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John & Amanda Tarrant

John & Amanda Tarrant's finished extension project

John and Amanda self-managed an extension to their existing house in Surrey and used the NSBRC to find solutions to the construction challenges they faced.

What is the floor area of your project in sq ft or sq m?

26 sq m.

Could you tell us any interesting facts or remarkable features about your project?

What makes it of interest is the method we had to employ to build over the existing 600mm storm drain that was 3m underground and went directly through the middle of where we wanted to build. We had to build in such a way that no load was placed on the pipe and I was going to forget the whole project as it seemed too difficult, however, when I saw the helical pile system at the exhibition centre, I realised that the foundation could be done easily with minimal digging and spoil if I also used a steel ring beam and a lightweight SIPs construction.

Experience at the Centre

How many times have you visited The National Self Build and Renovation Centre before? Just once so far.

What would you say is the most helpful feature or resource at the NSBRC?

Being able to see products as they are intended for use in mock-up displays.

Did you use any exhibitors at the NSBRC? If so, who? Helical Systems.

What did you enjoy most about your visit to the NSBRC? Finding solutions to problems! The coffee was OK too.

Would you recommend the NSBRC to a friend, and if so, what aspects of the Centre would you recommend and why? Yes, I have recommended a visit to my best friend who is a traditional builder and has helped us with advice and guidance throughout our self-build projects. He has recently also used helical screw piles for a project after seeing them on my build and a walk around the stands together will be great for more ideas and information about other innovative products.

John & Amanda's Home Improvement Journey

What first inspired you to undertake project – what did you hope to achieve? The existing lounge was small and gloomy and not in keeping with the rest of the property.


What was the cost & size of the land? We already owned land at the side of our house.


How did you find the land? Do you have any tips for others currently searching for a plot? I went out the front door, turned left and bingo! There it was! (Sorry it’s lockdown and I’m just amusing myself).


Did you have any issues getting your planning permission granted or with building control? If so – why was this? It was massively difficult getting permission to build over the Thames Water infrastructure. In the end we had to agree to a Deed of Easement which basically allows Thames full access to their pipe under the building. Worst case would be they can knock down the extension to gain access if necessary! That said, they agreed that the condition of the pipe in the initial CCTV survey justified re sleeving it before we started which they did at their cost. I am confident that the method we used to build the extension means that you could dig out under the extension down to the pipe and the extension would be fine as the helicals are in ground a further 3m down! Not sure I want to test this theory though unless we have to.


Why did you choose your method of construction? Only cost-effective solution, and it was quick. Cost was comparable to a traditional deep trench foundation but there was no muck away costs, and no digging upheaval, no concrete at all which is good for the environment.


Did you use a project manager, or did you choose to self project manage? Self managed.


What was your budget and were you able to stick to it?

46K and yes, it came in under budget actually.


What is the value of the property now?

Approx. 900K.


What aspects of the process did you find stressful – and do you have any tips on how to avoid the pitfalls you encountered?

Sadly, the company that provided the SIP design and erection were very unreliable and shortly after completion they went into administration. They were clearly juggling sites and not keeping me informed. There were also mistakes made between them and their SIPs subcontractor (window positions) which I ended up accepting because I didn’t want more delays.


What did you find most enjoyable about working on your project? Satisfaction of doing most of it myself, with exception of screw piles and SIPs erection. The aim was to get as much value added to the house as possible with the budget we had. The budget came about by the maturing of an under performing endowment policy. We have essentially re invested the money back into the property to try and gain back the shortfall!


What is one of your favourite features about your project? Adding a super insulated air tight box to the end of the house has improved the comfort of the existing lounge. Knocking out the old external wall which was a traditional cavity wall with poorly double-glazed windows has got rid of this big heat loss wall.


Is there a possibility you would ever undertake another project in the future? Yes I think so, would like to do a whole house for retirement!


If so, is there anything you would do differently? Get proper references for any major suppliers / contractors.


What would your top tip be for other NSBRC Visitors about to embark on their first self build or home improvement journey?

Be open to new things! 

Our project was always about John building as much of it as he could as he loves building things. In contrast my idea of a fun Saturday is coffee in front of Netflix not power tools and sawdust! Unlike me my 82 year old dad is a keen amateur DIYer and he and John proved to be a great team, with Dad visiting frequently on Saturdays to help - he hadn’t any experience of building an extension either but had vast experience in most other aspects of DIY. He helped a lot during the main build but lockdown 3 happened part way through the addition of our new porch and he could no longer visit so I was drafted in! I soon found that a circular saw and a chop saw are actually easy to use and even with absolutely no experience I was able to measure and cut cladding and fix it to the baton, I even managed accurate angled cuts! We’ve been married for almost 29 years and John has always done all of the DIY but next time I’ll be much more confident about getting involved.  Have a go, try new things, you will surprise yourself! 

Be patient and be prepared to be flexible. 

We had always planned to have a log burner fireplace in our new lounge as I wanted a fire as a focal point. At the time of writing we don’t have a fireplace as we decided to divert funds to a porch instead - hopefully we can add our log burner in the future when funds allow. I bought candles and vases to accessorise my fireplace right back at the start of the process but they are still in boxes waiting - I’m sure that log burner will appear one day and then the vases and candles will be unboxed but I’m happy to wait until we can afford it. Plans and priorities can be changed, there’s no rush!