In a basement in its shell state, two shoring posts temporarily support the ceiling.
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Renovating

Basement ceiling insulation: insulation materials, methods and costs

Thomas Bott

Energy-efficient house insulation will save the owner a lot of money in the long run. Good basement insulation is particularly important – especially for older buildings that do not already have perimeter insulation. The surrounding soil makes the basement particularly cool. If this cold air finds its way into the ground floor and the living spaces above, the heating system there has to work even harder to maintain the right temperature. However, if you insulate the ceiling, you prevent about ten percent of heat loss from occurring. Various methods are possible, which in turn have a major influence on the price.

Insulating a basement ceiling: methods and materials

To determine the type of basement ceiling insulation you want to install, you should start by taking a close look at your ceiling. Ideally, it should be dry and as even as possible. If this is the case, installing insulation is quite straightforward. Insulation boards made of rigid polyurethane foam, rock wool or glass wool are available in specialist shops. The latter are particularly suitable for rooms with high levels of moisture concentration – such as laundry rooms. Insulation boards made of rigid PU foam, on the other hand, are compact and have very good insulation properties.

The insulation boards can be attached to a flat ceiling with building foam or simple adhesive mortar. An uneven basement ceiling will require a little more effort, as the boards will need to be fixed with plugs and screws. Another possibility for basement insulation is to use spray-on cellulose flakes. However, in comparison to the attachment of boards, this spray-on procedure cannot be carried out by homeowners themselves. Only experts have the special tools required.

Usability of the basement: the ideal material thickness

Whether the basement is intended to be a usable room or not, insulation is always worthwhile because you definitely don’t want any heating energy to be wasted. However, ceiling insulation that is too thick can mean that there is no longer enough room for higher cupboards, and the resulting lower ceiling height can have an oppressive effect. Experts calculate that the ideal thickness of an insulation board is around twelve centimeters. This usually ensures a good level of insulation. The minimum dimension is usually six centimeters.

Insulating materials are divided into different heat conduction groups, referred to as WLG. The following principle applies: the lower the number, the higher the efficiency. A WLG 032 board can therefore be thinner than a WLG 040 board with the same insulating properties. The difference is the price because materials from better heat conduction groups often cost more. A company that specializes in thermal insulation can show you various board thicknesses in advance of the work and help you to select the one that suits your individual requirements.

What to consider when it comes to basement ceiling insulation

If you carry out the insulation of the basement ceiling yourself, there are a few important points to note. First of all, the ceiling should be free from adverse factors. You should remove any loose plaster and flaked paint. Protruding nails or concrete projections also prevent ceiling insulation from being fitted. If pipes or wires are attached to the ceiling, you must cut the insulation in the appropriate places. Make sure, however, that you also close the gaps with loose insulating material, otherwise the insulating effect will be compromised.

No adhesive should get into the spaces between the boards. Instead, it is important for the insulation boards to be placed as close as possible to each other. If any unwanted gaps appear, you can use loose insulation material to fill these as well. The transition from the ceiling to the walls can represent another weak point. You should therefore cover the walls to a depth of about 40 centimeters. If you want to use the basement as living space, you should look for insulation boards with a visible underside. This saves you from having to paint them, which can be very time consuming.

An open access to a basement room with simple wooden stairs.

You can also insulate your basement ceiling yourself. This requires good preparation and a little manual skill.

Special case: a vaulted basement with a curved ceiling

The insulation boards available in specialist shops are not suitable for vaulted basement ceilings, and a custom-made product from an expert can be very expensive. A support structure may be a good solution in this case. Here, battens serve as supports for flexible insulation mats. Gypsum boards ultimately clad the entire construction.

The cost of an insulated basement ceiling

If you carry out the work yourself, you will need to purchase basement ceiling insulation boards and adhesive. Depending on the material and heat conduction group, these cost between 15 and 30 francs per square meter. However, don’t forget to include the insulation for the transitions between the ceiling and the walls. The adhesive costs about 10 francs per cartridge. You will also need to factor in the cost of the corresponding tool.

If a workman carries out the work, you should expect to pay at least 60 francs per square meter. Spray-on insulation can easily cost twice as much. Under the Swiss Federal Building Program, you can benefit from a subsidy under certain conditions. You can learn more about this at www.dasgebaeudeprogramm.ch.

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