Reality Check

Be realistic when it comes to budgeting both time and money for any one of six potential building projects in your home. Here’s our easy guide…

ROOF TERRACE

• Typical building cost per square metre – £1,000 + VAT*

• Time allowed for planning – a minimum of 8 weeks. Party wall agreements (PWA) can take up to 10 weeks

• Time allowed for the build – a minimum of 2 weeks, depending on access to the site

*Cost is based on replacing an area of roof, to install thicker timber floor joists layered with Celotex insulation, a layer of plywood, a weatherproof top layer such as an EDPM rubber membrane, then decking boards or tiles. Additional costs are a handrail (a glass balustrade would be £400 per linear metre) and decking which ranges from £30 square metre for pine to £150 per sqm for Millboard composite decking | Source: John Osborn Design

SIDE RETURN

• Typical supply and install cost per square metre – £2,000-£4,000 + VAT – with glazing and mid-spec finishes

• Time allowed for planning – 8 weeks

• Time allowed for the build – 12-16 weeks

The labour prices can vary considerably depending on whether a high specification finish is required or just a basic shell with a value kitchen and flooring, no under floor heating, smaller rear doors and glazing, and no under-thestairs loo | Source: Dermarta Construction.

UNDER-GARDEN BASEMENTS

• Typical building cost (waterproofed basement shell, fitout, professional fees) per square metre – £5,000 + VAT

• Time allowed – around 12-14 months from start to finish

• Initial design, surveys and planning application – 3-4 months

• Party Wall Agreement – 1-3 months

• Detailed design (in parallel with PWA) – 2 months

• Basement shell construction – 4-6 months

• Fit-out – 2-3 months
In broad terms, costs include the connecting access to the main house and any underpinning required | Source: Ensoul

GARDEN

• Typical cost per square metre including seating areas, planting, hard landscaping, lighting, bespoke elements such as firepits, pergolas or outdoor cooking areas – around £1,000 to £1,500 per square metre depending on elements involved. A bigger garden would typically result in a lower price due to larger areas of lawn.

• Design £1,000 – £5,000

• Budgets can be as little as £500 per square metre but these schemes would be much simpler and would need to make use of existing structures rather than more complex construction and hard landscaping materials.

• Planning rarely required, but 6-8 weeks for permission for any permanent structures such as outdoor offices. Current lead for permission for tree removal is 6 weeks.

• Typical project build duration 4-6 weeks

NB. Information based on a typical 5 square metre to 8 square metre Victorian terraced garden

Cost will vary depending on what is involved before the beautifying stage. Is there work required to boundaries? Is there clearance, removal of existing material/plants/ construction and is there work required to change levels? All these will affect the price. Quotes here are exclusive of VAT | Source: Harrington Porter

LOFT CONVERSIONS

• Typical building costs per square metre – £1,000 +VAT

• Time allowed for planning – 8 weeks, but obviously much quicker if you can build your loft conversion under permitted development rights.

• Time allowed for the build – this is around 8 weeks +/- 2 weeks either side depending on spec and size, and assuming you have all architectural plans, structural calculations and any necessary party wall agreements in place | Source: Simply Loft

UNDER-HOUSE BASEMENT

• Typical building cost per square metre – £4,000 + VAT

• Planning permission standard application – 8 weeks after validation (which can take 2 weeks)

• Time allowed for the build – realistically 9 months for a full basement of a standard terraced house (85-90 square metre basement) | Source: Good London Builders