ᐅ Cracks in Stair Treads / Causes

Hello, in our new house (solid construction) we have a straight concrete staircase.

The treads are made of 4cm (1.6 inches) thick stained oak wood. The risers are made of birch.

The steps were installed in mid-March. The treads are developing more and more cracks. I first noticed this on an upper step, where there is a bulge and also a crack. Since today, the bottom step also has a crack.

There is clearance on both sides to allow the wood to expand.

Do you have any idea what might be causing this?

What was the humidity level during installation and what is it now? How are the steps fixed to the concrete? And how about the riser?

The humidity level is now neither higher nor lower than before; it is simply normal.

The treads are attached to the concrete with a type of adhesive foam. Below them is the riser, and in front is the next tread.

Coletrickle_7808 schrieb:

The humidity level is neither higher nor lower than before; it is just normal.

The treads are attached to the concrete with a type of adhesive foam. Below that is the riser, and in front is the next tread.

Yes, the answer could hardly be more vague. Did you measure the humidity? How wet was the building when the stair treads were installed? Had it already been heated and finished for months? Was the wood stored on-site temporarily? Are you currently living in and heating the building? What is the current indoor humidity level? How is the ventilation managed? And are the risers firmly connected to the treads or do they just rest on them?

The staircase was installed in mid-March, specifically on 17.03.22, and was one of the very last things completed. It is therefore less than 4 weeks old.
Heating was already on, and the walls were fully finished… as mentioned, it was the last thing done. Ventilation is done as recommended, using shock ventilation.

I cannot say where the steps were stored, nor do I have any information regarding the risers.

Okay, so you don’t know the humidity level in your home. I recommend getting a suitable measuring device.

A new build releases residual moisture for quite a long time, so indoor relative humidity often stays above 65% even in winter. If the heating is then increased, the relative humidity can drop to around 35%, which can cause wood to crack at its natural weak points. This happens less with glued laminated timber, but if the moisture levels are not right, cracks can develop there as well.

If the wood was not stored properly before installation, that can also cause damage. Additionally, if the glue joints were not made perfectly, this can lead to defects that look similar. There are many causes and many factors involved.