Things to Consider Before Starting a Major Home Extension -

Thinking about extending your home?

Having a major extension carried out on your home can be one of the best decisions you ever make. If done correctly, you can create extra space, value and a completely new atmosphere. If done incorrectly… it could empty your savings account and stress you out for months.

The good news?

Many of these common mistakes are completely preventable. You simply have to know what to look for before the builder arrives on your driveway.

Here is what every homeowner should consider…

Things you’ll discover:

Why Home Extensions Are More Popular Than Ever
Budget & Cost Considerations
Planning Permission & Legal Stuff
Structural Roof Alterations Explained
Choosing The Right Builder

Why Home Extensions Are More Popular Than Ever

Moving house is expensive. Like, really expensive.

Which is why more and more homeowners are opting to extend. Why pay stamp duty, estate agent fees and removal costs when you could be spending that money increasing the value of your existing home?

Recent government planning statistics from the UK government show there were 157,700 householder planning decisions in the year ending March 2025. These are permissions for extensions, loft conversions, conservatories etc. So that’s a lot of people deciding to expand their existing homes.

And the payoff?

Add value like a boss with your extension build. Research across the country shows that you can gain up to 20% property value from a single-storey extension. Nice right?

Before you start pinning away and daydreaming about extravagant floorplans… There are a few important things to consider.

Budget & Cost Considerations

This is the page nobody wants to read. Except it’s the part that will help you the most.

Extension projects have a habit of blowing their budgets. Materials increase in price. Unexpected issues arise. Scope creep occurs. Your little “easy” rear extension ends up costing six figures.

Here’s how to avoid the budget nightmare:

Obtain a minimum of 3 estimates: Don’t settle for the first builder who throws you a number. Get quotes from several reputable contractors.
Have a contingency fund: No matter what, budget 10-20% of your overall budget for emergencies. You’ll thank yourself later.
Take into account EVERYTHING: Architect fees, structural engineer fees, planning, build regs, finishes, decoration, kitchen/bathroom fittings etc. etc.
Look at the big picture: Cheap stuff breaks and costs you more down the road. Invest in the important things.

One good illustration of how budgets can become complicated is the cost of a loft conversion with a roof lift. Roof lifts are more complex than regular loft conversions because they require the entire structure of your roof to be lifted in order to create the extra headroom. When done correctly, they can turn your unusable loft into a gorgeous new living area – you just need to plan your budget carefully from the outset.

Pro Tip: Always request a fixed price quote when possible. This ensures you are not paying more than the agreed amount in the middle of the project.

Planning Permission & Legal Stuff

This is where lots of homeowners trip up…

Extensions do not always have to be built with full planning permission. There are “Permitted Development Rights” which allow you to simply get on with it. Others (particularly larger or more complicated ones) will need permission.

Here’s what you need to check:

Are you in a conservation area or a listed building? If yes then you rules are stricter.
Does your project exceed permitted development limits?
Are you planning a two-storey or wraparound extension? These almost always need permission.
Are there Article 4 restrictions on your street?

The good news is that your chances of getting permission are pretty good. Government stats reveal that 89% of householder applications were approved in the year to June 2025. So if you plan carefully and design within the guidelines, permission is likely.

Speaking of Building Regulations don’t forget about them as well. Don’t assume that because you don’t require Planning Permission you don’t have to comply with building regs. For example:

Insulation standards
Fire safety
Structural integrity
Drainage and ventilation

Things you don’t want when selling your home. Selling your house with unapproved work.

Structural Roof Alterations Explained

Now this is where things get really interesting…

Major structural alterations to your roof are right up there as one of the most significant changes you can make to your house. We mean changing the structure of your roof here, not just adding a few more tiles, or fitting a Velux window.

There are several types of structural roof alterations to consider:

Roof Lifts

Roof Lifts are where your whole roof is lifted up to create additional head height or living space. Roof Lifts can be done where you want to convert your loft but don’t have enough roof height. Roof lifts are major construction jobs but they can transform your house.

Hip-to-Gable Conversions

A hip-to-gable conversion is where you change a sloped (hip) roof into a vertical (gable) wall. Hip-to-gable conversions offer increased usable space within the loft and are particularly popular for semi-detached and end of terrace properties.

Mansard Roof Extensions

A mansard extension is where the roof is rebuilt at a steeper pitch (typically 70 degrees). Mansard roofs are very common in London and other cities where larger extensions may not be feasible.

Dormer Extensions

Dormer extensions involve the addition of box structures that project from the roof. Dormers are one of the most popular structural roof extensions as they create lots of space.

Why Should You Care? Well designed structural alterations to your roof can increase your property value by up to 20%, which is massive if you live in a built up area and don’t have much outdoor space.

The most important thing when undertaking any structural change to a roof is to use the correct professionals. You will need a structural engineer, an architect and a builder who has experience with this type of project. Don’t skimp.

Choosing The Right Builder

This is probably the single most important decision you’ll make in the whole process.

Poor construction can destroy your project. Excellent construction can ensure your project flows effortlessly from start to finish. But how do you find that builder?

Here’s the checklist:

View their portfolio: Have they done work like this in the past? Request photos of previous jobs.
Read reviews: Look at Google, Trustpilot, and Checkatrade reviews. Look for consistent feedback.
Talk to past clients: A confident builder won’t mind giving you referrals of past clients.
Check qualifications: Are they members of the Federation of Master Builders or equivalent trade associations?
Get a written contract: Covering payment schedule, timetable, materials, and remedies for problems.

Don’t rush through this step. Take your time finding someone you trust. You’ll be working with them closely for months.

Oh yeah, one last thing. Don’t pay a deposit that covers the full price. A good contractor will gladly accept progress payments based on project milestones.

Final Thoughts

One of the largest undertakings you will ever do on your home is a major home extension. Exciting. Scary. Overwhelming. All at once.

To wrap things up, here’s a quick recap of the key things to consider:

Budget properly — and always include a contingency
Sort the legals — planning permission and building regs
Understand structural roof alterations — especially if you’re going up
Pick the right builder — this makes or breaks the project
Plan for the long-term — quality work pays for itself

Get them right and your extension will give you space, value and happiness for years to come. Get them wrong and… eek!

Research, research, research. And ask questions along the way.