The ventilation needs to move sufficient air volume, IE to carry away the radiated heat from the roof sheeting faster then it can build up. On a 35C summer day the very best one might expect is a roof cavity at 35C. In the real world it will always be a little hotter. This may still be too warm for your water if that is a significant concern. In a tight roof space the proximity of the water pipes to the roof sheeting may also be a factor. So somewhere between what you see now and how hot the day is outside.
Ventilation is not your only consideration or option.
In a restricted roof cavity the heat build up can be more concentrated and air flow more restricted. If you have access or are doing a roof replacement the plumbing suppliers sell expanded high density foam insulation for copper piping. It is intended to keep hot water hot, and to insulate air con piping or water that are cold. There is a split version which is suitable to post install if you have safe access, although some just split one edge of the solid round section and tape over. Iāve only worked with the solid round on residential size piping, and moulded split versions on larger.
Installing insulation under the roof sheeting will also make a difference, in particular to reduce the heat transferred from the roof sheeting or tiles. For a roof space that is constrained the sort of task best done at the same time the roofing is being replaced.
For powered ventilation fans look at how the motor and fan is mounted. A large component of any noise is from vibration of the fan blades/air and motor. The vibration can be readily amplified through the roof structure. A similar effect to how resonance amplifies sound from a guitar or violin string.
P.S.
From the long hot summers we spent in Townsville I understand the issue with the water pipes in the roof too well. It could add 15C to the water over the outside air temp, and up to 20C in the roof cavity. We got used to wasting a little water some days or using it to start the washing up or shower, cold tap only to start.
I have two of the Twister whirlys on my roof.
After having had them installed on cement tile roof and put 4 eve vents in as well .
So I reckon they do work
If the roof space temp is heating the water to the point itās a problem a Whirly isnāt going to help much, better off grabbing some foam lagging and electrical tape from Bunnings and insulating the pipes. Then throw bats over the top and itāll do more than a Whirly of any type.
Hi @Mick_J, welcome to the community.
Great to hear how it has gone for you, especially noting that you included eve vents in your install.
Iāve been surprised by how much draft an open ceiling manhole can generate in a typical tin roof on a warm to hot day in Qld. Weāve owned homes from all three recent Australian centuries as a guide.
The early Queenslanders developed to include features such as pressed metal ceiling roses with punched out fret work. This allowed them to cover an opening in the ceiling to draw hot air out of the room. The older portion of our current home was more primitive with three rooms and three manholes in the centre of each room. The norm was to open the manhole in summer. The house eves are not sealed and have a Python sized gap between slats of 2x1 hardwood. Typically roofs were fitted with a variety of ventilated ridge capping, peaked caps or static vent pipes. Ours are long gone. The sun heated air naturally rose drawing air through the roof space and also from the cooler verandahs into the open rooms.
The difference with time then was insulation as we know it did not exist, so drawing hot air out of the roof was the way to go. If you look carefully at some heritage properties the grander offices or homes may actually have a double roof. The give away is slat like panels below the gutter line like an extended facia. More homes for the pythons, pigeons, bats and possums, locale dependent. Ventilation of the roof space has relative benefits. Iāll not comment on the pythons further.
We have just installed a solar air exchanger in our walk in robe (5x2 metres). It is very effective and you can actually feel the air go past as it is drawn out. Not sure how this would be in a larger area but I am sure it would far surpass regular whirlybirds.
Useful advice again - I will pass it on. The time to fix the hot cold water would have been in the building stage 11 years ago. Hot cold water pipes in a hot climate must be a known problem, but I guess the property developer hasnāt been troubled by it. The roof space is very tight and I think that insulating the pipes now would be difficult.
The roofer (business owner) implied that it was some sort of regulation that prevented them from working below the gutter line, presumably a state-wide rule. I found it bizarre that they werenāt allowed to fit the inlet vents. If it is true, other people having roof vents installed will have the same problem.
My parents in regional Aust installed a solar activated fan on the side of the house under the pitch. Pretty simple and straight forward. Just an exhaust fan powered by a solar panel. Dad said they noted a reasonable drop in temperature in the house after it was installed. I would think it would be a good idea to run it through a manual switch so it does not run in winter.
Anyone who has been in the roof cavity in summer can se the significant build up of heat that occurs in that area.
Hi I live in Perth and have been researching solar roof extraction fans. I have looked at three in particular. Solar arc sav-20, solar king 2100cfm, solar whiz R-2300. Can anyone give me feed back on personal experience on these fan efficency. Also value for buck. I want to remove a great deal of heat out of the list. Thanks Patrick
I have moved your post to an existing thread which has similar content and may assist in answering your question. I am sure that if any members have specific information on the products you are interested in, they will also provide feedback for you as well.
I recently brought a solar King rood extraction fan and fitted myself. It has prooved a good investment and I am very happy. It has dropped the roof space temp to the same temp as the outside temp and subsequently dropped the inside house temp by around 8 deg. I also made up under eve vents to allow air into the loft, as they we previoulsy boarded up under the eves to stop rats. I had to remove the old boards between the truss ends and made up simple frames from 9mm ply to suit that sizing and with an open area max the vent size and stappled ss fly screen to the back of the frame. They work great both to let heat out and also get fresh air in. Cost wise the extraction fan was good value at around $400. Cuts donw on use of air con on moderately warm days.
