, comprising the farm house, buildings & land to be sold as a Farm.
Hostels; Hospitals; Residential Homes & Residential Schools
Property Portfolios
Unsafe Properties & or marked for demolition.
the above is by no means exhaustive, more info. from:
www.homeinformationpacks.gov.uk/industry/149_doyouneedpack.html
There is no specific time lapse before a HIP is out of date, one "School of Thought" is that a HIP is out of date as soon as it is published, whilst from the "University of Thinkers": A HIP should never be out of date and will be as current as it's last update and once a HIP has been created, it should continue to be part of that property's historical record. see Product 3 (created by the University of Thinkers)
See: A simple explanation of a Home Information Pack, HIP
There is nothing to say you must appoint anyone to compile a HIP for you. In fact you are quite at liberty to DIY; It would be prudent to appoint a Solicitor and an Estate Agent to act for you, when selling your property, but you don't have to use their HIP Provider. You can use the HIPSIS website to compile, and archive your HIP. You, and those acting for you can make as many copies, as required, all FOC.
Just take the time to browse further; then make the decision you feel comfortable with.
A Home Information Pack will in itself, not sell a property, it might or might not help in the sale of the property, depending on the objective and unbiased information it contains, but it will contribute to the property selling process by providing the Buyer with information they previously would have had to purchase, after they had made an offer. See also; FAQ 2; and More Info. on the *Required (compulsary) elements (1; 5; 6; 7) of a HIP.