Positive input ventilation in a modernised property

[phatboy]

Hi,

I live in a 50's bungalow, that is solid blockwork. We have had it externally insulated, and have fitted Kingspan between all floor beams, foamed and taped. The whole place has been re-skimmed and new windows and doors throughout.

I appreciate it's hard for anyone to answer, but is this work (I think it's done well) likely to make a PIV system ineffective, as there is a lack of places for the stale air to get naturally pushed out? We didn't go about it aiming for eco-home status or anything like that.

The external insulation and under floor made a huge, huge difference to the condensation mould we were suffering from. Now we just get bits in areas where the air doesn't flow very well and are cooler - mostly our bedroom in the corners, and under the bed.

We have a good kitchen extractor, and a large inline bathroom extractor, but neither run in a continuous mode.

Many thanks!
Tim

 

[^woody^]

Positive pressure fans rely on the being a way for air to exit the building, which is normally via suitable vents installed as part of the installation assessment.

 

[phatboy]

Positive pressure fans rely on the being a way for air to exit the building, which is normally via suitable vents installed as part of the installation assessment.

Thanks Woody, but there are no specialists listed for Jersey who undertake assessments or installation. I think our standard air conditioning engineers don't deal with this.

I am hopeful of doing the work myself, but obviously want it to do what it's designed for!

 

[Doggit]

Do you have any trickle vents in what I assume, is the recently installed double glazing. If you're still getting mould, then that suggests that you aren't ventilating the house properly.

 

[^woody^]

I would suggest that a PP unit is not the most appropriate solution.

Firstly, you should not be getting any condensation dampness with EWI. The cold spots should have been removed, so are you sure that it has been installed correctly and fully?

Then you need to be sure that you are doing all you can to minimise your production of most air, and deal with that which you do produce. Ventilation at source and then trickle ventilation should be enough. Constant trickle fans with boost are in favour now to control the internal air.

Heating patterns should be less of a factor with EWI as the walls should be holding heat for longer, but still worth considering to check that you are not creating extreme hot and cold periods.

But the main thing is to check those areas where mould is forming to see why the surfaces are so cool to allow it in the first place.

 

[phatboy]

Thanks for the replies - I am happy to be challenged on any part of this as I certainly don't know all the answers!

We do not have trickle vents - the old (leaky I guess!) windows also didn't, and I didn't want to ruin the "A rating" of the window. We do however often leave them on 'night vent' for a period of time, and run a dehumidifier daily which collects up to 2L before RH is 50%

The EWI I believe was done to a good standard, I posted photo's on someones thread a couple of weeks ago of photos from pretty much start to finish.

However, one thing that wasn't done which is part of the issue.... they insulated up to soffit level externally, which is about 170mm lower than ceiling level inside. In the coldest north facing room we got mould on the top edge of the room. Last weekend I pushed rock wool down from the loft into this space (easy to get to in our loft), and it has made a huge difference - main part of the wall is 19.5degrees, and the bit I have pushed rockwool into is now 18.5degrees. A bit I couldn't get to in the corner was 16degrees.

However, the rest of the mould is forming in fabric boxes that are not near an external wall, and under a bed that is up against the external wall but the items are about 3ft away.

We have storage heaters that get 8 hours of heat split over 24 hours, so the place is never cold, but the bedrooms rely on panel heaters but we have turned these up recently, keeping the rooms at around 19degrees.

 

[^woody^]

A thermal camera is very good for finding poor EWI. The external finish and appearance is not the issue, but the detailing and coverage, to ensure no cold spots or thermal bridges is crucial - and is often undetectable visually. EWI actually increases condensation risk at uninsulsted cold spots.

Otherwise you seen to be on top of things.

If you are confident that heating patterns are not contributing, and fans are functioning and used, and would not like to consider constant trickle fans, then yes PP unit should work. But will need vent outlets in rooms to push the air out.

 

[mwatsonxx]

A fan door test will show how well sealed the house is. These test are normally carried out to prove the efficacy of gaseous fire suppression systems. As a starting point try a local fire alarm company.