Is Positive Input Ventilation (PIV) the best solution for mould and condensation?

Lumen wrote: »

Surely mechanical extract is fundamentally better for mould and condensation?

Think about the airflow.

Assuming the building fabric is leaky (otherwise you'd get HRV) then if you pressurize a room with PIV some of the air is going to leave via the hole in the wall, and some of it via leaks in the building fabric. Those leaks will take moist, warm air and condense it in the building fabric.

Alternatively, if you're depressurising a room with MEV, then that same leaky fabric is going to be pulling fresh air in, which won't cause condensation because it carries less moisture and is being warmed up as it enters.

I know this is all theoretical but I just can't see how PIV makes sense over MEV.

It makes sense because it s a cheap and quick fix. Hence companies selling it to cure your damp.


I like your explanation and you might be right, but in my case the fabric is brick/concrete so the volume of damp that's going to build up, will have little effect... i hope.
The "damp" in a house that condenses on the cold surfaces is initially relative humidity. My understanding is that its key to reduce RH as much as possible, to prevent it condensing and turning to moisture/damp. Air and its RH will exit via the easiest path, especially with the sort of pressure being put in by the PIV... its next to nothing. So PIV must be coupled with trickle venting and open windows or background vents drilled through walls. Without these, PIV will not work well..IMO.


The RH outside my house right now is ~65%. Before we had the PIV, inside would match and exceed this, 70%++.
We have trickle vents permanently open and the heating controlled via smart thermostat. The house has so far stayed warm and thankfully no sign of the damp we saw last year. Granted, we both now WFH so maybe the heating on more regular has helped too. We are getting the house wrapped next month so that will seal up more of the gaps in our fabric. I'll be watching the RH and increasing the trickle vent size if it starts to go up as a result.



PIV is worth a shot, if you can do it yourself its cheap as chips.

Calahonda52 wrote: »

RH values without the dry bulb temp and the dew point temp is not that useful.

https://en.wikipedia.org/wiki/Dew_point#/media/File:Dewpoint-RH.svg

Dry bulb ?

Calahonda52 wrote: »

RH values without the dry bulb temp and the dew point temp is not that useful.

https://en.wikipedia.org/wiki/Dew_point#/media/File:Dewpoint-RH.svg

So dry bulb=Ambient temp indoors= 18-20degrees always for me. The damp guy we had assess our place said to keep temps above 17 degrees always.

zoom_cool wrote: »

If you install PIV do you close some of your wall vents?

Absolutely not, the PIV needs to have something to push air out of. Wall vent or trickle vents on the windows are still needed.

I am having a serious issue with damp in the main bedroom in our apartment which has an en suite. I dont even know where to begin to solve this issue. Can anyone recommend an independent surveyor that can recommend and carry out works necessary to solve the problem? Thanks

jellybeans wrote: »

I am having a serious issue with damp in the main bedroom in our apartment which has an en suite. I dont even know where to begin to solve this issue. Can anyone recommend an independent surveyor that can recommend and carry out works necessary to solve the problem? Thanks

I've got the same issue so would appreciate if someone could pass on a recommendation.

The window glass and frame is literally dripping wet on cold mornings even though it's triple glazed. This is causing mould on the sill, all around the window frame and on the ceiling in the bedroom as I just can't keep it dry enough.

moon2 wrote: »

I've got the same issue so would appreciate if someone could pass on a recommendation.

The window glass and frame is literally dripping wet on cold mornings even though it's triple glazed. This is causing mould on the sill, all around the window frame and on the ceiling in the bedroom as I just can't keep it dry enough.

That would imply that your window and frame are the coldest of all surfaces in the room. The mould on the ceiling means that location is missing insulation in the attic above. Easily fixed

It also implies that you have far to much moisture in your home generally referred to as humidity levels.

The moisture can be any number of sources but it is only ever dealt with via proper ventilation.

Check your sources of moisture such as drying clothes, showers, even leaks. But even more importantly check the ventilation in that room and the house in general.

Getting triple glazing and closing all vents for example won't solve your problems it creates mould.

@suritlbgrand wrote

No. As described earlier in the thread you need permanently open wall vents to let the moist air out.

How do you have a new build underway without a ventilation strategy? What does the architect say?