How to Measure Up Your Property for an Extension Quote

For a contractor to provide anything more than a very rough ballpark, they need to understand the scale of the proposed works. The key measurements are:

**For a rear extension**:

• *Existing property*:
• •Overall width of the rear of the house (external measurement, from wall face to wall face) — this determines the maximum span of any extension
• •Existing rear projection (the depth of any existing ground floor projection — bay window, utility, conservatory) — the new extension starts from the main rear wall of the original house, and any existing projection is counted in the PD depth calculation
• •Width of the rear garden and distance from the rear of the house to any boundary — relevant for planning and for understanding site constraints
• •Height of the existing rear wall from ground level to the underside of the first floor joists — determines the headroom available under any 'wrap-around' or extension below the first floor

• *Proposed extension*:
• •Proposed depth of extension (how far into the garden): e.g., 3m, 4m, 5m
• •Proposed width: the full width of the house, or a partial width?
• •Proposed height: single storey (height matches or slightly exceeds the first floor window sill level of the existing house), or higher?

• **For a loft conversion**:
• •Overall length of the house (front to back, external) — relevant for the ridge line and dormer positioning
• •Overall width of the house (side to side, external)
• •Existing ridge height above ceiling of top floor — measure from the top floor ceiling level to the underside of the ridge board (access via the loft hatch if available)
• •Hip-to-gable measurement: if the house has a hipped end (the roof ends at the gable with a slope, rather than a vertical wall), the contractor needs to know the width and height of the hip
• •Number of roof windows or dormers required
• •Type of staircase access envisaged (spiral, straight, dog-leg): determines space required on the floor below

• **For a refurbishment**:
• •Floor plan with room dimensions (or sketch of the layout with approximate dimensions)
• •Number and type of rooms: bedrooms, bathrooms, kitchen, living areas
• •Floor area (approximate m² or square footage)
• •Number of floors being refurbished
• •Any structural alterations planned (wall removals, new openings)

**For a loft or extension + refurbishment combination**: Provide measurements for both — and flag that both are part of the same package. Pricing both together often produces a better combined cost than pricing them separately.

A site visit allows a contractor to see the property in person — but a good set of photographs sent in advance means the contractor can arrive briefed rather than needing to spend the first 15 minutes simply orienting themselves. For an initial quote or ballpark, photographs alone (without a site visit) can often produce a useful early estimate.

**Essential photographs**:

• *External*:
• •Rear of the house from the garden — ideally standing back far enough to see the full rear elevation including any existing rear extension or bay
• •Side of the house showing the full elevation from rear to front — essential for understanding party wall and boundary position
• •Garden from house looking toward the rear boundary — shows garden depth, any outbuildings, trees, hard landscaping, or access constraints
• •Front of the house — allows confirmation of property type and style

• *Internal (at the area of proposed work)*:
• •Kitchen from each corner if a rear extension is planned — shows existing back door position, window positions, boiler location, and floor level
• •Rear room layout at ceiling level — shows proximity of joists, position of any chimney breast
• •From inside looking out through any rear opening — shows the extent of any existing rear projection and the relationship between interior floor level and garden level

• *Loft (if a loft conversion is being considered)*:
• •Standing in the loft looking toward the ridge — shows pitch, obstructions, and the relationship between the ridge height and the top of the party wall
• •Any water tank, dormer cheeks, or existing roof structure features
• •Looking down through the loft hatch to the landing below — helps the contractor understand the staircase access challenge

• *Structural specifics*:
• •Any existing cracking, previous repair, or visible structural issue relevant to the proposed works
• •The fuse board / consumer unit
• •Boiler and any accessible pipework (relevant for M&E works)

**Photographs with a ruler or tape measure for scale**: If you can hold a tape measure or a standard A4 sheet of paper in the frame when photographing a specific item, it gives the contractor a useful scale reference for items they can't measure remotely.

If the property has been extended or altered previously, there may be existing drawings that a contractor can use as a base for understanding the property.

**Useful documents to provide**:

• *Planning drawings from previous approvals*:
• •If a previous extension or loft conversion was built under planning permission, the planning drawings will be on the local council's planning portal (accessible free of charge at PlanningPortal.gov.uk or directly at the council's own planning search)
• •These show the layout, dimensions, and external appearance of the property as built or approved
• •They are planning-quality drawings, not construction drawings — they give approximate dimensions and general arrangement rather than detailed technical information

• *Building Regulations drawings (structural drawings)*:
• •If a previous structural alteration was carried out under Building Regulations approval, the drawings submitted to Building Control may be available from the council's Building Control department (some authorities hold these; others do not for older applications)
• •These drawings show more construction detail than planning drawings and may include foundation specifications, structural element positions, and floor build-ups

• *Estate agents' floor plans*:
• •Simple area-based plans often included in property listings — not dimensionally accurate but useful for layout understanding

• *Anything you commissioned yourself*:
• •If you have had the property measured up for a previous project that didn't proceed, the architect's drawings are often the most accurate record of the existing building

**What to do if you have no drawings**: Most Victorian and Edwardian terraces in London have no drawings at all — this is completely normal. The contractor will take measurements during the site visit (or appoint an architect/surveyor to measure the property as part of the design service). For a ballpark estimate, approximate measurements and photographs are sufficient. For a detailed quote, a measured survey (either by architect or contractor) is the appropriate starting point.