Once the concrete pad of ground floor assembly is poured, the bricklayers can continue to erect the masonry. Both skins are continued upwards off of the initial masonry under the ground. Whilst the specific materials under the ground are typically concrete blocks on both skins, this arrangement can change at this point depending on the criteria of the build. In modern construction, the inside skin is most often constructed from lightweight aerated concrete blocks. These blocks are engineered to meet the appropriate load bearing criteria involved in supporting the first-floor joists and roof structure. The outside skin may be composed of a handful of different materials depending on the desired finish of the outside of the building.

For structures that are going to be rendered or cladded, or otherwise covered with another finish, concrete blocks can continue to be used. Alternatively, a face brickwork skin may be desired, in which case face bricks are used. These bricks are decorative and come in a variety of different colours and finishes - all depending on the type of clay that is used to make the brick. Different colours can be combined in patterns to create specific aesthetics. In addition to this, the mortar between the bricks can be dressed to create a specific look. This practice is known as pointing and can be carried out in a plethora of different styles. The most common of these styles include concave, struck, and raked pointing, as shown in the diagram. There are also a variety of different “bonds” that can be used during the erection of face brickwork. This refers to the arrangement in which the bricks are laid. The most common is known as brick bond or running bond. This is the typical arrangement that we think of when imagining laid bricks. The centre of each brick sits directly above the perp joint of the two bricks below it. Other more decorative but not so commonly used bonds include Flemish bond and English bond. 

Some other decorative masonry components include sailing courses, soldier courses, and brick corbels. These common features are often included as a part of new build face brickwork and can help to create a nice aesthetic.  

A layer of DPC is installed on both skins at around 150mm off of the common ground level. This modern plastic material is impervious to water and prevents rising moisture from travelling up the masonry past the level of the floor. The two skins are built up together in increments, with wall ties installed at regular intervals to tie them together. Cavity wall insulation is installed tight against the inside face of the internal skin of the cavity. This insulation begins at the height of the DPC, to prevent any moisture from travelling up the cavity via the insulation. 70mm of rigid foam insulation or fibreglass quilt batts are used in a common 100mm cavity in order to maintain an air gap within the cavity. The purpose of the insulation is to prevent the warm air inside the house from condensing inside the cavity where it meets the cold air. Rigid insulation is held in place in the cavity through the use of special clips that receive over the wall ties in the cavity, pinching the insulation in place. 

Expansion joints in long runs of masonry are required at specific intervals, depending on the criteria of the build and the materials that are being used. These expansion gaps are physical breaks in the bond of the masonry, with the two pieces connected together through the use of slip joints. These joints tie the masonry together whilst also allowing lateral movement to take place. A foam buffer is also installed between the two sections of masonry to seal the gap and allow for expansion. On the outside of the external skin, this expansion joint is sealed through the use of a silicon sealant or mastic product. Specific lengths of unsupported masonry may also require the implementation of piers in order to provide stability to the masonry. This is very common for garages, where perpendicular walls are not present to provide stability. According to NHBC, concrete blockwork requires an expansion joint at roughly every 8m of length, with clay face brickwork requiring one every 10-12 metres. Masonry piers should be installed at regular intervals of around 3m where required.  

As the inside skin is constructed up to a decent height on the ground floor, a datum can be struck around the building at a set height to provide an accurate point of reference for the rest of the build. The datum can be used to determine the height of the first-floor joists, as well as for the height of the screed later on in the build. Nails can be hammered into the soft internal block along the datum so that a tape measure can be lowered down from above and hooked on when working off of trestles or a scaffold.  

Where extensions are concerned, there are a few different methods of connecting the new and existing masonry together. Fur fixings can be installed into the existing masonry via plugs and coach screws to provide a suitable anchor for the new masonry to be built off of. These anchors consist of a rail that runs up the wall that is designed to receive small restraint tabs. These tabs are laid in the mortar beds of the new masonry courses, tying the two structures together. It's important for a cavity to be cut in the existing masonry between the two new skins to promote effective air flow throughout the structure.  

Alternatively, the existing masonry can be “toothed out” - removing alternating courses of the masonry structure to provide a suitable anchor for the new masonry to be erected from. This is most commonly seen on face brickwork, where an existing opening has been bricked up, or where an existing face brickwork structure is extended. The new brickwork can then be laid in the same bond style as the existing masonry.