Dripping Shower Fan / Roof Vent Question

[ProDave]

I have a customer with a problem. New built house (2009) all bathroom fans are in the ceiling and are vented with 100mm flexi hose to roof vent tiles a bit like these http://www.screwfix....lour-grey/79071

Are they really suitable for venting a fan over a shower? the description says so.

His problem is condensation. There's probably about 8 feet of flexi hose straight up from the fan to the vent tile. But the inside of the hose gets condensation that then runs back down inside the pipe.

First of all I replaced one of his fans about a year ago as it had failed due to the moisture. today, I was called back because the replacement fan (still working) has fallen off the ceiling because the plasterboard is rotten where it keeps getting wet from dripping condensation.

I've suggested we abandon the roof vents and instead drill through the gable end and vent the fans out of there, and do the main run in solid drain pipe with a slight fall towards the vent so any condensation will go outside.

The owner would like to try and get the builder to pay for this (NHBC warranty) so I'm trying to find any documentation that says roof tile vents should really not be used for venting the fan from a shower room.

Any ideas?

He's asked the neighbours and most of them have had some issues. One says they regularly go up into the loft with rags to dry the inside of the pipe.

I think this house may be worse than many on the estate as in this case the roof vent tiles are on the north side of the roof so never get any sun and are always cold.

 

[sparkytim]

Hi Dave

Building regs Part F has all the info, if going straight up then Xpelaire do a condensation trap to fit at the bottom and pipe out. I would go with ducting out of gable end and slope pipe to outside. I have had similar problems and now always cover over ducting with insulation to minimise temp change.

 

[Evans Electric]

Wot Sparkytim says . Not many sparks bother with condense drains TBH. Sometimes you get away with it , sometimes not .

Doesn't help when the customer has the timers on minimum either.

Also I don't think most of the ceiling fans we fit , have the guts to function against 3 mtrs of ducting , fine for a 12" tube through a wall.

How about a more powerful fan mounted in the loft with a grille on the ceiling .? I could recommend the Vortice Lineo , fitted loads and not been called back. Around £50.

My neighbour,s had a bathroom refurb then 2 years later asked me to replace the fan/light unit which had packed up. In the loft the 3mtrs of flexiduct had been left lying on the ceiling with the end sticking up , filled to the brim with water , I could hardly lift it , must have been 3 gallons in there.

 

[Doc Hudson]

As the gents have said, I would also suggest that this problem requires, a Centrifugal in line fan, not a ceiling mounted axial fan. The duct itself will need insulation to a similar degree that the loft is insulated and the timer must be left to run on sufficiently after the shower has been vacated to allow the warm moist air to dry out, typical at least 15minutes possibly 20+. The roof vent itself should not be a problem providing it has an opening of equivalent area to the ducting CSA.

Doc H.

 

[Sharpend]

The ducting Dave is it the insulated type? I do many new builds and it is a requirement,AFAIK, that ceiling fans in roof space must have the insulated ducting, can't say I've had any comeback to date.

Can't get the link to open, any chance of pic?

Finally got link to open. Don't see them as a problem, have had something similar before.

 

[Andy™]

condensation trap with pipe leading outside should fix the problem. along with insulated pipe and a longer time

 

[wozz]

When i done new builds you never would have got away with non insulated in a loft. Correct fan and ducting and you should be fine.

 

[ProDave]

All good ideas and common sense.

It's easy enough to re engineer it to solve the problem, but nothing has yet led to a document saying what they have done is wrong. Clearly it is wrong otherwise the fan would not have fallen through the ceiling due to the plasterboard being rotten.

Before he pays any money to anyone (me) to fix it, he wants to try and get the original developers to fix it for free, and for that we still need a code of practice or a document that clearly shows what has been done is wrong.

 

[Sharpend]

In that case Dave a call into the local building control office should clear up any uncertainties, they should also have details of site etc which may or may not help. Even though NHBC check the build, I do believe that the lbco's also stick their nose in for a gander.

 

[Evans Electric]

Can Part F of the Building Regs be quoted ?

 

[M107]

http://www.tlc-direct.co.uk/Products/BGCT.html

 

[ProDave]

Can Part F of the Building Regs be quoted ?

Part F seems to be all about ventilation. how much you need for what room etc. These days it seems concerned with heat recovery etc. Clearly it's been updated recently (2010 I believe up here)so for a start I need the older version of part F that was in force when this house was built, not the current version.

And even than I can't find any specific guidance on the physical installation of ducting and roof tile vents. About the only bit of "workmanship" guidance is when installing a horizontal run of flexi ducting, not to allow it to droop down otherwise it will fill with condensation.

Even on the Vent axia site, I've found their condensation trap (for installation in RIGID ducting not flexi) but no diagrams. they just repeat the same diagram of a droopy horizontal flexi duct (now not to do it)

I've spent some time searching and cant find what I want.

I could perhaps convert to rigid ducting with the condensation trap, it would still need a bit of flexi at the top as the vent tiles are not exactly directly above each fan, but not far off.

[rant]

P.S why are these condensation traps so poorly designed? "you will need duct tape" FFS. You don't use duct tape to join proper plumbing pipes, so why is a condensation trap for ducting made to be such a poor fit with no seals?

And why does it vent to 20mm pipe? that's not a standard plumbing size is it? so we drain off the condensate with a bit of 20mm PVC conduit. Make sure to solvent weld the bends then to make them watertight.

[/rant]

 

[NozSpark]

I've just had a look at Approved Doc F

Look at the end of Appendix E - under General Notes

It says that insulated duct should be used in unheated voids or lofts,,, and that condensation traps should be used when a fan is extracting moisture rich air

 

[Andy™]

And why does it vent to 20mm pipe? that's not a standard plumbing size is it? so we drain off the condensate with a bit of 20mm PVC conduit. Make sure to solvent weld the bends then to make them watertight.

[/rant]

dont forge to use inspection elbows for access at the corners later

 

[Sharpend]

20mm is generally used by plumbers for condensing boiler overflow, water tank overflows and the macerators.

 

[Sharpend]

Dave google part F 2006, think this was last edition, could be wrong?

 

[Sidewinder]

20mm is generally used by plumbers for condensing boiler overflow, water tank overflows and the macerators.

21.5mm actually, I have a load to install tomorrow on a medical job!

 

[Sharpend]

What's 1.5mm to argue over, besides I was rounding off for simplicity!!

 

[Sidewinder]

Try getting 21.5mm overflow into 20mm conduit fittings then you'll know! ; )

 

[batty]

Installer has not read manufacturers instructions they always state a condensation trap is needed when going out through the roof. I prefer to go out through a wall if possible but sometimes you can't. I always use 4'' soil pipe when going out through the roof which is the correct size for condensation traps.