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How Much does a House Extension Cost You?

No, we are not going to focus, here, on actual monetary costs but cover important considerations for you to keep in mind about various house extension scenarios. 


At Thomson’s Cleaning & Property Maintenance Company we know there’s no way that you can get a uniform answer on how much your house extension will cost, as each project is highly individual. 

That’s right. 

The numerous factors involved in extending your home, be it upwards, expanding on the same property level or going underground, can only give you a rough estimate.

Also, as you can probably guess, finding out the extension cost per sq. metre by a professional handyman is like going on a wild goose chase…

You can expect to get a vague guesstimate rather than a reliable price quote, considering the vast choice of materials you can use, the size and construction complexity of your future additional space, the manpower needed for the project completion and so on. 

And finally, let’s not forget the local market prices per hour or day, as we estimate some projects at hourly rates, excluding the materials. The cost will vary from one location to another.

So, you could be charged for labour within the range of £40 to £80 per hour, depending on where you live and the complexity of the house extension you want to build.

Why Extend But not Move to a Larger Property

But first things first. 

Why consider a house extension in the first place and not embark on the road of house hunting for a larger house? Well, here are just a few of the reasons that might prompt you to stay put.

You Like It Where You Are

The sentiment for your home comes first to mind, of course. 

You love the area and get on with your neighbours. Your kids won’t need to move schools and wave goodbye to their friends. You don’t fancy changing jobs or commuting for over an hour to work if you were to move.

You’ll Skip on the Moving-homes Hassle

Well, turning your home into a building site for months might be a dreaded prospect but think about the headache of relocating to a different place. And we are not talking about just the logistics of decluttering, packing, hiring a removals company, transferring utilities, taking time-off work, unpacking and so on. 

Consider the psychological strains associated with one of the most stressful events one could have in life.

It Could Work Out Cheaper to Extend

It’s not always the case, but more often than not, it’s more costly to purchase a new house than extending your existing one. You’re going for a much bigger property, after all, and inevitably this will come at a cost. Not to mention, all the fees and expenses related to purchasing, re-mortgaging and moving that you need to size up, including estate agency fees, stamp duty and moving company costs.

You’ll remodel your house the way you want to

Surely, moving to a new house comes at a compromise. You may be getting that extra baby room, but your kitchen is on the small side. Or the dark, north-facing living room is just way too uninviting.

In contrast, a house extension can be done exactly to your pre-planned design, with the materials and features you want and to your precise specifications.

Avoid the Stress of Negotiating Relocation Specifics with Family Members

And here come the endless arguments about moving. Should we move? Where to move? I don’t want to move…

Instead of turning your house into a warzone, especially if it comprises over one generation, you can enhance your multigene family’s lifestyle and living space through a cleverly designed house extension.

What House Extension Aspects Influence the Cost

Below, we’ll look into the various elements of a house redesign project that will impact the final cost.

Read on about each in more detail – from the initial architectural design plan that corresponds to your existing property, the actual building work and its possible revisions midway to the interior finish and the materials you choose to complete it with. 

Not all may apply to your particular situation, but these factors will give you a general picture of what to expect.

Construction-related Factors

  • Preliminary planning costs: planning permission, building regulations approval, surveys, architectural design fees, interior design fees, etc.
  • The soil type and the state of the house foundations – the age of your house relates to the condition of its foundations; the type of terrain (on a slope, level), as well as the soil type,  will affect any digging work and new utility installations;
  • The complexity of the design and the size of the project, including: reinforcing structures and roofing (two-story extensions); the size and shape of the extra room(s); whether you’ll be adding a new space or converting an existing one; utility fitting or repositioning (plumbing, heating, gas, electricity, storm drains, sewers); the scope for design or structural revisions, if needs be, etc.;
  • The level of access to your property during building work – naturally, difficult access to your house will affect everyday building operations and your wallet;
  • The type of materials you select for the exterior and interior finishes: Products you choose are interrelated to the final house extension expense from building and insulation materials, roof tiles and exterior paint to the interior fittings and finishing materials (tiling, flooring, painting),;
  • The need to temporarily relocate during the construction period – this will add to the financial cost of your project if you need to rent a place short-term.
  • The need to handle the cleaning chores after builders are done. Waste divides into recycle and non-recyclable, where the latter needs specialised handling.

Different house extensions will vary in their cost, especially if one involves redesigning an already built room, and another requires building a new structure from scratch.

Types of Extensions  


  • Barn conversion – expect large-scale remodelling and building work to take place – from re-roofing, floor installation, window and doors fitting, insulation, connecting to utilities, etc.
  • Loft conversion – the costly building work will revolve around reinforcing the floor, insulating the roof and the floor, extending your existing utilities, as well as all the interior work required to make the place livable;
  • Cellar/basement conversion – as with the loft conversion, insulation, securing existing structures, repositioning/installing plumbing, heating and electrical wiring are the priority works that will cost the most;
  • Garage conversion – it is the least expensive one, due to the relatively small size and the level of complexity of the project.

New extensions

  • Two-story extension – this is usually the most expensive type of house extension, as it involves building another storey with four walls and a roof, and possibly some demolishing work;
  • Ground-level extension – depending on the size of the new space, added to your existing property (a small conservatory or a whole new granny flat), the cost will, of course, differ;
  • Underground extension – excavation work is costly without a doubt, as it requires careful consideration of the building above its foundations and any underground utility lines.

To get a better picture of some renovation and building work prices around the world, look at the Archicentre Australia brief cost guide for inspiration, and if you’re considering ways to fund your new home improvement project, check out the helpful guide from Mortgageable

House Extension Tricks to Save on the Final Cost

Well, we will not advise you on doing the extension yourself with the cheapest materials from dubious suppliers. But you can save some money if you do your homework during the design and decision-making stage. 

On that note, it’s always worth it in the long run to go for a custom house extension, conversion, or interior redesign rather than copying what your neighbours have done with their place. 

Below you have tips to help you decide if a full-on house extension is the right thing to do, based on your family’s needs:

  • Utilise the partition-wall concept
  • Create an open-plan living space
  • Go with a simple design
  • Convert your existing space
  • Don’t overspend on fittings and furnishings
  • Embrace the alfresco lifestyle

Utilise the Partition-wall Concept

So, you want to have a dream baby nursery for the new addition to your family? 

Well, you could easily split the large guestroom which is rarely used, in two, instead of adding a new room to the property.

Create an Open-plan Living Space

Your living room is on the small side? 

Then knock a wall down and get rid of your cluttered storage room. You’ve got an attic for all your junk, remember?

Go for a Simple Design

If you must build an additional room, it’s always cheaper to keep it simple. According to home renovation experts HomeRenoGuru, any fancy design of irregular shape will spiral the cost.

Convert your Existing Space

A new home office can be easily created in your garage, as your car is most of the time parked in your drive, anyway.

Don’t Overspend on Fittings and Furnishings

Expanding your kitchen outwards to fit your extended family and guests is a costly enough venture. So, save some cash by going for a modern kitchen flat-pack design from a reputable brand.

It can be fitted in a day or two, so you’ll save on labour costs, too.

Embrace the Al Fresco Lifestyle

And finally, with our gorgeous climate, why not extend your living space outside without enduring any major building work? 

Simply, reevaluate carefully your needs for extra space. And if a new decking, which connects your outdoors with the interior through bi-fold doors, will do the job, then, act smart and go for it. It won’t break the bank, either.

Bethany Thomson
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Author: Bethany Thomson

I'm a wife, a mother and a housewife. I've learned a lot of tricks that help me deal with the household in the fastest way. And I'm going to share them with you.

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