Floor venting in old property

[cappsie]

Hi there,

I'm looking to manage moisture levels. I'm considering wall venting in all rooms with the potential addition of extracting humidistat fans if worth while. I would also like to equalise the air throughout my old flat (c. 1901) by way of having a floor vent into the void below the flooring.

What are the thoughts on this type of radical venting? Any pros or cons etc.?

Thanks,
Adam.

 

[ree]

I've just looked at your july 2013 posts where you finally appear to have provided adequate venting to your flat?

Is this round two or something else?

I noticed in your 2013 posts that you mention some kind of "expert" had treated the bare interior brickwork with something like a Vandex Tanking Slurry.

Tanking the walls might have created a barrier - hence, when moisture laden air hits this tanking barrier it might condense?

FWIW: have you noticed what happens when warm moisture laden air hits a glass pane or tiles?

 

[drpepe]

It'll be cold!

Why are you venting the room rather than under the floors? (or is that what you meant?)

We have recently (last autumn) added extra ventilation to reduce humidity/condensation and damp smell in our victorian terrace house.

This included:
A new airbrick under our front door ventilation.
Exchanged normal for large airbrick at rear (multiple airbricks not possible due to conservatory).
Dug out subfloor (lots of damp rubble, mud up to the joists in places).
Lowered external ground levels at front of house.

This winter was much improved - the humidity has dropped by 15-20% in the problem hallway (from 80% to 60%), no more noticeable damp smell when coming into the house! Plus, no more slugs... (touch wood)

 

[Joe Malone]

Hi there,

I'm looking to manage moisture levels. I'm considering wall venting in all rooms with the potential addition of extracting humidistat fans if worth while. I would also like to equalise the air throughout my old flat (c. 1901) by way of having a floor vent into the void below the flooring.

What are the thoughts on this type of radical venting? Any pros or cons etc.?

Thanks,
Adam.

It is not radical, it is odd and put quite simply, it will not work. Why on earth would you want to 'equalise the air' into the subfloor void?

Wherever humidity is generated, and remember that key moisture generation areas are the kitchen and bathroom, then those higher humidities come with increased vapour pressures that will naturally equalise into other areas unless immediately dealt with at source. Firstly you must understand that uncontrolled ventilation such as open windows and air vents is very bad. It causes transient condensation and makes it more difficult to keep surface temperatures above dew point. Ventilation must be carefully managed by judicious use of effective mechanical ventilation. My advice is to avoid humidistat controlled fans and to install silent continuous running centrifugal fans so that air changes occur over a 24 hour period. In the kitchen the boost speed will be managed by a pull cord whilst in the bathroom the boost speed will be linked to the bathroom lighting circuit. Rooms containing an extractor fan should not have a window or vent open as this short circuits the extraction process.
The sub floor should be well ventilated by air bricks being installed roughly every 2 meters on the external wall base. If there are high sub floor relative humidities then the last thing you want is for this moisture to be adding to relative humidity levels in the main habitable space.

 

[cappsie]

Hi Joe,

While I'm not against centrifugal fans, the air would need to be drawn in from somewhere, would it not? What do you suggest for that scenario?

I'm happy to consider any and all suggestions.

The reason for the floor venting suggestion was based upon the floor being significantly cooler to the touch. There are not high sub floor relative humidities, rather the opposite is true. I simply felt it might have added to the condensation issue.

However, I will check the air bricks. Do you feel digging out the floor void would improve things, or should I simply leave well alone?

Presumably the centrifugal fans would be boxes attached to the internal wall(s) and be ported out through a core-drilled hold in the wall, itself fitted with a plastic (auto-closing?) plastic vent?

The bathroom fan is woefully underpowered so any suggestions would be good. I tried the envelope test and it didn't hold it. I did notice that some bright spark had rendered over much of the vent. This is probably the reason I have reduced air flow out from the bathroom.

All thoughts welcome and thank you all for your input; it's much appreciated.

Thanks,
Adam.

 

[ree]

OP,

you say "thank you all for your input; its much appreciated." Perhaps you would show your appreciation by responding to my post?

 

[cappsie]

I've just looked at your july 2013 posts where you finally appear to have provided adequate venting to your flat?

Is this round two or something else?

I noticed in your 2013 posts that you mention some kind of "expert" had treated the bare interior brickwork with something like a Vandex Tanking Slurry.

Tanking the walls might have created a barrier - hence, when moisture laden air hits this tanking barrier it might condense?

FWIW: have you noticed what happens when warm moisture laden air hits a glass pane or tiles?

Yes. Quite right and apologies for not responding to you directly. Yes this is a sort of round two as I never got around to venting the flat. And I suspect you have a point with tanking the walls and creating a worse situation.

A professional damp proofer hacked off the plaster back to the brick work. He then applied some damp proofing render stuff, a dark grey colour, to half an inch to an inch thick. He finally rendered standard plaster over the top.

There is some surface disruption where I can only assume some residual moisture has snuck through.

On to the glass panes/tiles moist is present at the bottle of windows on the glass.

I guess my thinking was to vent the flat en mass and allow a better circulation all round with whatever kit.



Thanks,
Adam.

 

[ree]

Thank you for your post.

The glass/tile business was merely an example of how condensation works.

Maybe "residual moisture has snuck through" but i suspect that your difficulties are from condensation.

In essence, condensation requires a constant circulation low heat and a constant trickle of ventilation. Research on here and google for info. on this tricky and massive subject.

 

[cappsie]

Thank you for your post.

The glass/tile business was merely an example of how condensation works.

Maybe "residual moisture has snuck through" but i suspect that your difficulties are from condensation.

In essence, condensation requires a constant circulation low heat and a constant trickle of ventilation. Research on here and google for info. on this tricky and massive subject.

Ok thanks. It's starting to sound like the heating will need to remain on low while the venting balances both heat and humidity. It doesn't sound like a small project

Thanks,
Adam.