Telescopic ventilation, drainage and bifolds

[Keymon]

Hello,

I have this terraced house, and we have suspended timber in the front and concrete slab in the rear. I am considering rebuild the concrete and keep the timber. The rear is 9 meters of concrete, so I want to add several telescopic vents (likely 4x or 5x, every ~1m or less) under the concrete to try to add as much ventilation as possible to the suspended timber.

But we will have some big bi-fold doors at the end, so no space for all telescopic vents. At least one vent has to go under the bifold.

Also: the rear garden is elevated, at same level that the internal ground. It is a bit lowered (15cm) within 1m by the wall, with some paved ground. This paved ground in the back, right now, gets flooded due poor drainage.

Finally, we would like to have the same level between indoors/outdoors in the bifolds, so thinking to add some decking.

So, I am considering:

• Lower the ground in the back (within 1m or 1.5m area), so the ground  low enough to fit vents just under the bifolds and over the ground. Pave it.
• Add some channel drainage by the wall (or maybe a french trench).
• Add some composite decking, but by the wall above the airvents, add a open steel mesh.
   

Something like this based on the drawings from https://www.pavingexpert.com/drain06

 

Then, the vents that are not where the bifold, just a bit higher... but no real reason for this, it is that it feels wrong having it under the decking

Thoughts?
 

[Olf]

Is there any specific problem with suspended timber floor, that prompts you to lift up a slab?

If venting under the timber is an issue and you have all this challenges at the back (slab, ground level) have you though about venting at roof level ? That will likely involve boxing of pipes, but will still be much quicker and cheaper, with better effect (due to 'chinmney' action).

[Keymon]

4 hours ago, Olf said:

Is there any specific problem with suspended timber floor, that prompts you to lift up a slab?

 

Not sure if I understand the question. The reasoning to keep concrete in the back is commented here, but basically: it is already concrete, better insulation, works better with underfloor heating, and my neighbors  have also a slab, so the DPC might be in bridge.

 

4 hours ago, Olf said:

have you though about venting at roof level ?

No, not at all, i did not know that was an option. Happy to do that if it works, do you have any references on how this can be done?

[Olf]

17 hours ago, Keymon said:

The reasoning to keep concrete in the back is commented here

Now I get it, somehow missed the fact that underscore is not an emphasis, but a link

 

Regarding the venting, no I was lucky to not to have to research it, but feels like the obvious thing to do: 

- typically one uses stock vents above ground level (airbricks)

- if levels are off, you use telescopic version of that

- if a wall obstructed (eg by an extension), then run piped connection from existing airbricks to a new wall

- if that cannot be done (and it seems to be your case) the only way is up...

Whatever you'll do, it looks like to be of non-standard approach, so run it with your BC to make sure they're happy.

 

 

 

[Keymon]

Yes, so basically I though several approaches:

 

1. Avoid the bifold windows, by running the vents in diagonal. The bifold is not that big.
2. Put the vents under the bifold, by lowering the ground level in the front as I mentioned above. I do like it much, what if that rear area gets flooded!
3. Add at least one vent to the roof

I will discuss this with architect today and lets see what BC say 🤞

Edited July 5, 2022 by Keymon