Timber ceiling (nailed truss construction)

After the external walls, roofs and upper floor slabs are the largest surfaces through which valuable heating energy is lost. If the space beneath the roof is unoccupied and unheated, insulating the roof is neither necessary nor worthwhile. It is considerably more expensive, and the amount of heating energy saved is always less than if, as described below, the ceiling is insulated. In private residential construction, nailed truss structures are less common, but they do exist. Due to their structural irregularities, neither panel nor mat insulation materials are suitable for achieving a seamless insulation layer.

You can find qualified tradespeople here.

How is it insulated?

A nail-truss structure is insulated from above using blow-in insulation. In line with the principle ‘if you’re going to do it, do it properly’, it is advisable to choose the greatest possible insulation thickness – approx. 40 cm. To allow access to the loft after insulation has been fitted, a walkway plank is laid in the centre. Often, old and poorly installed insulation is already in place. This does not need to be removed, as

it does provide a certain degree of insulation
removing it would incur unnecessary costs and labour
existing insulation should be utilised in the interests of sustainability

Important: This insulation measure is one of the simplest and can be carried out extremely quickly. You should therefore always choose the maximum possible insulation thickness.

Best-practice example from North Hesse

Economic and environmental indicators:

Insulation thickness

Up to 40 cm

All the benefits at a glance

Thermal insulation: If the U-value of the upper floor slab was previously approx. 1.3 W/m²K (watts per kelvin per square metre), it can be reduced to approx. 0.14 W/m²K (subsidy standard) through insulation measures. This represents a thermal improvement in the upper floor slab of approximately 90 per cent.

Summer thermal insulation: the temperature in rooms beneath uninsulated ceilings can reach up to 35°C in summer. Insulating the ceiling can reduce the temperature by up to 10°C (provided that solar gain through windows etc. is prevented).

Heating costs: The heating costs of a single-storey building can be reduced by up to 30 per cent. In multi-storey buildings, the percentage reduction is lower, but the absolute energy saving for the entire building remains the same.

Further benefits:

Comfort is improved due to higher temperatures in the upper storey ceiling
Summer heat protection is significantly improved; the attic remains pleasantly cool even in summer
CO₂ emissions are reduced.
Heating energy consumption and heating costs are reduced

Costs/Cost-effectiveness: Depending on the level of difficulty, the total cost of the work can be up to €27.50 per m² (including grants and VAT). Thermal insulation can be improved by up to 90 per cent. The project pays for itself within 2–3 years.

Subsidy: This project is subsidised by the government at 15 per cent of the total costs via the BAFA (an energy adviser is required in each case; an additional 5 per cent is available when an iSFP (individual renovation roadmap) is drawn up) or via the tax incentive (Section 35c of the Income Tax Act) – in this case, a 20 per cent tax relief

Can I install the insulation myself? No, you need blow-in insulation equipment. However, the costs can be reduced by helping out (setting up the site, feeding the insulation material into the blow-in machine, cleaning up and dismantling the site, and, if necessary, constructing the walkway for the chimney sweep). Ask a specialist contractor!

Download document:

Fördermittel - Bundesförderung effiziente Gebäude .pdf