A good ventilation strategy is required even during the construction stage

 

 

Especially now in the winter time it´s easy to see indicators of high humidity levels in new buildings, which are still at a certain construction stage. It starts with condensation at the window panes and can easily end as seen on the photos down below.

But where is all the dampness coming from, especially when the house isn´t finished and no one occupies it? Reason number one is the infiltration of rain during the early construction stage, when the windows haven´t been installed and the roof wasn´t covered. The second reason is mostly not considered, because the most people can´t imagine the total amount of water, which needs to be added during the construction stage. It starts with the pouring of concrete, continues with the blocklaying and finishes with the plastering. All these trades require a certain amount of water, which ends in a few hundred liter in total.

The dampness inside of the building needs to dry, which takes long enough during the summer time. It´s getting more complicated in the winter, because of the lower temperatures.

Another huge problem, that extends the drying process, is the well insulated and tight structure of the house.

 

What needs to be done?

- prevent the ingress of rain during the construction stage as much as you can

- remove (visible) standing water on the floors as soon as possible

- ventilate the building properly when the windows have been installed

- cover all accesses to colder building areas (cold roof attic, crawl space,...) temporarily

- wipe of all traces of condensation and do not store the damp cloths in the building

- consider a temporary heat source for the winter time, to create warm indoor climate

 

It´s a fact that warm air is able to store more moisture in comparison to cold air. That means a good ventilation strategy for the unfinished building during the winter is:

1.  get fresh air in by opening the windows (even on a damp day the external air will be dryer than your wet internal air)

2.  close the windows and heat the building to approx. 15° Celsius

3.  ideally use fans, to get the air well circulated in the entire building

4.  switch of the heat source and open the windows again to replace the warm humid air against dryer cold air

5.  repeat the cycle until you lowered the humidity in the building

 

As a short side note: If you want to use a dehumidifier, please make sure that you have a certain indoor temperature and do not try to dehumidify your entire building by using a domestic dehumidifier, which might work for a single room.

 

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