Now considering that solar insolation is around 1000W/m2, imagine beaming 200 bar radiators onto the roof.
How much moving air or water do you think would be required each minute to keep the roof from heating up?
Browse Forums Eco Living Re: Roof space heat - eave vents and whirlybirds ... 23Nov 14, 2009 4:06 pm Builder; Big M Design; Soho 32 Facade; Ascent Blog; http://mickeyb-soho.blogspot.com Trend; viewtopic.php?f=31&t=23990 Re: Roof space heat - eave vents and whirlybirds ... 27Dec 15, 2009 9:16 pm A lot of people live south of Rocky Where you are coming from is where you are going to... Re: Roof space heat - eave vents and whirlybirds ... 28Dec 15, 2009 9:45 pm onc_artisan A lot of people live south of Rocky To my knowledge there are no studies looking at roof ventilation in a temperate climate but the issue remains the same. Foil does a much better job at reducing the heat load than trying to remove it with ventilation once the ceiling has gotten hot. Imagine sitting on every square metre of roof is a portable bar radiator pointing down at the ceiling. Next imagine what kind of breeze you would need to whip up to prevent the ceiling heating up. Ventilating in a mixed climate brings its own issues. Bulk insulation works best in keeping the warmth in when the air is still. An open roof space is only going to make this worse. Re: Roof space heat - eave vents and whirlybirds ... 29Dec 18, 2009 4:33 pm Today is a reasonably warm day in Perth. At 1.30pm at my location the outside temp is 34.2C. Inside the roof space it is 40C. I can't see any difference between the lower level right on top of the insulation or 2 metres higher up but I could only stay up there for 20 minutes so measurements were taken for 10 minutes at each level. The temp under the insulation is 27.1C while below the room temp is 24.4C. Given that tomorrow will be almost identical and the overnight minimum is going to be around 20C (and not for very long either) the trapped air inside the roof space will have a head start on climbing above 40C during the day. I am just waiting till we get another hot spell with 4 or more consecutive days over 38C and overnight mins of around 28C.... I don't hold up much hope that the 14cm of trapped air inside the insulation will be able to hold out for too long under those conditions. When it finally succumbs (as it must do) there is only the 13mm of plasterboard to limit the temperature due to the extremely hot air inside the roof space coming through that final barrier. I am going to buy me a Powervent 300 as soon as I can afford the $660 and see if it does help reduce the temperature up there. Re: Roof space heat - eave vents and whirlybirds ... 30Dec 18, 2009 4:51 pm It will I did and it does Where you are coming from is where you are going to... Re: Roof space heat - eave vents and whirlybirds ... 31Dec 18, 2009 8:04 pm RossH I am going to buy me a Powervent 300 as soon as I can afford the $660 and see if it does help reduce the temperature up there. Or $660 buys you 130m2 of reflective foil which will block out >99% of the radiant heat load. I will look forward to your report before and after measurement of under-surface ceiling temperature with your vent. Re: Roof space heat - eave vents and whirlybirds ... 33Feb 12, 2010 11:41 am I think you can do both. They are both cheap. Just lay concertina foil batts across the top of your bulk insulation, getting where you want to from d69's perspective ... this will cost less than $1000 and does make a difference (I have done it in the last two house I have been in). Then, given the cheapness of the power vent (or csr edmonds), why not do that as well. d69, surely this give you an incremental benefit each time. Also, you should put an eave vent on the south side of the house. Also, you must put a thermostat on the fan ... otherwise it will work when you don't want it to. Re: Roof space heat - eave vents and whirlybirds ... 34Feb 12, 2010 12:05 pm If the ambient temp remains a constant like in the tropics the drawn air will be warm air, not cool like in the temperate areas of Aussie. Tropics make up about 40% of the country but a LOT less people live there... ... so the main population could have some more benefit from Wbirds IMHO only. Where you are coming from is where you are going to... Re: Roof space heat - eave vents and whirlybirds ... 35Feb 12, 2010 12:43 pm Does insulpaint coating work on the roof? I have also heard of e-vent by Combined Metal Industries and would be interested in them if I needed it living in Perth, thank goodness I requested a surfmist roof. Re: Roof space heat - eave vents and whirlybirds ... 36Feb 12, 2010 1:06 pm I thought I would never had to say this but I am starting to reconsider the whirly debate. A member of another forum who lives in Melbourne has been data logging roof space temperatures during summer. Interestingly he has shown that roof space temperatures don't fall to ambient levels at night time. It makes we wonder if this is inhibiting passive cooling of the building fabric after sunset. This might also be exacerbated by the presence of insulation and radiant foil Although I will maintain that whirlys are insufficient at countering the immense heat load during the day, they may help accelerate roof space cooling at night so that the house can shed its accumulated heat prior to the next day. Of course, this is with the onc_artisan's proviso that night-time temperature do significantly fall. In the past roof space ventilation was advocated for hot/humid climates to improve comfort but paradoxically its benefit may be actually be more appreciated in more moderate climes. This is all speculation of course and a proper study for houses south of Brisbane may be in order. The only concern is that uncontrolled roof space ventilation will not be helpful for retaining heat during winter so some means of blocking it is required during the winter months. Re: Roof space heat - eave vents and whirlybirds ... 37Feb 12, 2010 1:15 pm Good to here some more localised testing is happening Dymonite69... I have to agree. it is my finding also they make a diff' albeit here in the south west. We here are after all on the same latitude a Sydney, so I figure without expiriencial data we are quite blind as to the benefits. And hoping as you know is not good enough. perthhomelover - I imagine you will get a negative response... The thing that concerns me with roof painting, is that paint uses surfactants to help ingress the substrate. Surfactants are what are in your soap ...if you intend to harvest your roof runoff (rainwater) I would advise against it. kind regards, Onc Where you are coming from is where you are going to... Re: Roof space heat - eave vents and whirlybirds ... 38Feb 14, 2010 9:59 pm I have enquired about a solar-powered roof vent which was advertised in a local paper during the week. The product is called Solar Star by Solatube. They claim 1 of them is equivalent to 14 whirlybirds... http://www.sydneydaylight.com.au No pricing on their website, but there is pricing (US$?) on this one: http://www.ecohaus.com/C-22/solarstar+attic+fans Re: Roof space heat - eave vents and whirlybirds ... 39Feb 22, 2010 7:53 am Hi, Can anyone help here please. What is the best height/location to install whirly birds on a house? For example, when looking at the house from the street, should the birds be installed very high on the roof (close to the peak), or further down, maybe half way up the roof height? Other info: Concrete roof tiles, 25 degrees roof pitch, sarking, 2 whirly birds. My signature is distracting people from my wise posts ... Re: Roof space heat - eave vents and whirlybirds ... 40Feb 22, 2010 3:51 pm Seeing as heat rises, wouldn't it be common sense to put them as high as possible? BTW, No response from the company to my email requesting info on the Solar Star a week ago. Slack! (And now 3/3 companies to ignore emails/contact requests through their website in the last few weeks!) Shade the brick with large eves. Since going to minimum of 600mm eaves on my build, I've noticed much improved cooling off the house after hot summer days. Can see the… 1 2976 Old Home Restoration / Renovation Cheers mate! This is exactly what I was thinking but wasn't sure if it was something I'd find on the shelf. I agree with you, fixing the brackets to the board will look… 2 4042 retail its around double the price of a similar sized actron/dakin system from memory, They are excellent systems though. But with how builder gouge on AC/heating, you… 4 16442 |