Keeping the roof area cool

[UKJASE]

hey guys, we are at the tiling stage of our new build. the steels are all in, and 2moro they start to lay the tiles

we have the silver reflective foil for under the tiles, and we are going to put vented Shera boards in to get some airflow through the roof, plus air vents at either ends of the house

i have bought some extra vented Shera boards, plus a couple of 10 inch Mitsubishi ceiling extractor fans. i am thinking of putting these vented boards into the ceiling structure, and using the fan to extract hot air through the ceiling vents, and into the roof space. we could then turn the fans on at the end of the day, and suck the hot air out of the house, which will then be replaced by cool air from outside

i think this could work great especially if we have the fans on a timer, turning on at say 5am, and drawing some of the day's coolest air into the house before we wake up

it seems like a good idea to me, but i havent seen many mentions of people doing it, and the wife thinks i am a bit daft

i was also thinking about maybe getting some extractor fans fitted into the centre of the roof space, and then using some ducting to extract the hot air out the vents at either end of the roof

do you guys think it would be worth the effort? any of you have similar in your abodes? any tips on do's and don'ts?

[bankruatsteve]

The attic fan stuff is great for climates that have big temperature difference day/night and are not so <deleted> humid. Those who do it here always claim it helps a lot - but I doubt it. Get some ceiling fans and A/C and it doesn't really matter what your attic is doing. (Except the reflective foil WILL help.)

[JesseFrank]

The reflective foil is supposed to be under the battens not on top of them.

Edited July 1, 2014 by JesseFrank

[cooked]

Insulating the attic side of the ceiling will be of more use. Venting is good but I don't think that fans will help much. You will, sooner or later, install air conditioning.

[UKJASE]

we are having AC installed too. but dont want to use it all the time, and would like way of dropping the temp by a few degrees if we can

[JesseFrank]

we are having AC installed too. but dont want to use it all the time, and would like way of dropping the temp by a few degrees if we can

Air is a good insulator, so it is important that you create an air-buffer between the room and the hot roof tiles. This you only can do with insulating the ceiling.

Edited July 1, 2014 by JesseFrank

[bankruatsteve]

For me, the best ways to keep your house cool are: using wall construction with high R factor (Q-Con, Superblock), well blinded windows in direct sun, reflective foil in the attic space, and minimize air leaks at doors and windows. Then try to convince the family that keeping doors and windows shut will actually help.

[UKJASE]

we have the Qcon bricks, we have small windows that are shaded throughout the day, we have reflective foil etc

what i am really looking for information regarding using ceiling extractor fans to remove hot air

we are not big AC users, so this alternative method is being considered

we will consider using insulation above the ceiling to keep the daytime heat from penetrating through the ceiling, but it is very expensive and our internal ceiling is 268 m2

[stoneyboy]

You could always move to Thornaby,

Much cooler this time of year.

Edited July 1, 2014 by stoneyboy

[UKJASE]

You could always move to Thornaby,

Much cooler this time of year.

roof tiles often go missing in thornaby, so keeping the roof cool wouldnt be such a problem i wouldn't think

[bankruatsteve]

OK - think about it. When the ambient temperature is hot, extractor fans will only exchange hot air with somewhat less hot air. You will not notice any diff. Insulation over the ceiling will not be much a factor for keeping heat from draining down - b/c it's not much of a factor in any case.

[UKJASE]

OK - think about it. When the ambient temperature is hot, extractor fans will only exchange hot air with somewhat less hot air. You will not notice any diff. Insulation over the ceiling will not be much a factor for keeping heat from draining down - b/c it's not much of a factor in any case.

we tend to find in our current house that the temp inside is a fair few degrees warmer than the air temp outside, at say 7am (remember we dont use the AC very much),

so wouldnt putting extractor fans on for say two hours in the early morning, and pulling a fair bit of that cool air into the house, whilst removing the hottest air (as the air near the ceiling will be the hottest) from the house, help us to reduce the average air temp within the house by at least 3 or 4 degrees, whilst not incurring much greater costs to our electric bill?

[yankee99]

we have the Qcon bricks, we have small windows that are shaded throughout the day, we have reflective foil etc

what i am really looking for information regarding using ceiling extractor fans to remove hot air

we are not big AC users, so this alternative method is being considered

we will consider using insulation above the ceiling to keep the daytime heat from penetrating through the ceiling, but it is very expensive and our internal ceiling is 268 m2

Amazing how <$2,000 to bring your house to western standards is to expensive.

[JesseFrank]

OK - think about it. When the ambient temperature is hot, extractor fans will only exchange hot air with somewhat less hot air. You will not notice any diff. Insulation over the ceiling will not be much a factor for keeping heat from draining down - b/c it's not much of a factor in any case.

we tend to find in our current house that the temp inside is a fair few degrees warmer than the air temp outside, at say 7am (remember we dont use the AC very much),

so wouldnt putting extractor fans on for say two hours in the early morning, and pulling a fair bit of that cool air into the house, whilst removing the hottest air (as the air near the ceiling will be the hottest) from the house, help us to reduce the average air temp within the house by at least 3 or 4 degrees, whilst not incurring much greater costs to our electric bill?

My house has concrete cavity walls, with 1 meter roof overhangs, I have a low pitched roof (17°) with ventilated ridges and reflective foil under the battens. I have a further 6" fiberwool on the ceiling.

This afternoon it was 36.4° in the shadow under the covered patio, while it was 31.2° in the livingroom without a fan or aircon running. Whenever I sit in my office during the day or right now, I have a single ceiling fan running at the lowest speed.

[sotsira]

OK - think about it. When the ambient temperature is hot, extractor fans will only exchange hot air with somewhat less hot air. You will not notice any diff. Insulation over the ceiling will not be much a factor for keeping heat from draining down - b/c it's not much of a factor in any case.

we tend to find in our current house that the temp inside is a fair few degrees warmer than the air temp outside, at say 7am (remember we dont use the AC very much),

so wouldnt putting extractor fans on for say two hours in the early morning, and pulling a fair bit of that cool air into the house, whilst removing the hottest air (as the air near the ceiling will be the hottest) from the house, help us to reduce the average air temp within the house by at least 3 or 4 degrees, whilst not incurring much greater costs to our electric bill?

Those ceiling extractor fans are only designed to remove odour from a small bathroom or toilet.

They are very weak in creating airflow and therefore won't be efficient for your idea.

You should just concentrate on venting the attic and create an airflow inside the attic by putting in as many vents as possible, then insulate your ceiling properly.

[NeverSure]

Don't forget that you need vents low in the attic to let outside air in and vents high to let hot air rise and escape. You need to have a "heat powered" flow from low to high.

Dang right you need to insulate above the ceiling in the attic. Penny wise and pound foolish, as they say.

[IMHO]

The reflective foil is supposed to be under the battens not on top of them.

Not aimed at you in any way Jesse, but...

I've seen this mentioned several times on these forums, but if you look at the (Thai language) installation guides, several brands recommend both ways (under the battens or on top of them) - the only difference to each method is the direction you lay the foil (top-to-bottom if under the battens, left-to-right if on top of the battens). That said, we always install under the battens in order to try and avoid "short circuits" that might make the foil a heat conductor, but I've seen and experienced an awful lot of houses where the foil is on top of the battens, and there's no doubt the foil is still working.

@OP Extraction fans going into the crawl space can indeed help - but maybe not exactly in the way you're thinking....

In my experience, they're good only in the very early morning, when outdoor air temps are lowest, to cool down the non-AC areas of your house. Normally, they don't need to be turned on for more than about 10 minutes to do the job. Effectiveness depends on the temp difference between inside and outside air of course, but can be very noticeable - they will very quickly get the inside temps close to outside temps, if placed right.

[Naam]

The attic fan stuff is great for climates that have big temperature difference day/night and are not so <deleted> humid. Those who do it here always claim it helps a lot - but I doubt it. Get some ceiling fans and A/C and it doesn't really matter what your attic is doing. (Except the reflective foil WILL help.)

those who think that accumulated heat in the attic doesn't really matter are entitled to receive the certificate "possesses a wealth of no idea concerning thermo-physics".

[Naam]

OK - think about it. When the ambient temperature is hot, extractor fans will only exchange hot air with somewhat less hot air. You will not notice any diff. Insulation over the ceiling will not be much a factor for keeping heat from draining down - b/c it's not much of a factor in any case.

we tend to find in our current house that the temp inside is a fair few degrees warmer than the air temp outside, at say 7am (remember we dont use the AC very much),

so wouldnt putting extractor fans on for say two hours in the early morning, and pulling a fair bit of that cool air into the house, whilst removing the hottest air (as the air near the ceiling will be the hottest) from the house, help us to reduce the average air temp within the house by at least 3 or 4 degrees, whilst not incurring much greater costs to our electric bill?

you are on the right track but you can't shoot elephants or rhinos with an air gun. various discussions on this topic exists. this is one of them:

http://www.thaivisa.com/forum/topic/478649-whole-house-fan/

[JesseFrank]

The reflective foil is supposed to be under the battens not on top of them.

Not aimed at you in any way Jesse, but...

I've seen this mentioned several times on these forums, but if you look at the (Thai language) installation guides, several brands recommend both ways (under the battens or on top of them) - the only difference to each method is the direction you lay the foil (top-to-bottom if under the battens, left-to-right if on top of the battens). That said, we always install under the battens in order to try and avoid "short circuits" that might make the foil a heat conductor, but I've seen and experienced an awful lot of houses where the foil is on top of the battens, and there's no doubt the foil is still working.

The reason it is installed under the battens is that you need to create a space where airflow can happen. Of course you will need ventilated eaves and a ventilated ridge to make this happen.

Because it is done on top of the battens in so many house doesn't mean it is right.The majority of Thai producers of whatever product have in fact not a clue of what they are selling or how it should be used.

A foil on top of the battens will always create shorts and function as a heat conductor, because the foil will move all the time. You could as well just paint the underside of the tiles with reflective paint, it will be as useless as reflective foil on top of the battens.

As I said I have a very low pitch roof, which therefore collects a lot of sun radiation, but with vented eaves and ridges and with the space of the size of a batten between the foil and the roof tiles.

I have an easy accessible loft and can could have lunch in there during the hottest part of the day without a fan.

Whenever I enter the loft I can hear the wind continuously blow between the foil and the tiles, and the foil does feel cool, but when i push it up to the tiles I will burn my fingers.

The correct way to install is as shown in this picture. Courtesy to another member, but I forgot who , who posted it in a thread about the same subject.

Edited July 2, 2014 by JesseFrank

[chiang mai]

You might find some pointers in here:

http://www.thaivisa.com/forum/topic/733978-roofingventilation-works/

[IMHO]

The reflective foil is supposed to be under the battens not on top of them.

Not aimed at you in any way Jesse, but...

I've seen this mentioned several times on these forums, but if you look at the (Thai language) installation guides, several brands recommend both ways (under the battens or on top of them) - the only difference to each method is the direction you lay the foil (top-to-bottom if under the battens, left-to-right if on top of the battens). That said, we always install under the battens in order to try and avoid "short circuits" that might make the foil a heat conductor, but I've seen and experienced an awful lot of houses where the foil is on top of the battens, and there's no doubt the foil is still working.

The reason it is installed under the battens is that you need to create a space where airflow can happen. Of course you will need ventilated eaves and a ventilated ridge to make this happen.

Because it is done on top of the battens in so many house doesn't mean it is right.The majority of Thai producers of whatever product have in fact not a clue of what they are selling or how it should be used.

A foil on top of the battens will always create shorts and function as a heat conductor, because the foil will move all the time. You could as well just paint the underside of the tiles with reflective paint, it will be as useless as reflective foil on top of the battens.

As I said I have a very low pitch roof, which therefore collects a lot of sun radiation, but with vented eaves and ridges and with the space of the size of a batten between the foil and the roof tiles.

I have an easy accessible loft and can could have lunch in there during the hottest part of the day without a fan.

Whenever I enter the loft I can hear the wind continuously blow between the foil and the tiles, and the foil does feel cool, but when i push it up to the tiles I will burn my fingers.

The correct way to install is as shown in this picture. Courtesy to another member, but I forgot who , who posted it in a thread about the same subject.

Radiant Barrier & Vented Ridge Diagram-L.jpg

Yep, the main benefit is minimizing thermal short circuits . The only way I can see to truly achieve the kind of effect in the image would be to heavily "sag" the foil between the trusses - without that you just have dozens of horizontal battens blocking airflow upwards..

Edited July 2, 2014 by IMHO

[Crossy]

We have something similar to Jesse's diagram.

1. Roof tiles (no foil, it was 'forgotten')
2. Cathedral ceiling using sheet-rock with foil facing, 3" or so of insulating batts on top
3. Vents in the eaves
4. Gable vents (with fixings for fans but no fans installed), no ridge vents.

Whilst I wouldn't want to have lunch in the accessible attic space, it's certainly not roasting hot, there is a good airflow out of the gables (ridge vents may be better).

By general consensus this seems to be the way to go (with foil under the tiles of course).

[IMHO]

One other point on extraction fans is that they are most effective when the ceiling they're installed in is already higher than average - i.e. so heat naturally rises to the fan's location for maximum efficiency, and to help work around dead spots where air just won't flow.

[JesseFrank]

We have something similar to Jesse's diagram.

1. Roof tiles (no foil, it was 'forgotten')
2. Cathedral ceiling using sheet-rock with foil facing, 3" or so of insulating batts on top
3. Vents in the eaves
4. Gable vents (with fixings for fans but no fans installed), no ridge vents.

Whilst I wouldn't want to have lunch in the accessible attic space, it's certainly not roasting hot, there is a good airflow out of the gables (ridge vents may be better).

By general consensus this seems to be the way to go (with foil under the tiles of course).

The reason it is still hot under your loft is that the air enters your loft space, where in case of installed foil the air enters at the eaves, stays between the tiles and foil, and the exits at the ridge.

The constant movement of the air prevents that the buffer between the tile and the foil heats up.

Edited July 2, 2014 by JesseFrank

[JesseFrank]

The reflective foil is supposed to be under the battens not on top of them.

Not aimed at you in any way Jesse, but...

I've seen this mentioned several times on these forums, but if you look at the (Thai language) installation guides, several brands recommend both ways (under the battens or on top of them) - the only difference to each method is the direction you lay the foil (top-to-bottom if under the battens, left-to-right if on top of the battens). That said, we always install under the battens in order to try and avoid "short circuits" that might make the foil a heat conductor, but I've seen and experienced an awful lot of houses where the foil is on top of the battens, and there's no doubt the foil is still working.

The reason it is installed under the battens is that you need to create a space where airflow can happen. Of course you will need ventilated eaves and a ventilated ridge to make this happen.

Because it is done on top of the battens in so many house doesn't mean it is right.The majority of Thai producers of whatever product have in fact not a clue of what they are selling or how it should be used.

A foil on top of the battens will always create shorts and function as a heat conductor, because the foil will move all the time. You could as well just paint the underside of the tiles with reflective paint, it will be as useless as reflective foil on top of the battens.

As I said I have a very low pitch roof, which therefore collects a lot of sun radiation, but with vented eaves and ridges and with the space of the size of a batten between the foil and the roof tiles.

I have an easy accessible loft and can could have lunch in there during the hottest part of the day without a fan.

Whenever I enter the loft I can hear the wind continuously blow between the foil and the tiles, and the foil does feel cool, but when i push it up to the tiles I will burn my fingers.

The correct way to install is as shown in this picture. Courtesy to another member, but I forgot who , who posted it in a thread about the same subject.

Radiant Barrier & Vented Ridge Diagram-L.jpg

Yep, the main benefit is minimizing thermal short circuits . The only way I can see to truly achieve the kind of effect in the image would be to heavily "sag" the foil between the trusses - without that you just have dozens of horizontal battens blocking airflow upwards..

Sorry IMHO, but now you disappoint me. How does the batten block the airflow under a curved roof tile? The flat side rests on the batten, while the curved side is completely unobstructed .

This is just a picture taken of the web, but in real life the curved part of the roof tile is even bigger than the flat part .

Edited July 2, 2014 by JesseFrank

[Gsxrnz]

At the Hospital on Soi 4 Sai 2 Pattaya, they have a large glass/plastic sheeting ceiling that covers the reception area and is fully open to sunlight allowing it to light the whole area. Thay have recirculating running water that cascades slowly down the sheets of plastic which appears to be on a timed pump or possibly a thermostat as it is not constantly running.

I've often wondered if this could be used to cool a house ceiling cavity over tiles in conjunction with the usual insulation methods.

Just a thought.

[lopburi3]

we have the Qcon bricks, we have small windows that are shaded throughout the day, we have reflective foil etc

what i am really looking for information regarding using ceiling extractor fans to remove hot air

we are not big AC users, so this alternative method is being considered

we will consider using insulation above the ceiling to keep the daytime heat from penetrating through the ceiling, but it is very expensive and our internal ceiling is 268 m2

As was said this does not work well for most. There is no large difference between inside and outside air temps with the setting sun here and just having normal cross flow between windows/doors will quickly get rooms in house down to same temp without electric cost of extractor fan. In places like Denver such fans work well. But here, if living in city, you will likely want AC at least part of the day - outside cities you may get along well with fans and open windows. But remember open windows also means open noise. Such fans depend on open air between rooms - AC depends on closed rooms - so at cross purpose if AC ever going to be required.

[IMHO]

Yep, the main benefit is minimizing thermal short circuits . The only way I can see to truly achieve the kind of effect in the image would be to heavily "sag" the foil between the trusses - without that you just have dozens of horizontal battens blocking airflow upwards..

Sorry IMHO, but now you disappoint me. How does the batten block the airflow under a curved roof tile? The flat side rests on the batten, while the curved side is completely unobstructed .

This is just a picture taken of the web, but in real life the curved part of the roof tile is even bigger than the flat part .

Fair call, but the popular curved tiles used in Thailand (Monier Elebana, V-Con etc) don't have anywhere near the gap that your photo has. Here's an actual photo I just took

Also, if you look at this, you'll see that whether the foil is on top of the batten, or under it, the gap remains the same (save a few microns), and that airflow gap is only about the thickness of the tile itself at the junction with the C-Line (batten). If you mounted the foil under the C-Line, then "sagged" it down, you'd have some decent potential airflow though.

I remain a proponent of foil under battens BTW, just sayin'

Edited July 2, 2014 by IMHO

[JesseFrank]

Yep, the main benefit is minimizing thermal short circuits . The only way I can see to truly achieve the kind of effect in the image would be to heavily "sag" the foil between the trusses - without that you just have dozens of horizontal battens blocking airflow upwards..

Sorry IMHO, but now you disappoint me. How does the batten block the airflow under a curved roof tile? The flat side rests on the batten, while the curved side is completely unobstructed .

This is just a picture taken of the web, but in real life the curved part of the roof tile is even bigger than the flat part .

Fair call, but the popular curved tiles used in Thailand (Monier Elebana, V-Con etc) don't have anywhere near the gap that your photo has. Here's an actual photo I just took

Tile-Cline-Gap.jpg

Also, if you look at this, you'll see that whether the foil is on top of the batten, or under it, the gap remains the same (save a few microns), and that airflow gap is only about the thickness of the tile itself at the junction with the C-Line (batten).

I remain a proponent of foil under battens BTW, just sayin'

The picture of the tile was taken from the Monier website, so I assume that is how the gap from a Thai Monier tile looks

http://www.monier.in/roof-solutions/roof-ventilation.html

When you put the foil on top of the batten, There is no way to straighten the foil, and the wind will blow under the foil and push it towards the tile thereby blocking any airflow.

While where under the battens the foil can be straightened easily because the battens are screwed on top, and there is no way that the foil can blow upwards, because first of all the eaves opening are higher than the foil and the foils is stretched.

That means you don't save a few microns, but about 1 inch.

Edited July 2, 2014 by JesseFrank