House Extensions: 25 Things Your Builder Wishes You Knew

Home Extension

A house extension could be the finest answer for a space shortage in your home. To get the most out of your project, go into the process with some must-know knowledge.

A house extension can be a highly appealing alternative for folks who are short on space within their home but have plenty of outside space.

However, because extending your home is going to be a costly undertaking, it’s critical to get it properly the first time and make it work for you.

Whether you’re planning a single-story extension to expand your kitchen or a two-story extension to add much-needed office space, there are a few things to consider before starting your extension project to ensure you get the most out of both the design and construction stages.

From budgeting and hiring craftsmen to the legalities and logistics of a project, we’ve compiled a list of 25 of the most important factors to consider to avoid renovation hassles later on. Your builder will be grateful!

1. Ensure that your house extensions increase the value of your home

To make house extensions financially viable, you must ensure that the value added exceeds the project cost. It can be tough to judge, but looking for similar properties in the area and seeing how much they sold for can help.

Be aware of your area’s ceiling value and be ready to change your plans if necessary.

2. Building Regulations and House Extensions

Even if your house extension is permitted under Permitted Development, the work must be built by the Building Regulations.

The Building Regulations provide minimum standards for:

  • structural soundness
  • safety from fire
  • efficiency in terms of energy
  • dripping proofing
  • ventilation
  • And other important factors that contribute to a building’s safety.

With the exception of replacement windows, underpinning, and rewiring, most repair work is exempt from Building Regulations. All new building work, including alterations, must comply with the Regulations, with the exception of some new buildings such as sheds, outbuildings, and some conser­vatories.

Typical types of work that requires approval include:

  • Extensions to a house
  • Conversions of lofts
  • Internal structural modifications, such as demolishing a load-bearing internal wall
  • Installation of new drainage or waste plumbing for baths, showers, and WCs
  • The installation of new heating equipment
  • New flues or chimneys
  • Openings for new windows have been altered.

3. What size should my house extension be?

Extending projects are frequently focused with thinking just in terms of square metres, rather than what that size adds to the house. When it comes to house extensions, more isn’t always better, and there are often ways to create the illusion of additional space without installing a major extension.

This is frequently accomplished through creative design, not only of the new space but also of what already exists.

4. Select the Most Appropriate Designer for Your Home Extension

When it comes to the design of your extensions, you have a few alternatives to pick from.

These are some of them:

  • architects
  • technicians in architecture
  • designers who are experts
  • In-house design teams of package build businesses

Request referrals from friends, family, and neighbors, but also search online for firms that have completed jobs comparable to yours.

5. design for efficiency from the start

You may be able to greatly exceed the U values and airtightness requirements set by the Building Regulations by focusing on the fabric of your new house extension.

However, adding a thermally efficient extension to a badly insulated home will not make it cheaper to run over night, so you should focus on improving the efficiency of the main house while the builders are on the job.

6. Getting a Glimpse of the Party Wall Act

Even if it necessitates entry into their land, your neighbors cannot prevent you from building up to, or even on, the line between your properties (providing you have planning permission to do so, and there are no restrictive covenants).

The Party Wall Act allows you to work on or up to your neighbors’ land and buildings, formalizing the relationship while also safeguarding everyone’s interests. This is not a problem that falls under the purview of planning or building regulation.

You must comply with the Party Wall Act if your house extension entails digging or building foundations within 3m of a border, party wall or party wall structure, or digging foundations within 6m of a boundary. In certain situations, a surveyor may be required to intervene on your behalf. Scotland is exempt from the act.

7. Constructing an Addition to a House on or Near a Sewer

You must notify your local water board if your house extension will be built over or near a sewer before work begins. “The position of sewers must be carefully considered,” says Milton Keynes Architectural’s Jonathan Durndell. “If your extension is within 3 meters of a shared sewer (one that serves many properties), a Build Over Agreement with your local water authority is likely to be required.”

These can be difficult – and expensive – to install, especially if a new manhole is required or an existing one must be relocated.

8. Extensions to a Single-Storey House

While it may appear desirable to add a second story to a single-story extension or garage, these buildings may not be capable of supporting the weight.

If the previous structure isn’t up to snuff, there are a few options: underpin existing weak foundations; reinforce or bypass the existing with a steel frame anchored in new concrete pad footings; or demolish and rebuild. In many cases, the latter is the most cost-effective option.

9. Service Planning for a House Extension

If you’re extending your kitchen, you’ll need to know where your cabinets, work, and white goods will go before you start working on the electrical, ventilation, and plumbing.

The same is true if you’re building a two-design extension with a new bathroom or en suite.

10. Is Your Boiler Up to the Task of a House Extension?

House extensions will increase demand on existing hot water systems, which may be unable to meet it.

It’s a good idea to figure out how much heat the new extension will require, taking into account your boiler’s output, the size of the radiators, the size of the hot water cylinder, and the reheat time.

11. Do I Have to Live on-Site?

Living on site during a house extension is doable, but aside from the dust and filth, you may end up slowing down progress as the builders try to work around your schedule.

If you’re not willing to put up with the inconvenience, you should absolutely look for temporary housing (short-term rental, hotel or staying with family or friends).

12. Take Access Restrictions into Account

If you live in a terraced house with limited access, your design options for a house extension may be limited. You might not be able to utilize certain building methods, or you might need to make agreements with your neighbors to temporarily remove fence panels or store items on their property.

13. Bringing the Old and the New Together

The project’s success will surely be determined by how well the additional space integrates with the original property. While there are no hard and fast guidelines, you must decide whether you want your new house extension to blend in or stand out from the existing house.

14. Off-site construction could save time and money

On house extension projects, off-site construction technologies such as cross laminated timber (CLT), oak frame, structural insulated panels (SIPs), and wood frame often work effectively. The majority of the work is done off-site at a factory, and components are subsequently transported to the job site ready to assemble.

15. Should I Manage My Own House Extension Project?

Bob Branscombe, project manager, states, “I would always believe that the best person to oversee an extension that you are planning to use and enjoy is yourself.” “No one knows the space or the building like you do, and no one cares more about doing it right than you.”

Any type of building project necessitates a great level of patience, organization, problem-solving, and decision-making abilities. A professional PM, main contractor, or package company is a required if you don’t feel confident dealing with the issues that arise on a build site or don’t have the time.

16. In your area, the Community Infrastructure Levy may apply to house extensions.

You should find out if you’ll have to pay the Community Infrastructure Levy before starting any house extensions (CIL). This method is used by some councils and applies to extensions with a gross internal size of more than 100m2 (even if they are built under Permitted Development).

However, as Jonathan Durndell of Milton Keynes Architectural explains, a self-relief builder’s may apply: “To benefit from the self-relief, builder’s the applicant does not have to physically construct the extension themselves, but they must intend to live at the property as their main residence for at least three years from completion.”

17. It’s a Must to Have Site Insurance

When building a house extension, you’ll need site insurance from an A-rated insurer to cover the existing structure as well as the new additions until the project is finished.

Even if your builder has insurance, double-check their documentation because the majority of policies include liability coverage, which means you’ll have to establish blame in the event of a claim, which can lead to protracted court fights. Natural disaster claims, such as fire, flood, and storm damage, may also be excluded.

If you’re leaving the house while it’s being built, you’ll need site insurance or unoccupied buildings insurance, which is normally a six-month coverage. Before you begin any work, make sure to notify your current insurance carrier.

18. Conservation Area Planning Regulations

In Conservation Areas, Permitted Development privileges are limited. Each local government has its own strategy for these types of locations, but the overarching goal is to preserve the area’s uniqueness. Always contact your local conservation officer first if you’re considering a house extension.

19. Privacy is a significant factor

If your house is visible to passers-by or neighbors, you’ll want to think about your glazing options.

One way is to think about your border treatments, which may need to be adjusted to retain privacy, while integral screens in your glazing provide privacy without obstructing your view.

20. Check to see if trees are protected

Tree Preservation Orders (TPOs) safeguard some trees (TPOs). Even if house extensions do not require planning permission, you cannot change or even cut a tree that has a TPO without it.

All trees within a Conservation Area are legally protected and essentially have a TPO on them if their trunk diameter is higher than 75mm. Altering a tree that is protected by a TPO is a criminal offense that can result in hefty fines, so be cautious if you’re planning a home extension near a protected tree.

21. Don’t Forget a Rainy-Day Fund

A healthy contingency to cover any unforeseen expenditures – the commencement of an extension project, for example, may reveal issues with the current house that need to be addressed.

We recommend having a 10-20% contingency in place.

22. There’s a Good Chance You Won’t Get VAT Relief

Most house additions will be liable to VAT at the usual rate of 20% on labor and materials, especially if you hire a contractor to complete the work. You can save 20% on labor by using local tradesmen who are not VAT registered, but you will still have to pay VAT on materials at the usual rate.

Work to listed buildings (zero rated), the conversion of an existing home that modifies the number of units (reduced rate of 5%), and work to a building that has been uninhabited for at least two years are all eligible for VAT reduction (reduced rate of 5 percent ).

If you’re extending a listed building or renovating an unoccupied home, you’ll need to hire a VAT-registered builder; you won’t be able to recover the VAT yourself.

(Learn more about reclaiming VAT.)

23. Your House Extension Must Be Notified to Building Control

You must submit either a building notice or a comprehensive plans application to building control before any work may commence. A building notice will allow work to begin swiftly, but you will be without the assurance that the design has been approved by building control, and you will be responsible for correcting any work that fails to satisfy Building Regs’ criteria upon inspection.

24. Light Ingress Must Be Controlled

Though getting additional light into a home is frequently a desired result of an extension project, mismanaged light ingress can cause issues with solar gain.

When building glass elements into an extension, designers should be aware of this and account for solar gain to prevent situations where, like poorly built conservatories, the extra space is only accessible for a limited portion of the year. Screen textiles can also be used to filter light and decrease glare.

25. Can I Add a Lot of Glazing to My House Extension?

According to Jason Orme, an experienced extender and H&R’s Editorial Director, “Part L of the Building Regulations limits the total size of glazed features in an extension to a maximum of 25% of the extension’s floor area.”

“This is a concern, especially on small extensions. A tiny kitchen extension, say adding 20m2, might easily have its allowance swallowed up by bifolds – 4m(W) x 1.8m(H) = 7.2m2 or 36% of the floor area – and so be refused by building control.

“There are a few ways to get around this. To begin, subtract from your increased total the total area of the windows and doors that will be lost as part of the extension. If it doesn’t get you below 25%, you’ll have to demonstrate that the new glazed extension can fulfill the energy performance standards of a non-glazed extension in other ways.