Structural Changes

Here we advise on the broad principles to be considered when making structural changes such as removing internal walls and chimney stacks and chimney breasts. It is recommended that professional advice is sought for these projects.

Knocking Down Walls

Before making structural changes, like removing an internal wall, you should first seek the advice of your local authority; the change may require Building Control approval.

For yourself, you must understand what the wall contributes to the structural strength of your house. Knock on the wall, and on the walls above in any other storeys. Do they sound hollow? If so, they are probably made of wood, with lath and plaster. If the sound is 'dead', then they are of brick or stone.

Stud walls, with their wooden framework, with lath and plaster rather than a brick in-fill, are not significantly load bearing but removal may cause minor cracks in plaster above as the joists take a slightly increased load.

If the walls are 'solid', then you can make a doorway without risking a major problem. But removing most or all of such a wall requires the advice of a structural engineer. It is likely that a Rolled Steel Joist (RSJ), an H-shaped steel beam, will be required.

Rolled
              Steel Joist (RSJ)

You will normally find that the RSJ has to be below the current ceiling as it has to replace the structural strength of the wall - so there will be 25cm of wall at either end on which to sit the ends of the RSJ. It is thus typical to set this below the ceiling too so that the top 25cm of wall is also left - with the coving in place. So you have a square arch with the top being the RSJ and on top of that the remnant of wall.

In 'knocking through' in this way, the plaster coving will probably crack but can be repaired.

The electrical work is not complex, but any gas pipes will need a Corgi-registered person.

The work will typically take six man-days at say £120 per day, plus some materials. It will take two days to knock the hole and put in an RSJ. Then two man-days to move the services, and two more for replastering and tidying up.

Removing a Chimney

If you are thinking about removing a chimney stack and/or the chimney breasts below you must consider:

  • Structural strength
  • Fire safety
  • Sound insulation
  • Maintenance of neighbours chimney
  • Damp prevention
  • Ventilation to rooms

Structural Strength

A typical one or two storey house with an external or party wall one brick thick has the front and back walls less than 9m apart. These front and back walls give adequate resistance to wind or other lateral loads acting on flank or Party walls. It is therefore possible to remove a chimney breast from the flank or party wall without affecting the strength of the wall. For larger buildings a structural engineer may need to check the adequacy of the wall and a buttress wall or pier may need to be provided instead of the chimney breast.

Any work involving a Party Wall must be performed with the agreement of the neighbour.

When the hearth and chimney breast have been removed, the floor joists will normally have to be extended and the floorboards replaced.

If you wish to keep the chimney above the roof, it must be supported. This is usually done with an RSJ, a steel beam and post, or a gallows bracket. The option chosen will depend on the quality of the brickwork and mortar, and the size of the chimney to be supported. The advice of a structural engineer is essential. If the chimney stack is to be removed, the roof timbers must be extended, the roof covering made good and flashing reinstated.

When a chimney breast is removed, sometimes a recess is found in the wall for the flues. This recess needs to the filled with brickwork to make up the wall locally to the same thickness and density as elsewhere for sound insulation. Small areas can be built up with bricks on edge, tied back to the wall at 450mm intervals. All joints must to be packed with mortar to their full depth.

Fire Safety

Typically at least a one-hour fire resistance is required to walls between neighbouring properties.

Maintenance of Neighbours Chimney

If the separation between flues is damaged, tests should be made for carbon dioxide and carbon monoxide leaking from the neighbour’s fires.

Damp Prevention

If the stack is to remain, a ventilated cap must be added to each chimney pot and a vent added at the base of the remaining stack or flue.

Room Ventilation

Removing or blocking a flue reduces the amount of ventilation to a room. In the UK, Building Regulation Part F2 advises rooms to have permanent ventilation of at least 8,000mm2. An alternative source of ventilation should be provided.

Planning Permission

Listed Buildings and some conservation areas may require an application to be made. Contact the planning department of your local authority.