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10 most frequently asked questions by architects on a topic of timber constructions

We get asked the same questions when discussing timber constructions with architects and designers. Which type of the construction to choose (massive, timber or hybrid) and when? What is the price of a timber house? What is the maintenance of timber cladding and its lifespan? Here you can read some answers to the ten most frequently asked questions:

* Massive construction system - the load-baring structure is brick, concrete or iron-concrete. *

What limitations of the architectural design are there for timber constructions? What should you be always careful about?

The language of architecture expresses thoughts and ideas of both, a client and an architect and that alone creates the uniqueness of each project. With todays experience and technologies in a field of timber constructions, almost anything can be realized. There is no need to stick to just standardized solutions. The features of the timber constructures are different from the massive ones. That's why it's good for an architect to take it into account already in early stages of the design. That applies mainly to the scope considered, zone planning, the energy standards to be achieved, the suitability of internal surfaces, etc. Judged by our own experience the most effective solution is a dialogue - in other words a professional partnership. That is why we are here.

What is the lifespan for the timber construction?

The oldest existing timber construction in the Czech Republic dates back to 1355. This shows that the duration of life for timber constructions is very long.

The lifespan for timber constructions is over 200 years. In contrast to that, the moral lifespan for these buildings is "only" 25 years. That's a great unevenness. So the question is: For how long do we want to use the timber constructure in its prime, original state? 

It is essential to build the construction to its perfection so it wouldn't get damaged. This could be ensured by using the Certified DNK System (National Quality Document) by ADMD Association.

Is the timber construction cheaper or more expensive than the massive construction?

First: let's compare apples with apples, not apples with pears. Let's define what services we are comparing. There is a great variety of possibilities in both construction systems (timber or massive). The choice of a construction has nothing to do with a size of Your budget nor Your preference of a construction system. It all depends on Your expectations from the construction as a whole. What is the standard completion rate? What are the secondary benefits? What are the sizes of the rooms?

According to our experience, timber constructions mean a cost increase up to 8% compared to massive constructions - in accordance with project's specifications.

But if we look at the cost from the construction's lifecycle point of view (realization, maintenance, demolition), the timber construction usually comes out as the cheaper one.

From what we have experienced, the most efficient way is to make the choice of a construction system already while preparing the design's proposal of the project. Only then it's possible to optimize the architectural solution directly to Your chosen construction system.

Can we determine approximate cost per square meter of usable area?

Theoretically the price can be specified - however, it is often a game to sum up  inaccurate assignments with the expectation of precise and binding result.

Other specific factors  (a crane, transports, production machines, construction joints, etc.) must be included in the cost of timber construction in order to obtain a meaningful price. These costs are influenced by the size, the complexity of delivery and static measures that differ from one project to another.

 An illustrative example of why the price calculation based on square meters (the same as for m3) does not always work.

Same usable area. A difference in delivery for the peripheral walls 44%.

Resume - the subsequent calculation of the price per m2 will never be the same number.

 Yet with all considerations above, we've achieved high accuracy in our price estimations over the last few years. We process it for free.

Is the maintenance cost of the timber construction higher than with the massive construction?

The task of a maintenance for all types of construction is to manage and maintain all built-in materials and to keep them in the best possible condition. However, the amount of such cost depends on the size of the building, the materials used, the choice of outer and inner surfaces, rather than the type of load-baring structure used.

The maintenance cost changes throughout the lifetime of the construction in connection with the change of the construction's value, which is also gradually diminished with no reference to the type of the structure used.

What about a heat protection during summer?

The physical properties of the constructions, ie the amplitude of a heat resistance and the phase shift, are nowdays insignificant informations for a quantification of thermal insulation in summer and don't lead to desired comfort.

The value of the heat transfer coefficient for timber constructions is now at such level that there are no extreme heat loads in the rooms. In the summer season, it's the level of glazing, windows orientation, sunshield, ventilation, technical equipment and the level of occupancy what's much more determinative.

It is advisable to solve the heat load of the timber structure while still working on the proposal for the project and minimize any changes at the point of a construction' solution.

The tools at construction level are: sun protection and storage (absorption) weight of the construction. We can find these in the construction of a rough floor when it comes to timber constructions.

The users' behaviour plays a key role as well. It is based on their smart use of the sun protection and especially on undertaking suitable ventilation routine.

What is the lifespan of the timber cladding facade?

The alpha and omega is the right design and execution of its details combined with regular inspections and maintenance. This prevents from any damage to its functionality. The choice of wood species, the surface treatment system or other details (such as distance to terrain) have a great impact on its durability. If You take care of the timber facade properly and You keep the advice of our consultants on Your mind then You can expect long lifespan. The needs and wishes of investors vary with each project. We are capable to design and execute a maintenance-free timber facade for many decades to go.

What is the optimal treatment interval for a modified timber facade?

The requirements for the surface treatment and construction of the timber facade vary - to protect it from wind, storm, rain, snow or sun. It is often intended to fulfill some creative, aesthetic, sometimes artistic function too. Just like it was with our ancestors. There are many factors that affect the renovation and maintenance interval of the timber facade, such as the location of the construction, its orientation to the world's directions and of course the constructional protection of the timber.

In general, the optimal interval of 5 to 10 years can be considered - unless a maintenance-free solution is proposed in the project.

Is it necessary to use the vapour barrier/airtight layer?

 First of all, it is necessary to decide in time what type of construction(diffusion wise) we’re planning to execute, open diffuse or closed diffuse. The difference lies in the order and the choice of the materials for the timber constructions. The vapour barrier layer is not always necessary and may have a variety of forms (foil, textile membrane, CLT, plywood, etc.). We design constructions structures carefully and responsibly - all structures are tested and checked by the building physicists. We provide air tightness according to DNK (National Quality Document) for each building. This quality of the building is elemental in order to meet all energy requirements and to achieve the building's final condition. This all is to prevent from any flow of hot indoor air out through the construction joints and vice versa to the cold outdoor air inwards.

The connection of individual components, such as windows, doors, electrical installation, is combined with a sophisticated design and it's airtight. In many construction cases we associate the function of the vapour barrier with an airtight layer, ie we use the same material for both. This vapour barrier prevents the penetration of moisture from the interior into the thermal insulation of the structure. This prevents the formation of condensation in the insulation layer.

How is it with the fire protection of timber constructions? Is the risk any higher than with the massive construction?

Czech Republic has one of the highest safety standards for fire protection in the world. Compared to the fire protection regulations and standards of all progressive european countries (Germany, Austria, Switzerland and Scandinavia) we unfortunately have still a long way to go. Particularly in Switzerland, from 1st January 2015, a new fire protection standard is in place, which sets the same conditions for massive and timber constructions. This allows the unlimited height realization of timber constructions. Therefore there is no problem to build 100m tall timber construction(skyscraper). Just to make it easier to visualize, it is a building of 30-35 floors.

Even though the timber constructions in Czech Republic are being dismissed a lot, we will not give up the fight against the windmills. We keep collecting experiencies even abroad and that gets us prepared for anything.

The fire risk usually depends on the layout and all equipment of the interior (furniture, curtains, etc.) not to forget the related activities of its users. Therefore there is a rule of no greater fire risk for timber constructions than there is for other types of constructions.


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