Steps to Building Your Own House – Block Work

Once you’ve poured and floated your ground floor slab you have completed the substructure of your house and are ready to begin the superstructure. This means everything above ground.

Depending on the size of your house the next couple of weeks will be entirely taken up with block work and brick work which, depending on whether your house is a bungalow or multiple story house, is taken up to ground floor ceiling level.

The main things to watch with your block layers, unless you are building it yourself, are the Damp Proof Coursing (DPC), the wall ties and your wall insulation. For the purpose of this article we will concentrate on a 300mm cavity wall which is one of the most common methods of house construction.

In order to prevent rising damp coming up your walls it is vitally important that a layer of DPC is placed at ground floor level beneath each wall. For example if you’re building a 215mm (9″) block on flat wall a 215mm wide layer of DPC should be laid out first and then built on top of. Appropriate DPC should also be incorporated around windows and doors ie. underneath and behind window sills, up the jambs of the doors and windows and also across the heads (tops) of windows and doors. Any good home building manual will display detailed drawings for the positions and sizes for appropriate DPC’s in specific areas.

Correct DPC’s are one of if not the most important detail to get right when building your house and will prevent lots of potential problems further down the line if done right.

For the external walls, using the 300mm cavity wall example, consisting of two 100mm wide blocks on edge separated by 100mm the other two details to watch are the wall insulation and the wall ties.

The wall ties are used to tie the two separated leaves of block work together and make them more stable. Generally ties sit on top of the first course of blocks spaced at 900mm centres and then spaced 450mm vertically as block work rises. The drip built into the middle of the tie is to stop water from bridging the cavity from outside to inside. There is also usually a plastic clip on the tie which is used to hold the wall insulation in place.

The wall insulation, generally between 50mm and 75mm in thickness (seek advice from your engineer) is to be placed in the cavity tight against the inside leaf of block work and the main thing to check is that there is not a gap between the block and the insulation as this can have a big impact on the effectiveness of the insulation. Other places where insulation is necessary during the block work stage of construction is at the back of the window sill to prevent a cold bridge from forming from outside to inside.

The heads of the windows and doors must be spanned by an appropriately sized lintel. Generally speaking opes of less than 2.5m wide can be spanned by a concrete lintel bearing 200mm either side of the opening. If the opening is wider than this you should consult your engineer for an appropriate type of lintel, eg. an RSJ or a steel cathnic lintel.

Once the block work has reached the level of your downstairs ceiling (generally about 2.4m depending on your house design) you are ready for your floor joists or your roof to begin. If you are building a bungalow, it is up to you whether to build you gable peaks before or after your roof timbers are fitted. If you are building a 2 storey house you can fit your floor joists and deck them out and then return to building the remainder of your block work to roof level using the same principles as discussed.

This concludes the block work section of your build, next will be carpentry.