Structural insulated panels are being used more for extensions as people look to make their homes more eco-friendly.
But do the costs justify this? This article will break down what you can expect to pay for SIP extensions and buildings.
Structural Insulated Panel Cost Per m²
The following two tables give a good indication of what you can expect to pay per m² for SIPs panel walling.
| Item | Labour cost / m² | Material cost / m² | Total Cost / m² |
|---|---|---|---|
| OSB Board - Outer Leaf 18mm | £12 | £21 | £33 |
| DPM | £2 | £1 | £3 |
| Slab Insulation - 150 thick Celotex | £7 | £26 | £33 |
| OSB Board - Inner Leaf 18mm | £12 | £20 | £32 |
| Studs; inc. top and bottom plates | £44 | £32 | £76 |
| Plasterboard Internal lining; skimmed | £14 | £6 | £20 |
| Total | £91 | £106 | £197 |
You’ll then need to choose a covering of your choice. Add the total external cladding cost onto the total SIPs panel (£179/m²) for a final cost per panel. Here are the prices for the most popular external cladding choices:
| Item | Labour cost / m² | Material cost / m² | Total cost / m² |
|---|---|---|---|
| Timber Panelling | £20 | £55 | £68 |
| Metal Cladding | £93 | £210 | £303 |
| Render | £34 | £22 | £56 |
| Brick Slips | £16 | £57 | £73 |
Professional fees are ordinarily excluded from estimates as they can be vague and vary considerably.
For example, some jobs may have an architect, structural engineer, M&E engineer, quantity surveyor etc. Another job may only have an architect and quantity surveyor for example.
Within that one professional may charge £35 an hour, another £85 an hour etc.
SIPs Extension Price Cost Per m²
For a SIPs extension or building itself, expect to pay approximately £1250 / m². By comparison, an extension using traditional masonry construction would cost about £1200 / m².
SIPs are less common on ground floor extensions but much more common when building an entirely new property or vertically extending a house. For example, converting a bungalow to a 2 storey house.
This is because SIPs are light and can often just rest on existing foundations. In these situations, SIPs can help save on costs because it reduces the potential costs of substructures, structural steelwork as well as the need for load-bearing internal walls.
Factors that Affect Cost
- Extension size – Although a larger extension will cost more overall, the cost per m² will be reduced.
- Specification / design of the system – elements of the design can change on the cost. These range from variables such as the the size of studs used and the thickness of insulation.
- Choice of external covering – Timber panelling and brick slips have similar costs. Render is slightly cheaper, whereas metal cladding is far more expensive.
- The weight of the roof structure Heavier roofs may require the building to be reinforced. This is because SIPS can’t support heavier roofs that materials like traditional masonry can.
- Location – The above rates are for the South East/Outer London Area. You can use the following adjustments depending on where the roofing needs to be done. These are based on the BCIS and Spon indices.
| Region | % Adjustment |
|---|---|
| South East (Southampton, Oxford, Kent, Outer London) | 0 |
| Inner London | +4% |
| South West (Bristol, Exeter) | -4% |
| West Midlands (Birmingham) | -10% |
| East Midlands (Northampton, Nottingham, Leicester) | -10% |
| East Anglia (Cambridge, Norwich, Ipswich) | -5% |
| North West (Liverpool, Manchester) | -12% |
| Yorkshire and Humberside (Leeds, Sheffield) | -11% |
| North East (Newcastle, Sunderland) | -10% |
| Scotland (Edinburgh, Glasgow) | -6% |
| Wales (Cardiff, Swansea) | -9% |
| Northern Ireland (Belfast) | -12% |
Benefits of SIPs vs Traditional Materials
Faster Build Time
Installation crews that are well trained to use structural insulated panels can result in a 55% framing time when compared to conventional wood framing. Because the panels arrive on-site ready to be installed, there are fewer individual operations. For example, things like electrical chases are typically added in the core of panels so there is no need to drill through studs for wiring.
Energy Efficient
SIPs extensions use up to 50% less energy to heat and cool than stick-frame houses. The R-values of SIPs are far higher than stick-framed walls and because of their standardised design, they create an extremely air-tight envelope. This results in a more sustainable energy design with lower energy bills.
Excellent Durability
SIPs have excellent fire resistance, tested to offer 73 minutes of resistance. This exceeds British Fire Safety regulations. Because they are made from foam, they are not susceptible to pests either.
Get Prices on SIPS Extensions Near You
SIPs are still pretty new in the UK market. This means finding professional builders with experience can be difficult.
We work with all the best SIPs extension builders ready to price your job. Get free, no-obligation quotes in your local area and compare prices using the form below.
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About the Author
Alex Johnson is a qualified quantity surveyor and writer with a passion for conducting original research and uncovering the true cost of jobs. His cost data has been referenced by EDF Energy and the Scottish Government.