When planning a house extension in the UK, one of the early decisions is how to build the internal walls and whether to use a timber frame structure or a masonry build with plasterboard linings. The two approaches have different cost profiles, build speeds and performance characteristics. This guide looks at both options honestly so you can make the right call for your project.
Understanding the Two Approaches
First, a clarification on terminology. The comparison here is between a timber frame extension (where the structural shell is built from engineered timber panels or site-cut studwork) versus a traditional masonry extension where the structure is block or brick and the internal surfaces are finished with plasterboard on dot-and-dab or on a timber batten framework. In both cases, plasterboard is likely to be your final internal finish, so the real question is about the structural approach beneath it.
Timber Frame Extensions
How It Works
A timber frame extension uses structural studwork panels to form the external and internal walls. These can be fabricated off-site (a system build) or constructed on-site from individual timbers. The frame carries the load, and insulation is fitted between and around the studs. External cladding, render board or brick slips then finish the outside.
Advantages of Timber Frame
- Faster build programme - a timber frame shell can be watertight in days rather than weeks
- Lighter weight - useful on sites with poor ground conditions or where existing foundations have limited capacity
- Better thermal performance by design - thicker stud cavities allow generous insulation without building out excessively
- Easier to hit low U-values - required under Part L of the Building Regulations
- Less wet trade - no brickwork drying time, which suits tight programmes
Disadvantages of Timber Frame
- Higher material cost upfront - engineered timber panels cost more than block and mortar per square metre
- Requires careful detailing at junctions - poor workmanship at airtightness barriers leads to heat loss and condensation risk
- Fire performance - timber frame requires fire-rated board linings (typically 12.5mm or 15mm fire-rated plasterboard) and careful cavity barrier specification
- Less thermal mass - the structure stores less heat, which can cause temperature swings in lightweight extensions
Masonry Extensions with Plasterboard Linings
How It Works
Traditional masonry construction uses concrete blocks or brickwork as the structural element. Internal surfaces are then lined with plasterboard, either on a direct bond (dot-and-dab) or on a studwork frame built off the blockwork. A wet plaster skim is often applied over the board to give a smooth finish.
Advantages of Masonry Build
- Thermal mass - dense block absorbs and releases heat slowly, helping to stabilise internal temperatures
- Robust and familiar - most UK builders and Building Control officers are comfortable with masonry construction
- Better acoustic performance - particularly for party walls and walls adjacent to neighbouring properties
- Lower material cost per square metre for the structural shell itself
- Easier to hang heavy items - shelving, radiators and kitchen units fix directly into blockwork
Disadvantages of Masonry Build
- Slower programme - brickwork and blockwork need to cure before the next trade can follow
- Requires drying time - wet mortar and plaster add moisture to the building that must dry out before decorating
- Meeting Part L targets is harder - to hit required U-values, cavity widths need to be wider or more expensive insulation is needed
- Heavier - may require stronger foundations, which adds cost on some sites
Cost Comparison
On a straightforward single-storey extension in the UK in 2026, rough structural costs compare as follows:
- Masonry blockwork shell (external walls only, unfinished) - approximately £85 to £120 per square metre of wall area
- Timber frame shell (site-built, external walls, unfinished) - approximately £95 to £140 per square metre of wall area
- Offsite timber frame system - approximately £120 to £180 per square metre, but savings in programme time and fewer wet trades often offset the premium
These are structural costs only. Plasterboard linings, insulation, skimming and finishing are additional in both cases.
Building Regulations Considerations
Both approaches can meet Part L (energy efficiency) and Part B (fire safety) requirements when specified and built correctly. Timber frame requires careful attention to cavity barriers at every floor, ceiling and roof junction, plus fire-rated board thicknesses. Masonry builds generally have an easier path through Building Control on fire compliance, but need more thought on insulation to meet modern U-value requirements.
Which Should You Choose?
The right answer depends on your specific project conditions:
- Choose timber frame if you need a fast build, have a tight programme, are working on poor ground, or want to achieve a very low energy spec
- Choose masonry if acoustic performance matters, if you want lower upfront material costs, if the site suits a traditional build, or if your labour force is more comfortable with masonry methods
In practice, many extensions in the UK use a hybrid approach: masonry outer skin for robustness and appearance, with timber studwork inside for insulation and services runs. This is a well-proven method that gives you the thermal mass of masonry alongside the insulation flexibility of a studwork cavity.
Whatever you choose, the finish quality of your plasterboard lining will have a significant impact on the final result. Use the right board type for the location, screw at the correct centres, and always tape and skim joints properly.
