Timber Frame or Blockwork?

There’s a rather amusing end to a fairly dry research document entitled Energy Efficiency and Sustainable Building Options With Modern Masonry: Information Paper, which is presented as a technical document on the website run by the Traditional Housing Bureau (the lobby group advocating greater use of concrete in construction). To all initial appearances the paper looks as though it could be an independently researched scientific document — it’s properly annotated and written in neutral language, and to the casual reader it would seem to be a worthy read.

It’s only when you get to the end, having read 11 pages worth of findings that all seem to point suspiciously to the overwhelming conclusion that blockwork is the only viable building method in the UK, that alarm bells ring. For, after all the statistics, research and conclusions, there’s an innocent-looking section called ‘Acknowledgments’ and in that section five people are thanked for their ‘input’. And every one of them represents a leading block manufacturer.

It’s not just the blockwork lobby group that only presents one side of the story. The UK Timber Frame Association, which represents the leading timber frame companies in the UK, has a section on its website promoting The Benefits of Timber Frame, most of which point not just to the energy-saving qualities of timber frame homes but the low-impact nature of timber frame construction.

For someone choosing a construction route, it’s all very confusing. I’m intending to build again this year for the second time and I’m not quite sure what to choose this time. My first home was blockwork, and I’m really happy with it. It feels solid, it’s very quiet, and it’s what the builders were used to building in. But is it worth switching to something else? I’m curious about the claims made by the two different groups and I’m also interested in the other alternative building systems. This article is the result of what I found, looking at the different claims and issues in turn.

The Claim: "Timber Frame is More Green Than Grey"
The UKTFA claims that timber frame is more energy efficient than blockwork. Is that really the case?

If you want an energy - efficient home, then the critical issue is the specification, not the choice of construction system. Timber frame suppliers’ claims of wall U-values in the region of 0.26 – 0.3 are perfectly accurate — but it’s a claim that blockwork home suppliers can match. “With a 100mm cavity fully filled with the top-of-the-range DryTherm 32 insulation, with a structure of brick, cavity, insulating blockwork and dry-lining, we achieve around 0.25,” says Dan Mutti from Design & Materials. “The main issue is the wall thickness for blockwork homes. We tested extending the cavity to 125mm (the standard is 100mm) and fully filling it — this achieved wall U-values down to 0.223, for an additional average cost to our clients of around £1,500.”

Design & Materials decided against introducing the extra-wide cavity as standard on their packages because of the difficulties for builders in getting hold of non-standard insulation and lintel sizes off the shelf.

Joe Mortaccia from timber frame manufacturer Potton says that a standard 140mm timber frame wall will achieve a Uvalue of around 0.24 — on a wall thickness less than half that of its blockwork equivalent.

Independent SAP Assessor Simon Bovington admits that “it is going to be more difficult for blockwork to meet future energyefficiency requirements without resorting to greater wall thicknesses”.

Simon, who has over 30 years in the industry and has measured the energy efficiency of hundreds of homes, says that the key to energy efficiency is in the specification of the house, not in the construction technique. “The things that drive energy efficiency are bespoke specification issues such as levels of insulation or airtightness — not necessarily the choice of timber or blockwork.”

It’s also worth noting that clients may be mistaken if they place too much emphasis on the U-value of the walls alone. “In all honesty the key to energy efficiency is just as much in the design of the house,” says Dan Mutti. “More and more people are these days wanting bigger windows and more of them — meaning that you can battle all you want on the relative efficiencies of wall construction, but if they’re next to loads of large windows that have U-values of 1.8 then it all becomes a bit arbitrary.”

With the roadmap set out to ensure all new homes meet ‘Zero Carbon’ status by 2016 — and Building Regulations getting tighter and tighter all the time, it’s fair to say that the lines between the different construction techniques are likely to blur to nothing in coming years anyway. Zero Carbon may well go some way to unifying the manufacturers in ways thought impossible several years ago.

Our Verdict: Energy efficiency is about specification of insulation, good design, on-site building practices, airtightness and a whole range of other things — much more so that simply arguing the toss between the relative merits of timber or concrete. The differences between wall performance are now so small that the argument has rather moved on and it’s down to individual bespoke specifications much more than choosing one system over the other.

The Claim: "Lenders and the public don't like timber"
Will choosing timber frame affect your resale value, finance arrangements or ability to insure?

Patrick Sawdon, Head of Professional Services at the Halifax Valuation and Surveying Services said this about mortgages: “Halifax takes the view that properly constructed timber frame housing with a suitable external cladding is equally as good as housing which is built in brick or block, and we make no differentiation in the lending terms offered on either form of construction.” Timber frame construction is recognised by the NHBC and Zurich Municipal for guarantee purposes. Steve Birt of the Association of British Insurers says, “Insurance companies generally draw no distinction between modern timber frame and brick and block construction.”

In terms of sale price, current research by SmartLIFE, confirms this summary of public attitudes:

• There is a sentimentality for brick among some homebuyers (which may also explain why so many housebuilders choose to put a brick exterior on frame-built homes).
• Most people have no idea what form of construction has been used for their homes.
• And unsurprisingly most people don’t really care — if you offer someone a spacious, energy-efficient home at an affordable price close to local services, it doesn’t matter how that home is built.

Our Verdict: The fact that so many developers choose timber frame nowadays is testament to the fact that for the resale market your choice makes no difference whatsoever.

The Claim: "Something's eating away at my home"
Timber frames are targets for rot and destruction, claims the THB. True or false?

One of the oldest clichés about timber frames is that they pose a fire risk. One assumes this started sometime after The Great Fire in 1666 but it’s safe to say that despite spurious attempts by the blockwork lobby groups to again link timber frame construction to a recent construction fire in London, modern building regulations and the strict fireproofing of timber and dry lining mean that fire is simply not an issue to consider for today’s self-builder. According to the Government: “People should not worry that timber frame presents significantly more danger from this type of fire than buildings of other construction types.”

Rot and infestation is also not a problem for timber frame homes provided wood that gets wet is allowed to dry out properly and timber is treated with the proper stains and paints. Modern timber frames are pre-treated against many of the potential problems that blockwork lobbyists claim. Rot-producing fungi will only attack wood that has a moisture content consistently over 20%. It’s also worth noting that some of the world’s oldest surviving structures are timber frame.

Our Verdict: This is one of the most controversial of all the claims and counterclaims made by the two sides. Modern Building Regulations are so strict that rot, fire risk and decay are no longer serious issues to be considered.Warranty providers certainly don’t consider them problems and neither should self-builders.

The Claim: "Blockwork homes are less noisy"
Are timber frame homes really noisier — and does blockwork really reduce noise problems, as the THB claim?

Noise transfer is an issue that has bedevilled the timber frame industry for many years. “The reason for this is that many people’s experiences of timber frame housing is of homes that were built in the 1960s and 70s,” says Joe Mortaccia from Potton. He breaks down the approach to reducing sound into two different approaches — density (favoured by the blockwork lobby) and decoupling, which means creating cavities and spaces for air to fill. That’s why Potton like to have a cavity between the internal panel and external cladding.

“Part E of the Building Regulations is pretty strict in terms of any new home’s adherence to building practices that reduce sound transmission,” continues Joe. “All timber frame homes obviously have to meet this criteria.” It’s also true to say that many blockwork homebuilders still use stud walls for internal partitioning. The fact remains that if you want blockwork partition walls you will need a solid first floor structure to build them off and the only system that will let you do this is a blockwork skin. The Traditional Housing Bureau (the blockwork lobby group), claims that a room made out of blockwork walls will have a decibel rating of 46dB as opposed to a studwork wall which has a rating of 35dB — meaning that the blockwork wall is a better airborne sound insulator by 11dB.

“There are easy ways to improve the performance of stud walls,” says Joe. “First of all, you can add insulative quilt into the stud, which works really well — or you could add a double layer of plasterboard.”

The UKTFA has spent a lot of time trying to refute the claims that timber is a poor acoustic insulator and cites research on the UK’s largest database of test cases on sound performance going back over 17 years, carried out by Dr Sean Smith of Napier University. He says: “Our research shows that timber frame party walls are the best performing in the industry — for current and future regulations… If all dwellings had sound insulation as good as that measured in party walls of timber frame homes, the problems of noise from neighbours would be greatly reduced.”

Our Verdict: Specified correctly, timber frame walls can easily provide effective acoustic insulation — but this is an area where blockwork still reigns on a like-for-like comparison.

The Claim: "Timber Frame Homes cost more to build"
The perception is that blockwork is cheaper — but does that translate to reality on site?

In terms of cost, the two are probably more similar than is generally understood. In his definitive The Housebuilder’s Bible, H&R Contributing Editor Mark Brinkley reckons that to have replaced the blocks on his 110m2 benchmark house with a 140mm timber frame would have added around 20% to the cost of that part of his project — but this part of the project only accounted for around 14% of the project’s costs. Don’t forget that you’ll still need an outer skin with your timber frame, so the element of that which could be swapped for timber frame accounts for perhaps 10-15% of the total cost. The family who built the contemporary Potton house currently featuring in their advertising spent around 25% of their total build cost on their Potton kit (the total build cost came in at a little over £1,000/m2).

What to make of this? Well, there appears to be no real pattern. Mark Brinkley claims that the prefabrication of the timber frame adds to the relative cost and “you would expect to pay between £2,000 and £5,000 for the service”. He goes on to say that these costs are offset somewhat by a quicker time on a site that’s less prone to things going wrong.

A cursory survey of the case studies that have appeared in H&R over the past 18 months provides interesting results. Blockwork homes had an average build cost of £1,338/m2; timber frame (we included oak, but not SIPS in the survey) came in at £1,285/m2.

The Claim: "Timber Frame's 30% Quicker"
Blockwork’s slow, timber frame’s fast, claims the UKTFA — but how true is it in reality?

Tom Somerville from Design & Materials acknowledges that, from a standing start, timber frame homes are likely to be marginally quicker on site than an equivalent blockwork house. Joe Mortaccia from Potton claims, “I wouldn’t disagree with the UKTFA’s claim that timber frame homes are on average 30% quicker than blockwork equivalents. If you take a look in our factory you’ll see two men putting together a 6m2 panel in less than a minute, and it won’t take them much longer to bolt it all together on site. Compared to the time it takes to lay blocks, and the time it takes them to dry out enabling future work, timber frame has to be quicker.” In response to this, many blockwork manufacturers have been introducing largeformat blocks which despite being more difficult to handle can, they claim, bring about 50% time savings on site.

David Snell, H&R Contributing Editor, author of Building Your Own Home and 10-time selfbuilder, has produced a very handy wall chart showing a projected schedule of a house construction project for both timber frame and masonry construction. According to the chart, while timber frame homebuilders get to first fix stage about four weeks quicker than their masonry equivalents, the end result ends up being perhaps a week or two quicker in total. He claims that this equates to reality on site due to longer lead-in times for factory construction of the frame.

One of the wilder claims that you often hear of timber frame homes is that they can be built in just a handful of days. As anyone who has built a home will know, this figure can only be realistically achieved with a massive amount of prefabrication, meaning that while the time on site may be minimal, the time off site is likely to be long.

Our Verdict: Timber frame’s quicker — but probably not by as much as manufacturers claim. Greater savings can be enjoyed by being able to order early — so get organised

Read about the alternatives to Timber Frame and Blockwork