Timber Frame Extension Questions

Will a prefabricated timber frame structure for our kitchen extension be quicker and cheaper than bricks and blocks?

YES, in principle, and taken as an overall project.

Todays’ higher Building Regulation standards make it increasingly difficult to make basic ‘like for like’ comparisons.

This means we need to consider the eventual performance of the building.

Generally timber frame weighs much less than bricks and blocks, so the foundations can be easier and less costly to build.

If the insulation is factory fitted in the timber frame this can reduce time and waste on site.

Because the ‘build’ process is quicker, you need fewer preliminaries & other site costs, like project programming and management, the rent of equipment, scaffold and fencing.

Depending on design, the external ‘rain screen’ of bricks or blocks can be replaced by (near) dry cladding applied direct to the frame.

This can further reduce weight and be applied very quickly without being delayed by bad weather.

Work inside your timber frame structure can be started as soon as the frame is up and be executed at the same time – or even before – the outside walls are finished.

Because timber frame construction is mainly a ‘dry’ process, you avoid the drying out delays of a ‘wet’ build structure, e.g. for decoration.

This also means that (as recognised by the NHBC) you should experience less movement, settlement, shrinkage and other ‘snagging’ issues with timber frame than with masonry.

Overall this can add up to considerable time and cost savings.

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How will the new extension be fixed to the existing structure ?

We determine this as part of the design process.

Obviously it depends to some degree on the materials your existing structure is built from, and how the external walls are – and will be – finished.

For aesthetic reasons it is often a good idea to make a small, deliberate break between wall surfaces.

Skilfully done, this can make your extension look as though it is part of the original building.

This is one of the specific issues we address when we are instructed to carry out the full design for planning permission as a precursor to doing the engineering and structural design for manufacture.

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Can you provide and fit windows and external doors ?

YES. This can be done as part of your order.

However, there are a great many types of each of these and decisions need to be made early on as to which to use.

For example:-

a)      do you want uPVC, Softwood, Hardwood, Modified Wood, Aluminium, etc?

b)      what sizes do you want for each room?

c)       what insulation and other performance values do you want from each?
(remember that external doors now have to be insulated too!)

d)      what is your budget for these?

(They can cost more than the timber frame structure).
We can provide initial budget prices for guidance if required. 

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How easy is it for alterations be made at a later date ?

This is usually quite a simple process, providing you know what to look for and what precautions to take.

If required we can provide you with drawings showing where all the main structural timbers are so that you can avoid damaging these – or make alterations that incorporate additional structural provisions.

However, we recommend that you try to envisage what possible alterations might be required in the future, e.g. for putting in a new doorway or window, and let us make provision for these in the engineering, design and manufacture.  The positions of these can be shown on the drawings.

If this is done at the outset it can enable you – or some future owner – to do the work quickly and at modest cost.

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Can I put another floor on top of my new extension at a later date ?

In most cases YES.

All of our walls are made from the same materials as we use for building up to 6 storey apartment blocks, so they are pretty strong.

Generally most single storey structures can take loads from up to 2 additional upper floors without much difficulty.

However, there are other considerations to take into account, like:-

a)      the type, thickness and spacing of floor joists.

b)      where the upper floor levels have to meet with the existing structure.

c)       How the roof levels will connect

d)      Where door and window heads should best be positioned.

If you think that this is ever likely to be a future requirement, we recommend that you discuss this with us at the earliest possible stage; preferably before you finalise your planning application drawings.

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If our house is brick and we build a lean-to extension in timber, would we face any problems with planners ?

One of the advantages of timber frame is that you can use many types of cladding.

This means your extension can be designed to fit in with the character of existing buildings and surroundings. It is ideal for conservation areas and national parks, for example

Since planners are interested in appearance, rather than structure, this can be a great benefit for you.

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If our house is brick and our extension is timber would we face problems with condensation because of the different materials ?

There are two parts to this quite technical question:-

Condensation does not result from the use of different materials, but from moisture in warm air meeting cold surfaces.
If one surface is colder than another, then it is the one most likely to 'attract' any condensation.
It is therefore important to 'design out' these cold surfaces and opportunities for excessive moisture build up in the air inside buildings.
To do this the building designer should try to eliminate 'cold bridging' between the inside and outside of external walls.
Putting insulation in these walls, but leaving areas where there is none can result in such a 'cold bridge'.
Fortunately timber is itself a good insulator, so the risks of this are reduced when using a timber frame.

Moisture in the air inside buildings comes from anything that has water in it.
We may see this as steam, as from boiling a kettle, running a bath, taking a shower, or washing clothes.
Or we may feel it as sweat on our skin as we perspire, or breath out onto a cold part of our body.
But the outside air may also be 'humid' and quite 'wet', introducing the issue of 'relative humidity' between inside rooms and the inside and outside of the building.
Again these are issues dealt with as part of the building design.
UK Building Regulations require windows to have 'trickle vents' in the heads, that can be opened and closed if required.
While they also require a minimum air tightness equating to circa 10 air changes per hour, a standard timber frame achieves around 5 to 6.
Since 'air leakage' is a major source of heat (and thus energy) loss, new houses have to be subject to a special test to verify that at least the minimum standard is reached.
Advanced systems are taking this down to below 1 air change per hour.
However, if the house is very 'airtight' (e.g. below about 2.5 to 3 air changes per hour) it may be necessary to install a mechanical ventilation system.

Many people are finding that specifying a timber frame for their house - or home extension - is one of the easiest ways of addressing these technical issues and statutory requirements.

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I have planning permission for a traditional extension (block/brick), I wondered if these plans could be used to give an estimate for a timber built extension?

Yes, most certainly..

We regularly get asked to convert 'wet build' brick and block construction drawings into timber frame structures. This is increasingly the case with extensions since the relative lightweight and design flexibility that these provide are well suited to extensions.

Also, modern timber frame structures are able to deliver very high energy saving building envelopes, making them very economical to run, as well as build.

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I have a brick & block kitchen extension on the back of my house. Can I build a timber frame extension on top for a bedroom or bathroom ?

In principle YES you should be able to put a timber frame extension on top of your brick & block kitchen extension. In fact this is probably the best choice for your build because it will be relatively lightweight and be more easily carried by the ground floor and the foundations.

However, you will need to have the foundations and the structural suitability of the kitchen checked out for any structure. Depending on when it was built, your local Building Control department should have plans that can provide the answers to this. If you have a word with them at the same time as you get the 'as built' drawings, they may be able to tell you there and then if you can do this.

When you have their OK you will still need to have plans drawn up for their formal approval, and probably also for planning approval. Depending where you are in the country we may be able to do these drawings for you as well as the subsequent timber frame and some other works.

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