Building Costs ‘Per Metre Squared’ do not exist

This article deals with the COST of materials which are used to build and complete your extension. The price of materials has increased exponentially in the last two years and a lot of that is because of the demand on materials due to economic factors. There are some materials which are required to complete your extension which your builder should always use (for building regulations) but there are also materials which are not required but add to the aesthetic and, often, the efficiency of your house.

In our line of work, we hear a lot of customers telling us that they are shocked by the quotes they receive for building work. Often, you will have ball-park figures by reviewing costs online (these are completely outdated) or your architect may guide you with a ‘cost per metre squared’. In reality, no two extensions can be compared on cost because so many factors are variable.

There is no simple way of providing an accurate cost for your extension without full architectural and structural engineering plans. The specifications which are on your plans may have a dramatic effect on the overall cost. The higher the specifications, the more expensive materials which will be required to complete your project. For example, if you install a higher spec insulation and expensive AAA rated bespoke windows, these will cost more. However, over time, it will be worth it to increase your home’s efficiency.

For example, I can compare 2 single rear extensions which we have completed. Both were an area of 28m2. One extension cost £73,000 and the other one cost £48,000. The price per metre squared had no relevance on these extensions but rather the quality of and the extent of the materials used. The picture below is an illustration of how the cost of two extensions which are the same size can not be compared because they vary so much.

Some key MATERIALS which affect the PRICE of your extension are;

1. Steel – this is a required cost if you want to remove walls and create a gorgeous open space in your extension…and to ensure your house doesn’t fall down. Steel should be fire proof and fit only by trained builders. The requirements for your steel are calculated by your Structural Engineer. Steel has increased by 30% since the Russian/Ukrainian war began.
2. Glass – AA/AAA rated glass is expensive. You can reduce costs by going with a standard colour frame or reducing the amount of glass in your extension (AA rated is the requirement for building regs). If your windows or doors are going to be bespoke, then you have to factor this cost into your overall budget. There are often delays with these types of specialist materials too.
3. Underfloor heating or specialist flooring – discuss your requirements with your builder. This is often an item customers are willing to lose as you can achieve quality flooring without spending a fortune. Wet underfloor heating is expensive to buy and install. Will you even use the underfloor heating now with the cost of living crisis? Preparation for specialist flooring may take longer and may even require you to remove your existing house floor.
4. Quality of finishes – We only use high quality timber for internal finishes, insulation, bricks etc. For example, if cheap softwood Pine is used for skirting and architraves, the finish will not be as good as MDF (lots of knots remain and the decorator won’t be able to cover them). Cheap bricks which are not matched to your current property look terrible and this can devalue the price of your house. As these materials affect the entire aesthetic of your finished project, this isn’t something you should look to do cheaply….although we do see this a lot in cheaper builds.
5. Specialist insulation or render – If you’re working to make your property more efficient, these are great materials but they can add a lot of cost to your project. The requirement for insulation now has to be 25% more than it was in June 2022 within the walls, floors and roof space so this will automatically increase the cost of the materials on your build.
6. Specialist stone to match existing property – If you live in a stone house, then the cost and availability of the stone is something you and your builder will discuss. Stone work takes longer to build and this will add extra time and cost to your project. Incorrect or badly matched stone looks terrible so you need to ensure that you choose a builder who is an expert with stone work.
7. Roof tiles – slate or bespoke coloured tiles will be more expensive so this is something you need to consider when determining the cost of your extension.
8. Groundworks – the price of concrete and cement has increased because of the cost of fuel crisis and in general, this is about 15% more expensive now. The price of groundworks will largely depend on the size of your extension and the type of ground which is being built on (does it need piling?).

The following non-exhaustive list of materials are also worth mentioning as the more complex your project, the more the cost of these materials will be; Scaffolding, PPE, Waste Removal, Specialist Heating, Solar Panelling, Roofing etc….this list could go on.

As you can see from the above, the cost of your extension will mostly depend on your design.

In general, anything which you make bespoke to you will cost more to build and install. You can reduce the cost of your extension by making some key changes at the planning stage….and don’t try to calculate this based on the meterage of your extension!

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