new poster: never seen condensation do this...

[joelst82]

Hi all, Love the site and everyones input. first time home owner, newly married, lacking in time and lots to keep busy with working on our 45ish y/o fibro & cladded home. Lots of experiences already to speak of. blocked drains, subfloor flooding, stormwater to nowhere. Fun for all. I woke thismorning to find marks on my ceiling that thought strange. Our roof is cement tile with sarking, but no insulation in roofspace. Freshly painted ceiling. Of a morning the front of the house is shaded by trees until around 10am and the temp of late has been around 7 degreesC. Windows are usually heavily coated with condensation until late morning. We do have plaster vents in walls to circulate air out through eaves. photo attatched. why would this happen?http://s556.photobucket.com/albums/ss7/joelst82/?action=view&current=26062009399.jpg
sorry if it ends up in the wrong section.
Thanks in advance.
http://s556.photobucket.com/albums/ss7/joelst82/?action=view&current=26062009399.jpg

[Honorary Bloke]

You are getting heavy condensate along your ceiling joists, which accounts for the strange pattern. Your attic space is wet as and you've got to dry it out. The heat from inside is leaking through the ceiling and when it hits the cold air . . . voila . . .water.

Ceiling insulation will stop this heavy condensation. Lacking that, heating the attic will stop it (but is a silly idea). Finally, installing blowers in the attic to vent the air might help.

Ceiling insulation is your best alternative and will help your home in other ways as well.

On the bright side, the problem should disappear when summer returns. :rolleyes:

[joelst82]

Thanks Honorary bloke. That makes sense. I guess insulation gets shifted up the to do list.

[gpkennedy]

Joel
you should also check that any ceiling exhaust fans dont vent directly into the ceiling space. Check in bathroom, kitchen & laundry. They will build up moisture in the roof cavity.
George

[joelst82]

good point george!
I recently replaced the bathroom exhaust fan as the previous one didn't seem to be moving much air. a trip to bunnings was almost useless. the only one on the shelf that had a quoted air movement rate was a non ducted model. around 750m3/h. in fixing one problem i've created another.

[gpkennedy]

Joel
the new exhaust fan in the bathroom may have added to the problem. If you have sarking under the roof tiles the moisture from the bathroom has nowhere to escape. It will condensate on the sarking and run down the slope of the roof and drip off onto the ceiling and create stains as seen in your pics. More moisture & stains at the plaster at the external walls than in the center of the ceiling.
You should research venting the bathroom exhaust fan to outside the roof.
Good luck.
George

[gpkennedy]

Joel
after you have fixed the moisture in the roof cavity, and let it dry out, you can repaint the ceiling with a good paint product.
http://www.zinsser.com/product_detail.asp?ProductID=86
Get a can of this, at Bunnings. ($15) Shake the can as per instructions and lightly feather spray it onto the stains in the ceiling. It is a can that sprays vertically and is designed for ceilings. Give it a light cover (keep your hand moving) and let it dry before giving it a second coat. Take your time. Let both coats dry before applying a ceiling paint by roller, next day. There are some ceiling paints that paint on pink and turn white as they dry. They are a good idea if you are painting white over white on a ceiling.
Cheers
George

[joelst82]

Hi George;
I'm looking around for a suitable ductable ceiling exhaust. the ratings on the current fan are 800m3/h 222litre/s extraction. the main brands for sale at bunnings are mistral and heller. few others. the heller's specs don't exceed 200m3/h for any models. will check out some electrical suppliers. as for paint and this other product you've suggested, the ceiling was recently painted with taubmans paint. thankfully the condensation marks have only shown up once and were gone by next day. having shorter, not so hot showers until the problem with the fan is fixed. i'm hoping repainting wont be necessary. I'll see how it pans out.

thanks for the advice again.
Joel

[gpkennedy]

Hi Joel
not exactly sure what type of fan you are looking for, general attic extraction or just for bathroom.
http://www.westaflex.com.au/_pdfs/ventilation/Vent_Bathroom_Ventilation.pdf
Look at showerlite kits P4 from this mob. They vent shower steam directly to outside, come with a 3m exhaust hose, and fittings.
Need a sparky to install. I have not used them but worth a look.
George