10 things most people do not consider before converting a garage or extending their home (but really should)

A garage conversion or extension feels straightforward on paper. You picture the extra room, the new kitchen diner, the home office, the utility. Then the reality hits: delays, extra costs, last minute changes, and decisions you did not know you needed to make.

The good news is that most of the pain is avoidable. The best projects are won before the first brick is laid, by spotting the hidden issues early and setting the job up properly.

Here are 10 things homeowners often miss, and what to do instead to save time, money, and stress.

1. Planning permission is not the only paperwork that matters

Many people assume they either need planning permission or they do not, and that is the end of it. In reality, there are a few common traps:

• Previous planning conditions that say the garage must stay as parking
• Conservation areas or listed buildings where rules are tighter
• Converting a garage into a separate dwelling, which often changes what is required
• Neighbours and lenders wanting proof the work is lawful
  
  What to do instead
  If it looks like it falls under permitted development, consider getting written confirmation via a Lawful Development Certificate. It is a small upfront cost that can save a lot of hassle when you come to sell.

Planning Portal notes planning permission is not usually needed for an internal garage conversion, but there are clear exceptions.

2. Building Regulations can be the bigger challenge than planning

A garage is not built to the same standard as a habitable room. People budget for plasterboard and paint, then get caught out by what Building Regulations require.

Common cost and time surprises include:

• Insulation upgrades to walls, floor and roof
• Ventilation requirements, especially if you are adding a shower room
• Fire safety measures, including doors and protected routes
• Drainage changes and soil pipe routing
• Floor build up and damp proofing, especially where the garage floor sits lower than the house
  
  What to do instead
  Decide the room use early. A playroom needs different services to a utility room or annex. Then get the spec right from the start so you are not redoing work.

Planning Portal is clear that garage conversions will normally require Building Regulations approval.

3. The existing structure might not be doing what you think it is doing

This is where budgets often blow up. You assume a wall can come out, or a garage opening can be infilled easily, or the roof is fine.

But the hidden reality can include:

• Load bearing walls and the need for steelwork
• Under sized lintels
• Settlement cracks hiding bigger movement
• Roof structures that need strengthening
• Foundations that are not suitable for a new storey or heavier loads
  
  What to do instead
  Treat the early stage like an investigation. A good builder will ask awkward questions, take measurements, and flag risks before quoting properly. If structural changes are significant, a structural engineer input early can save weeks later.

4. Drainage and manholes can dictate the whole layout

A manhole cover in the wrong place can affect where you can extend, where you can place doors, and what foundations are possible. The same goes for shallow drains, shared sewers, and surface water routes.

Typical surprises:

• Needing to relocate a manhole
• Discovering drains right where your new foundation trench needs to go
• Soakaway requirements for new paving or roof areas
• Extra groundworks and reinstatement costs
  
  What to do instead
  Locate drains and inspection chambers early and design around them where possible. If building over drains is unavoidable, get the right approvals and allow time for it.

5. Services capacity often gets missed until the very end

You can create a beautiful new space and then discover the existing house systems are already at their limits.

Common examples:

• Consumer unit needing an upgrade when you add kitchen loads, underfloor heating, or an EV charger
• Water pressure not sufficient for an extra bathroom
• Boiler capacity not enough for added radiators
• Gas pipe runs needing upsizing
• Internet and cabling left as an afterthought, then chased into fresh plaster
  
  What to do instead
  Do a quick capacity check before you finalise the plan. It is far cheaper to plan upgrades than to scramble mid build.

6. Materials lead times can wreck your programme

The build can be ready for windows, doors, kitchen units, or a particular tile, but the items are not on site. That is how you end up paying for downtime and re visits.

High risk items include:

• Bifold or sliding doors
• Roof lanterns
• Bespoke glazing
• Kitchens and worktops
• Specialist finishes and bathroom fittings
  
  What to do instead
  Choose your critical items early, or be flexible on alternatives. A good project plan will tell you what decisions need to be made and by when.

7. You might be buying a problem: asbestos and legacy materials

Garages and older extensions can contain asbestos containing materials in roofing, soffits, panels, and old cement products. It is not something you want discovered halfway through demolition.

What to do instead
If the property is of an age where asbestos is plausible, plan for a survey where appropriate and do not ignore warning signs. Safe handling is non negotiable, and it is always cheaper to plan for it than to emergency stop a job.

HSE guidance highlights typical locations where asbestos can be found and stresses that work on asbestos can be dangerous.

8. The Party Wall question is not just for London terraces

If you are close to a neighbour’s boundary, sharing a wall, or excavating near their foundations, you may be inside Party Wall territory. Even when it is not legally required, early communication can save huge stress.

What to do instead
Talk to your neighbours early, show them what you are planning, and get advice if the work is likely to fall under the Act. The cost of doing it properly is usually far less than the cost of a dispute.

The Party Wall etc Act 1996 provides a framework for preventing or resolving disputes relating to party walls and excavations near neighbouring buildings.

9. Access and logistics are part of the build cost

Most homeowners think about the end result, not how the job physically happens day to day.

Hidden time and cost factors include:

• Where the skip goes and whether you need permits
• Scaffold access and protection to existing roofs
• Storage space for materials
• Keeping part of the house liveable if you are staying put
• Protecting driveways, floors, and garden areas
• Security, especially if doors and windows are changing
  
  What to do instead
  Agree logistics before day one. Clear access, a tidy site, and a sensible sequence reduce delays and keep the whole project calmer.

This is one of the big differences between a job that feels organised and a job that drags.

10. Finishes and “making good” usually cost more than people expect

This one catches almost everyone, because the quote looks like it covers everything until you look closely.

Often missed items:

• Decoration and final snagging
• Flooring supply and fitting
• Lighting design, not just a single pendant
• Wardrobes and storage
• External making good, rendering, paths, drainage details
• Landscaping and reinstatement after groundworks
  
  What to do instead
  Ask for a clear scope. What is included, what is excluded, and what allowances are assumed. If you want a true like for like quote comparison, you need everyone pricing the same finish level.

GMD Developments covers both construction and landscaping, which helps avoid the classic “build is finished but the outside is a mess” problem.

 
A quick checklist before you commit

If you do nothing else, run through these questions:

1. Do we have proof the work is lawful (planning, permitted development, or certificate)?
2. Have we confirmed Building Regulations requirements for insulation, ventilation, fire safety and drainage?
3. Do we know what is load bearing and whether steelwork is needed?
4. Have we located drains and manholes and planned around them?
5. Can our electrics, heating and water handle the new space?
6. Have we picked the long lead items early enough?
7. Is there any asbestos risk we should investigate?
8. Do we need Party Wall notices or at least a neighbour chat?
9. Is access, skip location, storage and protection agreed?
10. Is the scope clear on finishes and making good inside and out?
     
    Want a conversion or extension that runs smoothly?
    
    If you are planning a garage conversion or extension in Bristol, Torbay or across the South West, GMD Developments can help you pressure test the plan, flag risks early, and give you a clear route from first visit to finished space with tidy workmanship and straight communication.