Passive or Vapour vent / Internal insulation

[greenfox]

Hello,

I'm fitting new kitchen units against two external walls that have suffered black mould - particularly behind the base corner unit where the walls meet. The underside of the wooden worktop is especially badly affected where it touches the wall. Would it help to -

1) Fit a vapour or passive vent behind the units. Like these
http://www.airtechenvironmental.co.uk/pages/passivewallvent.html
http://www.airtechenvironmental.co.uk/pdf/vapourvent.pdf

2) Cover the wall behind the units with an insulation layer so the wall doesn't get as cold and the worktop doesn't come into direct contact with the wall. (Obviously after getting rid of the mould and treating the surface with anti-mould paint first). Something like this:
http://www.screwfix.com/p/airtec-double-insulation-1-5m-x-25m/50913

3) Both.

I should say that this is in addition to installing extractor fans in the kitchen and the bathroom and following all the usual precautions about wet washing etc.

Thanks in advance.


(I decided to create this post with a specific question after I'd done more research on my rather wordy earlier post.
//www.diynot.com/forums/building/mould-ventilation-insulation-do-you-agree.293546/ )

 

[mointainwalker]

So what specific reasons do you have for fitting Airtec ?

 

[^woody^]

Those vents are not appropriate for use in that situation, but more than that no vent will remedy that problem and may make it worse

You just need to sort out your condensation/ventilation issues elsewhere in the property. In extreme cases you could insulate the wall to remove the cold surface. And lag any pipes

 

[greenfox]

Thanks woody.

My reason for wondering about venting behind the units was that I saw another discussion where someone had black mould behind bedroom wardrobes. Some were suggesting that vents behind would help.

If the issue is poor ventilation, why would a vent there not help the moisture-heavy air to escape, rather than condensing onto the walls?

I understand that the focus should be on effective moisture control and ventilation throughout the flat... but guess I'm just trying to do belt and braces approach because a) I'm redecorating anyway and b) any future residents may not be as vigilant as I am (may rent it out in future).

I'm happy to install vents elsewhere if that would be more effective. I have a kitchen and bathroom extractor and one vent in the lounge (non external wall, and unsure if it's working). How would I decide which vents to fit and where?

Excessive googling has not helped me - but quite possible I'm just a bit too clueless!

 

[greenfox]

So what specific reasons do you have for fitting Airtec ?

None at all. Hadn't even heard of these vents before my post, I just found through googling and wanted to give examples of what I was talking about. Should I be concerned about them?

 

[mointainwalker]

I was referring to the insulation. Hadn't noticed that the vents are also AirTec

 

[greenfox]

I was referring to the insulation. Hadn't noticed that the vents are also AirTec

Nor had I. I just googled wall insulation. Do you have any views on using this type of product (of whatever brand) to solve the specific issue I described?

 

[^woody^]

If the issue is poor ventilation, why would a vent there not help the moisture-heavy air to escape, rather than condensing onto the walls?

Because the principles of ventilation are to move air around a room not a tiny awkward gap behind cupboards

By fitting a vent, you will introduce cold moist external air to the space behind the cupboards and all it will do is linger and potentially make the problem worse

 

[mointainwalker]

Do you have any views on using this type of product (of whatever brand

I have little faith in these foil insulation materials. It is also unusual to give an insulation value as Screwfix does saying " ..insulates up to R xxxx " Why "up to" ? You normally see "R = 5" or similarly specific.

You should also note that you need to have a 25 mm air-gap either side of the foil and this should be still air which is the exact opposite of what you require in your situation.

I would use expanded polystyrene or PIR - probably the latter because it is much harder and will therefore not shed lots of bits as the PS will.

I am uncertain about simple vent-grilles. If you insulate sufficiently then the ventilation shouldn't be a problem and no I can't say what "sufficiently" is. Condensation is a moving feast governed by internal temperature and humidity and external temperature and humidity so what works today may not be good enough tomorrow.

Look at this and play with the numbers if you want to see what happens under different conditions.

http://www.dpcalc.org/

 

[Deluks]

Fit insulated tilebacker board to the wall using tile adhesive. Beware, this may interfere slightly with the cupboards/worktop when fitting them against the wall. Only 10mm thick though so shouldn't be a problem.

You say you have a kitchen extractor, does it actually vent to the outside? and does everyone use it when cooking, and washing up, and boiling the kettle? All these things will introduce water vapour into the room.

 

[greenfox]

Thanks all for your replies, very much appreciated.

Woody - makes sense when you put it like that

mointainwalker - cheers, that calculator looks really useful - I'm going to get myself a cheap hygrometer and keep an eye on the humidity levels in the flat. Will help me to decide if another vent is necessary.
I've also been looking at the PIR but was concerned about a couple of things I'd read about using boards to combat damp:

1) they can actually attract condensation if they are not fitted properly to the wall with zero gap behind. Would you seal the edges with mastic or something? I'm thinking especially where the boards join together in the corner, or where the worktop touches the board?
2) Fitting boards may cause the damp problem to migrate to the next-coldest spot. If that happens to be above the worktops on an uncovered wall I'm guessing that will be preferable because it will evaporate more readily than if trapped in confined space.. but if it's in a smaller space, still below the worktop then it could potentially be an issue - any thoughts here?

 

[greenfox]

Deluks - thanks, hadn't seen those before, space is a bit tight but should be able to afford 10mm. I'd only fit boards below worktop level though because there is no mould issue above and I don't want to re-surface the whole wall. Instinctively the boards seem like a good idea but have a couple of concerns based on what I've read, (see above post).

Have you used them yourself and found them to work well?

Yep my kitchen extractor will vent outside, and I'm going for a decent extraction rate - currently looking at a 750m3/h model. The kitchen is being fitted in a couple of weeks, hence my wanting to get the best solution(s) in place now - don't want to be ripping stuff out to deal with mould in a year's time!
There's only little ole me in the flat and I will certainly be vigilant about using the extractor, and the bathroom one too.

Thanks again.

 

[Deluks]

No, but they should make enough of a difference to keep the wall at a temperature where condensation shouldn't form. Using tile adhesive to fully bond them will eliminate any gaps behind them.

If you extract then I don't see how you can have a problem. Leading to my next question...

Do you have any heating in the kitchen? Radiator? underfloor heating? plinth heater? An electric plinth heater might do the trick, would only need running for a few minutes (if the kitchen is small) to take the chill off in the mornings, plus add a few air vents to your plinths to allow air to circulate behind and under the cabinets.

 

[JohnD]

you will introduce cold moist external air

cold external air is not moist.

An electric plinth heater might do the trick, would only need running for a few minutes (if the kitchen is small) to take the chill off in the mornings, plus add a few air vents to your plinths to allow air to circulate behind and under the cabinets.

warming the air in the kitchen, without the walls getting equally warm, will cause condensation to form on the walls.

2) Cover the wall behind the units with an insulation layer so the wall doesn't get as cold

putting insulation on the warm side of a wall will make it colder, not warmer.

 

[Deluks]

Lets all beat JohnD up after school