Self Build Guide - Timber Frame House

Timber frame and brick and block are the two main forms of house construction in the UK. Both have their advantages and disadvantages, so the method you go for will depend on your own personal preferences.

Both timber frame and brick and block houses have an outer skin (usually brick) and a cavity (usually 50mm). Where they differ is in the construction of the inner wall. With a standard timber frame this consists of a waterproof membrane, sheathing board, structural timber frame, vapour barrier and inner lining of plasterboard. The insulation is placed between the timber frame uprights, and its thickness matches the size of the frame (usually 90mm). With standard brick and block, the inner wall consists of aggregate block and an inner lining of plaster. The insulation is placed directly in the cavity, which is either partially or completely filled.

The main difference between the two types of construction is how the loads of the house are taken. With timber frame, the frame itself supports the weight of the house, while with brick and block, both the outer brick and the inner block take the weight.

The internal walls and floors also vary in construction. With timber frame, dividing walls are plasterboard stud partitions, and floors are typically of timber construction (although ground floors can be concrete). With brick and block, dividing walls are usually solid block, and the floors are typically of solid beam and block construction.

A range of outer claddings can be applied to both timber frame and brick and block houses, including brick, stone, render, hanging tile and timber boarding. With timber frame the actual timber structure is often exposed as a design feature.

Windows in timber frame houses are fixed to the inner timber frame, rather than to the brick outer skin, which results in a deeper external sill. This feature helps to distinguish between the two types of construction from the outside.

With timber frame the option exists to expose the timber ceiling beams for a Cathedral-style look. These are particularly common in Scandinavian house designs. Some timber frame suppliers build post and beam houses. Here, vertical posts (as well as horizontal beams) form an integral part of the structure and character.

With brick and block, dummy timber posts and beams can be added to masonry walls. These are not structural, but can look just as authentic.

With timber frame, only dry-lined plasterboard can be used for the walls and the ceilings, while with brick and block, wet plaster can also be used. With dry-lined plasterboard, wallpaper can be put up immediately, whereas with wet plaster you have to wait six months. Dry-lined plasterboard walls can sound hollow when you tap them, while wet plaster on masonry walls makes for an all-round heavier, more solid structure.

Weight is important to good sound insulation - remember sound waves are vibrations, and it is hard to vibrate a heavy wall. Solid concrete walls offer an obvious advantage here, while lightweight plasterboard-finished walls require more care. Sound insulation can only be improved by suspending mineral fibre between the stud partitions, which will absorb some of the sound.

Although solid concrete gives good resilience against airborne sound, such as music and voices, it offers little in resistance to impact sound, such as footsteps. Concrete floors are particularly prone to impact sounds, but laying a resilient layer, such as a carpet, onto the floor will guard against this.

Isolating two structures is also important for good sound insulation, as it breaks the sound path. Cavity walls in both house types perform this function. Floors constructions can also be isolated with the use of a floating floor system. The two parts are separated by mineral wool, which gives resistance to both impact and airborne sound. A timber floor construction is lighter than a concrete floor, so to achieve the same levels of sound insulation, additional layers of board can be fitted to increase the total weight.

An airtight structure is also important for good sound insulation. It is pointless spending money on sound insulating either a timber frame or brick and block house, if the sound can pass around a partition via an poorly sealed window, door or service duct.

Both timber frame and brick and block houses have to comply with energy efficiency targets set out by the Building Regulations. The minimum U-value (insulation level for each component of the build) required for exposed walls is 0.45 W/m2K.

A standard brick and block house offers a U-value of 0.43 W/m2K. Whereas a standard timber frame outperforms the mandatory ratings, achieving a U-value of 0.41 W/m2K. The latter can be improved to 0.29 W/m2K by increasing the frame size from 90mm (standard) to 140mm (enhanced), which increases the space for insulation. This gain is at comparatively little extra cost.

For brick and block to match the same levels of thermal insulation achieved by an enhanced timber frame, insulated dry-lining with vapour check has to be included in the wall construction, increasing costs considerably.

Timber frame builds are lightweight, have little thermal mass and the insulation is close to the inside of the house. The combination means that they respond quickly to changes in temperature, so when the heating is switched on, the house heats up quickly, and when the heating is switched off, the house cools down quickly.

Brick and block builds are heavy, with a high thermal mass. When the heating is switched on, the plaster and inner block slowly absorbs the heat. Although the house takes longer to warm up, it also takes longer to cool down once the heating is turned off. Brick and block is therefore a good choice for families with someone at home for most of the day, while timber frame is suited to families who are out for most of the day.

As long as the same wall, floor and roof insulation levels are specified, there will be no difference in the overall energy usage between timber frame and brick and block. This is only one part of creating an energy efficient house, with windows, doors, and heating specification playing an increasing important part.

It is generally accepted that a timber frame house is quicker to construct than a brick and block house. In good conditions, a timber frame house can be built in around 12 weeks, and a brick and block house in 18 weeks.

A timber frame house is usually wind and watertight by week five of the build, so while the bricklayers work on the outside, work can begin on the internals. By contrast, a brick and block house is not normally wind and watertight until around week nine or 10, so work on the inside starts later in the build programme. This is slowly improving with several block manufacturers developing systems that make it possible to build a house up to first floor level in a day.

Build timetables can be misleading, as many don't take into account the time it takes to order and manufacture a timber frame kit.

Good organisation and site management ultimately influences the build time. There is no benefit in having a wind and watertight shell built in under a week if the first fix plumber and electrician is not available to start work. Package companies and architects are happy to offer advice on pre-planning and placing orders, to ensure that a build goes as smoothly as possible - whatever method of construction is used.

In the past, architects, builders and tradesmen received little training in timber frame construction. Today, while the majority are still more familiar with the techniques required for brick and block, attitudes are changing. Many timber frame package companies offer plenty of support, introducing their customers to local builders with plenty of experience in timber frame house construction.

Representatives of both timber frame and brick and block agree that there are no measurable differences in cost between the two constructions if designed to minimum Building Regulations standards. What ultimately determines build costs are individual specifications, build route, labour and plot details.

If high thermal insulation standards are specified, timber frame can be significantly cheaper, whereas if good sound insulation is a priority, then brick and block is easier on the finances.

If timber frame is chosen for its quick build time, savings can be made on the interest on money borrowed for building, storage and rented accommodation. That said, with timber frame a large amount of money is required earlier on in the project to pay the kit manufacturer. With brick and block, build costs are spread over a longer period of time. Whatever method of construction decided upon, the Accelerator mortgage offered by the Self Build Advisory Service can help with finances and cash flow during the build, by providing funds at the beginning of each stage, rather than the end. With growing concern for the environment and global warming, it is in everyones' interests to keep energy demands as low as possible.

Building energy efficient, well-insulated homes to reduce fuel consumption and running costs is essential. However, what many self-builders do not realise is that even before a house is built, the materials used in its construction have a Product Energy Requirement (or PER), which refers to all the energy (expressed in kilowatt-hours) that goes into producing and transporting a product.

Timber has the advantage here as it is produced by natural means - sun, water and air, so its energy requirements are all in the extraction and transportation of the logs from the forest.

A timber frame wall in a typical three-bedroom detached family house has a PRE of around 7,450kWh, while a concrete block wall in the same property requires 1.7 times more energy, with a PRE of around 12,816 kWh.

Timber is also the only renewable structural building material available, and the majority of timber frame package companies invest heavily in well-managed replanting programmes.

Continue Reading: Building Regulations

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Services Timber Frame House Building Regulations

September 2004

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