The Passive House (passivhaus) standard combines superinsulation with other techniques and technologies to achieve ultra-low energy use. Superinsulation will also be used by zero carbon buildings (ZCB) and Energy Plus Buildings which have a negative carbon footprint.
Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss (and gain) by using much higher levels of insulation and airtightness than normal building standards require. The benefits are very low running costs and excellent environmental performance.
Superinsulation is one of the ancestors of the passive house approach and requires: –
- Very high levels of insulation, typically R-Value/ RSI of at least 7 walls and R-Value/ RSI at least 10.6 roof. The corresponding to U-values are therefore of 0.15 walls and 0.1 roof W/(m²·K)
- Construction details ensure insulation continuity where walls meet roofs, floor, and other walls
- Airtight construction, especially around doors and windows to prevent air infiltration pushing heat in or out.
- A heat recovery ventilation system to provide fresh air
- No large windows facing any particular direction
- Much smaller than conventional heating system, sometimes just a small backup heater
As a rough guide, please find below calculated examples of insulation to meet passive house standards, however, these should all be confirmed by a certified passivehaus designer:-
Roof Insulation – a continuous layer of 450mm mineral wool quilt insulation which does not taper at the edge of a pitched roof, therefore, sloping roof timbers would need to be set slightly higher than normal construction if the ceilings are flat. Any roof space access hatch would also need the same standard of insulation, but this could be achieved using 250mm of polyurethane foam insulation laid on top of a 12mm plywood hatch.
Wall Insulation to (0.15 U-Value):
Timber framed – 10mm hardboard cladding, outer timber frame with 100mm mineral wool quilt insulation, 100mm mineral wool quilt insulation between frames, inner timber frame with 100mm mineral wool quilt insulation, internal plasterboard lining.
Masonry Construction – brick outer leaf, 150mm mineral wool batts, 115mm aerated concrete block (450Kg/m3), 40mm polyurethane foam insulation board, plasterboard internal lining and plaster skim.
Floor Insulation – (0.15 U-Value) 150mm reinforced concrete slab laid on 200mm expanded polystyrene or 0.12 U-Value can be achieved by using 250mm expanded polystyrene
Window Insulation – windows are manufactured with exceptional low U-values, typically 0.85 to 0.70 W/(m²·K) for the entire window including the frame. These normally combine triple-pane insulated glazing (with a good solar heat-gain coefficient, low-emissivity coatings, sealed argon or krypton gas filled inter-pane voids, and ‘warm edge’ insulating glass spacers with air-seals and specially developed thermal break window frames.
Nisson & Dutt (1985) suggest that a house might be described as “superinsulated” if the cost of space heating is lower than the cost of water heating
Interstitial condensation can be an issue with retrofit building insulation
This can be dealt with using vapour control and breathable membranes which also provide airtightness.