The equilibrium moisture content of timber under Hungarian conditions, in non-closed airspace of pine-wood 12 - 18 % and hard-wood 9 - 15 % The Hungarian architects plan in non-closed airspace the pine-wood structures for 50 years, the hard-wood structures for 150 years term,

The chance of wood deterioration after decades and centuries is high. Because of the long term leak and the fluctuating humidity, fungi and insect can attack the wood and results stability reduction.

Experts evaluate of wooden structures from time to time. They establish the measure of damage and the fact of timber stability reduction. They make on offer for structural engineer. responsible for renovation for change of parts or full timber structure. In this process the data of strength is missing.

In the Wood NDT Lab of the University of Western Hungary I worked out a method as a result of intensive research. Using the method we can predict the momentary bending strength of the built-in timber. The standard error of strength estimation is +/- 8 MPa During the examinations of the built-in timber I measure the screw withdrawal force and the stress wave velocity using CS-600 screw withdrawal force meter and FAKOPP microsecond timer.

If we substitute these data for the empirical equations of pine-wood and hard-wood we would calculate the values for momentary bending strength. The measurement fit in to the present evaluation system well.

The structural engineer who responsible for the structural evaluation, receives the result of the timber protection expert examination and the residual bending strength data. Using this evaluation technique we can save more historical structure then by traditional technique. Then we have to make the exercises of timber protection and some timber structure reinforcement. This new method I have tested several historic timber structures.

The Headquarters of State Monument Renovation and Restore m Hungary attracts the attention of the importance for this examination and gave me some contracts for historic timber structure evaluation. Using this technique we can reduce the costs of renovation and maybe we can save historical timber structures.