Thank you Cesspadilla & Setanta
It is very informative I have also carried out my search and found as given below in Codex Hygiene principles
4.2.2 Internal structures and fittings
Structures within food establishments should be soundly built of durable materials and be easy to maintain, clean and where appropriate, able to be disinfected. In particular the following specific conditions should be satisfied where necessary to protect the safety and suitability of food:
• the surfaces of walls, partitions and floors should be made of impervious materials with no toxic effect in intended use;
• walls and partitions should have a smooth surface up to a height appropriate to the operation;
• floors should be constructed to allow adequate drainage and cleaning;
• ceilings and overhead fixtures should be constructed and finished to minimize the build up of dirt and condensation, and the shedding of particles;
• windows should be easy to clean, be constructed to minimize the build up of dirt and where necessary, be fitted with removable and cleanable insect-proof screens. Where necessary, windows should be fixed;
• doors should have smooth, non-absorbent surfaces, and be easy to clean and, where necessary, disinfect;
• working surfaces that come into direct contact with food should be in sound condition, durable and easy to clean, maintain and disinfect. They should be made of smooth, non-absorbent materials, and inert to the food, to detergents and disinfectants under normal operating conditions.