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Avoid Extra Costs In Your Extension

Why do so many extension projects go over budget? Avoid Extra Costs In Your Extension.

How can you avoid such issues?

So you get a competitive quote from a builder. How do you know the costs are not going to go up?

What are the key areas of uncertainty?

  1. In the ground
  2. Finishes (what kind of bathroom fittings/ flooring/ light switches)
  3. Changes
  4. Unknowns
  1. In the Ground

Ok, this one sends homeowners into an instant panic as it happens on almost day 1.

So the builder digs the foundation, usually about 1m deep. The Building Inspector comes along and says can we have it deeper please!

But the builder should know, the Architect should know? the Engineer should know?

Well unless you get a soil test, it’s unknown, but there are some things you can do.


a) Are there any trees in proximity? This can lead to deeper foundations, Willow trees are the worst

b) Is the ground highly shrinkable clay? Both trees and shrinking clad can make your foundation move in the summer.

c) So get the Builder to include for prices for 1m, 1.5m, and 2m in their quote. So if it’s needed, you know how much it will cost.

If your budget is for 2m foundations and it’s okay at 1m, then you start with a financial win!

Shared Sewers

Make sure you know if the manhole in proximity (3m) is yours or if your neighbour also uses it.

If it’s shared, you will need a build-over agreement with the water authority.


Get the Architect to do a drainage plan and get the Builder to check it will work by removing manhole covers and checking routes.

It’s typical that no one quite knows what’s in the ground until you get there. So your Architect is not Harry Potter!

2. Finishes

So if you start choosing very complicated floor finishes and such, this could surprise the builder, especially if it needs the coordination of thickness and other complications.


Give your builder a list of all items and finishes including floor coverings/ tiles/ bathroom fittings/ light switches and plug types.

This will stop delays and coordination and frustration issues.

3. Changes

So Builders really don’t like changes mid-job, delays and frustration, or unexpected knock-on effects of changes are usually a problem.

A simple change leads to a complication down the line.


a) If at all possible don’t change things.

b) get lots of options and talk with your Architect prior to going on site. So you have looked at the options. Architects that use 3D software can do a zoom and show you everything in 3D, so you are less likely to be surprised when it’s on site.

c) Ask your Builder before you start how to handle changes, but be upfront about it.

4. Unknowns

So sometimes you can not know everything in an existing building. Things happen or need fixing. An example is a chimney that is not properly supported when the breast was removed previously. It could be the previous owner.


a) Ask the Builder what to do if something unknown pops up. Have a plan before.

b) Ask the Builder/ Architect / Engineer what are the usual unknowns or typical things not accounted for. Then you can be aware and ready if something does pop up.


Have a good mindset and be ready for issues and then you can hopefully avoid or at least minimise the loss of time and also the stress these things can create. Make it a team scenario so everyone wants to help out rather than run or play the blame game. This will not get your extension built on time or budget and how you want it to look at the end.

Be nice, and you will get it in return.

Read this to avoid other issues Most Common Planning Issues


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Post Author: Gordon evans

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