Checklists · Additions
Additions & Conversions Planning Checklists
Extending or converting means adding to something that already exists, so the existing property matters as much as the new part. These checklists help you describe what is already there, work out what the new space has to do, and think about how the two meet.
Nothing here states what may be built, whether permission is needed, or whether an existing structure can carry a change. Those are matters for qualified professionals and the relevant authority, and they vary by property and location.
30 checklists in this category
What this area covers
Planning topics in this category
Each checklist prepares one specific conversation or decision point. None of them determines compliance, suitability or cost.
- What the new space has to do day to day
- Existing-condition information to gather
- How the addition meets the existing property
- Consent and structural topics to raise as questions
Checklists in this category
Browse by project stage
Each checklist sits at the earliest point in a project where it becomes useful. Every checklist in this category appears in exactly one stage below.
Thinking it through
Before anything is committed — working out whether the idea suits you at all.
Home Extension Planning →A preparation checklist for owners weighing up an extension: describing the existing house, defining what the new space must do, and framing the questions professionals will need answered.Rear Extension Planning →Everything the back of a house carries, before anything is proposed for it: the elevation, its fittings, how the garden is really used, and what to confirm locally.Garage Conversion Planning →What a garage really does today, before it becomes a room: the door opening, the floor and head height questions, and where the car and the storage would go.Attic Conversion Planning →Head height, roof structure and the staircase that eats a room below: how to record a loft accurately, and which tank, chimney and escape questions to raise.Loft Room Daylight →Getting ready for the daylight conversation about a loft: recording the roof you already have, working out where light is needed inside, and what to ask.Basement Project Discussion →Owner-side prompts for anyone weighing new space below ground: what to record about the house, the ground, the neighbouring properties and the access route.Cellar Conversion Questions →What to observe and write down before converting an existing cellar: damp signs, headroom, the stair, air movement and what the walls are already doing.Outbuilding Conversion →For owners weighing conversion of a garage, store or workshop: recording the existing fabric, the floor, the openings and the gap back to the main house.Garden Room Planning →Where a detached garden room could stand, what lies under the ground at that spot, and how supplies and people would reach it, recorded before you speak to anyone.Annexe Planning Questions →Working out who an annexe is for, how independent it has to be, what would be shared with the main house, and what becomes of it when the need changes.Porch and Entrance Addition →How an entrance fails in daily use, what genuinely has to fit inside a new porch, and what already sits on the front wall, gathered before any design conversation.Conservatory Comparison →Setting out one list of requirements, then weighing a conservatory, a solid roofed room and a full extension against it on the same footprint and orientation.Headroom and Volume →Establish how much usable height a loft, cellar or garage conversion really has, where every slice of it would go, and which height answers belong with professionals.Daylight Impact Questions →A daylight impact checklist for owners planning an addition: what to record about the rooms it would stand in front of, and which questions belong with a designer.Addition Drainage Questions →Preparing for a drainage conversation about an addition: what to look at outside, which covers matter, and who can actually answer the questions raised.Conversion Floor Structure →For owners converting a garage, loft, cellar or outbuilding: what to notice about the floor underfoot and which floor questions belong with a qualified professional.
Early planning
Gathering what you already know and shaping the project before drawings begin.
Single-Storey Extension →Questions to prepare before a ground-floor addition is designed: roof form, floor levels, daylight to the rooms left behind, and what sits under the footprint.Two-Storey Extension →A second storey asks about the landing before it asks about the footprint: how the new rooms are reached, what happens to the roofline, and what belongs with professionals.Side Return Extension →The narrow strip beside a house, examined properly: what it holds, whose boundary runs along it, where the old roof drains, and what filling it does to daylight.Wrap-Around Extension →Two arms and a shared corner: setting out both directions at once, sequencing the work, more than one affected neighbour, and what the rooms in the middle are left with.Connection to Existing House →Prepare the junction itself: where a new space would break into the old, what happens along the seam, and which parts of that connection belong with a professional.Extension Roof Form →Get ready to talk about an extension roof: where it stops against the house, what it leaves overhead inside, and how it looks from the windows above it.Conversion Insulation →A space that was never meant to be lived in raises its own insulation questions: where the warm envelope moves to, what it collides with, and who answers them.Conversion Heating and Services →Line up the services conversation for a conversion: what already lives in the space, what has to reach it, and which supply questions belong with qualified people.Conversion Stair and Access →Think through how a converted space would actually be reached: what the new access takes from the existing house, where it lands, and what must go to professionals.Boundary and Overlooking →Set out the boundary and privacy side of an extension or outbuilding: where the line appears to run, who would see what, and what only other people can settle.Addition Foundation Discussion →How to prepare for the first conversation about the foundations of an addition: what to observe, what to mark out, and what to leave openly unknown.Addition Scope and Phasing →Decisions to weigh and write down when an addition may be split into stages: what has to be in, what can wait, and what only makes sense while everything is open.Conversion Future Flexibility →For owners converting a space: how to plan so the room can change use again later, what stays reversible, and what would be permanently given up.
Brief & professionals
Writing the brief and preparing the conversations with qualified professionals.
Go deeper
Related Build Design Hub guides
Explanatory guidance behind the decisions these checklists prepare you for.
Additions & conversions →Explanatory guides on extensions, conversions and added space.Home design planning →How design conversations for added space are usually structured.House renovation →Whole-home planning topics that an addition sits inside.All checklist categories →Back to the full Project Planning Checklists library.