Positive Input Ventilation (PIV) Systems - worth it? (mould in bedrooms)

Soldato
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Hi all, this query has come off the back off a house I own that is current rented out getting some quite bad mould problems around the eaves in the bedrooms (It's a 1930's semi where the eaves come down into the bedroom at the walls).

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When I used to live there it was a problem with mould collecting in the corners of the ceiling and the tenants are currently experiencing the same issues in the bedrooms.

They tell me they have done all the usual leaving windows open and what not however it's not really getting any better and short of cleaning it off and attacking it with anti-mould paint and repainting I was trying to look at the causes.

The main one that comes up is around insulation in the roofspace. Now the loft is currently unboarded but does have a hell of a lot of insulation up there, so i'm not sure if its actually too much or if its been fitted correctly or if its something completely unrelated, but as I don't live local it's difficult to get there to have a look (and the loft hatch is hideously small which makes it even more difficult).

After Googling, PIV systems have come up and seem to universally tackle issues with damp air in homes and in particular mould. Does anyone have any experience of these? Do you think this will help with issues? I am also potentially looking at changing the front bedroom window as that gets mould around the inside of the window frame where it meets the wall but thats a seperate issue.
 
Soldato
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At a guess, despite the roof insulation it looks like the condesation is forming on the "ridge" part of the roof which is presumably not actually insulated as that would mean blocking the airflow in the eaves so that's the coldest part of the ceiling.

As mentioned above it will need remedial works / repainting, but a decent PIV would stop it returning.
 
Soldato
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Yeh I did wonder that as you're not supposed to block the eaves to allow for airflow in the loft so I was wondering how you combat it as it's going to always be colder than internal.
 
Man of Honour
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Yes ideally in the roof space you want to leave a gap of say a foot in the insulation towards the eaves so air can circulate. As its not boarded you should be able to just fold back the last bit along each section.
 
Soldato
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Yes ideally in the roof space you want to leave a gap of say a foot in the insulation towards the eaves so air can circulate. As its not boarded you should be able to just fold back the last bit along each section.

The problem here though is that appears to be created a cold-bridge with that sloped part of the roof, thus the condensation and mold.
 
Soldato
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Read another thread on here somewhere suggesting to insulate that sloping bit of the eaves by rolling some insulation down. Ensuring there is a reasonable gap above it for air to circulate still.
 
Soldato
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Well in a weird turn of events I remembered my mum mentioning when she moved into her bungalow she used to have a weird vent in her hallway ceiling that she had removed when she redecorated when she moved in. I decided to chance my luck and look in her loft and sure enough there was an old Nuaire Drimaster unit sitting unused to one side, it turns on and still works by the looks of it so that's half of the puzzle solved, looks like I just need to buy a diffuser.

I put a job on MyBuilder to get it fitted and an electrician quoted me £120 to come and install it along with pulling a power feed into the attic for it (off a light I imagine). I know they are pretty easy things to fit in principal, but that seems a tad cheap. Or should I bite his hand off?
 
Soldato
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A dehumidifier would probably be a better bet than a PIV. PIV will just suck moisture from the house into the roof space where it might just condensate on the roof lining and drip all over your insulation.
 
Soldato
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A dehumidifier would probably be a better bet than a PIV. PIV will just suck moisture from the house into the roof space where it might just condensate on the roof lining and drip all over your insulation.

Thats not how they work, the just push fresh air from the loft into the house and the air escapes through any means it can - because its creating positive pressure it doesn’t go out the way it comes in.

They work very well, I had an envirovent one in my old bungalow and it pretty much solved all condensation issues - all a dehumidifier does is temp solve the issue costing lots of money in power and work in emptying the water tray (did this before the PIV was installed) and even though mine was a preheat one it reduced my gas bill as ‘wet’ air is colder and harder to heat that dry air.
 
Soldato
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Thats not how they work, the just push fresh air from the loft into the house and the air escapes through any means it can - because its creating positive pressure it doesn’t go out the way it comes in.

They work very well, I had an envirovent one in my old bungalow and it pretty much solved all condensation issues - all a dehumidifier does is temp solve the issue costing lots of money in power and work in emptying the water tray (did this before the PIV was installed) and even though mine was a preheat one it reduced my gas bill as ‘wet’ air is colder and harder to heat that dry air.

Ah, it must be slightly different from the couple of systems I've had in properties, both definitely vented into the loft, causing no end of issues.
 
Soldato
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Slightly aggrieved that a new diffuser costs £48! Seems excessive for what is a glorified plastic grill. The filters look a tad grey and dusty but not too bad.

I had Envirovent down to come and do a survey next week but after doing some more reading and seeing what others were quoted (in excess of £1000) I may just cancel it and take my chances on this in the first instance.
 
Soldato
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Have you considered getting someone in to fix the problems rather than masking them with a PIV? Is it just a condensation issue? Does it happen even when it's not raining?

Have you considered moving the loft insulation away from the eaves and/or adding roof lap vents?

It seems like a serious amount of mould and something that would be beyond resolving from. Just a PIV. I previously had one in an old house to resolve condensation but it was far less than what you've indicated.

£120 to fit it seems reasonable to me and will take a couple hours+travel to site etc.
 
Soldato
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Yes i'm also having the windows looked at as it appears the front bedroom ones the panes may have failed and it looks like there may be some kind of water ingress around the edges of the frame as they are damp. It's an old protruding bay type window with a wooden sill, but one which has been there for many years and looking down the street I can see a lot of people have had them removed and just had a normal window fit which is what i'll likely do depending on price.

I will be asking the contractor to check over the insulation in the loft aswell to make sure none of the eaves are blocked.
 
Soldato
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Ah, it must be slightly different from the couple of systems I've had in properties, both definitely vented into the loft, causing no end of issues.

You had extractor system then by the sounds, PIV is positive input so it puts positive pressure into the house, taking it from the loft space.
 
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