PIR insulation
What makes a building passive, and what determines its construction cost?
A passive building needs very little energy for space heating while maintaining indoor comfort. The cost of reaching that standard depends on the building’s shape, plot, windows, construction details and services. Compare it with a building of the same size and use. This shows which costs result from better performance and which come from the architecture or choice of finishes. An annual space-heating demand of up to 15 kWh per square metre is a common reference figure for the Passive House standard. It measures heating demand. To estimate the total energy bill, include hot water, appliances and other energy uses separately.
In this guide
Which figures describe the Passive House standard?
Space-heating demand is only one part of the building assessment.
Airtightness, comfort and an energy balance calculated using the chosen method also matter. Performance depends on the whole building. Check the figures for the actual design and verify the construction on site. A well-insulated building described as energy efficient may still fall short of the Passive House criteria.
What should you compare in cost estimates?
Prepare two options with the same use, floor area and standard of finish. Comparing a simple passive home with a large, elaborate villa tells you little about the cost of saving energy. List land purchase, site preparation, structure, envelope, services and finishes separately. This makes the differences easier to identify.
Check that competing quotations include the same details. A lower price may leave out tapes, seals, labour around windows or commissioning tests. Ask whether scaffolding, transport and protection of materials are included. Small items add up when a large number of junctions have to be finished precisely.
Record whether prices cover first-grade materials, full-size components and the specified technical documentation. A cheaper batch with restrictions on use is comparable only if it meets the design requirements. Compare prices on the same tax basis and apply the same delivery terms. Both can change which quotation looks cheaper.
When can PIR reduce other project costs?
A PIR board can provide the required thermal resistance in a thinner layer than an insulation material with higher thermal conductivity. This can be valuable at a roof or eaves detail, or where floor build-up height is limited. Alongside the board price, compare the effect on flashing heights, timber quantities and available space.
The facing, required fixings and other layers determine whether the thinner board has a practical advantage. Mineral wool can contribute to fire and acoustic performance, while a suitable XPS product can cope with demanding moisture conditions. Select the insulation to meet the needs of the particular roof, wall or floor assembly.
How does building shape affect costs?
A compact building shape reduces the number of difficult junctions and makes continuous insulation easier. A simple roof has fewer valleys, corners and cuts. This can make labour and material quantities more predictable. Measure the effect using a take-off for the actual design.
Cut-to-length metal tile sheets and modular tiles can produce different cutting layouts on the same roof. With trapezoidal sheets, the profile must suit the supports and loads. The most economical covering depends on the roof geometry. Include flashings, gutters, seals and installation in the price for the complete roof.
How can you estimate running costs?
Base the running-cost forecast on calculated demand and the efficiency of the chosen systems. Include servicing, fan electricity and replacement filters. These costs remain relevant in a well-insulated house. The means of supplying hot water can make a substantial difference, particularly in a larger household.
Use more than one energy-price scenario in the financial comparison. Check how different room temperatures or financing costs affect the result. A single payback figure can depend on optimistic assumptions. A table showing how the outcome changes with the inputs is easier to assess.
What should you request to assess a quotation?
Request detail drawings, a schedule of material properties and a list of inspections and tests. Clarify who will connect the roof insulation to the wall insulation and seal service penetrations. Several trades contribute to the energy target. Assign responsibility for the junctions between their work so they are completed.
Arrange for as-built records and the measurements required by the chosen standard. The word “passive” on a quotation does not establish a particular result. Look for a clear description of assumptions, scope and verification. These make it possible to assess what the project delivers beyond its advertised price per square metre.