HOUSE EXTENSION COST

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RICS gives a guide cost of between £1,260 and £1,680 per square metre for an extension with plastered finish.

Source: Royal Institution of Chartered Surveyors (RICS) May, 2015. Builder Sheriff prices range depending on overall size, but all are nos here are assumed a standard spec with no additional items.

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EXTENSION COMPONENTS

TYPICAL KEY COMPONENTS

  • Strip Foundations (1000mm deep x 500mm wide)
  • Damp Course
  • Soakaway
  • Cavity Walls (Brick and Block or Rendered Block and Block)
  • Roof
  • Plastered Walls
  • Skirting Boards & Architraves
  • Power: 2 Double white sockets (original consumer unit may need upgrading)
  • Lighting: Central light and switch (original consumer unit may need upgrading)
  • Heating: 1 Radiator connected to existing heating
  • Chipboard / Plywood / concrete flooring ready for flooring finish eg tiles, Wood
NOTE: It does not include Drawings , Planning Applications and Building Control
SOURCE: Builder Sheriff, http://www.buildingsheriff.com/extension-calculator-cost.htmlw.

ADDITIONAL ITEMS

  • Structural works (Knock through)
  • Under pinning (not obvious until ground works start)
  • Bi Fold Doors
  • Roof Lanterns
  • Extra Lighting
  • AV: Integrated speakers etc
  • Extra power sockets
  • Heating (Under floor heating / Extra radiators)
  • Flooring (Wood, tiles, carpet)
  • Kitchen

TIMEFRAME

DESIGN

1 - 2

Month
  • INITAL DISCUSSION
  • OUTLINE DESIGN
  • SURVEY / FORMAL PLANS (Architect Scale plans with elevations)

Initial estimate

APPROVAL

2 - 3

Month
  • PLANS UNDER PLANNING APPROVAL

Investigate Thames water build over agreements & party wall agreements


Finalize structural calculations / Finalize Quotation

BUILD

3 - 4

Month
  • Ground works & foundations, Walls (Block & Brick), strutural floor.
  • Strutural works
  • Roof
  • 1st Fix including electrical, heating, dry lining walls / ceiling)
  • 2nd Fix

INITAL DISCUSSION

4

OUTLINE DESIGN

3

  • We will work with you to understand what you want, and help design that.
  • Critical to establish how you want the end result to be, at the start
  • Design where your furniture will go / Kitchen if new etc.
  • Establish electrical and heating requirements.

“AS SCALE” DRAWINGS

5

“TO BE” SCALE DRAWINGS

6

GROUND WORKS

First fix comprises all the work needed to take a building from foundation to putting plaster on the internal walls. This includes constructing walls, floors and ceilings, and inserting cables for electrical supply and pipes for water supply.

Second fix comprises all the work after the plastering to a finished house.

BEFORE / AFTER