Browse Forums Building A New House 1 Aug 20, 2012 10:15 pm Hello... So our builder said we didn't need Sarking under our colourbond roof... We had reached over 6 stars rating but I said I actually wanted it for condensation not star rating ... Anyway our roof Is pitched and has one whirly bird and they upgraded our batts from 3.5 to 5 in the roof So is that goin to help That we upgrade the batts Is condensation really a lot in Victoria in colourbond roof Is it going to damage anything ?? Re: No Sarking in colourbond roof - Victoria 2Aug 20, 2012 11:20 pm Our builder also said we didn't need it here in Brisbane but we are going to insist (I just don’t get project builders thinking on this). Get it – make sure the sarking is a backed foil e.g. Thermofoil. Why rely on your batts being upgraded when you’ve got the chance to keep the roof void that bit cooler in the first place. Apart from dealing with condensation, it will quieten the noise of the rain and insulate your roof space, also it’s not something that can be done after it's built easily. ----------------------------------------------- http://pab34newdigs.blogspot.com.au/ ----------------------------------------------- Re: No Sarking in colourbond roof - Victoria 3Aug 21, 2012 9:58 am Thanks our roof was already laid unfortunately. We were under the impression it came as standard.... In hindsight the builder upgraded our ceiling batts from 3 to R5 so that was good. Hoping the better insulation will help with heat/cold. I only thought the foil was for condensation not insulation - upgrading the batts to R5 would Be a better insulator then a foil under the roof?? We are located in Victoria so the climate here is Alot different and not humid just fresh. It can get a alot of hot days in summer though! We have eaves all at the front - not sure if tht helps Also our roof is pitched at 22.5 degrees dont know if any of this helps...! Re: No Sarking in colourbond roof - Victoria 4Aug 21, 2012 10:37 am You wait until you have a cold night followed by a sunny day. I reckon you will get lots of condensation dripping off the underside of the roof sheeting. I'd seek local independent professional advice on this. Stewie Re: No Sarking in colourbond roof - Victoria 5Aug 21, 2012 10:05 pm Hi Ashy85, The risk of condensation is dependent on the dewpoint of the air within the roof void, and the surface temperature of the inner roof surface. There are two issues to tackle: 1) Roof air dewpoint. In winter, the air vapour pressure & dewpoint within the house will be well above that of outside air, because the space is heated, and moisture is added via respiration. To properly address this, the vapour barrier needs to be on the Room side of the Roof void to prevent room moisture entering the roof space. This is more important in cold climates. A reflective foil facing is a vapour barrier. Having it under the roof acoustic insulation is not ideal, as it traps moisture withing the roof void. I note 99% of houses are built this way though. 2) Roof inner surface temperature. You need insulation on the undersie of the colorbond sheeting to address this. But you can have a vapour permeable barrier instead of foil, which allows moisture in the roof to escape. If you have R5.0 insulation, why bother with roof ventilators???? There will be minimal gains to be had, and you run the risk of a leaky roof in the future. I suggest you get insulation below your roof. Foil backed insulation is usually ok, but if it gets really cold where you are, condensation remains a risk with this arrangement, as the foil temperature can fall below the roof air dewpoint. To be sure, have a vapour barrier the ceiling, and use a vapour permeable barrier (with insulation) behind your roof in lieu of foil faced insulation. Go to www.dctech.com.au for some guidance. Re: No Sarking in colourbond roof - Victoria 6Aug 22, 2012 9:29 am actually a requirement and the sarking is meant to extend into the gutter so that the condensation runs off into teh gutter. even with sarking one can get condensation, but it runs out to the gutter . refer to australian standard leighton from clark new homes Re: No Sarking in colourbond roof - Victoria 7Jul 29, 2014 4:40 pm Just want to know how sarking could avoid condensation, I believe the blanket is laid on top of timber batten, so I think the water will form and running down but block by the timber batten, rather than running into gutter?? Anyone can explain this? Thanks Re: No Sarking in colourbond roof - Victoria 8Jul 29, 2014 7:42 pm fzxbeetle Just want to know how sarking could avoid condensation, I believe the blanket is laid on top of timber batten, so I think the water will form and running down but block by the timber batten, rather than running into gutter?? As this is the underside of the roofing that we're talking about, any condensation wouldn't run into a gutter; it would just trickle down until it hits something which it would moisten or pool on. The anticon blanket is up against the metal, so the air that's carrying all that moisture is instead against the underside of the blanket. Temp difference between that air & the anticon blanket won't be as large as the temp difference between the air & the metal (which is closer to the temp of the outside air), so less moisture condenses on the underside of the blanket than would condence on the underside of the metal without the blanket. Roughly speaking, at least. 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