Can SIPs be used for garages / garden buildings / basements etc?

Yes, definitely.  Sips can be used wherever you desire as long as they are detailed to comply with the Building Regulations.  Common projects which SIPs are used for include:

1. New builds (residential or commercial)
2. Home Extensions
3. Modular Buildings
4. Uses – Insulated SIP Roofs

Click on each of the projects above to see example schemes.