How your home was built: roof, walls and floors

The construction of houses built in the last half-century dffers markedly from those put up before about 1920. Houses built during the intervening generation of change incorporate both traditional house-building techniques and some of the new methods of construction that were being introduced.

Knowing how your home is built before embarking on DIY jobs can save you time and money. Understanding how the roof, walls and floors are put together and what they’re made of will help you to plan improvements and alterations, and to deal with any faults that may develop as time goes by.

A glance in the loft will tell you what sort of roof you have. Traditional timber roofs, assembled on site, have open space below the rafters for storage.

Roofs constructed in the past 50 years usually have roof trusses—prefabricated timber frames incorporating rafters and ceiling joists. These are factory-made so the roof structure can be erected quickly, but the design and number of the trusses leaves little room for storage.

If you live in an older house with a boarded roof—one with planking laid across the tops of the rafters—don’t have it stripped off if you ever have a new roof put on the property.

The boarding insulates the roof space far better than a layer of roofing felt alone, and areas which are rotten can be replaced easily with sections of new pressure-treated wood.

Old roofs are usually covered with natural slates or clay tiles, and were designed to take the weight of these. Before you replace them with concrete tiles, which are usually much heavier, ask an expert whether the roof timbers will need to be strengthened.

If the timbers do need reinforcing, the cost is likely to cancel out any saving you might make by re-rooÏng with manufactured tiles—in which case, you’re better off leaving the roof structure alone and replacing like with like.

The bricks in solid walls are laid in patterns known as bonds. What they all have in common are headers—bricks laid end-on so that they pass right through the wall to give it strength.

A solid wall will be as thick as the length of a brick (215 mm) plus the thickness of plaster inside and any rendering outside. You can measure the wall at a door or window opening.

Only the long faces of bricks, known as stretchers, are on view if your house has cavity walls. The walls are a minimum of 255 mm thick (two single leaves of brickwork, each 102.5 mm thick, separated by a 50 mm wide cavity) and more if the cavity is wider or the internal leaf is built of thicker blockwork.

Cavity walls have several advantages over solid ones. Any rain that penetrates the outer leaf of brickwork cannot bridge the cavity and instead runs down its inner face to ground level, so the inner leaf stays dry.

Interior wall surfaces are warmer because the air in the cavity acts as an insulator, and extra insulation placed in the cavity during or after building makes them warmer still.

Timber-framed houses have an inner leaf consisting of load-bearing wooden wall panels clad with external plywood sheathing and Ïlled with insulation

Ground floors in houses built before about 1950 are usually covered with floorboards laid over timber joists which are suspended over an underfloor airspace.

In the past 50 years solid concrete ground floors have become the norm, although they may be overlaid with timber strip flooring or chipboard. Accessing and altering plumbing and heating pipework under a timber floor is a relatively simple matter; getting at pipes buried in concrete is much more difficult.

Concrete floors in the kitchens and sculleries of old houses are prone to rising damp because they were laid straight onto the earth, with no separating damp-proof membrane (DPM).

Inherent dampness in a solid floor also makes it cold and so liable to condensation. Where concrete floors have been laid next to wooden ones, they can hinder ventilation of the underfloor space, increasing the risk of rot in the wood floor.

Nowadays, Building Regulations ensure that concrete ground floors are underlaid with a DPM of heavy-grade polythene, and since 1990 they have also had to be insulated. 

In older homes, the ends of the joists supporting timber ground floors are embedded in external walls, making them prone to rot if the walls are damp. The square-edge floorboards used until the 1930s let in underfloor draughts—a problem largely cured by the use of tongue-and-groove boards, although at the cost of making the boards more difficult to lift.