Home Extension Planner – Single & Multi-Storey Materials
Home Extension Planner
Plan a single-storey extension or additional floors. Build one connected materials, cutting and quotation pack.
Your project stays in this browser unless you download or print it.
Bulk Entry
Your extension project pack
Review the level totals, supplied specifications and outstanding items, then print or export.
Calculate the extension to see materials and cutting stock.
Inputs changed. Recalculate before printing or exporting. Previous results are out of date.
Print or export your current project
Print opens browser print controls, including Save as PDF. Outstanding items remain attached. Download the editable project backup from stage 1.
Turn your extension estimate into a professional quote
Create a clear customer document with the Handyman Hub Quote & Invoice Generator.
- Create quotes and invoices
- Add your business logo and customer details
- Itemise materials, labour and services
- Print or save your document as a PDF
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This separate product is optional. The planner, materials lists, cutting schedules and project printouts remain free. Transfer your checked estimate items into the generator.
Build a clear material estimate for a single- or multi-storey extension
Use this planner for the supported rectangular extension footprint and aligned floor levels. Identify the build route, floor and wall packages, openings, roof arrangement and supplied specifications before entering prices. A known-cost subtotal is only the priced part of the recorded scope; quotations and unresolved work packages still need checking.
For a separate building in the garden, use the garden room and man cave planner. It estimates a different project scope and should not be used as a shortcut for connections, alterations or making good to an existing house.
Use the excavation calculator for separately measured foundation digging and spoil removal, the concrete calculator for supplied footing or slab dimensions, and the aggregate calculator for specified sub-base purchases. Reconcile their results with the extension packages so materials included in a builder’s quote are not counted twice. These tools do not select structural dimensions.
Plan a home extension, one floor at a time
The Home Extension Planner brings single-storey and multi-storey quantities into one connected project. Start with a rectangular footprint and add floor levels, then specify walls, floors, openings, the roof and the work needed to connect to the existing house. Print a merchant quotation list, component cutting schedule or combined project pack.
Start simple, then add detail
- Choose a new ground-up extension or additional floors above an existing structure.
- Enter the external footprint, complete wall depth and new wall sides. The rear wall is treated as the existing-house junction unless selected.
- Add floor levels and their construction routes. Prices, openings, partitions, extra materials and services are optional.
- Review the estimating examples in the material specifications. Replace product coverages, member sizes and assembly details with supplied information.
- Scope foundations, knock-throughs, temporary support, beams/lintels, stairs, weathering, fire/acoustic work and services.
- Enter missing accessories and exact structural cuts, calculate, and review outstanding items before printing.
- Save a named scenario and download a project backup for another device.
What changes when another floor is added?
Each level adds its own walls, floor construction, ceiling and openings. The roof remains one project roof; foundations and whole-project work packages are counted once. An upper timber floor uses supplied joist blank dimensions and gross deck blanks; stair openings, trimmers, bearings, connections and supporting structure require the project's design.
Adding a floor above an existing building is a separate route. The planner excludes new ground-foundation quantities and keeps assessment/strengthening as an explicit work package. It does not establish whether existing foundations, walls or beams can carry extra loads.
Materials versus cutting lists
The merchant list shows new purchases with specifications and quantities. Coverage products are rounded per level, then matching owned stock is deducted. Linear timber and sheet blanks are allocated to selected stock with kerf, trim and whole-stock spares. Different material IDs/specifications are kept separate.
Sheet pieces are gross rectangular blanks: doors, windows, stair voids and supported joints require site/design trimming. No sheet rotation or minimum-stock guarantee is assumed. Structural floor/partition examples remain provisional; roofing member cuts must be supplied explicitly. A quotation pack can be printed while items are unresolved, and those items remain attached.
Roof and wall assumptions
The first version supports one aligned rectangular footprint, up to four levels, and selected new wall sides. Masonry options include brick/block cavity walls or rendered block/block cavity walls; a supplied wall-package route covers other systems. Mortar and insulation depend on the selected products and their declared coverages, not on a universal bag or board assumption.
A flat roof uses one rectangular deck and membrane order size. The single-plane mono-pitch option uses footprint area divided by cosine of the supplied pitch. Gable/hip roofs need separate supplied roof-plane schedules or the complete-package route. Both masonry leaves use external-face areas as conservative estimates; the supplier should adjust for bond, corners and differing leaf lengths. Gables, hips, valleys, dormers, abutments, supporting timber and roof accessories are separately specified. Check the chosen manufacturer's minimum pitch, gauge, laps and fixing system; see Marley's roof-pitch guidance.
Use the Planning Portal extension guides as an England starting point and check the requirements for your location. This planner does not grant permission, establish compliance or replace supplied structural/assembly specifications.
Worked example
A 6 m × 4 m footprint gives 24 m² gross floor area per level. With three new walls totalling 14 m and a 2.4 m clear height, the new-wall area is 33.6 m² per level before openings. Two levels give 48 m² floor area and 67.2 m² new walls before openings, while the roof remains one roof. With a 150 mm overhang each side, its rectangle is 6.3 m × 4.3 m = 27.09 m². Adding a 200 mm membrane edge allowance gives 6.7 m × 4.7 m = 31.49 m².
Frequently asked questions
Can I plan both single-storey and two-storey extensions?
Yes. Use one level for a single-storey extension, then add up to four supplied levels. Each level can use its own height, openings and floor route. All levels share one aligned rectangular footprint.
Can I add floors above an existing extension?
Yes, as an estimating route with explicit structural/foundation assessment and strengthening scope. It does not assume the existing building is suitable. Select a supplied suspended floor or floor package, not a ground slab.
Can I take the results to a builders' merchant?
Print the unpriced merchant list for quotations. Resolve missing product specifications with your designer/suppliers. The pack identifies work packages and accessories still to specify rather than silently treating them as included.
Does it include cutting diagrams?
Yes, for supported rectangular timber cuts and sheet blanks. Enter exact supplied structural/roof cuts where automatic dimensions are not appropriate. Stock diagrams include component labels, kerf, trim, owned stock and remaining offcuts.
Can I import a larger schedule?
Bulk Entry is available for levels, openings, partitions, foundation runs, components, materials and costs. Use the labelled CSV template, preview and validate, then replace or append. Edited project details invalidate an older preview.
Are prices and services required?
No. Blank prices remain unpriced; zero means an explicit zero cost. Services, toilet and kitchen packages are optional. Closing a section does not exclude it; use the inclusion or covered-elsewhere control.
How do I save my project?
Save named scenarios in this browser, and download a versioned JSON backup for another device. Saving is explicit, not automatic. Clearing browser storage can remove local saves. The planner and these outputs are free.
What is outside the automatic calculation?
Structural sizing, foundation suitability, planning approval, service routes, stepped/irregular geometry, complete manufacturer-specific fixings and unprovided roof/stair/junction details. Add supplied components or work packages and keep unresolved items visible.
Related tools
Prepare a clearer home addition quote scope
Read the home addition budget checklist for a checked gross-versus-internal floor example, existing-house work packages and questions to send with each quotation request.