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The Essential Guide » Timber Frame | Sips » Structural Stability of Timber Framed Houses
Structural Stability of Timber Frames
Q: How strong are Timber Frames? – Which is stronger – Timber Frame or Traditional Construction?
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If you are thinking about a Self Build project and you are even considering using a timber frame construction, I bet this is one of the main questions in your mind.
Here in the UK we are used to houses being built in brick and block (traditional construction). – It’s what we grew up with. – It’s what we know most about, and it’s what we have always thought and been told is best.
Part of the reason for this thinking is that as some of the big commercial house builders started to try to cut costs in the seventies and eighties, instead of using all solid blockwork internal walls, they started to use timber “stud” walls. – These walls were often just 3” x 2” timbers at about 2’ centres, with 3/8” plasterboard either side. – With no insulation in the cavity and often with the plasterboard being badly fitted, so that there were gaps around the edges where sound could easily be transmitted from room to room. – You are sure to have been in one of these houses at some time where you are able to almost hear people breathing in the next room!
That type of building was what started to give the words “timber” “timber stud” “timber framing” a bad name in terms of house construction.
The problem for trying to get timber widely accepted as a building method in the UK was compounded when the first Timber Framed houses started to appear, built by the commercial builders. – Within a short time of the first ones being completed, problems started to appear. – Serious problems! (Or so it appeared).
In some of the early timber framed houses in the UK, the external skin of brickwork or blockwork would start to come away from the timber frame itself, and this would result in the brickwork beginning to “buckle” or “bow”. – Obviously this was a serious matter, especially for the people who had bought the houses, and were not only left with a house that was literally falling apart, but that was also pretty much worthless when it came to trying to sell it.
The problem was actually nothing major at all. – The biggest Part of it was nothing to do with the timber frame itself, but the wall ties that were used in the construction. – They were simply not up to the job.
Either the ties were coming away because the screws that they were fixed to the frame were inadequate, or the screws themselves were actually rusting and failing, allowing the external skin of the wall to start to bow outwards.
The problem was easily fixed by changing to more substantial stainless steel screws and ties, and there have been no other real concerns about timber frame in the UK since that time.HOWEVER! – Because of these two problems related to timber and timber frames in house construction, the reputation of “Timber” and “Timber Frame” as a material for use in house building was pretty much in tatters! – And it would take many years for us as a nation to start to accept and embrace Timber Framed Construction as a genuine alternative to Traditional Build.
So, where are we with the “Timber frame versus Traditional Build argument now?
Well, it still rages! – But not in the same way. – Timber Framed Housing is now completely accepted by the industry and by the warranty companies as being just as suitable for house building as traditional construction, and there have been major advances in the past 20 years in the construction methods which have improved many aspect of timber frame in respect on structural stability, longevity, soundproofing, heating insulation etc.
So, that's all very well, but the reason you are reading this article is probably to find out which choice is going to be better for your project:
Should we choose Traditional Build or Timber Frame?
If I had to answer that simple question for most Self Builders, I would immediately say “Timber Frame”.
If I had to answer it for “Commercial House Builders”, I would be more likely to say “make them build traditionally” (but, unfortunately that’s not going to happen).
Why would I say that?
Well the easiest question to answer is the second one:
Many Commercial house builders tend to “throw” houses up as quickly as possible (sorry guys, but I’ve worked for some of you and know this to be the case!). They also usually have very tight budgets to adhere to. – If there is a way to be able to build quicker and cheaper, many of them will be using it as soon as they find it! – Unfortunately this policy ends up with many of the large house builders producing inferior quality houses (compared Self Build for example), many of which have those “soundproofing” problems I mentioned earlier along with all sorts of other problems which are not apparent when people look around the shiny new show houses. – Things like creaky floor boards, badly fixed wall boarding, poor plasterboard jointing, cheap materials which “fail” after a short time....... the list goes on.
When the commercial builders who are trying to save every penny, use timber frame, they will sometimes tend to cut all the corners they can, and with timber frame this is quite easy to do. – They will use the cheapest timber frame at the lowest spec possibly that will get past building regs. – They will grind the supplier down in price so that the THEY have to start to find ways to save money on the cost of production. The result of this cost cutting will often be a pretty shoddy end product which can cause both structural and cosmetic problems for the owners a few months or years down the line. – If commercial builders were forced to build traditionally, at least they would be forced to use materials that are harder to “downgrade” (bricks are bricks, blocks are blocks, mortar is mortar. - End of story!)..
Why should Self Builders consider using Timber Frame when it comes to the structural stability?
In probably 90% of cases where a house is being built by a Self Builder, when it comes to Structural Stability, I would strongly recommend using Timber Frame (or SIPS).
(Note: If you have read other sections of this guide, you will know that for me to say that, there must be a good reason. – I was about as “anti timber frame” about 20 years ago as you could be! – I actually lived in a timber frame that had the wall tie problem!)
There are a number of reasons, including:
1) Most Self Builders do not have a high level of experience with major building projects. – Everything they do is “a first”, most decisions they make are “best guess”, based on masses of information that they are faced with. – Every trade they deal with use words and building terms which are completely foreign to them, and they have to try to make sense of everything at the same time as getting every decision right and planning the next stages of the projects. – This is what puts many people off even starting a project – It can all be just TOO much.With a timber frame, a lot of the decision making and a lot of the requirement to know about dozens and dozens of different subjects is taken away from the Self Builder, - because the timber frame manufacturer takes care of it all. – As long as you use a reputable company, this usually has the effect of helping to ensure that things are done properly. – If things are done properly in the first place, then there will be less chance of encountering problems, structural or otherwise, later on.
2)
With Timber Frame, prior to starting, the design and specification process is usually made easier, - along with getting the building regs approval.
Self Builders have a habit of changing the designs a number of times before the work actually starts (and even after building has begun!)
If a timber frame manufacturer is looking after both the design and the manufacturing process, then the designs will normally be done "In house" on a software package which specializes in designing timber frames. – This means that when and if the client wants to make changes, the spec can be altered easily and quickly at any time in the process. These changes will be made straight onto the original designs within the software packages and all the implications of the changes are usually highlighted and automatically dealt with.
The result of doing things this way is that there will usually be less chance of errors being made which will surface further down the line, than if different people are doing different parts of the design and specification work (e.g. if an Architect designs a house, then Structural Engineers design the foundations, a Quantity Surveyor takes off all the Material Quantities and a builder prices up the work to build the “Shell” of the house, then there are 4 sets of people who have to coordinate with each other to make sure that the implications of any changes are fully noted, covered and costed. If any one of them gets their bit wrong, it will increase the chances of things wrong, either structurally, financially or cosmetically).
3) When it comes to the building work, once the foundations and slab are completed, the timber frame comes along on the back of a wagon and your house just appears!
Even if you just buy a basic timber frame, you don’t usually have to worry about choosing, measuring, finding and, pricing up all the materials that will be needed to build the shell of the house (meaning that, even for a basic frame, in many cases you won’t need to measure up and order such items as blockwork, dpc, lintels, cavity closers, cavity insulation, wall ties, joists, floor boards, roof trusses, fascias, soffits, barge boards and a number of other items).
This fact ensures that if you don’t have a great deal of knowledge of building, you will still get all the right materials in the right quantities at the right time without spending all your time trying to work out every item that you’ll need, quantifying it, finding it, pricing it and making sure it is delivered just at the right time.
(As an example of this: Would you know that lintels generally need 150mm seating either end, but on a corner, when they sit on a 100mm block, then they need to just have the 100mm seating and not cross the cavity – If you don’t, then you might order the wrong sized lintel. – The brickies may just use it anyway without thinking (because waiting for another to be ordered and delivered would slow them down too much), and you end up with a structural error that could theoretically cause problems with damp getting across the cavity. – If all the lintels are part of a timber frame package you don’t need to worry!)
The more your timber frame package includes, the less you have to worry about ordering.
4) For each item that the timber frame provides as part of the package, the timber frame erecting gang will usually also take care of the “labour aspect”. – They won’t just “deliver”, they will also, “build”. – This means less work for you finding people to do those jobs, getting prices for the work, getting them to site when you need them, and making sure all the materials are there ready for them.Getting this part of the job wrong can have 2 effects:
i) If materials are not available when your subcontractors are there on site, you could end up either paying “daywork” rates for them to be standing around waiting for deliveries which “you forgot”, OR, it could result in them going off you job, leaving work open to the elements until they return. – If there is bad weather during that “down time” you could then have soaking wet insulation in cavities, wet structural timber which will take longer to dry out and other potential problems which could surface further down the line
ii) Because all Self Build houses are “one off’s” there is a learning process to building them. – The big developers will make their mistakes on the first dozen or so of a new house design and generally “get it right” after that. – Builders working on a “one off” Self Build are likely to get a few things wrong as they work. – These errors may be insignificant, but could just as easily be things which cause structural or other problems later.
5) Self Build house projects tend to take a long time to build. – Mainly because of the inexperience of the Self Builders themselves. – Trying to get everything running smoothly and fast whilst also having family commitments and usually a full time job to include in the equation, means that free time for organising the building works is often limited. – If a Timber Frame all comes along on the back of one or two wagons, how much easier is that going to be on you when it comes to demands on your time?
If it is easier on you, then there is less chance of you missing something that could cause the job to stop, or worse still, of you missing something important. – If you DO miss something important and no one picks it up, then it could cause problems with the structure of the house in the future (Did you use the right type of lintels? – Did you order the right grade of joist? – Did you use the correct fixings everywhere? Etc etc).
6) Self Builders don’t have the same tendency to build as cheap as possible (as some commercial house builders do). – Instead, they will usually tend to upgrade the spec of the timber frame to a higher level than is actually required. – This means that they don’t tend to encounter the problems that using inferior materials can cause. - If a timber frame is used, it is easy just to ask the designer to build in "upgrade" features than is it for traditional build. - There will be various levels of upgrade to choose from - strructural, insulation, components, preservative treatments etc, but they are all fairly standard and can be discussed, chosen and included quickly and without fuss.
Conclusion:
Having read this article you’ll probably get the strong impression that when it comes to the structure itself, I don’t think that traditional build is a particularly good idea for Self Builders who don’t have much experience of building. – You’d be right!
I have seen too many things going wrong on projects which were the result of lack of knowledge and experience on the part f the Self Builders themselves – This is not only bad news for the people it happens to, but gives the Self Build market a bad name with the lenders who are stumping up the money and wanting a good quality product which they can sell on if they ever need to. – The more problems which happen with Self Build projects generally, the harder the lenders make it for everyone to get the funding they need.
I am not saying don’t build traditionally, BUT I am saying that if you are not at least 90% sure that you can do a good job in terms of quality and that you can pick up on all the important aspects of the project (any one of which could cause you problems further down the line), then you would be well advised to consider the timber frame or the SIPS option (see next chapter for details on SIPS).
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