Are you considering a DIY garage conversion, or maybe you’re just worried about the huge difference in floor levels between your garage and home? Either way, I guess you are reading to find out what you need to do to the floor of your garage conversion.

Your choice of garage conversion floor options will depend on several factors:

  • Existing Floor Level vs Desired Floor Level
  • Condition of your existing floor
  • Budget
  • Choice of heating system

This article will discuss the different scenarios that may be applicable to your build and the various solutions such as floating floors and suspended timber floors. But before we do here’s a quick Q&A section for those of you in a rush and looking for a quick answer.

Garage Conversion Floors - Q & A

Do you have to raise the floor in a garage conversion?

No, its not a strict requirement. However, matching the floor level helps the room feel more connected to the rest of the home. It’s less of a trip hazard and will also allow you to include layers of insulation which will improve the comfort of the new living space.

Whats the minimum garage conversion floor U Value?

The existing floors U value is acceptable in most cases. The building regulations reference to floor values of 0.18 W/m2is for new construction. To achieve this level in many garage conversions would involve demolishing the existing concrete floor to make space for the insulation needed. While this would produce a room with better thermal properties and reduce the heating costs and therefore ongoing carbon emissions of the home, it also means several hundred kilos of concrete (the existing garage floor) will be removed. Possibly ending up in landfill. Therefore, building inspectors are normally happy to sign of conversions that use the existing concrete floor. 

Whats the minimum floor insulation for a garage conversion?

None, see the answer above.

What’s the best floor for garage conversions?

It completely depends on the existing scenario, preferences, and budget. If the design is technically correct and compatible with the existing build, then the floor will be up to the job. 

Can we include underfloor heating into the new floor.

The difference in floor levels may provide the perfect opportunity to include underfloor heating. First speak to your designer or heating installer about the build up of the system. Once you have the confirmed depth of this heating installation you can work out how much insulation you have room for underneath. Underfloor heating can be achieved in many ways.

How to raise the floor level in garage conversions

There are 3 typical methods of raising the garage floor level to match the level of you existing homes floor.

  • Using a suspended floor consisting of joists spanning the width of the garage supported by wall hangers.
  • A floating floor consisting of rigid sheets of insulation loosely laid between membranes and finished with an interlocking chipboard such as “Weyroc”
  • A cement screed of at least 65mm laid on top of sound existing surface with a damp-proof membrane in between.

Choosing the most suitable method depends on many factors especially the difference in levels. For example, if the garage floor is 50mm below the house it is too small for a screed which should be at least 65mm thick to avoid cracking. Conversely, a 150mm gap would be a large depth to screed yet would be easy to build up with 120mm sheets of PIR insulation and 22mm Chipboard. The purpose of the room will also affect the floor design. A home gym with a heavy multi gym and free weight area may require larger joists than a garage to bedroom conversion.

Layers of a floating floor install

Floating Floor Layers

The image above shows the black DPM layer lapping up the wall, the DPM is under the silver PIR insulation boards. On top of the boards is the green slip layer and moisture control layer, this will also be lapped up the wall. The install is finished with the tongue and groove chipboard.  

If you are attempting to DIY this task, please speak to a professional such as an architect or surveyor before starting the work. Although the building inspector can not suggest the method they may help and will normally alert you to any areas of obvious concern.

How to insulate a garage conversion floor.

Now that we are familiar with the different floor construction solutions, I will present the solutions in a tabulated format. Because insulation can be achieved in many ways with different materials, I have suggested more than one method. The performance-based approach uses the highest performing materials without considering the environmental cost of manufacture. The eco approach prioritises sustainability by choosing the insulation material with the smallest upfront carbon cost which are typically natural materials. This does not mean that the performance of the eco solution will be lower, however, more material may be required to achieve the same U values and performance levels.

Floor Type

Performance Based

Eco Based

Suspended Timber Floor

Appropriate thickness of PIR boards in between joists resting on a stop lat. All gaps sealed with spray foam.

Sheep wool retained in place by mesh mechanically fixed to the underside of the floor joists.

Floating floor

Suitable thickness of PIR laid on a DPM with a Slip layer / moisture barrier over the top.

Suitable thickness of rigid compressed Woodfibre boards laid on a DPM with a slip layer / moisture barrier over the top.


PIR insulation on top of DPM

Garage Conversion Floor - Mistakes to avoid!

Suspended Floors

A suspended timber floor needs ventilation beneath it, the distance from the bottom of the floor joist to the garage floor should be 150mm. With the depth of the garage conversion floor joist being at least 120mm this could mean you have to demolish the floor and excavate to use a suspended floor design.

Levels

Garage floors will normally fall towards the garage door, this small slope is designed to stop water entering the garage and allow any internal water to drain to the outside. This fall must be accounted for when laying a new screed or placing a floating floor on top of the existing garage floor. A couple of bags of self-levelling normally does the trick.

Finished Floor Depth

Consider the depth of the finished floor surface to avoid being left with a nasty lip and potential trip hazard. For example, if you are using a thick floor tile which needs a bed of adhesive and decoupling membrane then these layers will add up. It can be hard to think that far ahead but you should choose your finished floor design and material before starting the build. This way you can speak to the flooring installers, confirm the thickness of the finished floor, and work back from this level. 

Final Thoughts

The humble garage floor conversion can throw up a lot of questions and potential issues, hopefully this article has helped to narrow your choice and avoid costly mistakes. Thinking ahead is key along with communicating your intentions to the professionals and trades involved in the job.

Take the next steps in your conversion by getting a quote for.

About the Author Michael NEGC


Michael is the Architectural Designer and Surveyor at North East Garage Conversions.
Michael has a HNC in Civil Engineering and a HND in Construction Management. Previous experience includes multiple renovations, a self build plus working as an Architectural Technician, Designer and Project Manager.

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