Job takeoff
Extension shell, one or two storeys takeoff
Build a masonry extension to weathertight: pegging out, footings and the walls below the damp course, the ground floor, cavity walls with ties and insulation, a tiled lean-to or pitched roof, gutters and the openings, with the beam into the house and every structural member listed and never sized.
A takeoff is the trade word for the shopping list a job produces — every material, and how much of each, worked out by its own cited calculator.
- 14Measurements in
- 25Trades out
Choose the build-up
Each layer changes the materials below; the dimensions stay the same.
Calculators behind the other choices:
Calculators behind the other choices:
Compare one layer at these dimensions, with the rest of the build-up held as you have it:
Give the job once
Every figure on the right follows these, in the units you choose.
Been given a quote for this job?
Paste it into the extension shell quote check: each line is read against these same calculators — what it leaves out, what it adds, and what to ask.
Check the quoteEvery trade, from those dimensions
then change a dimension, and each line shows what moved.
| Trade | Quantity | |
|---|---|---|
Setting-out diagonalsCourt Diagonal and Squaring Triangle CalculatorThe diagonal of the footprint, corner to corner, that both diagonals must match before the pegs are trusted, with the legs of a 3-4-5 triangle in the working to square the first corner off the house. The house wall is one side of the rectangle, so check it is straight before squaring off it.How this figure was reached
Resting on
Change any other figure on the Court Diagonal and Squaring Triangle Calculator | 21.01 ft | |
Footing trenches, dugTrench Excavation & Backfill Volume CalculatorThe trench under the three new walls, along their outside face, at the footing's width and the trench depth. The working's excavation line is the hole in the ground; the headline adds a quarter for the ground bulking once it is dug, the volume that leaves the site.
Why this quantity?
Resting on
The loose-volume allowance: set by the Extension shell, one or two storeys takeoff. Change any other figure on the Trench Excavation & Backfill Volume Calculator | 13.77 yd³ | |
Dig over the floorTrench Excavation & Backfill Volume CalculatorThe ground inside the walls taken down to the depth you gave, bulked by a quarter in the same way, dug once the walls stand at the damp course.
Why this quantity?
Resting on
The loose-volume allowance: set by the Extension shell, one or two storeys takeoff. Change any other figure on the Trench Excavation & Backfill Volume Calculator | 7.92 yd³ | |
Footing concreteContinuous Footing / Grade Beam Volume CalculatorConcrete for the footings under all three walls at the width and depth you gave from the design, with the calculator's waste allowance. The mix and any reinforcement are the designer's.
Why this quantity?
Resting on
The waste factor: the calculator's working figure, a trade convention. Change any other figure on the Continuous Footing / Grade Beam Volume Calculator | 8.26 yd³ | |
Blocks below the damp-proof course, both leavesConcrete CMU Block Counter & Grout Infill CalculatorBoth leaves from the top of the footing up to the damp course, laid solid with no cell grouted: the run twice over, at the trench depth less the concrete plus the damp course's height above the ground. The cavity below ground is filled or closed to the design.
Why this quantity?
Resting on
The waste factor: the calculator's working figure, a trade convention. Change any other figure on the Concrete CMU Block Counter & Grout Infill Calculator | 151 blocks | |
Hardcore under the slabGravel Base Layer Tonnage CalculatorCrushed stone over the floor inside the walls at the calculator's opening compacted thickness and density, by weight. The thickness is the design's, and the sand blinding over it is not in the row.
Why this quantity?
Resting on
Change any other figure on the Gravel Base Layer Tonnage Calculator | 6 tons | |
Floor insulation boardsFoam Board Insulation CalculatorRigid boards over the floor inside the walls, at the calculator's opening sheet and cutting allowance; the upstand round the slab's edge is strips cut from them. Under a slab they go on the membrane; over a beam-and-block floor, under the screed.
Why this quantity?
Resting on
The cutting waste: the calculator's working figure, a trade convention. Change any other figure on the Foam Board Insulation Calculator | 7 sheets (4x8 ft) | |
Floor slab concreteConcrete CalculatorThe slab over the insulation and membrane inside the walls, at the calculator's opening thickness and waste allowance; the thickness, any mesh and the mix are the designer's.
Why this quantity?
Resting on
The waste factor: the calculator's working figure, a trade convention. | 2.37 cubic yards | |
Scaffold round the new wallsScaffold Face Area and Hire Quantity CalculatorThe face along all three new walls up to the eaves, the platform the upper courses and the roof are built from.
Why this quantity?
Resting on
Change any other figure on the Scaffold Face Area and Hire Quantity Calculator | 340 ft² of face | |
Inner leaf blocks, clear of the openingsConcrete CMU Block Counter & Grout Infill CalculatorThe inner leaf from the damp course to the eaves wherever there is no opening: the run less the openings' total width, at the storey height, laid solid. The run is measured along the walls' outside face, as the footings are, which is longer than the inner leaf by about four wall thicknesses at the two corners and the two ends against the house, so the row runs a little over. The working gives the mortar the blocks take.
Why this quantity?
Resting on
The waste factor: the calculator's working figure, a trade convention. Change any other figure on the Concrete CMU Block Counter & Grout Infill Calculator | 260 blocks | |
Inner leaf blocks, above and below the openingsConcrete CMU Block Counter & Grout Infill CalculatorThe inner leaf over and under every opening, counted as one run as long as the openings' total width and as tall as the storey less the opening height. A door has none below it, so the courses sit above it; a window has some of each.
Why this quantity?
Resting on
The waste factor: the calculator's working figure, a trade convention. Change any other figure on the Concrete CMU Block Counter & Grout Infill Calculator | 18 blocks | |
Facing bricks, clear of the openingsBrick CalculatorThe outer leaf wherever there is no opening, the run less the openings' width at the storey height, at the brick and joint the sizes below set. The working gives the mortar in bags.
Why this quantity?
Resting on
The waste factor: the calculator's working figure, a trade convention. | 1660 bricks | |
Facing bricks, above and below the openingsBrick CalculatorThe outer leaf over and under the openings, one run as long as their total width; the soldier course or arch over a lintel, where there is one, is laid from the same bricks.
Why this quantity?
Resting on
The waste factor: the calculator's working figure, a trade convention. | 114 bricks | |
Wall ties across the cavityBrick Veneer Wall Tie Density CalculatorTies over the wall less its openings, at the calculator's US spacing of one tie to about 0.25 m² (2.67 sq ft). A British cavity wall's ties follow their own spacing, and the extra ties up each side of an opening are in neither figure.
Why this quantity?
Resting on
Change any other figure on the Brick Veneer Wall Tie Density Calculator | 89 ties | |
Cavity boardsFoam Board Insulation CalculatorRigid boards against the inner leaf over the wall less its openings, held by the ties with a clear cavity left in front, at the calculator's opening sheet and allowance. The thickness is the energy calculation's.
Why this quantity?
Resting on
The cutting waste: the calculator's working figure, a trade convention. Change any other figure on the Foam Board Insulation Calculator | 9 sheets (4x8 ft) | |
Weep holes at the damp courseCavity Wall Weep Hole Spacing CalculatorWeeps along the foot of the outer leaf above the damp course, at the calculator's opening spacing. The cavity tray over each lintel lets water out through weeps of its own, which this row does not count.
Why this quantity?
Resting on
Change any other figure on the Cavity Wall Weep Hole Spacing Calculator | 23 weep holes | |
Lean-to raftersRoof Truss Spacing & Count CalculatorRafters from the far wall's plate up to the house, spaced along the extension's width at the calculator's opening centres, with one at each end. Their size, the plate or hanger at the house and the centres themselves are the designer's.
Why this quantity?
Resting on
Change any other figure on the Roof Truss Spacing & Count Calculator | 10 trusses | |
Fascia along the eavesFascia Board CalculatorFascia along the lean-to's one eave, in stock lengths with the calculator's allowance. The two verges take a dry verge or a barge board, which is not in the row.
Why this quantity?
Resting on
The cut and scarf allowance: the calculator's working figure, a trade convention. | 2 x 12 ft boards | |
Underlay over the lean-toRoofing Underlayment CalculatorThe slope's area, the width by the rafter length from the eaves overhang up to the house, with the calculator's lap allowance, in its 1,000 sq ft (about 93 m²) synthetic rolls. A British breathable membrane comes in smaller rolls, so the lapped area in the row's working is the figure to buy by.
Why this quantity?
Resting on
The overlap allowance: the calculator's working figure, a trade convention. Change any other figure on the Roofing Underlayment Calculator | 1 roll | |
Batten courses up the slopeRoof Batten Spacing Calculator (Tile Roofing)Courses of battens from the eaves up to the house at the calculator's opening gauge; the tile maker's gauge table sets the real one. The battens to buy are the courses times the roof's width, plus a lap at every joint.
Why this quantity?
Resting on
Change any other figure on the Roof Batten Spacing Calculator (Tile Roofing) | 15 rows | |
Flashing where the roof meets the houseExterior Flashing Layout Trim Sheet CalculatorCover flashing along the top of the lean-to where it meets the house wall, counted in pieces at the length the sizes below set: 1.5 m (5 ft) Code 4 lead in metric, a 10 ft (3.05 m) coil piece in imperial. The cavity tray in the house wall above it is listed as work.
Why this quantity?
Resting on
Change any other figure on the Exterior Flashing Layout Trim Sheet Calculator | 2 sheets | |
Gutter along the eavesGutter CalculatorGutter along the one eave in stock sections; the row's working counts the downpipes (downspouts) it needs, and the drain each one discharges into is listed as work.
Why this quantity?
Resting on
| 2 x 10 ft sections | |
Gutter bracketsGutter Hanger Spacing CalculatorBrackets along the same eave at the calculator's opening spacing, one at each end.
Why this quantity?
Resting on
Change any other figure on the Gutter Hanger Spacing Calculator | 10 hangers | |
Flashing tape round the openingsWindow Opening Flashing Membrane CalculatorSelf-adhered tape round every opening, sill, jambs and head, with the calculator's run-past at each corner and its allowances. A frame set into a masonry cavity against closers, as a British one is, is sealed to them instead and the row can be left out; the doors and windows themselves are items.
Why this quantity?
Resting on
The waste allowance: the calculator's working figure, a trade convention. Change any other figure on the Window Opening Flashing Membrane Calculator | 99 ft | |
Skip (dumpster) loads for the spoilSkip & Dumpster Size CalculatorThe trenches and the dig over the floor, bulked by a quarter, as soil. Soil can reach a skip's weight limit before it fills the skip, so the working's count of loads by weight is the figure to book; a grab lorry is loaded the same way.
Why this quantity?
Resting on
Change any other figure on the Skip & Dumpster Size Calculator | 21.7 yd³ | |
Setting-out diagonalsCourt Diagonal and Squaring Triangle CalculatorThe diagonal of the footprint, corner to corner, that both diagonals must match before the pegs are trusted, with the legs of a 3-4-5 triangle in the working to square the first corner off the house. The house wall is one side of the rectangle, so check it is straight before squaring off it.How this figure was reached | 6.4 m | |
Footing trenches, dugTrench Excavation & Backfill Volume CalculatorThe trench under the three new walls, along their outside face, at the footing's width and the trench depth. The working's excavation line is the hole in the ground; the headline adds a quarter for the ground bulking once it is dug, the volume that leaves the site.
Why this quantity? | 9.75 m³ (loose) | |
Dig over the floorTrench Excavation & Backfill Volume CalculatorThe ground inside the walls taken down to the depth you gave, bulked by a quarter in the same way, dug once the walls stand at the damp course.
Why this quantity? | 6.11 m³ (loose) | |
Footing concreteContinuous Footing / Grade Beam Volume CalculatorConcrete for the footings under all three walls at the width and depth you gave from the design, with the calculator's waste allowance. The mix and any reinforcement are the designer's.
Why this quantity? | 6.14 m³ | |
Blocks below the damp-proof course, both leavesConcrete CMU Block Counter & Grout Infill CalculatorBoth leaves from the top of the footing up to the damp course, laid solid with no cell grouted: the run twice over, at the trench depth less the concrete plus the damp course's height above the ground. The cavity below ground is filled or closed to the design.
Why this quantity? | 108 blocks | |
Hardcore under the slabGravel Base Layer Tonnage CalculatorCrushed stone over the floor inside the walls at the calculator's opening compacted thickness and density, by weight. The thickness is the design's, and the sand blinding over it is not in the row.
Why this quantity? | 5.37 metric tons | |
Floor insulation boardsFoam Board Insulation CalculatorRigid boards over the floor inside the walls, at the calculator's opening sheet and cutting allowance; the upstand round the slab's edge is strips cut from them. Under a slab they go on the membrane; over a beam-and-block floor, under the screed.
Why this quantity? | 7 sheets (2400x1200 mm) | |
Floor slab concreteConcrete CalculatorThe slab over the insulation and membrane inside the walls, at the calculator's opening thickness and waste allowance; the thickness, any mesh and the mix are the designer's.
Why this quantity? | 1.79 m³ | |
Scaffold round the new wallsScaffold Face Area and Hire Quantity CalculatorThe face along all three new walls up to the eaves, the platform the upper courses and the roof are built from.
Why this quantity? | 32.5 m² of face | |
Inner leaf blocks, clear of the openingsConcrete CMU Block Counter & Grout Infill CalculatorThe inner leaf from the damp course to the eaves wherever there is no opening: the run less the openings' total width, at the storey height, laid solid. The run is measured along the walls' outside face, as the footings are, which is longer than the inner leaf by about four wall thicknesses at the two corners and the two ends against the house, so the row runs a little over. The working gives the mortar the blocks take.
Why this quantity? | 221 blocks | |
Inner leaf blocks, above and below the openingsConcrete CMU Block Counter & Grout Infill CalculatorThe inner leaf over and under every opening, counted as one run as long as the openings' total width and as tall as the storey less the opening height. A door has none below it, so the courses sit above it; a window has some of each.
Why this quantity? | 19 blocks | |
Facing bricks, clear of the openingsBrick CalculatorThe outer leaf wherever there is no opening, the run less the openings' width at the storey height, at the brick and joint the sizes below set. The working gives the mortar in bags.
Why this quantity? | 1386 bricks | |
Facing bricks, above and below the openingsBrick CalculatorThe outer leaf over and under the openings, one run as long as their total width; the soldier course or arch over a lintel, where there is one, is laid from the same bricks.
Why this quantity? | 118 bricks | |
Wall ties across the cavityBrick Veneer Wall Tie Density CalculatorTies over the wall less its openings, at the calculator's US spacing of one tie to about 0.25 m² (2.67 sq ft). A British cavity wall's ties follow their own spacing, and the extra ties up each side of an opening are in neither figure.
Why this quantity? | 93 ties | |
Cavity boardsFoam Board Insulation CalculatorRigid boards against the inner leaf over the wall less its openings, held by the ties with a clear cavity left in front, at the calculator's opening sheet and allowance. The thickness is the energy calculation's.
Why this quantity? | 9 sheets (2400x1200 mm) | |
Weep holes at the damp courseCavity Wall Weep Hole Spacing CalculatorWeeps along the foot of the outer leaf above the damp course, at the calculator's opening spacing. The cavity tray over each lintel lets water out through weeps of its own, which this row does not count.
Why this quantity? | 23 weep holes | |
Lean-to raftersRoof Truss Spacing & Count CalculatorRafters from the far wall's plate up to the house, spaced along the extension's width at the calculator's opening centres, with one at each end. Their size, the plate or hanger at the house and the centres themselves are the designer's.
Why this quantity? | 10 trusses | |
Fascia along the eavesFascia Board CalculatorFascia along the lean-to's one eave, in stock lengths with the calculator's allowance. The two verges take a dry verge or a barge board, which is not in the row.
Why this quantity? | 2 x 3.6 m boards | |
Underlay over the lean-toRoofing Underlayment CalculatorThe slope's area, the width by the rafter length from the eaves overhang up to the house, with the calculator's lap allowance, in its 1,000 sq ft (about 93 m²) synthetic rolls. A British breathable membrane comes in smaller rolls, so the lapped area in the row's working is the figure to buy by.
Why this quantity? | 1 roll | |
Batten courses up the slopeRoof Batten Spacing Calculator (Tile Roofing)Courses of battens from the eaves up to the house at the calculator's opening gauge; the tile maker's gauge table sets the real one. The battens to buy are the courses times the roof's width, plus a lap at every joint.
Why this quantity? | 15 rows | |
Flashing where the roof meets the houseExterior Flashing Layout Trim Sheet CalculatorCover flashing along the top of the lean-to where it meets the house wall, counted in pieces at the length the sizes below set: 1.5 m (5 ft) Code 4 lead in metric, a 10 ft (3.05 m) coil piece in imperial. The cavity tray in the house wall above it is listed as work.
Why this quantity? | 4 sheets | |
Gutter along the eavesGutter CalculatorGutter along the one eave in stock sections; the row's working counts the downpipes (downspouts) it needs, and the drain each one discharges into is listed as work.
Why this quantity? | 2 x 4 m sections | |
Gutter bracketsGutter Hanger Spacing CalculatorBrackets along the same eave at the calculator's opening spacing, one at each end.
Why this quantity? | 10 hangers | |
Flashing tape round the openingsWindow Opening Flashing Membrane CalculatorSelf-adhered tape round every opening, sill, jambs and head, with the calculator's run-past at each corner and its allowances. A frame set into a masonry cavity against closers, as a British one is, is sealed to them instead and the row can be left out; the doors and windows themselves are items.
Why this quantity? | 29.7 m | |
Skip (dumpster) loads for the spoilSkip & Dumpster Size CalculatorThe trenches and the dig over the floor, bulked by a quarter, as soil. Soil can reach a skip's weight limit before it fills the skip, so the working's count of loads by weight is the figure to book; a grab lorry is loaded the same way.
Why this quantity? | 15.86 m³ |
Estimates, not a quote. Each row gives its base, the allowance on top, the adjusted figure and what to order; change an allowance on the row, or open its reasoning to see every figure it rests on. A trade's own page carries what it does not cover — open the one you are about to order against.
Labour and programme
Person-hours for the rows going in, from trade rules of thumb: a range for each piece of work, never a price.
- Footing trenches, dug1.7 h (0.7–5.1)
- Dig over the floor1.0 h (0.4–2.9)
- Footing concrete14 h (7.2–30)
- Blocks below the damp-proof course, both leaves13 h (8.3–24)
- Hardcore under the slab2.5 h (1.0–7.4)
- Floor insulation boards2.9 h (1.6–8.1)
- Floor slab concrete4.0 h (2.0–8.2)
- Inner leaf blocks, clear of the openings22 h (14–42)
- Inner leaf blocks, above and below the openings1.5 h (1.0–2.9)
- Facing bricks, clear of the openings56 h (37–116)
- Facing bricks, above and below the openings3.9 h (2.5–8.0)
- Cavity boards3.9 h (2.2–11)
- Fascia along the eaves4.0 h (2.0–10)
- Underlay over the lean-to1.1 h (0.7–2.3)
- Flashing where the roof meets the house4.5 h (1.5–9.1)
- Gutter along the eaves2.0 h (1.0–4.0)
- Flashing tape round the openings12 h (3.0–24)
About 151 person-hours in the rows that carry them, between 86 and 315.
Trade by trade
- Plant operator1 plant operator + 1 labourerunder a quarter of a day
- Labourer2 labourers + 1 mason + 1 plant operator1 day
- Mason1 mason + 1 labourer6 days
- Carpenter1 carpenter + 1 labourerhalf a day
- Roofer2 roofershalf a day
- Glazier2 glaziers1 day
About 8½ days, one trade after another at eight hours a day. Left out: drying and curing, deliveries, inspections, trades overlapping.
8 rows carry no hours of their own
- Setting-out diagonals: Setting out is not rated here: it is a short task whose time depends on the drawings and the site, not on a quantity.
- Scaffold round the new walls: Scaffolding is not rated here: it is usually erected by a scaffolding firm and priced as hire, and where your own crew puts it up, the system and the height set the time.
- Wall ties across the cavity: counted with Facing bricks, clear of the openings and Facing bricks, above and below the openings
- Weep holes at the damp course: counted with Facing bricks, clear of the openings and Facing bricks, above and below the openings
- Lean-to rafters: The roof structure is not rated here: its span, pitch and the engineer's details set the time more than any count of members.
- Batten courses up the slope: its rate is per sq ft; this row gives rows
- Gutter brackets: counted with Gutter along the eaves
- Skip (dumpster) loads for the spoil: counted with Footing trenches, dug and Dig over the floor
Labour and programme
Person-hours for the rows going in, from trade rules of thumb: a range for each piece of work, never a price.
- Footing trenches, dug1.6 h (0.6–4.7)
- Dig over the floor1.0 h (0.4–2.9)
- Footing concrete14 h (7.0–29)
- Blocks below the damp-proof course, both leaves9.2 h (5.9–17)
- Hardcore under the slab2.4 h (1.0–7.3)
- Floor insulation boards2.9 h (1.6–8.1)
- Floor slab concrete3.9 h (2.0–8.1)
- Inner leaf blocks, clear of the openings19 h (12–35)
- Inner leaf blocks, above and below the openings1.6 h (1.0–3.0)
- Facing bricks, clear of the openings47 h (30–97)
- Facing bricks, above and below the openings4.0 h (2.6–8.3)
- Cavity boards4.1 h (2.3–12)
- Fascia along the eaves4.0 h (2.0–10)
- Underlay over the lean-to1.1 h (0.7–2.3)
- Flashing where the roof meets the house4.5 h (1.5–9.0)
- Gutter along the eaves2.0 h (1.0–4.0)
- Flashing tape round the openings12 h (3.0–24)
About 134 person-hours in the rows that carry them, between 75 and 282.
Trade by trade
- Plant operator1 plant operator + 1 labourerunder a quarter of a day
- Labourer2 labourers + 1 mason + 1 plant operator1 day
- Mason1 mason + 1 labourer5 days
- Carpenter1 carpenter + 1 labourerhalf a day
- Roofer2 roofershalf a day
- Glazier2 glaziers1 day
About 7½ days, one trade after another at eight hours a day. Left out: drying and curing, deliveries, inspections, trades overlapping.
8 rows carry no hours of their own
- Setting-out diagonals: Setting out is not rated here: it is a short task whose time depends on the drawings and the site, not on a quantity.
- Scaffold round the new walls: Scaffolding is not rated here: it is usually erected by a scaffolding firm and priced as hire, and where your own crew puts it up, the system and the height set the time.
- Wall ties across the cavity: counted with Facing bricks, clear of the openings and Facing bricks, above and below the openings
- Weep holes at the damp course: counted with Facing bricks, clear of the openings and Facing bricks, above and below the openings
- Lean-to rafters: The roof structure is not rated here: its span, pitch and the engineer's details set the time more than any count of members.
- Batten courses up the slope: its rate is per m²; this row gives rows
- Gutter brackets: counted with Gutter along the eaves
- Skip (dumpster) loads for the spoil: counted with Footing trenches, dug and Dig over the floor
Setups you have saved
The build-up, the dimensions and any allowance you changed — kept on this device, and reusable on any job. Your prices are not copied in: they stay in your price book, so a setup never holds a stale one.
How far does a budget go?
At your own prices, with this build-up unchanged.
About this job
An extension shell is priced from the ground up and goes wrong from the ground down. Before a block is laid the footprint is pegged square off the house, the drains, cables and pipes under it are traced, and the trenches are dug to whatever depth the ground and building control accept on the day, which is not always the depth on the drawing. This page builds the shell the way most extensions in Britain and Ireland go up: concrete footings, a cavity wall of block inside and brick or rendered block outside, a ground floor, and a roof tiled on battens, taken as far as a building that keeps the weather out. A timber-framed addition, the usual way in North America, is the framed exterior wall takeoff on the same foundation.
The walls are counted as they are laid rather than as a box with holes cut out on paper. The run is the three new walls, meaning the two returns and the far wall, and the doors and windows are given by number, width and height, so each leaf comes in two rows: the wall clear of any opening at full storey height, and the courses above and below the openings. The ties, the cavity insulation and the render (stucco) follow the same net area. Every run is taken along the walls' outside face, as the footings are, so the inner leaf, the ties and the cavity insulation, which sit further in, come out a little over. Where each return meets the house it is tied in, with a vertical damp course between old and new; that work is listed, and the ties to the house are not counted.
One storey or two changes the roof more than the height. A single storey takes a lean-to, one slope rising to the house wall, where a cavity tray cut into the house above the roof and a flashing dressed over the tiles keep the junction dry. A second storey brings a first floor, a way up to it, a scaffold twice as high, and a pitched roof of its own, gabled at the far end and joined to the main roof with valleys; a hipped end adds a third eave that the rows here do not count.
The brick and block sizes follow the units. Metric opens on the 215 × 65 mm (about 8 1/2 × 2 1/2 in) bricks and 440 × 215 mm (about 17 3/8 × 8 1/2 in) blocks a British extension is built in; imperial opens on the US modular sizes the brick and block pages use, a 7 5/8 × 2 1/4 in (194 × 57 mm) brick and a block with a 15 5/8 × 7 5/8 in (397 × 194 mm) face, which count a fifth to a quarter more to the square metre. The build-up below names the size, and either can be chosen whichever units are showing. Nothing structural is chosen here either way: the footings, the slab, the lintels (headers), the rafters or trusses and the beam into the house come from the designer, the truss maker and the engineer.
How each line reads
- Base
- What the calculator gives for these dimensions, before anything is added.
- Allowance
- Cutting waste, a lap or spare stock — named, with where it comes from, and changeable on the row.
- Adjusted
- The base with its allowance on top.
- Order
- What to buy: the adjusted figure in whole boards, bags, rolls or lengths.
The order this happens in
Quantities do not tell you the sequence, and on this job the sequence is where the money goes wrong.
- Send building control the notice or the plans the work needs, have the footings, lintels, roof and any beam designed, and trace the drains, cables and pipes under the footprint before pegging out.
- Peg out the three walls off the house, square them by the diagonals, dig the trenches, and have the bottoms inspected before any concrete arrives.
- Pour the footings, build both leaves up to the damp-proof course, and lay any drain that has to run under the new floor while the ground is still open.
- Dig out the floor, then lay and compact the hardcore, blind it, lap the membrane up to the damp course, and cast the slab or lay the beam-and-block floor, with the floor insulation.
- Scaffold the walls and raise both leaves together, bedding the ties and the cavity insulation as the courses rise, closing the cavity at every opening, setting a lintel over each and tying the returns into the house.
- Set the wall plate and fix the rafters or trusses, the fascia and the underlay; above a lean-to, cut the cavity tray into the house wall before the flashing, and on a two-storey roof form the valleys into the main roof. Then batten and tile.
- Hang the gutters, fit the windows and doors, and only then open the house wall, under a beam on padstones with the props left in until the packing takes the load, sheeting the opening until the extension is closed in.
- Render a block outer leaf once the roof is on, and clear the spoil and the waste before the scaffold comes down.
What this takeoff does not cover
- Every structural size: the footings, the slab, the lintels, the rafters or trusses, the first floor's joists, and the beam, padstones and props for the opening into the house. Each is listed as work with no quantity, or counted at the design's spacing, and the designer, the truss maker or the engineer sets it.
- A flat roof over a single storey. The flat roof replacement page's deck, insulation, membrane, upstand and trim rows, run over this footprint, are that roof.
- The tiles or slates, and their fixings. The batten rows count the courses up each slope; the tiles are the roof area times the tile maker's number to the square metre (square), which the page that counts roof fixings gives, with the fixings, when it is run over this roof's slope.
- The masonry above the eaves: the raking tops of a lean-to's side walls and the gable of a two-storey roof. The wall rows stop at the eaves; each raking top or gable is a triangle, half its base times its rise.
- The precast beams and infill blocks of a beam-and-block floor, laid to the floor supplier's layout, which sizes them; no operation lists them yet. The insulation over them is counted and the screed is listed.
- Planning permission, a party wall notice or agreement where the extension stands on or near a boundary, and a build-over agreement for, or a diversion of, a public sewer under the footprint.
- Movement joints in the new brickwork, and the detail where a return meets the house, which the designer chooses between a tie system, a toothed bond and a joint.
- Everything after weathertight: the first and second fix, plastering, the insulation in the roof, the floor finish and the decoration.
Quote check
Been given a quote for this job?
Paste it into the extension shell quote check. Every line of it is read against these same calculators and your measurements. Quantities only, never prices.
What it leaves out
Every line this takeoff has that nothing on the quote reads as.
What it adds
Labour, removal, hire, fees — each named for what it is.
What to ask
One list of questions, ready to copy. Never a verdict.
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Frequently asked questions
- What does the extension shell takeoff give for a typical job?
- Opened at Width along the house 5 m · Projection from the house 4 m · Wall height for each storey 2.5 m · Cavity wall thickness 0.3 m · Doors and windows in the new walls 3 · Opening width, each 1.5 m · Opening height, each 2.1 m · Footing width, from the design 0.6 m · Footing concrete depth, from the design 0.75 m · Trench depth 1 m · Damp-proof course above the ground 0.15 m · Dig over the floor 0.3 m · Roof slope factor 1.06 · Eaves overhang 0.3 m, it orders: Setting-out diagonals, 6.4 m; Footing trenches, dug, 9.75 m³ (loose); Dig over the floor, 6.11 m³ (loose); Footing concrete, 6.14 m³; Blocks below the damp-proof course, both leaves, 108 blocks; Hardcore under the slab, 5.37 metric tons; Floor insulation boards, 7 sheets (2400x1200 mm); Floor slab concrete, 1.79 m³; Scaffold round the new walls, 32.5 m² of face; Inner leaf blocks, clear of the openings, 221 blocks; Inner leaf blocks, above and below the openings, 19 blocks; Facing bricks, clear of the openings, 1,386 bricks; Facing bricks, above and below the openings, 118 bricks; Wall ties across the cavity, 93 ties; Cavity boards, 9 sheets (2400x1200 mm); Weep holes at the damp course, 23 weep holes; Lean-to rafters, 10 trusses; Fascia along the eaves, 2 x 3.6 m boards; Underlay over the lean-to, 1 roll; Batten courses up the slope, 15 rows; Flashing where the roof meets the house, 4 sheets; Gutter along the eaves, 2 x 4 m sections; Gutter brackets, 10 hangers; Flashing tape round the openings, 29.7 m; Skip (dumpster) loads for the spoil, 15.9 m³. Opened at Width along the house 16.5 ft · Projection from the house 13 ft · Wall height for each storey 8 ft · Cavity wall thickness 11.8 in · Doors and windows in the new walls 3 · Opening width, each 5 ft · Opening height, each 7 ft · Footing width, from the design 2 ft · Footing concrete depth, from the design 2.5 ft · Trench depth 3.5 ft · Damp-proof course above the ground 6 in · Dig over the floor 11.8 in · Roof slope factor 1.06 · Eaves overhang 11.8 in: Setting-out diagonals, 21 ft; Footing trenches, dug, 13.8 yd³; Dig over the floor, 7.92 yd³; Footing concrete, 8.26 yd³; Blocks below the damp-proof course, both leaves, 151 blocks; Hardcore under the slab, 6 tons; Floor insulation boards, 7 sheets (4x8 ft); Floor slab concrete, 2.37 cubic yards; Scaffold round the new walls, 340 ft² of face; Inner leaf blocks, clear of the openings, 260 blocks; Inner leaf blocks, above and below the openings, 18 blocks; Facing bricks, clear of the openings, 1,660 bricks; Facing bricks, above and below the openings, 114 bricks; Wall ties across the cavity, 89 ties; Cavity boards, 9 sheets (4x8 ft); Weep holes at the damp course, 23 weep holes; Lean-to rafters, 10 trusses; Fascia along the eaves, 2 x 12 ft boards; Underlay over the lean-to, 1 roll; Batten courses up the slope, 15 rows; Flashing where the roof meets the house, 2 sheets; Gutter along the eaves, 2 x 10 ft sections; Gutter brackets, 10 hangers; Flashing tape round the openings, 99 ft; Skip (dumpster) loads for the spoil, 21.7 yd³. Every figure follows the dimensions you give it.
- Which calculators does the extension shell takeoff run?
- 20 calculators, for 25 lines: Court Diagonal and Squaring Triangle Calculator, Trench Excavation & Backfill Volume Calculator, Continuous Footing / Grade Beam Volume Calculator, Concrete CMU Block Counter & Grout Infill Calculator, Gravel Base Layer Tonnage Calculator, Foam Board Insulation Calculator, Concrete Calculator, Scaffold Face Area and Hire Quantity Calculator, Brick Calculator, Brick Veneer Wall Tie Density Calculator, Cavity Wall Weep Hole Spacing Calculator, Roof Truss Spacing & Count Calculator, Fascia Board Calculator, Roofing Underlayment Calculator, Roof Batten Spacing Calculator (Tile Roofing), Exterior Flashing Layout Trim Sheet Calculator, Gutter Calculator, Gutter Hanger Spacing Calculator, Window Opening Flashing Membrane Calculator, Skip & Dumpster Size Calculator. Each has a page of its own with its formula and its sources; the takeoff runs them all on one set of dimensions.
- What does the extension shell takeoff leave out?
- 8 things, each named on this page: Every structural size; A flat roof over a single storey; The tiles or slates, and their fixings; The masonry above the eaves; The precast beams and infill blocks of a beam-and-block floor, laid to the floor supplier's layout, which sizes them; no operation lists them yet; Planning permission, a party wall notice or agreement where the extension stands on or near a boundary, and a build-over agreement for, or a diversion of, a public sewer under the footprint; Movement joints in the new brickwork, and the detail where a return meets the house, which the designer chooses between a tie system, a toothed bond and a joint; Everything after weathertight.
- Can I check a quote for this job against the takeoff?
- Yes. The extension shell quote check reads a quote's lines against these same calculators and your measurements, and reports what it leaves out, what it adds and what to ask. It reads quantities, never prices.