ᐅ Building Without a Ventilation System Using Porous Clay Blocks?

Hello everyone,

my wife and I are planning to build a house next year. We are considering using a hollow clay block filled with perlite without any additional insulation (such as expanded polystyrene or similar). How thick should the block be at a minimum to achieve a good insulation value (KfW 40)? What would the wall structure look like?

Is it possible to omit a ventilation system when using this type of block?

Please share any experiences from those who have built with hollow blocks filled with perlite.

Best regards, Fabian

Let's see if I can summarize this correctly and briefly:

The higher the KfW standard, the better the insulation and, consequently, the airtightness of the building. This makes a ventilation system increasingly important.
With a KfW 40 standard, you will hardly manage without one.

Hello,

Fabian S. schrieb:
We are planning to build with a perforated brick filled with perlite without additional insulation (such as polystyrene or similar). How thick should the brick be at minimum to achieve a good insulation value (KFW 40)? What would the wall construction look like?

Take some time to read through the forum.
You will find that no one can give you a definitive answer regarding your wall thickness.

Regards

Hello Fabian,

first of all, you should question whether your intention to build a "KfW40" house is really what you want. Having a "KfW" label as an insulation standard without referring to the related energy-saving regulation update is pointless. It’s like having a missing unit—like saying your car consumes just 3... uh, 3 gallons per 50 km (30 miles)...

So make sure what KfW40 really means—currently, it is basically the highest quality standard you can build to.

FOR THAT, you won’t get around using a (dense) brick if you want a monolithic wall.
By the way, a ventilation system is not a question of the insulation standard, but rather the construction method of your house. If you are considering an exterior brick wall, nowadays these are basically glued. Sometimes they are still dipped, but mostly a thin layer of mortar is applied using a mortar sled. That is already relatively airtight—normal mortar didn’t have any “gaps” either…

If you take advantage of KfW subsidies, you also have to meet airtightness requirements. These have to be proven after construction, monitored while building, and of course considered in the execution.

This especially applies to all building openings such as windows, doors, etc., where airtight installation is mandatory. In this context, you will frequently hear about installation according to RAL standards or installation by a RAL-certified company.

This in turn means that the ventilation rates required by standards can no longer be achieved by manual ventilation. The “trickle ventilation” of poorly installed windows is missing, so you would need to cross-ventilate approximately every two hours to maintain an acceptable air exchange rate.

In short: You can’t avoid a ventilation system if you want to construct the building according to the standards (and I consider it unrealistic that anyone would ventilate every two hours, even at night).

And by the way: You will love this thing.
Besides a bit of electricity and changing filters (which happen fairly often…), what you will get above all is:
Always fresh air! Everywhere. Every night I lie down, take a deep breath, and think how great this ventilation system is!!! No joke! Every night!!!
I would never build without one again! The comfort gain is enormous (never having to ventilate) and the feeling of well-being is immeasurable (always fresh air).

About your question… If you really mean KfW40 according to the 2009 energy-saving regulation, you will need a 0.07 brick in the direction of a 49 cm (19 inch) wall… whether that still makes sense is up to everyone to decide.
If you mean KfW40 according to the 2004 energy-saving regulation (which most people still mean today when they talk about KfW40 and keep hearing the term socially…), then that corresponds roughly to today’s KfW70/KfW85—which works with a 0.10 brick in 36.5 cm (14 inch)…
you see—it depends on your definition.

best regards
-Kalksandstein

Whether the brick is solid or has external polystyrene insulation, it makes no difference for ventilation...

If by KfW 40 you mean a house that consumes only 40% of the reference building according to the 2009 Energy Saving Ordinance, then the brick will have to be at least 42.5cm (17 inches) thick, depending on the type of brick you choose, it could also be 49cm (19 inches).

If you are opposed to a central mechanical ventilation system with heat recovery, there are simpler alternatives to ensure a minimum level of ventilation, so that at least the house does not develop mold... for example, trickle vents in window frames and additional exhaust fans in the bathroom and kitchen...

Hello Karliseppel,

I'm not generally against a ventilation system, but I am a bit concerned about the maintenance costs.
Now my next question is, approximately how much did your system cost, and what are the ongoing maintenance costs?
I've heard figures that were over 400€ per year.

Regards, Fabian