Internal walls

The origins of the timber stud wall can be traced back to the 1400s. Like many modern components, the system-built dry-lined partition wall is merely a descendant of earlier forms. The desire to pare down the number of structural components within a low-rise domestic property has led to the continued use and proliferation of non-load-bearing walls, with many loads being transferred to the external shell via long span composite joists. Coupled with the designing out of wet trades, the dry-lined wall and partition play major roles in dividing up the spaces of homes. The design considerations of these walls require a balance between speed of construction and eventual robust performance of the wall on site.

The lightweight nature of non-load-bearing stud walls makes them particularly poor at resisting the passage of sound. If incorrectly designed or installed, they can adversely magnify and transmit low frequency sounds. The continuity of sound insulation is particularly important, and designers have to be careful with buildability issues, as softer insulation materials have to be held in place prior to fixing. It is possible that in tight spaces or high, difficult-to-reach areas the insulation slips as the boarding is installed. The specification of the materials is also very critical to these walls, and it is difficult to assess if a material fitted is actually the type specified. Density of plasterboards and the correct type of insulation can all affect sound transfer. If the wrong type of material is fitted, the wall is very likely to fail sound tests.

The Victorians understood shrinkage and the cracking caused by the drying-out process, and developed skirtings, covings and architraves to cover up slight differential movements. The cleaner lines required by the typical modern home-owner make these components less prominent, so the role of crack prevention falls to adhesives, fillers and tapes.

Like so many details in construction, workmanship is critical to the quality of the final product, and many defects arise because of poor application of jointing tape, plaster dabs, sealants and paint finishes. The most likely causes of cracking will be poor preparation of surfaces before tapes or jointing compounds are applied. The remedy to hairline cracking of taped joints and cracks to corners is quite straightforward, but does require careful skill to remove the defective finish and re-prepare the walls.

Flex in plasterboards also causes finishes to crack, and this is usually down to insufficient fixings. This is particularly prevalent where boards are held to the masonry on adhesive dabs. Unless there is a solid line of adhesive around the wall and floor junctions or wall and ceiling junctions or openings, not only will the joints open, but the sound and fire performance will be seriously compromised. This can be remedied by injecting a backing foam, but the flamespread resistance of these must be carefully specified. The only other option is to remove the boards (which usually destroys them) and start again.

When examining stud walls:

• Check for verticality and flatness. This will give an indication of build quality. It is easy to plumb a stud wall. Any wall that is out of plumb should ring alarm bells.
• Tap all the walls and listen for the difference in the hollow sound. A wall that sounds different to similar walls in the same building is quite possibly different enough in construction to warrant an initial investigation. Do not rely on 'as built' drawings to make assumptions on how partition walls should behave, as they are often incorrect.
• Consider sound tests, but be aware that the current methods of defining sound transfer performance in some walls and floor systems are based on lab tests. This makes the assessment of adequate performance on site very difficult.
• Do not assume that all timber stud walls are non-load-bearing. Check the load paths down through the building, and check any anomalies. Changes and alterations to the building can unintentionally shift loadpaths.

Common defects:

• Cracks to perimeters: these can occur naturally as part of initial settlement but could be an indication of poor fixing.
• Walls shake when doors are slammed: this usually indicates poor fixing or design.
• The joints are visible as a ridge: either the boards are moving, which indicates too few fixings, or the workmanship was poor.
• Popped nail heads: this usually indicates poor workmanship. Most contractors now use screws to prevent this. The remedy for this is to fix new screws either side of the defective nail and re-fill. This could also be a sign that timber behind the boards has changed its moisture content from wet to dry, and could be a symptom of internal condensation.