Partition walls are an essential part of splitting your garage between the storage space and the new room area. The first thing to decide is where to place the dividing wall, our post on partial garage conversion layouts may help you with that. If you are a customer of ours, we will do this for you as part of our full design and build service. If you are tackling this yourself then once you have decided where to place the dividing wall this post will help you decide what type of wall to build and what materials, you will need to buy.

architectural detail of dividing wall

Types of Dividing Wall

Internal walls are typically built from masonry or stud timber depending on what job the walls need to perform. Structural or firebreak walls in the UK will most likely be blockwork whereas a partition wall with the sole purpose of dividing a room will be timber stud. The reason for this is it is quicker, cheaper, and easier to use timber studwork for dividing walls.

If you are converting your garage and retaining some storage space the new wall must be capable of 30 minutes fire protection to the habitable room side of the conversion. It must also have specific thermal properties to satisfy the regulations and building inspector. These requirements lead to a very specific set of materials and method of building which are shown in the diagram / wall detail drawing below.

Architectural wall detail for fire resistant dividing garage partition wall.


Make sure your garage door and mechanisms will not foul on the new wall when opening and closing. Some sectional doors may require changing, our post on keeping your garage doors discus's the options and compatibility of different garage doors.

How to build a partition wall to divide a garage

  • Mark the position of wall and attach self-adhesive weatherstrip / draught seal to the middle of where the wall will sit. Do this around the whole perimeter of the wall if possible. The draught strip should bridge any small gaps between the timber studs and wall. This is a small but important detail to stop air infiltration which is the number one cause of heat loss.
  • Cut and measure the first sole plate, this should be treated timber with a length of damp proof course (DPC) secured to the back side. Drill through the plate and into the slab and secure in place with 120mm concrete fixings.
  • Build the stud wall with the second sole plate and head as normal, there are lot of online tutorials for help with this if you are not confident. The double sole plate detail means you should be able to stand the new wall up and lift it into place on top of the treated sole plate.
  • Seal around the perimeter of the wall with a mastic sealant on the room side of the wall.
  • Secure stop lats to retain insulation flush with front of studs if required.
  • Fit insulation between the studs, make sure to cut these accurately and fill any gaps with expanding foam.
  • Overboard with second layer of insulation making sure to tape the joints with foil tape. The insulation may require clout nails to secure in place until the plasterboard covering is applied.
  • Fit the plasterboard and secure with 65mm drywall phosphate screws.
  • In the garage side overboard the studs with fire rate plasterboard (Pink Boards) secured with 38mm drywall phosphate screws.
  • Tape and fill or skim the plasterboards.


  • Build the wall with 400mm centres not 600mm
  • Consider additional pattress or play lining if you plan to secure lots of heavy tools on the garage side

Why timber stud?

The complexity of the dividing wall build up shown raises the question “is it easier to build a block work dividing wall”. It can also be argued block work walls are the logical choice as they have better fire and sound insulation properties than timber stud. However, your building inspector will normally insist a block or brick wall is built upon a foundation and this tips the scales in favour of the timber stud wall.

The reason for this is the garage floor slab despite being concrete does not qualify as a suitable foundation. The slab would require cutting with a Stihlsaw, digging out to an agreed depth and new footings poured or laid before you could lay a block to form the wall. This is a lot of extra work, materials and waste to dispose of (skip prices are not cheap). Therefore, all our partial garage conversions will normally favour a timber stud wall as detailed above.

Wall build up and U Value

The wall shown in the supplied diagrams and detailed in the table below is designed to a U-Value of 0.18 W/m²K to meet the current building regulations as of February 2023. This article, accompanying diagrams and information are for reference only. If you are attempting to build a dividing wall as a DIY project, you should check the building inspector agrees with this calculation.

Garage Dividing Wall (Target 0.18 W/m²K )

Thermal Conductivity (W/mK)

Thickness (meters)

Thermal resistance, R (m2 K/W)

Inside Surface






PIR Insulation Over




PIR Insulation between




Airspace Resistance




Fire Resistant Plasterboard




Outside Surface


R Value Total


U Value (W/m²K)


Final Thoughts

Hopefully this post has highlighted the thought and level of detail that goes into our builds and convinced you to choose us for your garage conversion. If you are a DIY garage converter and this has helped, please let us know how your project went and if this post could be improved in any way.

Fellow builders and architectural designers, what do you think? What would you change? how would you improve this design? Let us know by leaving a comment below.

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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