What Will it Cost? - Constructing Walls

Timber frame or brick and block. Which is cheaper? It’s a very basic question that keeps coming up time and time again. The short answer is that: “There’s not much in it.” They are both widely used in the UK: if one method was way more expensive than the other, then this simply wouldn’t be the case.

But the more you look into this seemingly simple question, the more complex the answer gets, because what you have are two rather different methods of building a house and the final cost of the project is greatly effected by the way you choose to build and the materials you choose to finish the house with.

Masonry

Although it’s often referred to as ‘brick and block’, what really distinguishes masonry build is the block bit, not the brick bit. You can choose any cladding (i.e. brick, stone, render, timber boarding) against any background. What concerns us here is the ‘background’ or inner skin, the structural walls that bear the load of the intermediate floors and roof above. Blockwork, set in mortar, has been the most popular way of building homes in England and Wales since the 1930s. The work is tradi­tionally done by bricklayers, who build both inner and outer skins of the cavity wall, as well as placing the joinery, the wall ties and the insulation as the walls go up. The work starts below ground where it is known as the footings, and breaks every time a floor has to be constructed. It also breaks at roof level, even when there is a gable wall to be erected under the roof.

Timber frame

Timber framed houses – the open or closed panel variety – are constructed very differently. Once the ground floor works have been completed, the superstructural work becomes solely the responsibility of the car­pen­ters. There are no breaks in the workflow between walls, intermediate floors and roof carcassing. Mostly in the UK, timber frame panels are built in factories and all the site crew have to do is erect everything in the right order: typically, this will take between seven and 12 days, depending on the size of house. The brick/block layers only return after the house is erected as the details they will work on, such as the wall claddings or chimneys, are not essential to the structure of the house.

This difference in the build methods explains just why it is so difficult to compare costs. Whilst masonry build naturally breaks down into walls, floors and roofs, with timber frame it breaks down into superstructure and clad­dings. In order to compare prices, work back­wards from a global price for a timber frame kit and try and analyse how much it would have cost had it been split into its constituent parts of walls, floors and roof structure. In this month’s article, we are con­cen­trating on walls so we effectively have to strip out the costs of floors (dealt with previously) and roofing (dealt with later in this series) but bear in mind that there are cost savings in simply erecting all these elements in one ongoing process, instead of switching between trades and break­ing up the workflow.

Wall comparisons

The standard British block wall costs around £18-22/m², of which two thirds is labour and one third is the cost of the materials, princi­pally the blockwork itself. This is the same for both the inner face of the external walls and the internal room partition walls. The cost of a typical timber frame wall varies as the con­struc­tion of the external walls and the room partition walls are different: the external walls need to be faced with plywood and incor­porate a waterproof membrane as well. The cost of the external walls work out more expen­sive than the blockwork walls (by around 25%) but the costs of the room dividing walls are cheaper (also by about 25%). They almost cancel one another out: almost, but not quite, as the typical house has a greater area of external walling than room partition walling.

As the load-bearing external walls and the internal walls combined make up no more than around 3% of the overall budget, you can readily see just how little the final bill will be affected by a decision to switch to timber frame or, indeed, from timber frame back to blockwork.

Alternatives

This article only looks at the very simplest wall designs. There are many alternative options out there both in the masonry field and in framed construction. Many of these seek to incorporate some form of thermal insulation into the wall design. This makes comparison difficult because the cost of insulation has been ignored when comparing the wall types — insulation is itself looked at later in this series. Rather than attempt to cost them individually, it’s as well to bear in mind that the cost of incorporating good levels of insulation into either block walls or timber frame walls is relatively low. Building regulations can be met within a budget of £3/m² using mineral wool, or £6/m² using foam boards. You can effec­tively budget £25/m² for insulated walling using either blockwork or timber frame: if any prod­uct being offered to you costs more than this, then you can tell at once that it won’t save you any money, even if you carry out the work yourself.

Overall costs

The benchmark house used for the basis of this series (see panel) has 190m² of inner skin walling (measured excluding joinery openings) and 144m² of internal partition walls (excluding door openings). The inner skin walls were built with blockwork, whilst the partition walls are a mixture of blockwork (downstairs) and stud­work (upstairs). The overall cost of this work, excluding insulation and joinery but including lintels and wall ties was £7,500 — or 5.5% of the overall build cost.

All costs and prices correct as of July 2005

Other Cost Guides:

• Getting out of the ground
• Insulation
• External Joinery
• Installing Services
• Roofing
• Internal Finishes

Further reading:

• A Guide to Construction Systems
• The End of Blockwork?
• The Evolution of Timber Frame