My in-laws have a fairly new bungalow and are looking to improve the insulation before Winter. There is no living space upstairs (ie not dormer) but they want to board it out as attic space. Currently there is a small amount of insulation in between the ceiling joists (about 100mm rockwool) - there is no further insulation in the roof at all. What are their options for improving their ceiling/roof insulation bearing in mind that they want to board out the attic?