Expect to pay at least £1400 per m² for a SIPs extension. However, this can increase considerably, particularly with the rises in material and labour costs.
SIPs Extension Cost per m²
For a SIP extension or building itself, expect to pay approximately £1400 / 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 story 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 they reduce the potential costs of substructures, structural steelwork as well as the need for load-bearing internal walls.
Breakdown of Costs Involved
1. Extension Cost
The following table gives a good indication of what you can expect to pay per m² for the extension before SIPs panels are used.
| Item | Total per m² |
|---|---|
| Substructures | £100 |
| Frame / Upper Floors/ Stairs (where required) | £77 |
| Roof | £156 |
| Windows & External Doors | £82 |
| Internal Doors | £70 |
| Internal Walls | £50 |
| Finishes | £130 |
| Fittings | £82 |
| Mechanical & Electrical Systems | £130 |
| Drainage | £23 |
| Miscellaneous | £55 |
| Total | £955 |
2. SIPs Cladding
You’ll then need to add the SIPS cladding covering of your choice. Add the total external cladding cost onto the total SIPs panel (£197/m²) for the cost before fees.
| 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 |
Here are the prices for the most popular external cladding choices in comparison:
| 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 |
3. Professional Fees
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 £50 an hour, another £100+ per hour etc.
Therefore, £955 + £197 + extra fees gets us to the £1400 per m².
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.
Benefits of SIPs vs Traditional Materials
Faster Build Time
Installation crews that are well-trained to use SIPs can result in a 55% framing time when compared to conventional wood framing. Because