'I remember being asked where we wanted the light switches in a room that didn't exist and it sent me mad' — 21 things homeowners wish they knew before extending their home

With any home improvement project, hindsight is a wonderful thing. But if you're planning on building an extension for the first time, you might feel like you don't have much experience to go off. To help, I've spoken to dozens of homeowners who have extended their property and asked them what they wish they knew before they took on a building project like this. And really is there anything better for a first time extender than hearing from the people who have been there, done it and got the extra space to show for it.

While the homeowners shared their sometimes negative experiences with me, the good news is that almost all of the people I spoke with (96%) said that, even if there were bumps along the way, their extension ideas transformed how they live in their home, while seven out of ten also said that they thought the additional space added significant value to their home.

If you want to feel more prepared to take on your own project of this nature, make sure you read what these homeowners had to say about what they wish they'd known before extending.

It can be hard to keep on top of costs

As with any significant home project, costs can be a huge make or break factor, and many of the homeowners I spoke to cited various cost measures as things they wish they'd known before they started their project.

1. 'I wish I'd known that you start the project saving money on your spreadsheet (.e.g buying radiators or appliances in the sales at less than budgeted) but then at some point the costs only get worse.' - Jon Restall, who added a single storey extension to his end of terrace property.
2. 'I wish I'd known that it always takes longer and to have even more savings aside for additional things that always crop up!' - Katy McPhedran, who also extended her terraced home.
3. 'VAT often doesn't get mentioned in quotes (not even '+VAT') so it's easy to forget that it's additional and get hit with unexpected cost.' - Jenni Burton on her single storey kitchen extension.

While cost control can be a challenge, making sure you get at least three quotes is key to ensure you pay a fair price. But having a clear understanding of what those quotes actually cover before you commit is key.

Those unexpected costs can be made worse when the project takes longer than planned. In fact, almost three out of 10 people I spoke to (29%) said the worst part of their extension project was the fact it took longer than expected, which can often mean going over budget - especially if you choose not to live on site, and are paying for accommodation elsewhere.

Working with tradespeople can be a challenge

Whether it's choosing the right tradespeople in the first place, or understanding how to get the best out of your working relationship, many of the homeowners I spoke to wish they'd understood more about this aspect of their extension project before they started.

4. 'I wish I got word of mouth recommendations from friends and family on tradespeople rather than relying on Rated People etc. To have not tried to cut costs on tradespeople. To have allotted more for going over budget. To have watertight contracts with tradespeople.' - Kate Ruocco on adding a kitchen extension to her 1960s property.
5. 'Buy your own materials, get a contract from builder and get an agreed end date.' - Claire Blake on her kitchen extension project.
6. 'I wish we knew that the builder we hired was not trustworthy. The mistake was that we just found a local builder; trusted him at face value, and it's embarrassingly simple but we didn't look into his reviews or testimonials. That would be what I would advise anyone who is looking to take on a project like this to do in the first instance.' - Emily Diamond, who added a single storey extension to her three-bed cottage.

7. 'I wish I knew that even if you have a recommendation for a builder and do all your due diligence, they can subcontract the work out to another builder and you have no power to stop it in reality.' - Homeowner Tanya Ely, who added an extra bedroom to her semi-detached home with a two-storey extension
8. 'Wish I knew the plumber was going through a divorce! (Not turning up when arranged!)' - Sian Llewellyn, who added to double-storey extension to her detached home.
9. 'I wish I knew that some building teams have limited time with a plumber or electrician so there are areas of a project which can run slower than expected if they are on other jobs.' - Jon Restall on his home extension project.

Design considerations

While project logistics are paramount considerations for people wanting to add more space to their home, getting the design right is just as important. Here, the homeowners I spoke to share what they wish they'd known from a design perspective, what they wish they'd done differently - hopefully it can help you avoid any design pitfalls in your own extension project.

10. 'How much complexity there is in getting everything right. There are so many different things to consider, that you don't even think about until you have done something like this. Required room sizes, wiring/socket locations...etc' - Nick Fisk on his two storey extension project.
11. 'I wish we'd known how many different components (from big stuff to small parts, finishes etc) we'd have to research and source, sometimes at short notice, depending on when certain tradespeople were available (e.g for electrics, tiling etc). We had a project manager from the company we did our extension with, who did help in this regard, but because we wanted to very much control the look/design/finish ourselves, there was more to think about than my partner or I had appreciated.' - Polly Glass on extending her end of terrace flat.

12. 'The amount of big and small decisions we would have to make about rooms we'd never been in. I remember being asked where we wanted the light switches and lights in a room that didn't exist and it sent me mad.' - Rob Ellis on building a two storey addition to his end-of-terrace home.
13. 'I would have spent more time on the overall floorplan but particularly in terms of the new structure of the roof. I thought I'd got everything spot on but in hindsight I should have pushed for more dormer windows and fewer sloping ceilings. That would have given us more head room in some of the spaces, such as the en suite, for more fittings, such as a shower rather than just a bath. It would also have swerved that slightly awkward corner you get here and there in a loft space. I'll know for next time!' - Lucy Searle on extending her Edwardian home.

14. 'I wish I'd planned future improvements better. I converted the loft and had to leave the water tank to feed my gravity fed shower and immersion heater. I then upgraded to central heating with a combi boiler which meant I no longer needed the tank and had it removed. I have a handy storage space as a result, but it takes footprint and changed the layout I could have had if I had planned ahead. The want for extra space probably should have come after the heating upgrade.' - Lindsey Davis on extending her mid-terraced home.
15. 'Locating the site of the sewage connection before starting the build would have been good. Also, wish I'd known how hard it would be to heat the new space in winter with all its lovely windows, and how hot it is in the summer.' - Dan Green on extending his 1920s terrace.
16. 'To put in as many electrical points as you can in as many walls as you can.... Don't skimp on flooring. Don't box in appliances that you might need to replace or move later.' - Jon Restall on extending his home.

Project management

Just over half (54%) of the people I spoke to acted as their own project manager, which can be a great way to save some money on the overall cost of your project. But to avoid this saving being a false economy, you need to make sure you have the skillset a project manager needs.

17. 'If you are going to do the project management yourself, you need to be good at negotiating, confident enough to make important decisions quickly, and flexible in what your expectations are.' - Christopher Flanagan on acting as project manager when extending his home - a former Wesleyan Methodist chapel.

Realities of living on site

A third of people we spoke to also cited living on site during the project was the most stressful part, with many underestimating just how challenging this would be especially when dealing with the amount of dust that building projects can generate.

18. 'Living in a building site will impact your day-to-day life more than you expect.' - Christopher Flanagan on extending his home.
19. 'We had really amazing builders and encountered no major problems but we were not prepared for the amount of mess they made, especially when they started new areas of the project without warning so we hadn't had chance to move things around.' - Jenni Burton on her extension project
20. 'It's probably fair to say I also underestimated how full-on it would be living in the flat during the works - our builders were very good (nice guys, very efficient, cleaned up pretty well) but I don't know if you can imagine that level of dust and rubble until you actually have it in your home!' - Polly Glass on extending her flat
21. 'I also wish we'd appreciated that, while the bulk of the actual build was done quicker than we'd anticipated, delays in delivery of certain things (door/windows/glass in our case) meant that we couldn't actually finish and move into our new bedroom until quite a bit later.' - Polly Glass

If you are thinking of managing your own extension project, make sure you do your research to make sure it's within your skillset, otherwise it may prove a false economy.