The main walls are a big section of the construction process and definitely the most noticeable. Not only must they be capable of bearing the load of the roof and/or top story, they must also be insulated and in keeping with the original property’s appearance.


External Finish and Brick Choice

Bricks account for around 4% of the cost of an extension but cover 70% of the appearance. There are thousands of different types but the best option is to select a style and size as close to the existing house’s as possible unless they are to be painted or rendered later. Even then, using a similar material will prevent cracking where the new walls meet the old property walls.



A standard cavity wall.

Wall types

Traditional cavity masonry construction is the most common type of wall construction in Britain by a long way. It’s construction includes a concrete block inner layer followed by a gap (cavity) then an outer layer which is usually built of brick, but can be built out of concrete blocks if the outer skin is going to be rendered or clad. These two skins are held in place by metal wall ties placed 900mm apart in width and 450mm apart in height. The average exterior wall has a thickness of ¬†280mm-300mm although can be more depending on the finish and material used for the outer wall.

An alternative form of construction is timber frame construction. It is normally cheaper to construct, warmer to live in, quicker to build and looks identical to standard cavity masonry construction extensions when finished.

To build a timber frame extension, pre-built panels made from timber studs and plywood sheets are erected in place of the inner layer of exterior walls which would be found in cavity masonry construction. These panels are filled with the chosen insulation. The outer layer of bricks is then built around the erected wooden panels. The only downside of this technique is that a greater level of accuracy is needed during the construction of foundations but this is not a problem for Marble who produce high quality accurate work as standard anyway.


Exterior Decoration

The outer layer of brickwork can be left exposed, but many people choose to use a finish to make an extension blend in to the existing property or just to suite a particular look the customer desires.

Different finishes can include:

  • Timber cladding
  • PVC cladding
  • Stone rendering
  • Tiling
  • Flint
  • Paint
This is an example of old Flemish bond brickwork

Different decorative styles of brickwork include:

  • Bands of dark engineering bricks
  • Bands of contrasting red brick
  • Flemish bond
  • English bond
  • Stretcher bond

Marble Construction have thousands of builds under their belts and are experts at matching styles of brickwork and finishes which would leave other less experienced companies clueless.


Types of Finishing

Once the customer has chosen the style of brickwork, the one remaining decorate feature to decide is the style of finishing. Finishing is the way the mortar is left between the brick, Styles include:

  • Flush- this is where the mortar is left square with the edge of the brickwork.
  • Bucket Handle- mortar is level with the edge of the top and bottom bricks but curves inwards in the middle.
  • Weathered – This style has the highest weather resistance, the mortar starts offset from the front of the top brick and slopes outwards until it hangs over the bottom brick.
  • Struck- this has the least weather resistance as it slopes inwards at the bottom leaving the underneath brick exposed. This makes struck unsuitable for exterior walls.
  • Recessed key- the mortar is left jutting inwards from the front of the brickwork so also leaves the bottom brick exposed to the weather.


Energy Efficiency

To meet building regulations, an extension will have to have an over all level of energy efficiency. It is also a legal requirement for all buildings to have an energy performance certificate similar to the ones you find on fridges or washing machines, a high rating is likely to attract buyers if the customer plans on selling the property at any stage.

If this is not enough reason to use wall insulation there is also the colossal savings in terms of heating. The insulation is normally placed in the wall cavity either during or after construction of the wall.


Windows and Doors

There are once again thousands of choices in terms of size and style. Whatever is picked by the customer should be in a similar appearance to the existing building in order to get planning permission. Doors and windows are only fitted once the roof is on and interior walls are constructed due to the risk of damaging them.


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