Installation ; the installers should be checking everything the surveyor has previously checked. Change and sleeve subfloor vents for wooden floors, the same with room vents, especially kitchen and bathroom vents, as these are the rooms which produce a lot of moisture. Check the appliances for ventilation requirements, most fires and boilers have a plaque on them with the fire/boiler ratings. This also applies to appliances on an inside or a outside wall, as when you have cavity wall insulation installed, the air flow will change around your property. An appliance on an outside wall will require a smoke check, or flue test – before and after installation so not to fill up the flues.
Barriers to be fitted if needed (by drilling a hole at the top and a hole at the bottom) dropping a long chain to hook out of the bottom hole to allow a large brush to follow, staying in the walls so the insulation doesn’t fall into the next door neighbours property!
Some mispractices can include;

Stopping the insulation machine too early – causing voids, not having the machine set up right – blowing material in too fast. A box test or flow rate check (depending on the material used) must be carried out before every job, recording the time and weight. Not changing the subfloor vents for wooden floors – they may put a brush over them or blow air brought them, this is not acceptable. Not fitting a cavity brush. Incorrect drilling pattern. Not smoke checking appliances before and after (outside wall appliances) THIS IS PARAMOUNT. Check inside your loft for any overspill, check they have stapled a flue test certificate in the loft. Nobody should be installing the insulation below where someone is above them drilling holes, as drilling will cause shards of brick/debris to fall on the insulation in the cavity – causing it to bridge and cause you problems.

By the way: I started a blog “Make my house warm”, http://makemyhousewarm.blogspot.co.uk/, where people can follow my quest in getting my house more insulated.

The silly thing is they are both right. Hot air is lighter than cooler air and does rise to the top of a ceiling. How do you think hot -air balloons work? There is no convection in a hot-air balloon as it is trapped. Convection is the circulatory effect of cool air being heated and rising. That is why a heater with lower and upper grills placed on a wall are called convection heaters. The air that is cool in a room drops down from a window etc and then is heated by a central heating radiator or electric convection heater and rises to the ceiling. If good loft insulation traps this air like the balloon under the ceiling not letting it escape then we have good loft insulation keeping the house warm and the bills low.