Building a masonry house: brick, block and the cavity between

The inner leaf carries floors and roof, and is usually built from concrete blocks. Aerated blocks are lighter and insulate better; dense blocks are stronger and heavier and hold heat and sound. The engineer's design and the thermal calculation decide which is used where. The outer leaf protects the wall from the weather and gives the house its appearance. Wall ties join the two leaves across the cavity.

The cavity itself is where the insulation goes, either filling it completely or partly with a clear gap kept open to the outer leaf. Either way, the insulation must be continuous, tight against the inner leaf, and kept clean of mortar droppings, which bridge the cavity and let damp and cold through. It is the kind of detail a warranty inspector or Building Control officer looks for, but only at the moments they are on site.

Most problems in masonry houses happen at the edges: above windows and doors where lintels, cavity trays and weep holes must direct water out; around frames where the cavity is closed; at the junction with the ground, where the damp-proof course and the floor's damp-proof membrane must meet; and at the eaves and gables where the wall meets the roof. These are also the places where heat escapes through thermal bridges.

Ask your builder how each of these junctions is detailed, and whether the drawings show them. Photographs of each stage before it is covered cost nothing and are valuable later, both for sign-off and if a leak ever needs tracing.

Masonry is built with mortar, and much of the inside is often finished with wet plaster and a floor screed. All of that needs time and suitable weather. Bricklaying stops in frost and heavy rain, fresh work has to be covered, and a new house releases a lot of moisture as it dries out during its first months.

For you this means a longer programme on site than a factory-built house of the same size, and the need for protection of the work in winter. The benefit is that the design can change later in the process, openings can be adjusted on site, and local builders with masonry gangs are available almost everywhere.

Blockwork on its own is not airtight. The air barrier is usually wet plaster or a parge coat on the inner leaf, plus careful sealing around joists, pipes and cables. A house that fails its airtightness test at the end has to be investigated and fixed with the finishes already on, so it pays to check the barrier before plasterboard or kitchen units cover it.

The outer leaf is what planners care about. Planning permissions often include conditions about external materials, and the council may want to approve brick or stone samples before building starts. Leave time for that, and do not let the builder order bricks until the condition is discharged.

• block types for each wall, and the outer leaf material
• cavity insulation type, full or partial fill, and how it is kept clean
• lintel, cavity tray and cavity closer details at openings
• the air barrier strategy and when airtightness is tested
• how work is protected in winter, and drying-out time in the programme
• who arranges Building Control and warranty inspections at each stage

Tell us about the plot, the planning status and the house you want. Builders who work in your area see this summary without your contact details. One builder, and no more, can buy it; it pays Offrano, and the service costs you nothing. Before that builder sees your details, we email you its name, address and phone number.

If no builder buys the request within 21 days, it is withdrawn, and you are never obliged to accept a quote. Offrano checks only that the buyer is a registered business, so ask to visit houses it has built and check its warranty provider registration.