Home DIY

Does the extract fan run on sufficiently long enough to reduce humidity levels? I've had problems in well insulated new builds with mould for this reason.
Also, is the door to the room left ajar to allow air to circulate? I used to get mould in the shower cubical of a previous home's en-suite that was cured by simply leaving the shower door very slightly open.

That beam is acting like a thermal bridge. In winter it will be stone cold and whenever you shower it will bead up with condensation; sounds like this might be running down the back of the plasterboard. Not good. This, you know.

Tricky one to solve. I guess you either insulate and seal the beam face (?) or seal the shower/extractor encosure better so that the moist air does not come into contact with the beam. This would require waterproof plasterboard or membrane or somthing better than plasterboard and glue. In addition you might need an uprated fan.

^^CHeers RG

I've tried leaving the fan on, the door ajar, sacrificing a chicken and pelting the beam with rum and pennies and the condensation still forms.

Olly398- yep, spot on, it is a startlingly effective thermal bridge, which runs around the top of every single room in the 64 apartment building. Woo!

What I was thinking of was to bond some foil lined insulation backed plasterboard to the beam (and wall).

I'll lose the insulation value of the wall, but equally I would hope to lose the thermal transmission of the beam.

^^ Showers mostly have built in anti scale features but, I guess, better quality showers will have better protection. I believe some use a gradual shut down rather than water straight off when you turn them off, as part of the anti scale function. Heating elements can also have anti scale coatings. Having said all that, they don't last forever and if it eventually does die on you you'll need to get a similar wattage unit and ideally one that fits straight onto your existing installtion so it's a simple swap.

Ta.

The current installation isn't optimal as I found out when I had to call a sparkie out to fix a bunch of stuff a while back so if it did die I'd be getting a bigger unit and rewiring it to cope.

^ what are you using as a seal between the turned down pvc socket and the (cast iron?) waste outlet?

Poo

think we covered that in post #1105

I've tried leaving the fan on, the door ajar, sacrificing a chicken and pelting the beam with rum and pennies and the condensation still forms.

Olly398- yep, spot on, it is a startlingly effective thermal bridge, which runs around the top of every single room in the 64 apartment building. Woo!

What I was thinking of was to bond some foil lined insulation backed plasterboard to the beam (and wall).

I'll lose the insulation value of the wall, but equally I would hope to lose the thermal transmission of the beam.

Stronger extractor fan is the first thing to do, 40-60l/s would be sufficient. Maybe duct the extraction at the ceiling level to get rid of the hottest wet air. Dry lining the entire wall will only improve insulation generally, but could hide condensation on the beam itself causing a bigger problem in the future.

^ also keep your rads on in the shower room, it needs to be a warm room to help prevent moisture condensing.

^ what are you using as a seal between the turned down pvc socket and the (cast iron?) waste outlet?

Stuff called CT1

Stronger extractor fan is the first thing to do, 40-60l/s would be sufficient. Maybe duct the extraction at the ceiling level to get rid of the hottest wet air. Dry lining the entire wall will only improve insulation generally, but could hide condensation on the beam itself causing a bigger problem in the future.

Current fan specification is "Extract Performance:85m3 per hour".

Insufficient I assume?

23l/s plus pressure drop in external duct, yes, probably

I've been painting our new flat the last week and a bit. Got very angry this afternoon on discovering the fourth coat of paint in the bedroom still hadn't dried after two days. I may have let my emulsions get the better of me.

WAHEY!

23l/s plus pressure drop in external duct, yes, probably

Cheers RG, I will get a more vigorous extractor fan.

Hmm, 12v/SELV extractors (which I got thinking that safety was a good idea, even though the fan is not in zone 1 or 2) seem only to be available in "weedy" extraction rates.

Bugger.

"We're gonna need a bigger fan"

Good advice from types btw.

Yeah, it makes sense- looks like I'm going to have to re-wire again though, as I cannot find any SELV fans that move anymore air than the one I have.

here's the manrose guide, might be useful > http://www.manrose.co.uk/fan_select.htm#

Thanks for that RG. next issue (!) is that whilst this one fits the bill with 60l/s extract, I don't physically have enough wall to widen the hole to 6", can I mount this over a 4" duct with a bit of adaption do you think?

I think you won't achieve desired flow rate because:

150mm duct area is 17,700mm sq

100mm duct area is 7,850mm sq

i.e. less than half the area

As the fan is fixed speed it won't be able to extract any more air than the duct area will allow.

The manrose CF400 will meet desired flow rate (centrifugal fan running at 2300rpm) and has a 98mm dia duct outlet, but it is noisier and operates at 230Vac, which may be prohibited if it's within reach of the shower.

But for a higher flow rate fan there has to be leakage air available for it to extract.

As an alternative you could consider embedding some low voltage heat tape in the plaster over the beam.

Ingress-air is not an issue, I can "adjust" the door/frame to allow more if needed.

Good point with regards to the area, that'd not occurred to me.

The extractor location is ~2m away from the shower, so not in a low-voltage required area (I believe), so I could use 230V.

I'm wondering about making some custom ductwork that would, basically, site a grill over the face of the beam leading down to the fan- I could fit that Manrose CF400 in that, conceivably.

ok, just make sure siting the fan complies with guidance given here > http://www.fantronix.com/acatalog/bathroom_Zones_Explained.html

forcing all shower vapours past the beam might exacerbate the problem

Beam is directly above the window- the extractor is mounted as high as possible.

The mould is forming top left, above the window.

oh, not helped by lack of paint/tile on plasterboard. do you have a second bathroom to use while you dry out, remove mould then finish this one off? otherwise sorting this could prove tiresome.