Internal walls

Internal walls in a tenement don’t just separate rooms, they may also be loadbearing, supporting the floor joists which run from front to back. These walls may be built of brick or timber stud. Cracks and noise are problems you may come across.


Brick walls

Most internal walls are built of a single skin of brick, 110mm wide, with lime plaster on both sides making the walls about 150mm thick. You may find thicker walls at ground level and where there are ducts or chimneys.

These walls extend from a foundation up to the roof. At solum level (the space under the ground floor) they may be built as a honeycomb wall to allow ventilation to the joists to help prevent rot.

Sometimes, such as above shops, internal walls are built on stiffened joists or large timber beams, and some movement is common in these cases.

In older tenements, door frames in internal walls are part of the structure of your building. The frames were built as ‘H’ frames with two vertical timbers joined with a horizontal timber lintel above the door. The space above the timber lintel would be filled with brick.

Sometimes timber battens are built into walls to provide stiffness – this is more likely to be the case in top floors where the lack of weight above allows the wall to flex.

Internal half brick wall. Note timber batten stiffening.

Timber and stud walls

Timber stud walls sound hollow when tapped.

These lighter weight walls are built from vertical timbers (studs) stiffened with horizontal timber pieces (dwangs). Lightweight timber laths with small gaps between them were nailed onto the studs, and lime plaster mortar, reinforced with hair, was then applied to the laths. Ridges of plaster would be formed as the mortar was squeezed through the gaps between laths. These nibs of mortar help hold the plaster to the wall. Lath and plaster may also be used on the inner face of external walls.

In newer and refurbished buildings, timber stud walls have a plasterboard finish. Double sheeting the plasterboard provides better sound insulation.


Skirtings are not just a decorative finish to a wall, they also help block gaps that can allow noise or draughts to come into your room. Quarter-round ‘mouse moulding’ was also used at the junction of the skirting and the floor to block gaps.

What is a loadbearing wall?

Walls which support floor joists or other walls above are loadbearing. Bed recess, corridor walls, and other walls which run parallel to the back and front walls of a tenement are normally loadbearing. Both brick and timber stud walls may be loadbearing.

Typical problems

‘Boss’ plaster is where the plaster sounds hollow when tapped, meaning it is coming away from the wall.

Cracks in plaster can be the result of old movement. If the plaster on either side of the crack is still firmly fixed to the wall, widen the crack and clean the sides before filling with fresh plaster.

Brick walls may be poorly bonded (tied in) to the external walls. This is often visible in the close walls, where they meet the outer wall. Internal decoration and ducting often disguises these ‘separation cracks’. If the cracking appears to be significant or recent, then it is wise to engage an engineer to inspect it. The engineer may recommend installing tie rods through the outer wall and securing them to steel plates which are then fixed to the thinner close walls. The steel can then be plastered or covered over.

Insulating walls

If your walls are cold, there is some very good advice on insulation from Changeworks.

Altering or removing walls

Don’t remove layers of plaster from both sides of a thin brick wall at the same time as this can make the wall unstable.

Be careful about changing doorways and doorframes as the side and top timbers of the doorframe may be holding up the brickwork above.

You have a duty to maintain your flat, so as to provide support and shelter to the rest of the building. This obligation extends to internal walls. You also need a building warrant to remove or alter walls and you will need to provide other support, such as a reinforced steel beam (RSJ) to support the joists or walls above. Props need to be used to support the weight of structures above while the wall is being removed and a new beam inserted.

Noise in walls – causes
  • ‘flanking’ sound can be carried by a thin internal wall to flats above and below – this, rather than defects to the floors, may well be the cause of sound problems between floors
  • when a property was converted, light internal walls that weren’t designed to prevent noise transmission may have been made into party walls between flats
  • thinner sections of wall, such as where there are presses and cupboards in the width of the wall
  • ‘boss’ plaster can reduce sound insulation
 Solving noise problems in walls
  • ‘flanking’ noise can be reduced by lining walls with at least 42mm of mineral fibre-backed plasterboard – other special lining boards are also available
  • check that any brick separating walls are fully plastered, as sound can travel through open joints in brickwork
  • mineral fibre-backed boards can be fixed to the face of the wall, although it is always best that a ‘parge’ coat or render is applied to the face of any brickwork before installing a lining
  • a resilient (padded) wall lining of metal or timber straps can be fixed to the wall, the gap lined with mineral wool, then sheeted over with a high-density plasterboard
  • an independent wall can be built beside the existing wall with an isolating air gap between the walls – however, the framing for this wall should not come into contact with the existing wall – a mineral wool quilt should be installed between the wall framing, and one or two layers of high-density plasterboard fixed to the new framing
Professional help recommended?

You should always seek professional advice if you plan to alter or remove walls.

With other repairs and improvements, although the work may appear straightforward, ensure your builder or tradespeople have the skills for the job. If in any doubt, get professional help to specify and organise the repair.

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