Converting your garage

Converting a garage is an excellent and affordable way to add extra living space to your home. If you want to do it yourself, or hire a specialist garage conversion company, whether you want to convert your garage into an extra guest-bedroom, home-office or luxury home-cinema - this guide is what you need. Converting your garage can be a tricky business so, to make things easy for you, we have divided this guide into easy to understand sections:

  • Reasons to convert your garage
  • How to convert your garage

Reasons to convert your garage

What do you use your garage for these days? With cars getting bigger and houses getting smaller, more and more garages are turning into wasted space. These days, garages tend to get filled up with forgotten fitness equipment, old toys and useless memorabilia that would take more time to throw out than it is actually worth. In days gone by the family car had to be protected from the elements - but that was before they were routinely galvanised. So, if you can park in the street, don’t let this valuable asset go to waste! Converting a garage can be one of the most cost effective ways to add space to your home and it can even add extra value too - a garage conversion's value will rise in tandem with the house price.

Moreover, a well-made garage conversion can bring extra daylight into your house. If your garage is attached to the side of your house, installing glazed doors for access will make that adjoining room lighter and more airy! Let’s take a look at some of the most popular uses for that defunct old garage:

  • Another lounge
  • An extra bedroom
  • An extra bathroom
  • A childrens’ play-room
  • A larger kitchen
  • A home cinema
  • A home-gym
  • A home-office

Another lounge is actually the most popular garage conversion. Think that having two lounges is excessive? Just wait till those cute kids turn into teenagers - you may not want to snuggle up on the sofa with your son and his spotty mates every night of the weekend. On the other hand, if you work for yourself and pay for office space elsewhere, perhaps you should size up the cost of having your own home-office, factoring in the added value to your house when you come to sell it. In comparison to building an extension or a loft conversion, converting your garage will most likely add the most extra floor space for the least extra expense. Read on for more about the conversion process!

Can I convert my garage?

Before you go ahead with your garage conversion, you need to know all the legal issues involved. There are three main things that you need to check first - if you go ahead without permission you could be forced to return everything to its original condition, at your own cost.

  • Restrictive clauses in your lease - You need to check your property deeds for any restrictive covenants. Some developers place a restriction on any building work that will affect the external appearance of the house. If there is such a clause, contact them, as it can often be circumvented for a fee. Your other option is to convert the inside of the garage without changing its external appearance. This is often achieved by keeping a front portion of the garage for storage space and converting the rest. Of course, the suitability of this option depends on your intentions for the garage.
  • Planning permission - You usually only need to apply for planning permission to convert a garage when you intend to extend the actual size of the garage. However, check with your local authority as the precise rules do differ.
  • Building Regulations - If you plan to convert any part of your house into a room to be used as habitable space, you will need to comply with government building regulations. A building control officer will probably need to check your conversion a number of times during construction. More information can be found on the relevant section of the government's website. Again, rules differ so you need to check with your local council. There are some instances where permission to convert your garage may be denied such as:
  1. You live in a listed building or neighbourhood - It is very likely in this case that the external appearance of the house must be maintained as it is.
  2. Your garage conversion would affect drainage - If you plan on concreting over your garden or anything similar, thus putting extra pressure on the existing drainage in place, you may need to invest in a solution to allay the potential for flooding or blocked drains.
  3. Additional insulation is needed - Some councils will allow you to simply add the extra fill to the existing construction, others demand that you dig up the floor and insulate it as if building from scratch. This will affect your budget, so always check first.
  4. Parking restrictions - In some cities where there is a particular shortage of parking spaces such as London, councils can refuse permission to convert your garage from a place where a car is kept.

What kind of garage do you own and is it suitable for conversion?

  • Single garage - A single garage will add around 150 square feet of floor space to your home.
  • Double garage - You may either convert the whole area, or just the nearest side to your house. If you convert it all, you can expect to add around 300 square feet of floor space to your home.
  • Tandem garage - As before, converting only the back will leave you with the best of both worlds.
  • Standalone garage - Careful, as you may need to make an application for permission to change its use.

How to convert your garage

If you intend to convert your garage, we would recommend contacting a specialist garage conversion company to ensure that the job is done professionally. A bad garage conversion can reduce the value of your home and, if it does not comply with building regulations or the specifics of your leasehold, you may be forced to return it to its original condition. Before committing to a builder or any other professional, remember to check that they are registered with a reputable trade organisation, such as the Federation of Master Builders (FMB).

In this section, we will take a step-by-step look in-depth at the various stages involved in converting a garage, and roughly what must be done in each to satisfy the Building Regulations stipends.

In-fill Garage Door

A traditional garage door designed for the easy access of automobiles is unlikely to be suitable for your garage conversion. It is neither practical in terms of insulation and light, nor aesthetically pleasing. To this end the old garage door will have to be filled in with a new wall to house a new door and possibly a window. The original foundation of the garage will most likely be a shallow slab and thus insufficient to support the new wall, in which case a deeper foundation needs to be dug. Soil type, adjacent buildings, nearby trees and the resulting drainage conditions need to be assessed in order to estimate what depth and type of foundations are necessary, especially if your house was built on a landfill site.

Walls below Ground Level

Depending on what foundations are deemed necessary for your particular conversion, a greater or lesser amount of wall construction needs to be undertaken. Walls underneath the ground (substructure) must support the construction above (superstructure) and, to be effective, these sub-walls must be made from brick that is resistant to ground frost and sulphates present in the soil.

New External Walls

It is likely that at least one completely new external wall will be needed for your garage conversion, such as in the case of the in-fill garage door. External walls constructed of timber and/ or masonry come in two types:

  1. Solid wall - Just a single wall. Due to present day thermal insulation requirements, it is unlikely that such a wall will be suitable.
  2. Cavity Wall - Two walls separated by an internal space, usually filled with thermal insulation.

Any external wall must be constructed in such a way as to repel and divert moisture coming from the ground (damp proofing) and stand up to the outside elements (weather resistance). Thermal resistance is the term given to how much heat the wall will retain and this is naturally affected by your construction materials. Fire resistance is crucial to stop the spread of fire in any eventuality, this is ascertained via minimum standards and affected by the proximity of any neighbouring structures. Lastly, the wall will have to bear its own weight, that of the other walls, the roof and any openings (doorways) as required.

Existing Garage Walls

It is most likely that your existing garage walls are of the solid wall (single) variety as detailed above. As such, they will probably fall short of Building Regulation minimums across a variety of categories such as Fire Resistance, Insulation, Weather Resistance and Damp Proofing. Furthermore, they may not be able to safely support any new roof you have planned. Therefore, they will need to be upgraded with a new internal skin and carefully assessed in terms of Damp-Proofing.


The existing garage floor is unlikely to be suitable for regular domestic use. The solid concrete floor can either be upgraded in terms of strength, damp-proofing and thermal insulation or, alternatively, a new suspended timber floor can be built on top of the existing concrete one. The process of making your garage fit for habitation differs according to which floor you wish to install:

  1. Solid Floor - This will need to be upgraded with a Damp Proof Membrane (DPM), which comes in solid and liquid form. Liquid DPM is often best suited for garage conversions. If required, thermal insulation should be placed on top of the membrane and a separation layer may be needed in between to see that the two layers do not react with each other. Finally, the floor is finished with what is known as a floating floor, a layer of wood or screed - depending on the insulation below. If screed is used, it should be around 75mm thick and safeguarded against cracking with a wire mesh.
  2. Suspended Timber Floor - Unlike your garage, the floor of your house may be constructed fairly high above the ground and, if you wish, you can install a suspended timber floor in your garage conversion to match this. Timber joists are laid from wall to wall with a minimum gap of 150mm maintained between the original concrete floor and the new timber one. A Damp Proof Course (DPC) should be laid underneath the timber floor and an intermediate wall may be necessary for further ventilation.

Garage Roof

Unless there is a room above it already, the existing garage roof - originally designed to keep the rain off your car - is most likely going to need to be upgraded in any garage conversion. Which type corresponds to your garage roof?

  1. Flat Roof - This will need to be ventilated with a 50mm gap between the underside of the roof and any insulation as standard.
  2. Pitch Roofs - Extra insulation can be placed between the ceiling and the roof, just as in a normal loft.


Any room in a house must have adequate ventilation and the level of ventilation required depends on the room type - bathrooms and kitchens obviously require more than bedrooms or studies. An opening window must be installed which equals one-twentieth the rooms total floor-area. Additional ventilation comes in the form of trickle ventilators and alternative means of ventilation may be discussed on a case-by-case basis with the Building Control Body. New kitchens, toilets, bathrooms, shower rooms and utility rooms must be fitted with a mechanical extractor fan with performance levels measured in litres per second.


Any electrical work needs to be carried out in accordance with the British Safety Standards 7671, you can find out more at the website of the British Standards Institution (BSI).

6 comments on “Converting your garage

  1. rachel Lister on

    My elderly father’s neighbour has “told” him that whilst converting their garage into a bathroom they will need to insert a ventilator from the bathroom to the outside wall, which is in effect, in my fathers back garden wall.

    can they do that?

    They seem to think they can but I can’t believe that they are having a job signed off by your team if they do do that? many thanks.

    • Franki Napolitano
      Franki Napolitano on

      Hi Rachel,

      It might be best to check with your local council about the property boundaries on this one, as without knowing the structure of the houses, it’s hard for us to comment.

      Not sure what you mean about ‘having work signed off by your team’ as we are just an online guide, we don’t give permission for, or carry out, any work on properties.

  2. Jon wood on

    I must say all the mentioned points are making some sense and Helpful for many individuals like me, who do not have much idea about the garage interior or renovation. Well done, Thanks for sharing such a helpful stuff.

  3. Ann Lewellen on

    Useful information, thank you. However our slab garage foundation (added 1975) is only 2 inches below the house floor and therefore would need to be dug out for insulation etc. Is this likely to affect the integrity of the existing walls?

  4. Simon on

    Hiya, I see very little information about converting a standalone garage into a ‘granny flat’.

    Has anyone done this ? Any information would be gratefully received.

    I presume planning information will be required for a change of use but is there any way to find out what criteria the decision is made upon? i.e. the chances of success! 🙂



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