Replacing your windows or doors it’s a big decision. To make sure you’re getting what you paid and the work is done right, Smart Sash Windows will provide you with a FENCA certificate. FENCA certificate is a declaration by us to prove that windows have been replaced and comply with building regulations, use energy-efficient products. However ?? doesn’t cover repairs. For example, if we install sashes into existing sash boxes it will be regarded as repair work by fencer and a certificate will not be provided.