Thinking about adding a flat roof extension to your home?
It’s one of the easiest ways to increase your living space and property value without moving. However, most people have no clue what they should be paying.
With a proper budget breakdown you can:
- Avoid getting ripped off by dodgy quotes
- Plan for hidden costs nobody warns you about
- Choose the right materials for your budget
Here is how to do it…
Here’s what’s coming up:
- Why Flat Roof Extensions Are Worth The Money
- Average Flat Roof Extension Costs Explained
- The Hidden Costs You Need To Budget For
- How To Save Money Without Cutting Corners
Why Flat Roof Extensions Are Worth The Money
Flat roof extensions have become massively popular across the UK.
Garden rooms tick all of these boxes. Garden rooms are much cheaper than pitched roof extensions, have a sleek and modern appeal and add value to your property.
Ok, now for some maths. The average flat roof extension cost can range from £25,000- £85,000+ on average. Depending on its size and specifications like roof material. That is quite a broad range we understand, which is why we have broken down the costs for you.
But the real question is… will you actually get your money back?
Nationwide Building Society research shows that an extension could increase your home value by up to 23%. Now that’s some investment value!
Here are the main reasons people go for flat roof extensions:
- Reduced cost per square metre — fewer materials used than a pitched roof
- Modern aesthetic — fits both contemporary and traditional homes
- Faster build time — you’ll be using your new space sooner
- More design flexibility — you can add rooflights and skylights easily
Pretty solid benefits, right?
Average Flat Roof Extension Costs Explained
Let’s break down the actual numbers you’ll be looking at.
Price is massively affected by how big you want your extension to be. A simple flat roofed extension of say 20m² is only going to set you back a fraction of the price of a 40m² extension. So here is a rough guide on what you can expect to pay:
- 20m² extension: £25,000 to £45,000
- 25m² extension: £30,000 to £55,500
- 30m² extension: £35,000 to £65,000
- 35m² extension: £40,000 to £75,000
- 40m² extension: £45,000 to £85,000
Prices include material and labour costs for a typical build. However size is not the only factor…
Location Matters (A Lot)
Your location within the UK will hugely impact the cost. If you’re located in London or the South East in general, you’re going to pay much more. Labour will be expensive and material deliveries may cost more also. If you’re located in the North or Scotland you will usually pay less for the same work.
Materials Make Or Break Your Budget
Your material choices will play a huge role in your final cost. The most popular materials for flat roofs are:
- EPDM rubber: Long lasting and cost effective
- GRP fibreglass: Durable but more expensive
- Felt roofing: The cheapest option but shorter lifespan
- TPO membrane: Modern, energy efficient option
If longevity is what you’re after then EPDM or GRP are generally your two best options. Initial cost is lower with felt but you’ll be forking out for repairs much earlier.
Labour Costs
Labour will typically account for 40-50% of your project cost. The Federation of Master Builders states you can expect to pay around £85 per hour for expert roofing labour. The larger your extension is, the more hours you’ll be paying for.
The Hidden Costs You Need To Budget For
This is usually what trips most homeowners… there are so many hidden expenses that aren’t always factored into the quote. If you aren’t prepared to spend extra, you can easily go thousands of pounds over budget.
Planning Permission & Building Regs
Depending on the size of your extension, you might need planning permission. Applications are around £206 for a household application in England. Approval from building regulations will set you back another £500 – £1,000 on top. Some smaller home extensions are classed as permitted development – but it’s best to check.
Architect & Design Fees
You will need suitable drawings before you can begin. Architect fees will cost you between £1,500 and £5000. Some builders will do this for you as part of their quote saving you money.
Skip Hire & Waste Removal
Construction work generates massive amounts of waste. Skip hire costs typically range from £200-£400/skip. You’ll probably need more than one skip.
Other Hidden Costs To Watch For
- Foundation costs: £100-£200 per square metre
- Electrical work: £1,500-£3,500
- Plumbing work: £1,000-£3,000 (if needed)
- Decoration: £1,000-£2,500
- VAT: Always check whether quotes include this
Budget 10-15% contingency, every time. Because pretty much every project needs it.
How To Save Money Without Cutting Corners
You don’t have to spend a fortune to get a good quality flat roof extension. Here are the top tips for keeping costs reasonable without skimping too much on quality:
Get Multiple Quotes
Ask for quotes from at least 3 builders. This is by far the easiest way to ensure you are receiving a fair price. Ensure each quote contains the same scope of work, otherwise you won’t know what you are comparing.
Pick The Right Materials
Inexpensive does not always mean cheap. You can spend a few pounds more now on a high quality membrane such as EPDM rubber and save thousands in maintenance and replacement costs over the next two decades. Think of your budget as 20 years, not 5.
Time Your Build Right
Occasionally building in the winter can net you discounts. Builders are busiest in the spring and summer seasons so if you schedule your build for autumn or early winter you could save yourself some money. Weather is a factor though.
Do Some Work Yourself
If you are a DIY person then you can cut costs by doing some of the work yourself. Painting, basic decorating and stripping out old features are all DIY tasks. Leave the structural changes and roof work to the experts.
Final Thoughts
Installing a flat roof extension is one of the best home improvements to invest in. Not only does it provide additional living space and extra value on your property, but you can customise the build to perfectly fit the needs of your family. The important thing is keeping realistic expectations when it comes to cost.
To quickly recap:
- Budget between £1,200 and £2,500 per square metre as a starting point
- Always include a 10-15% contingency for surprises
- Get multiple quotes from reputable builders
- Don’t cheap out on materials — you’ll pay for it later
- Factor in all the hidden costs like skip hire and permits
Take your time, plan wisely and don’t hurry things along. A flat roof extension is a major investment but will reward you for many years if done correctly.