The 6 Utmost Sash Windows Errors You Can Easily Avoid. Prior to going over the twists and turns of Casement Windows, let me ask you a question: do you have experience of Casement Windows? This article assumes that you don't. We have to start somewhere and I am led to believe that starting at the very beginning is a very good place to start! It’s my wish for each and every one of us to find out as much as we can about Casement Windows. Without further ado, here is 'The 6 Utmost Sash Windows Errors You Can Easily Avoid'. Enjoy! Attila likes to write about solar energy, heating technology, environmental protection, and sustainability. The range of durable flush sash windows we supply have been carefully designed to offer the appearance of traditional timber. One of the most appealing features of sash windows especially in summer is that they are extremely good at keeping your house cool in warm weather. Some are CERTASS registered which is a FENSA equivalent and in my professional opinion, a better option than FENSA.