Positive Internal Ventilation - does it help with condensation in the loft?

[Time Waster]

Some friends have issues with condensation issues in their loft. So a local builder / developer is putting PIV into their loft to solve the issue.

Does this work? Is it a cheaper option than vents low down and day ridge vents? Is it better?

We have had this issue once but somehow we did something and it stopped somehow.

 

[Kingfisher101]

My house has a lot of condensation and I've found a dehumidifier helps a lot and good condensation traps like Unibond 360s. Have your friends tried these before shelling out for builders which will be thousands?

 

[raleighnut]

Too much loft insulation in the wrong place. We had an electrician come round to do an annual check (british gas service plan*) and when it came to check the wiring on the boiler I told him it was in the loft, "same as mine" he said and then asked if ours packed up 3-4 times a year with the condensate pipe freezing. "No never has" I told him and we worked out that he had a 'super insulated' loft whereas we only have the old 4" stuff, I'd sooner have less insulation than be without heating and hot water for up to a week 3-4 times a year.

* we cancelled the 'service plan' after this guy condemned the supply board as "Not to current spec" despite being a new one fitted 15 months before by British Gas (under the service plan/insurance cover) as the old board was to current spec but the RCD had become 'super sensitive' and was no longer available, The Old Board had 8 circuits all RCD protected whereas the new one had 10 circuits 5 protected and 5 not also the guy who fitted it didn't have any 'blanking plates' and neither did British Gas in their stores so he had to fit breakers in the unneeded holes.

The protected circuits are Cooker, Shower, Boiler and Ring Main with one spare and the unprotected ones are Downstairs lights and First floor lights with 3 spare breakers

 

[lazybloke]

Condensation forms when moist air cools, eg when it encounters a cold surface.


Best managed by a combination of:
1) keep moist air away from cold surfaces (eg air-tight loft hatch and ceilings)
2) ventilation, particularly extraction of moist air from kitchens/bathrooms
3) insulate, so cold surfaces aren't.
4) breathe less!

But strange things can happen with loft spaces and natural temperature variations; i remember a workplace loft full of 3-phase electrical switchgear that was absolutely dripping with water on a hot sunny day...

 

[Once a Wheeler]

These are well worth looking into. Permanently functioning low-power extractors cost around £15:00 a year to run. Full information here:
https://www.envirovent.com/products/extractor-fans/cyclone-8/
Background information here: https://www.envirovent.com/
Good luck with the job. Envirovent are generally very reliable.

 

[presta]

I had an extractor fan in the bathroom which ran from when I got up in the morning until bedtime, but it never made a scrap of difference. Once the steam has condensed onto cold walls it's in no hurry to evaporate again, so the mould still thrives. When it expired from running 16 hours a day I never bothered replacing it.

 

[Time Waster]

I have discovered lap vents which are about £20 for 10. You go up into the loft and separate the felt lap under your tiles and shove one in to create an air gap. Then you go to another section of the roof and repeat until you have enough vents. They are not as good as low down vents in the facia or soffit with ridgeline vent tiles but they are better than nothing and might provide enough to stop condensation we have at times.

It was after we added insulation to the loft space at one end that we had the next winter with bad condensation. We put left the bathroom light on which is linked to the on switch of an extraction fan and we opened the window. Then cooked with the door ajar or windows open. In fact we probably spent a bit of time with the windows on the locked vent opening level. This lowered it by dealing with it below the loft. We have a new hatch too that might have played a part. It had gaps left around it because we needed the ceiling plastering around it. I put some mastic in the gaps too.
My friends got the moisture issue after cavity wall insulation was put in apparently. The issue is only in the loft so the builder (highly rated locally) recommended the PIV unit. He doesn't do roofs but can do whole extensions from design to build (with a tame architect). A strange thing that I think. I mean extensions need roofs too!!

We have a real issue getting trades to do work locally. There is high demand so they pick and choose. People are actually using out of area trades from just a leaflet through the door because it is so hard to get someone to do work locally. A real shortage or something is causing this. So I think they went with what this one reliable builder who you can get (he lives in our village so likes local jobs) offered that would help. In our case if we get this issue again I think I will rip out the loft roof lining the previous owner put in and fit lap vents from the inside. I think we didn't get much of an issue last year. IMHO if it is only a few patches on the plastic roof lining then we will open a few windows on vent for awhile and not worry. The first year we had it the condensation was really bad, dripping everywhere. It is not anywhere near that bad these last two winters.

 

[Kingfisher101]

Its very hard to get trades to do small jobs round here. They only want massive jobs with thousands to be made. If you wanted something like a new toilet or sink you could be waiting months. If you wanted a full bathroom renovation for a massive bathroom, there would be around 50 tradespeople expressing their interest. It's not right really. What I've found as well, that lots of handmen type people cant actually do the job in hand so you end up paying twice.

 

[T4tomo]

We had an issue in my OH's place which condensed badly on the window lintel on the upper bedroom which right up to the roofline with a shallow roof (was an odd 2.5 storey split floor town house). On the edge there was so little loft volume the air didn.t circulate well

That was solved with , pulling out some of the overstuff insulation and replacing 4 tiles with "ventilation mushroom" tiles for want of a more technical description.

It didnt cost "thousands" as speculated above just a few hundred, mainly for a bit of scaffolding

 

[CXRAndy]

Condensation in roof lofts is a big problem if left unchecked. It's normally caused by lack of ventilation when an upgrade to loft insulation. The fitters stuff it down against the felt(if it has some) by the soffits, blocking air from accessing the roof void. Pocket vents fitted low down will help but also drawing back the rock wool from soffits


When building a new house-
I installed 600mm wide, 150mm of foil back board down where the rafters touched the wall plate, then I didn't need to push the insulation into the tight area. I also used a thermal camera to check for any areas I'd missed with rockwool . Last thing you want is warm air passing into loft and condensing.

Last bit, but very important I installed a vapour barrier before plasterboard the upstairs ceilings. The Amount of household moisture that can pass through plasterboard is enormous.

 

[newts]

The lap vents fitted to gaps in the felt will provide adequate cross ventilation in most cases. I fitted 3 each side of the roof halfway up a few years back & we never get any condensation now. If a bathroom fan is correctly specced & ducted it will do its job, most people fit a small cheap fan from Screwfix etc & the air exchange rate is too low. Opening the bathroom window in winter allows cold air into the room & results in more condensate. Much better to close the window & let the fan pull warmer drier air from the house through the bathroom to dry it out.

 

[Time Waster]

After laying the extra insulation we got the condensation in the second winter. For some reason the first winter was colder but less of an issue with condensation. We bought the house over 3 years ago and it came with plastic tongue in groove lookalike panels on the underside of the roof and a little bit down from the roof to the loft floor. When it was a bad year for condensation we went up there and pulled a bit of it where it was the worst. This helped I think. So I suppose that the plastic sheeting is part of the issue. I think there is a vertical section then the sloping roof sheets. I think that if we open up the vertical sections it will open up the cavity wall airflow through the air bricks which may help it a bit

The first thing we did on finding out there was condensation was to move the extra insulation back from the edges of the loft space. I think this might have helped but I don't know why the worst section was where there was no extra insulation installed. Above there it postitively dripped. now the hatch was there but the worst bits were away from the hatch itself.

Anyway, I think it is a case that we do the little things we can do to help an hope that the issue is sufficiently helped to not be a problem. We moved back the extra insulation, we took off the low down plastic lining from the loft, we filled the gaps around the new hatch with mastic ahead of plastering that we have never done yet and a few other things I have forgotten. I tend to leave the bathroom light on more in winter as the light switch also controls the extraction fan that does work given enough time. I do not always open the window in the bathroom in winter neigther but I do occasionally. I think after that first winter when we found the issues the winter afterwards (last one) did not have so much of an issue. I think a few Lap vents might well clear the rest of it up.