Garage Conversions.

Original Article
January 17th, 2018


Is the residential domestic garage a thing of the past? Yes, according to an article on the ‘This is Money’ website (, 13 November 2015). Reporting the results of a survey carried out by Sainsbury Car Insurance, nearly four million homeowners have converted their garage into living space over the last 20 years. Of these:

·      Most converted garages are workshops (26%) or offices (20%);

·      16% have been knocked through to be part of the living space in the main house; and

·      13% have converted to a bathroom/shower room while 7% use them as a playroom for the kids.

Whether this research is an accurate representation of the situation, it fits in with what we are seeing on surveys and inspection. Increasing numbers of owners are using their garage for uses for which they were not originally designed. In this article, Phil Parnham outlines what we should look for when we encounter a converted garage.

Different types of garage

Before we get into detailed checklists, it might be worth reviewing the most common types of garage:

·    Detached garage – this sits away from the house and is not connected in anyway;

·    Attached garage – a common feature on many housing developments where the two buildings share one common wall and there is usually a connecting door;

·    Integral garage – this type is accommodated within the existing footprint of the house;

·    Attached carport – although this can’t be considered as a garage, many owners add additional walls (often informally) that can change the nature of the feature.

Step one – does it have permission?

This has to be the first question to consider and there are three types of approval:

Planning permission – according to the Planning Portal (, planning permission is not usually required, providing the work is internal and does not involve enlarging the building.

However, this ‘permitted development right’ has been removed from some properties. Typical examples include:

·    New housing developments where there might be a planning condition;

·    Conservation area especially where there is an ‘article 4 direction’ or the building is listed;

·    Some houses that have been converted; and

·    Flats and maisonettes.

You should include and appropriate recommendation in the ‘legal advisor’ section. 

Building regulation approval

The conversion of an attached garage, or part of a garage, into habitable space will normally require approval under the Building Regulations (see  Normally, the following elements of the conversion will have to satisfy the requirements of the Regulations when converting a garage. For example:

·      Doors and windows

·      Drainage

·      Electrics

·      External walls 

·      Internal wall

·      Roofs

 Similarly to planning permission, you should always include a recommendation in the legal advisor section. However, this should not be a vague and imprecise mention but should:

·    Name and describe the specific conversion – because there might be more than one. The legal adviser won’t know this;

·    The ‘approval’ should also include the issue of the ‘final certificate’ to show the project has been properly signed off.

We also add a short ‘what if not’ clause aimed at helping the client understanding the implications if the proper permissions are not in place. A typical example would be:

’If the conversion does not have the appropriate approvals, it could:

·    Affect the future saleability of the property;

·    Require retrospective building regulation approval. This can be expensive and disruptive; and

·    In the worst cases (for example, listed building), the unapproved work may have to be removed completely’.

Party wall award

If the garage shares a wall or is connected to a roof of the neighbouring property, the conversion work should have be subject of a party wall agreement. The legal adviser should be asked to confirm this and although this would not be a retrospective requirement, the absence of an agreement is another possible indicator of a sub-standard or informal work.

Step two – is the conversion likely to meet current standards?

Even if you properly advise your client to check whether the appropriate permissions are in place, you should still assess the standard of the conversion. This is because your client’s legal adviser is likely to take weeks to find out the answer to those questions and any bad news is usually discovered a few hours before contracts are exchanged. Alternatively, if you look for a few critical indicators you may be able to put your client in the right ball park so they can take a purchase decision earlier. For example, if I inspect a garage conversion that is likely to be below the current building regulation standard, I often use the following phrase:

Although you will not know whether the garage has the appropriate approvals in place until your legal adviser has investigated the matter, a number of features indicate the conversion may not meet current standards. These include:

·       The roof and walls are unlikely to be thermally insulated;

·       The electrical installation is below standard, and

·       The internal faces of the walls are damp.

These will need upgrading and this work will be disruptive and costly.

Critical indicators of adequacy

The elements controlled by the building regulations are a good starting point for this assessment and these include:

New wall in the former garage door opening

In most cases, this is likely to need an appropriate foundation. This is impossible to check so look to see if the new wall appears robust and properly built. Thin, timber framed infill panels are unlikely to meet the requirements.

Figure 1: this garage has been converted and the front wall looks robust and well built (as long as you ignore the gutter leaks).

The floor 

In most circumstances, the floorwill always require upgrading to meet the thermal regulations. This usually involves a new DPM, a layer of thermal insulation with either a screed topping or timber floor panels. Whatever the construction, this is likely to add 100 – 150mm to the floor level.

Look at the door threshold to the main house and existing garage door. Do these show evidence of a new/altered step? Garage floors are usually lower than those in the main house so level floors between the two could suggest they have been upgraded. A change of level down may indicate the floor may not have been upgraded.

It is vital the new DPM in the floor is linked with the DPC in the wall and although this will be hidden, it is vital to check the floor/wall junction for dampness especially to the wall between the main house and the new space.

IMPORTANT NOTE: Check those head heights! Although minimum head heights have been removed from the building regulations (apart from above staircases and below sloping ceilings), most commenters agree that ceiling heights should not be less than 2.1m. 

Figure 2: This accidental ‘green roof’ is over the converted garage shown in figure 1and is linked to the garage of the neighbouring property that has not been converted. The covering appears to be the same as next door so this should be a cold roof. In such cases, watch out for lower ceiling heights and look for ventilation around the eaves.

The walls 

From a structural point of view, the walls have to be robust. Standard cavity walls and one brick thick solid walls are usually satisfactory but care should be taken with half brick thick walls with piers, timber frame structures and concrete panels.

Most garages walls will require additional insulation. The easiest way to achieve this is through internal insulation and around 75 – 80mm of rigid foam insulation boards will be required. Look for additional thickness at door and window openings with overall wall widths of 200 – 250mm.

If the garage is linked with the neighbouring garage, the party wall will have to be sound proofed and have adequate fire resistance. Does it look like an additional thickness has been added on to the wall? Does it seem robust?

Cold bridging – In a similar way to the DPC/DPM junction, the thermal insulation in the walls, floors and roof all have to link up properly. If not, condensation will form on any cold bridges and mould growth will inevitably follow. Look at the junctions between the ceilings walls and floors for evidence of mould growth.

Upgrading thermal insulation in the roof

As with the walls and floors, the roof will need upgrading too. Pitched roofs will be straight forward (270 – 300mm thick mineral wool with ventilation) but with flat roof there are two choices:

Cold roof – this can be suitable where the roof covering is in satisfactory condition (so not very often then). With cold roofs, roof space ventilation is required above the insulation so the thermal standards cannot be achieved by insulation between the joists alone. Therefore, some thermal insulation has to be fitted below the joists required (and lowering ceiling heights). The visual depth of the flat roof (usually the fascia board around the edge) would not have changed and you might be able to see ventilation around the eaves. 

Warm roof – Where the flat roof is recovered, thermal insulation is usually placed on the decking changing it into a warm roof. No ventilation to the roof space is required and because all the insulation is placed on the deck, the visual depth of the roof construction will be much greater but without a loss of head room.

Where the garage is linked with that of its neighbour, has the junction between the two roof coverings been properly made? Does it look vulnerable to water leaks?

Electrical work

A new circuit is likely to be needed and especially if the conversions includes a kitchen, bath or shower, approval under Part P of the regulations will be required. Ask to see documentary evidence (either building regulation final certificate or a competent person’s scheme) and inspect the consumer unit; in most cases the garage circuit should be properly identified and protected with an RCD in most cases.

Smoke alarms

If the new rooms and spaces do not have a door out to fresh air then the conversion will require hard wired smoke alarms in the new rooms as well as in the circulation areas of the existing house.

Fire escape (windows)

Where the new room does not lead directly to an entrance hallway with a door to outside air or a door of its own, a window should be big to act as a means of escape. The usual dimensions apply.


If the radiators are extended into the new space then they will need both time and temperature controls. If the heating appliance is new (for example a wood burning), it may need an application of its own.

Other critical indicators

Integral garages

Because these are enclosed within the footprint of the existing dwelling, it is likely fire resistance and sound proofing of the ceilings and walls are likely to be very important.

Car ports

As long as the car port has two open sides, it doesn’t usually need building regulations. However, if an owner fills in the open sides with a couple of flimsy walls, they could create a number of problems:

·    It could affect the ventilation requirements to rooms in the main house;

·    It could necessitate the upgrading of the fire resistance of any doors or windows opening into it

·    The daylight into the main house could be affected, and

·    It  may affect gas appliances that discharge out under the car port.

Roof between the house and a detached garage

In issue 23 of the technical bulletin, we described a complaint that involved a gas meter in an external housing that was enclosed by the construction of a new corridor between a bungalow and a former detached garage. This is a common DIY project that can cause similar problems to those described for car ports above. The new ‘corridors’ are often used as informal utility rooms housing washing machines, dryers and dishwashers with all their attendant electrical and drainage connections. Many will not have the required building regulation approvals (see figure 3 for a typical example). 

Assessing the garage conversion

As described in Step Two above, our approach to assessing a garage conversion is to look at a series of ‘critical indicators’ based on the building regulation standards for garage conversions. Although you will not be able to come to a definitive assessment on each one, you should be able to get a ‘feel’ for the overall standard. If your impression is favourable, then a condition rating 1 with the usual legal adviser referrals may be appropriate. However, if you pick up some worrying signs then a condition rating 3 with a warning to your client of sub-standard work may be appropriate. 

Whatever your choice, make sure you take photos and in your site notes you make a note of the critical indicators and the rational you’ve used to come to that decision.

Figure 3: the main house is to the left and the garage is to the right. The passage has been roofed over using glass in aluminium glazing bars and the resulting space used as a utility room. The electrics and drainage connections were well below current standards and the fitted carpets laid over the original concrete path.