Refllective 'radiant' roof material

[brucefarang]

We are going to have a house built in the near future and have looked at our prospective builders present projects. I notice that reflective silver lining is attached under the roof tiles and my wife says it is to keep the suns heat out! My question is this. To keep the sun out the silver should be on the outward side under the tiles to 'radiate the heat out. Having it inside will reflect the rising heat downwards again-exactly what you do not want! to let the heat out you should have either slatted and screened  gable end 'windows' or those roof 'whirligigs which spin as the heat rises and sucks more heat out!

I M OPEN TO ANY HELP ON THIS MATTER WHATSOEVER!

[metisdead]

Moving to the DIY Housing forum for knowledgeable replies. 

[sometimewoodworker]

It isn't a reflective solution but a radiant barrier which does not radiate heat well, so NO it should be silver side down. Your roof is going to get much hotter than any heat rising from the house.

 

Yes ventilation of the roof is good.

[wgdanson]

12 minutes ago, sometimewoodworker said:

It isn't a reflective solution but a radiant barrier which does not radiate heat well, so NO it should be silver side down. Your roof is going to get much hotter than any heat rising from the house.

 

Yes ventilation of the roof is good.

Sorry but as you tell it, that is wrong. You want the heat coming in, down from the roof to be reflected back up. No? Heat rising from the house will hit the tinfoil first and reflect back down if it is as you say.

Edited May 4, 2019 by wgdanson

[Kwasaki]

1 hour ago, brucefarang said:

My question is this. To keep the sun out the silver should be on the outward side under the tiles to 'radiate the heat out.

Well if you think that do it. ????

Radiant roof barrier's.

You just have to keep the shiny side face down.

You might wonder why the shiny side facing down wouldn’t just reflect heat back into the attic.

The short answer is that it does, which is a benefit in the winter, but radiant-barrier sheathing is actually not designed to keep attics cool by reflecting heat.

It keeps them cool by not emitting heat in the first place.

[sometimewoodworker]

54 minutes ago, wgdanson said:

Sorry but as you tell it, that is wrong. You want the heat coming in, down from the roof to be reflected back up. No? Heat rising from the house will hit the tinfoil first and reflect back down if it is as you say.

You have made the classic mistake and may have forgotten physics 101.

 

The foil does not work by reflecting heat.

It works by not radiating heat.

 

That is why it is called a radiant barrier. 

 

Underside of Roof temperature 

 

radiant barrier in place

 

the same as ambient

[Fruit Trader]

2 hours ago, wgdanson said:

Sorry but as you tell it, that is wrong. You want the heat coming in, down from the roof to be reflected back up. No? Heat rising from the house will hit the tinfoil first and reflect back down if it is as you say.

Radiant barriers need air space to function efficiently or they will simply conduct heat.

 

If there was an air space between roof tiles and radiant barrier it would work how you have explained. If the tiles are directly on top and in contact with the barrier then the air space will be inside the roof and the radiant barrier will now act to reduce emission into the roof space.

[sometimewoodworker]

8 hours ago, Fruit Trader said:

 

If there was an air space between roof tiles and radiant barrier it would work how you have explained. 

Yes apart from the point that it would then not be a radiant barrier but a reflective barrier.

 

its the confusion between reflection and radiation that trips most people up, they see silver and assume it the good reflective properties that are in use as the understand that. They do not think of its very poor ability to radiate heat that is far more important as they do not have experience of that often.

[Denim]

I have found insulation on top of the ceiling to be more effective at keeping the heat out of the living space than foil under the roof tiles.

 

We have both plus the roof space is well ventilated but it still gets very hot up there as the day progresses.

[wgdanson]

10 hours ago, sometimewoodworker said:

You have made the classic mistake and may have forgotten physics 101.

 

The foil does not work by reflecting heat.

It works by not radiating heat.

 

That is why it is called a radiant barrier. 

 

Underside of Roof temperature 

 

radiant barrier in place

 

the same as ambient

Thank you for this. I looked it up on Wikipedia, not doubting your superior knowledge of coure, and I shall be looling into it as our big room gets SOOO hot. The main walls face South and West so have sun on them all afternoon and get very warm.

We have no gable ends on our roof so I shall look into one or two of those 'whirly gig ' things mentioned. Thank you again.

[RJRS1301]

5 minutes ago, wgdanson said:

Thank you for this. I looked it up on Wikipedia, not doubting your superior knowledge of coure, and I shall be looling into it as our big room gets SOOO hot. The main walls face South and West so have sun on them all afternoon and get very warm.

We have no gable ends on our roof so I shall look into one or two of those 'whirly gig ' things mentioned. Thank you again.

Try to get the solarpowered/mains assited whirlygigs, energy efficient and work when needed, not reliant on wind 

[sometimewoodworker]

1 hour ago, wgdanson said:

Thank you for this. I looked it up on Wikipedia, not doubting your superior knowledge of coure, and I shall be looling into it as our big room gets SOOO hot. The main walls face South and West so have sun on them all afternoon and get very warm.

Well in the case that you want to stop the walls getting hot then you want a reflective (to IR) surface so white paint is good as you will get a drop in IR being absorbed specially if you use the paints designed for that like this.

 

You could also try the film as it is also reflects, but it is more fragile than paint.

 

to stop the heated wall radiating its heat into your room the ideal is either the radiant barrier film stuck to the inside of your walls or foam + film. The problem with that is if you live with other people persuading them that silver walls look good.

[Denim]

On the subject of having a cool Thai house , I was thinking of getting some reflective film to stick on the inside of our sliding patio windows. The windows only get a bit of sun in the morning but the balcony area gets hot and I think the windows are a week point. There are thick curtains behind the windows bot I thought a bit of film as shown might help delay the heat passing through to the living room. Anyone tried this ?

 

 

Also, Beger make a paint ( Diamond shield ) that is supposed to be better than ordinary paint for preventing outside walls from absorbing heat. Does it work ?

 

[Fruit Trader]

3 hours ago, sometimewoodworker said:

Yes apart from the point that it would then not be a radiant barrier but a reflective barrier.

 

its the confusion between reflection and radiation that trips most people up, they see silver and assume it the good reflective properties that are in use as the understand that. They do not think of its very poor ability to radiate heat that is far more important as they do not have experience of that often.

Barrier - Something that prevents something else from happening or makes it more difficult.

Radiation - The emission or transmission of energy in the form of waves or particles.

 

We reflect some of the energy waves to prevent them from reaching the other side. We have installed a barrier and prevented something from happening. It would be correct to call this a radiant barrier.

Reflectivity and emissivity. This video explains the difference in a way most people will understand. 

 

 

 

[wgdanson]

44 minutes ago, Denim said:

On the subject of having a cool Thai house , I was thinking of getting some reflective film to stick on the inside of our sliding patio windows. The windows only get a bit of sun in the morning but the balcony area gets hot and I think the windows are a week point. There are thick curtains behind the windows bot I thought a bit of film as shown might help delay the heat passing through to the living room. Anyone tried this ?

 

 

Also, Beger make a paint ( Diamond shield ) that is supposed to be better than ordinary paint for preventing outside walls from absorbing heat. Does it work ?

 

Hmmmm, shall I go out and buy 4 tubs of this stuff, get Somchai to slap it on the front walls..............to find out it makes no difference.  LOL

[Denim]

4 minutes ago, wgdanson said:

Hmmmm, shall I go out and buy 4 tubs of this stuff, get Somchai to slap it on the front walls..............to find out it makes no difference.  LOL

Ha ha. Get back to us with the result.

 

Seriously though , If you are doing a build and intend to paint the outside walls anyway, a few extra baht for a wee difference might work out ok.

 

I have found that no matter what you do , there is no one thing

( apart from air con ) that will make your house cool....say 24 when it is 40 plus outside. However , every little thing can make your house cooler than it would otherwise be. Might only be a bit of a degree but every little helps.

 

Ever measure we took means that inside our house is pretty tolerable  until the late afternoon. By then it has warmed up a lot. All our contrivances just delayed the inevitable.

A bit like two saucepans of water on a two ring gas stove one turned up high the other low.  They will both come to the boil but the one on a low flame takes longer.

[cooked]

On the other hand you could try following the manufacturer's instructions. You know, that piece of paper that gets thrown away. Shiny side down.

[Rimmer]

We placed the foil on to the steel roof trusses it was held in place by the tile battens, the tiles are placed on the battens and are then about one inch or more away from the foil, forget if we laid it shiny side up or down,  each end of the house has what the Thais call air wind and is essentially a louvered wooden window in the gable ends, this clears out hot air between the roof foil and the ceiling boards. The house stays as cold as a meat locker in all but the hottest weather.

 

In a  previous house we used the spray foam, there is no air gap between tiles and foam, from our experience it holds the heat inside the house in the evenings also lifts the tiles creating many water leaks. 

 

EDIT
Looking closely at the pictures I would say we laid shiny side up

 

[utalkin2me]

The homes out there are ovens. 

 

wouldn't there be a huge difference between the, I would assume, cheaper aluminum roof material and the ceramic type?

 

I just laugh my ass off when I am out there because the only time the homes are habitable is in the early morning. But, everyone tries to get you out of bed so you can "do stuff" and not be lazy. But once you get outside everyone is just sitting around. 

 

Stuff like that makes little sense to me out there but I know it has its quaint pleasures of course. 

[Kwasaki]

4 hours ago, Denim said:

I have found insulation on top of the ceiling to be more effective at keeping the heat out of the living space than foil under the roof tiles.

 

We have both plus the roof space is well ventilated but it still gets very hot up there as the day progresses.

Agree and it is a fact that Insulation on top of the ceiling of upper rooms works well beneath a roof construction but as you say through ventilation within the loft space is essential. 

[Rimmer]

Here is an inside picture see top right of picture, foil is shiny side up.

[Kwasaki]

4 hours ago, wgdanson said:

Thank you for this. I looked it up on Wikipedia, not doubting your superior knowledge of coure, and I shall be looling into it as our big room gets SOOO hot. The main walls face South and West so have sun on them all afternoon and get very warm.

We have no gable ends on our roof so I shall look into one or two of those 'whirly gig ' things mentioned. Thank you again.

Do you have ceiling insulation ?

Don't know what type of roof you have but can vent the roof with ridge or hip venting tiles.

If a profile metal sheet roof you can vent ridge & hip too.

Your walls could be insulated lined internally or use reflective coating as others have said, banana trees would be better IMO.

Not really good aesthetic's but bamboo blinds or a lean too roof fixed from roof eaves could be done. 

[sometimewoodworker]

2 hours ago, Fruit Trader said:

Barrier - Something that prevents something else from happening or makes it more difficult.

Radiation - The emission or transmission of energy in the form of waves or particles.

 

We reflect some of the energy waves to prevent them from reaching the other side. We have installed a barrier and prevented something from happening. It would be correct to call this a radiant barrier.

Reflectivity and emissivity. This video explains the difference in a way most people will understand. 

 

 

 

Unfortunately they don't explain it well and they perpetuate the reflective vs radiant confusion, that is why I didn't post that link.

[Kwasaki]

10 minutes ago, Rimmer said:

Here is an inside picture see top right of picture, foil is shiny side up.

OK firstly are you concern is the foil used a Radiant Barrier Foil I can't magnify close enough to make it out.

[Kwasaki]

22 minutes ago, sometimewoodworker said:

Unfortunately they don't explain it well and they perpetuate the reflective vs radiant confusion, that is why I didn't post that link.

Confusion is caused because of the many types of roof construction.

 

[sometimewoodworker]

3 hours ago, Rimmer said:

Here is an inside picture see top right of picture, foil is shiny side up.

You have double sided foil, so yes it is shiny side up (doing very little) but it is also shiny side down and that's the bit that is only  radiating very little. 

[sometimewoodworker]

3 hours ago, Kwasaki said:

Confusion is caused because of the many types of roof construction.

 

In that video they clearly do not understand the meaning of the terms they are using as in the location it is being used it certainly is not radiant barrier with regard to heat from outside though if it is designed to keep heat inside the attic space then it could be.

 

In fact they actually say that it is acting as a reflective layer.

 

Having watched several of the videos they have posted they definitely don't remember the physics lessons and constantly confuse the terms. 

 

[Kwasaki]

45 minutes ago, sometimewoodworker said:

In that video they clearly do not understand the meaning of the terms they are using as in the location it is being used it certainly is not radiant barrier with regard to heat from outside though if it is designed to keep heat inside the attic space then it could be.

 

In fact they actually say that it is acting as a reflective layer.

 

Having watched several of the videos they have posted they definitely don't remember the physics lessons and constantly confuse the terms. 

 

Confusing to non-builders and it will be because radiant barriers can be used in different ways in roof design.

 

There's also many type of underlays & internal underlays,  vapour barriers, vapour membranes, silver film composite foam insulation, breathable membranes, breathable sarking membranes, some have or need a gap air-space some don't.

Profile steel composite foam insulated roof cover with a steel liner is the best you can get as used in cold stores.

[Fruit Trader]

1 hour ago, sometimewoodworker said:

In that video they clearly do not understand the meaning of the terms they are using as in the location it is being used it certainly is not radiant barrier with regard to heat from outside though if it is designed to keep heat inside the attic space then it could be.

 

In fact they actually say that it is acting as a reflective layer.

 

Having watched several of the videos they have posted they definitely don't remember the physics lessons and constantly confuse the terms. 

 

What exactly don't they understand or can't remember from physics lessons? The video shows foil + air gap + external roof material. 

 

Bring on the physics, why are they wrong.

[wgdanson]

6 hours ago, Kwasaki said:

Do you have ceiling insulation ?

Don't know what type of roof you have but can vent the roof with ridge or hip venting tiles.

If a profile metal sheet roof you can vent ridge & hip too.

Your walls could be insulated lined internally or use reflective coating as others have said, banana trees would be better IMO.

Not really good aesthetic's but bamboo blinds or a lean too roof fixed from roof eaves could be done. 

I know there is some sort of foil/fibreglass stuff up there. The roof is real tiles. I did consider fixing that foam with foil onto some of the walls, but have come to the conclusion that a lot is coming via the single glazed windows, sometime the glass is too hot to touch. So my Mrs, clever git, said why not pur car window film on them. I shall try on a couple of them.

If I put trees up to stop the sun, it would also stop my beautiful view. Ah well, can't win 'em all............like Man City !