Ventilation for new concrete floor...

[widgetyegg]

Hi,

This is my first post here and I'm fairly new to building/renovation so please excuse me if I get any terms wrong

We have a large house which we are reconstructing in South Bohemia (Czech Republic) and have come across some differing opinions about how we ventilate a new concrete floor. I will try to explain the current situation and the proposed solutions and would really appreciate it if people could give me pros and cons of each method.

For some background to this, the weather in Czech can be quite hot in the summer, up to 35 degrees, and very cold in the winter down to -20 degrees.

The house has been changed many time over the years and when we dug up the existing floor we found that it had been built up with earth above the level of the original damp proof course which has caused the brickwork to get very damp. We have dug a trench all the way around the room to below the damp proofing to allow the walls to dry out (which is well under way) The next stage is for us to lay a new concrete floor and the plan is to fill the trench with gravel and lay a pipe with holes in (sorry don't know what this is called) underneath it to provide ventilation...

Now this is where we are getting into a debate and have two alternative opinions.

1) We run the pipe around the edge of the room and vent it directly to the outside through the wall at ground level. The worry with this is that the floor will be very cold in the winter.

2) We run a pipe up to the attic where the air is warmer, use a small fan to push this air down and under the floor, then vent into the cellar. The idea with this is that warmer air would be passed under the floor.

So my question really is which method would be most effective, and more importantly would either of them be a big no-no which would damage the house?

Thanks

Mike

 

[cmother1]

What you are describing is called a French drain. They are used to keep down the water level in the ground around the walls of a building on the outside. Unless the trench you've dug is filling with groundwater I can't see the point of what you propose. Who suggested this idea? It's pretty unorthodox.
A more conventional approach would be to dig up the floor, re-lay with a damp proof membrane linked to the existing DPC and take the opportunity to bury some insulation in the concrete while you're about it.

 

[widgetyegg]

@cmother1

Thanks for your reply. Are you saying that it doesn't need ventilation under the floor, around the walls?

The main problem we saw was that it has just been built up with earth well over the original damp proofing, it was necessary (we thought) to dig the trench in order to dry out the walls (which seems to be working really well). It seems as well that the DPC is just on the bricks on the outside wall, but the inner walls are also getting damp.

Mike

 

[cmother1]

Seems odd that you've a dpc on the outer wall but none on the inside. Were they constructed at different times perhaps? Are they made of different materials?
If you don't have a continuous dpc through the wall it will be a headache. Frankly I can't see your pipe idea working. the perforations in the pipe aren't big enough to allow much airflow and the gravel would also impede it. It's designed to carry water draining under the force of gravity, not to act as an airbrick.
You might be better off digging the whole lot out and putting in plenty of ventilation and an insulated suspended floor.
Any other thoughts out there?

 

[alittlerespect]

The holes in the pipe are to allow ground water in, not air out!! They are a drainage pipe used in french drains!! Your best bet would be to put the 'french drain' on the outside perimeter of the building (insurance against future penetrating groundwater) then turn your attention to the inside!
Do a web search for french drain and you should get the correct details for a 'french drain'! Not as simple as digging a hole and putting a pipe into the ground.

There is no reason why you couldn't put in an insulated solid floor!

Construction detail would be along the following lines: 100mm clean hardcore, 50mm sand blinding, lay dpm dressed up walls beyond height of dpc, lay 100mm concrete - let cure and dry out (7 to 10 days) then lay mimimum 50mm PIR insulation and finish with 18mm flooring grade t&g chipboard and for good measure make it the moisture resistant type. Then fix skirting board, cut back excess dpm material, decorate and add floor covering.

Regards