Whether as storage area, play room or extra bedroom – depending on how you intend to use your attic, insulating the roof or the top floor ceiling is not only rewarded by cost and time savings, but is also good for the environment. This piece will tell you what the options for homeowners are, and what to watch out for when it comes to thermal insulation.
Insulating the roof should be your go-to option if the attic is to be used as residential accommodation and to be heated accordingly. Doing so will keep your attic from leaking heat to the outside. One of your insulation options as homeowner is the above-rafter insulation for pitched roofs. It consists of insulation material inserted between the timber trusses and the roof cladding. It is a particularly efficient approach because the on-top application of the insulation material prevents the formation of thermal bridges and thereby the leakage of heat from the inside of the roof truss. This way, the insulation forms an uninterrupted layer without leaky interstices. However, the approach will require the roof to be covered anew – which takes longer and costs more. Accordingly, choosing this method makes sense especially with new-build construction or when renovating the roof anyway. In the case of flat roofs, the above-rafter insulation could be cost-efficient even with existing buildings because the roofing costs are lower with this type of roof. If, however, you are not planning to develop your attic or to renovate and re-tile your roof anyway, another solution comes to mind.
If the attic is only to serve as unheated storage space, you need not insulate the roof. But even in this case, it makes sense to insulate the top floor ceiling. Here is why: The top floor ceiling or, differently put, the attic floor, marks the transition between heating living areas and unheated attic. Topping it with a layer of insulating material will keep the heat energy from escaping from the floor below. Since the costs of material and labour under this scenario are lower than with the roof insulation, it may be a suitable alternative to insulate the top floor ceiling. There are several options to ensure you can still tread on the attic floor after insulating it. On the one hand, there are combinations of joists and soft insulating materials such as mineral wool, which is laid in sheets in the gaps between joists. In this case, you can walk anywhere in the attic where the joists run. On the other hand, you could decide to install insulation boards made of extruded polystyrene rigid foam (XPS). These can be topped with sheathing, so that you can walk anywhere in the attic.
If you decide to convert the attic after the building is completed or the roof already redone, there is the option to install insulation between the rafters. Inserting the insulating material between the rafters will save you the trouble of having to replace the roof cladding. In addition, you could cover the insulation between the rafter with an additional layer mounted on the underside of the rafters. This combination will effectively keep any interior heat from escaping to the outside, and thereby intensify the insulating effect. However, it has the drawback that it may slightly reduce your interior living space.
Ultimately, it is up to the owner to decide whether or not to use the attic as extra space. In no case should the planning be rushed. Even if you put the interior fit-out on the back burner, you can still insulate the roof truss at some point and convert the storage area into a cosy living area later on.