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Reliable advice required on cooling.

(15 posts) (10 voices)

Started 1 year ago by Jaycotoy
Latest reply from Buzzman

Tags:

insulation

Jaycotoy
Member

My 25 year old house has a a simple gable roof, concrete tiles and 100mm fibre glass batt insulation laid between ceiling rafters. There is no sislation under the tiles. The roof area is approx 100 square metres (volume approx 100 cubic metere) with the ridge aligned east west. The external house walls are brick veneer. The internal linings are 10mm plasterboard. The house is quite hot in summer. I am in Brisbane Q.

After reading some interesting posts on this forum I thought an extractor fan of suitable capacity located in a gable end wall to remove heated air from the roof space would be worth persuing.

When I rang a fan manufacturer I was told that an extractor fan would not help my situation. He said there was a CSIRO research project about 15 years ago that ruled out such measures. He said the best approach is to install reflective sislation.

This would be difficult for me to do because the roof pitch is about 22 degrees and the bracing makes access tricky to say the least.

Is reflective sislation the best answer to my cooling problem?

Bob.

Posted Wednesday 29 Sep 2010 @ 1:27:14 am from IP #
ghostgum
Member

A radiant barrier (e.g. reflective foil laminate = RFL) sounds like the best solution.
Variations are:
Concertina foil batts laid on top of the fibreglass batts.
If the concrete tiles have reached end of life, then replace the whole roof with a light coloured colourbond metal roof with RFL underneath.

Posted Wednesday 29 Sep 2010 @ 1:35:49 am from IP #
dave lawrence
Member

reflective sisalation is definitely a good tip,
concrete roof tiles can last up to 40 years ,so even though replacing them with colourbond has merit , you will also probably have to add tie down to the roof trusses once replacing heavy roofing with lightweight roofing . all extra $$$.
I would say fans would be worthwhile but you would need to have them at both gable ends, coupled with close able ceiling vents and soffitt vents ,and other approaches too
In my experience a combination of factors is the best approach .. there is no single answer unfortunately (most of the time)

Posted Wednesday 29 Sep 2010 @ 4:45:22 am from IP #
cool at home
Member

Air Cell or something like it - a reflective product with an R rating of 2.7 (when correctly installed, and I don't think that is on top of the joists) can be laid under the rafters, and you might be surprised how well it could be done, even in apparently tight spots... insulation installers often look like jockeys... with good reason! We did this as a retrofit to our home and have been pleased with the results. I'd suggest contacting Air Cell for details of a supplier they recommend, and getting someone to look at your place. PM me if you are in Sydney and want to know who we used...

I'm sure there are other products similar to Air cell, but I don't know their names. Perhaps someone else can suggest similar products.

We originally had 'Sarking' with an R rating of 1.0, laid under the tiles/above the rafters at the time of building. I don't feel this was enough reflective insulation for Sydney, and batts really don't deliver that well in summer (IMHO).

Be aware that retrofitting in this manner is not a cheap exercise though....

Good luck

Posted Wednesday 29 Sep 2010 @ 4:57:07 am from IP #
termite
Member

It'll take time, but planting deciduous trees to shade all your surrounding hard surfaces (in particular the street) will also make a real difference.

Another point: I am also in SEQ. I am renting a house with no insulation but does have fixed awnings or verandahs that cover every exposed window. The windows also have bars, which allow me to leave windows open during the day while I'm out. It makes the house considerably cooler than it would otherwise be when I arrive home. Not having to cool that pent-up heat often means that fans provide enough cooling, and in extremis, the small air cond unit works quickly.

Posted Wednesday 29 Sep 2010 @ 6:01:59 am from IP #
amun-ra
Member

When your soup is hot do you A add a reflective barrier or B blow across the to of the bowl to cool the soup.the roof space will heat to the point that the batts will transfer heat eventually Maestro mechanical vent + the right amount of ceilling vents to match its airflow works for me in townsville

Posted Wednesday 29 Sep 2010 @ 6:39:15 am from IP #
ghostgum
Member

amun-ra, I choose method A. If you can't remove the soup from under the griller, then you need to put a radiant barrier between the heating element (sun) and the soup (you).
Regarding method B, the soup also cools down because the hot liquid is evaporating, drawing heat from the liquid as it does so. Blowing across it greatly increase the rate of evaporation. I'm hoping you don't have water sitting in your roof space!

Posted Wednesday 29 Sep 2010 @ 9:30:14 am from IP #
Benny
Member

I'm surprised no one has mentioned or asked about the walls. Simple brick veneer could be the main issue in terms of heat getting in. You really need to try and find out Jaycotoy why the house is getting hot. Is it a lot of sun directly on walls or is it the ceiling space getting hot and then through the insulation and then radiating down ? Or is it coming through windows ? You say you have 100mm ceiling insulation which sounds pretty decent and could be R3-4 so even if the roof space is hot, it might be that not a lot of heat is getting in from there. Is the roof space even passively ventilated ?

Posted Wednesday 29 Sep 2010 @ 10:18:31 am from IP #
cool at home
Member

"Amun-ra: When your soup is hot do you A add a reflective barrier or B blow across the to of the bowl to cool the soup."

That depends on why your soup is hot! Firstly, you remove it from the heat source. Given the number of hours the sun is overhead of your home in summer, that usually means reflective insulation in the roof space. Of course not all heat comes from this direction, so you will need look at a range of ways to get heat out of the soup/house, and cross ventilation, shading of windows and walls, etc, are an important part of this. Roof ventilation might help too, but is unlikely to be the most effective way to 'cool the soup' in this instance.

Posted Wednesday 29 Sep 2010 @ 11:18:37 am from IP #
dymonite69
Member

Without a radiant barrier it is like trying to blow on the soup while it is still on the burner.

In the day block the sun from heating the house. At night (if has cooled down sufficiently), ventilate like crazy.

Posted Wednesday 29 Sep 2010 @ 11:54:13 am from IP #
Jaycotoy
Member

Thank you to everyone who took the time to respond. Benny made a good point. I believe the walls are responsible for at least some of the heat rise. Placing a hand on the inside surface of the north facing wall in summer I can feel warmth. The bricks used are a very dark colour too which is no help, however the walls are protected by 600mm eaves and the windows have awnings. None of this makes me feel optomistic about making any real improvement without a lot of expense. There is one ray of hope though. In December last year we installed a solar water heater and a 2Kw solar PV system. These installations cover 21.5 square metres of the north side of the roof. The actual roof area including eaves is 96 square metres so about 20% is now shaded by solar collectors. We are not sure if it is just wishfull thinking or a milder summer but the house was not as uncomfortable this last summer. I must stress that we have had much more wet and cloudy weather this year. This has started me wondering if it would be feasible to fit a reflective shield above the rest of the roof. More solar panels is an option but without the Federal subsidy a bit costly. What do you all think? I'm serious by the way.
Bob.

Posted Wednesday 29 Sep 2010 @ 12:59:50 pm from IP #
dave lawrence
Member

some form of double skinned roof , and there are many ways of doing it , sounds like it could be well worth a try . I have not personally had experience with it, but have read about people doing it and claiming success .
Of course one of the main issues will be exactly how you do it. theory is one thing ,practice another . straddling part of the roof , without shading your PV panels ,now there's a challenge .
and yes I agree ,shading the dark brick west facing walls (even white washing them) would be well worth doing .suspend vines off them ... that would be my approach.

Posted Wednesday 29 Sep 2010 @ 8:35:00 pm from IP #
GBD
Member

Bob, Without photos or physically seeing the home, it's surrounds and overall layout, it's always hard to work out the cause, but as mentioned above by Dave - there will be a combination of many things that are adding to the issue.

When you say quite hot - what sort of temperatures do you consider hot?

A brick veneer house in Brisbane will tend to be a warmer house than most southerners desire - I'm saying that just in case you are new to the SEQ area.

re the heat.

I also don't think the roof fan will do much to improve it by the sounds of it.

Is the ceiling properly insulated?

Check the existing insulation in the entire roof space (have someone do it) and make sure it is properly installed - often lazy installers do not do the last 1 or 1.5m near the outside walls because it's too hard to get there and this area is where the heat gain is greatest, or they leave lots of gaps between batts or beside the joists so your insulations performance can be severely degraded.

Figures of 1/2 the R value if only 5 to 10% of the area is not properly insulated are not unheard of.

So you might be "thinking" the roof is insulated when it perhaps is only 1/2 the performance of what it should be. I saw a new house the other day where the entire ensuite bathroom had not been insulated and that was 2 months after being occupied. The insulation guys ran out and forgot to come back was the builders excuse.

I'd also be looking at your solar gain issues through walls and windows - test them inside - every hour with an infrared temp meter would be ideal and collate this data with the time that the sun begins to hit the external walls and you will see period of time that the inside gets warm which will correlate with a delay period of when the sun began hitting the wall several hours earlier.

If these walls are part of the issue - then the ceiling insulation would then help trap that heat - good in winter - not so good in summer.

So you need to stop the heat coming in to stop this factor.

If it's too hard to stop it entering the room - you can consider installing a through ceiling and through the roof ventilator that draws the air out of the room - but it has to go through the roof as well as one continuous tube - some skylights also offer this function - Otherwise you will just be allowing hot air to come back down from the roof space.

Plus you need to be happy with ambient outdoor temps inside the house as they will be drawn in as part of the process.

Un-insulated Brick veneer walls are very low insulators and rate around R0.4 - so they do not stop much anyway.

I'd also like to know how much ventilation the home gets, prevailing breezes etc.

Is there lots of paving that is heating up the ambient outdoor air which is then being moved to the inside of the house - which is warming it up and is being trapped by the ceiling insulation?

So - Sight unseen - my suggestions would be.

Check the ceiling insulation.

Check if the pavers patio etc is having an effect,

Monitor the walls and windows and see if one or more rooms is a heating up and acting as an internal heater when you don't want it to be -

Consider painting the roof white to reduce roof gain if the above are not an issue. This should be a lot less cost than a reflective foil retrofit.

Get the ventilation happening. Cooled air from plants and trees.

Plant some trees to shade the right areas but also make sure they will also guide and enhance the direction of the local breezes through the house and not block them.

Trust this helps give you some ideas.

Posted Wednesday 29 Sep 2010 @ 9:35:02 pm from IP #
cool at home
Member

Is reflective paint an option for your roof and walls? If you want to keep a dark colour, that is the easiest way to make a real difference... if your roof is a light colour it is not as effective to paint it with reflective paid.

As reflective paint is made for roof tiles, I can't see why it wouldn't equally work on your brick walls... particularly if it is just one side of the house creating most of the problem. It is relatively easy to apply but the surfaces have to be prepared properly, so you'd need to do some research or go straight to the supplier, eg: NuTech or similar. But white washing the walls is a great - and cheap - suggestion too.

Of course shading the walls with plants... preferably deciduous ones... is generally possible with single storey homes, but far less effective for two storeys.

I think GBD has given a great summary of things to consider. But if you do consider venting a room directly to the outside - and it's a great suggestion - you will need a closing vent (baffle) or you'll lose your winter heat outside too. I grew up in Brisbane and lived there into my 30s, and while the winter there is not long by southern standards, it certainly has some very cold nights. I remember being colder inside my Brisbane Workers Cottage than I'd been living in a well sealed unit in Richmond in western Sydney.

Posted Thursday 30 Sep 2010 @ 2:49:14 am from IP #
Buzzman
Member

Jaycotoy
The panels will have shaded the roof, so it's quite possible that the difference you noticed in ambient temperature will be sustained.

The addition of a second roof has long been shown to be beneficial. Even Land Rover did this on cars in the 50s and 60s - it was called the Safari roof, or tropical roof.

Posted Sunday 3 Oct 2010 @ 1:18:39 pm from IP #

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