PIV for loft condensation?

[clearprop]

Hi all

Having a problem with dampness in our attic room. Opened up the eaves storage (which was filled with junk) for the first time in 5 months to find mould on some of the rafters.

Have now had soffit vents and tile vents installed, but the installers have advised that as the existing roofing felt is made of plastic then the only way to properly stop the condensation issue is to replace it with breathable modern felt. Obviously a costly job.

Just wondering as an alternative, would a Positive Input Ventilation unit be of help to keep the air circulating in the roof space (especially now we’ve installed the extra vents)? Would save a lot of time and money..

Thanks

 

[freddiemercurystwin]

Plastic? Got a pic?

 

[clearprop]

Maybe the guys meant to say PVC..?

 

[ajstoneservices]

Looks like monarflex Geoff Capes used to stand on in the advert.

Edit: monarflex

 

[freddiemercurystwin]

A non breathable underlay is no problem in itself, felt does not breathe either, one fix is continuous ridge vents in addition to the soffit vents, assuming there's a gap all the way from the eaves to the ridge, roofers should have offered this solution first, they're either crap or trying to pull one.

 

[clearprop]

Yep 10mm air gap between the insulation and underlay, all the way up from eaves to ridge.

That’s promising to hear we can just look at ridge vents- thank you. Think it’s worth monitoring the situation for the time being now the soffit and vented tiles have been installed? Have a hygrometer up there in the eaves storage area and it’s currently reading 45% relative humidity.. not sure what an ideal RH is for such a place..?

 

[freddiemercurystwin]

10mm isn't ideal but should work, as you say monitor and see ....

 

[clearprop]

Sorry that was a typo.. it’s actually 100mm!

 

[freddiemercurystwin]

Well that's more than adequate then.

 

[clearprop]

Looks like monarflex Geoff Capes used to stand on in the advert.

Edit: monarflex

Thanks, your link to Monarflex specifically states that ventilation must be provided at eaves and ridge level, neither of which were installed when the previous owner did the loft/attic conversion in 1997.

Any thoughts on whether a PIV system
might help? Looking at the marketing material they make it seem like it’s the best thing since sliced bread but in essence are they just glorified fans..?

 

[^woody^]

PIV is designed for buildings with rooms and some natural or installed exit routes for the air movement, ie positive pressure is created. A roof void is different and can not be assumed to be a similar situation.

And no they are not glorified fans.

You have too much warm air getting into that void, and you should deal with that.

Has a 25mm ridge vent been fitted? Tile vents don't help much.

Also wedge the membrane laps open, to allow more air moment.

You need to hurry up with a remedy before that mould turns into dry rot fungus.

 

[clearprop]

Thanks. Have put in 10 lap vents now on what’s accessible (ie only in the eves storage, which is one side of the roof- the rest is plastered over for the attic room). No ridge vents whatsoever. Is only one 25mm ridge vent usually sufficient, or is is the case of the more the merrier?