Condensation in bedrooms. Positive Input Ventilation PIV?

[b0rn2sk8]

Install ventilation to aid the PIV

Yes, but the point is you can't because there is insulation between the rafters which should have a vapour barrier on the inside. All the vents would do is vent the small air gap between the insulation and the tiles. You'd have to install it elsewhere which also defeats the object of having a warm roof.

You are far better off installing proper ventilation in the rooms that are meant to be ventilated, you probably don't need the PIV if you do that. Also see my point above about the PIV having nowhere to push the moist air, it can't bring in fresh air because the old air can't escape.

PIV is a fine solution in certain circumstances but you have to be careful that you are not treating the symptom rather than the cause which is why I say it is not a magic bullet.

 

[rangor gubbins]

Firstly, try and eliminate the possible source of the problem, ease tally the humidity being created in the house.

Do you dry clothes inside, either on a clothes horse or radiators, do you use a proper extractor in the kitchen (that vents outside) and extractors in the bathrooms?

Also, how old is the house, is it solid wall (say pre-1930s) or a cavity? The wrong internal insulation inside an old house can cause no end of problems, they were not designed for it. It's really complicated and many people will get it wrong, even some soo called experts.

Clothes are dried in a condensing tumble dryer in a separate part of the house.
Kitchen has a proper extractor venting to outside. Bathrooms are the same.
House is about 1910, with solid brick walls.
Internal insulation is plasterboard backed with PIR (25 mm i think), dot and dabbed onto the original wall. No signs of damp on the walls, only condensation on the windows.

One thing that has dawned on me, we haven't used the shower in the bathroom on the first floor for a few weeks (it needs repairing), and there also hasn't been any condensation in the bedrooms for the past couple of weeks. Might be a coincidence, or maybe i just need to improve the extractor in the bathroom.

 

[rangor gubbins]

When you say it is not sealed to the outside, what do you mean? I'd expect there to be a few small vents for trickle ventilation but that is about it.

A PIV isn't a golden ticket some people make it out to be, they work well in specific circumstances but not in others. If your house is fairly well sealed which is sounds like it will be without any trickle vents, it is not going to work well if there is nowhere for the air to go and it will be like taking a wee into the wind. Likewise, it is the same for when you are running extractors in the kitchen/bathroom, if there is nowhere for the air to enter, you'll not be extracting anything.

The windows thing was explained a few posts above, the idea isn't to open them for a long period of time, its to do it for just 3 minutes to air the house and and close them all gain.

A dehumidifier will not cost much and may not be anything more than running a PIV or fully venting the house daily. That you spend in electricity, you save a bit in heating costs from less air changes. You also wouldn't need to run it all day every day, a few hours overnight will probably be sufficient.

But fundamentally, your house sounds like it lacks a bit of ventilation, it is a requirement under building regs to have vents or mechanical ventilation across the house, that is usually in the form of trickle vents in a typical build or MVHR in a high performance build.

I mean the loft has some air flow which i think is coming in somewhere around the wall plate. It not loads, but when its windy outside you can feel some air movement.

The house is well sealed, but it certainly not a passivehaus, there are still little gaps around the place, plus the ducted extractor in the bathroom. If air is pumped into the first floor from the loft, won't it find the easiest a way out somewhere, e.g. through the bathroom ducting for the extractor, or any other gaps around windows? The loft hatch might need sealing so the air doesn't just go in circle between loft & 1st floor.

You are right, the house needs a bit more ventilation. The question is how best to achieve this.

 

[dlockers]

Have you tried just opening the windows? We open them each morning now for a few mins....