Refllective 'radiant' roof material

[sometimewoodworker]

1 hour ago, Fruit Trader said:

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.

What are they trying to achieve? Without that being clearly defined. It's impossible to say that they are clearly correct.

 

They are using the terminology so loosely (radiant barrier and reflective film ) that anyone who doesn't understand the differences of use will certainly think they have understood but will not.

 

reflecting heat is not the same as not radiating heat.

 

in the example the reflective film will reflect heat back to the tiles. It will also prevent almost all heat inside the roof from escaping towards the tiles.

 

do please tell me which of these they want to achieve?

 

having watched several of the videos from that company it is confusion that they are passing on probably because they have heard the correct information but have mixed it up. Or they just don't understand the difference and just want to sell product.

 

[wgdanson]

3 hours ago, sometimewoodworker said:

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. 

Would stapling kitchen foil to the joists not have the same effect

[sometimewoodworker]

1 minute ago, wgdanson said:

Would stapling kitchen foil to the joists not have the same effect

Yes but it is much more expensive and fragile.

[Kwasaki]

10 minutes ago, wgdanson said:

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 !

Yeah sometimes to improve things take time and money even football teams. ???? 

Are the window frames a type that could be secondary glaze with mirror glass. 

Is there room in the windows glass frame to double glaze with mirror glass.

Banana trees grow quick with thick leaves, your have plenty of space to see either side em.

 

 

 

[sometimewoodworker]

33 minutes ago, wgdanson said:

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.

That will work, but the good stuff isn't cheap. Why not replace the glass with Low-E glass it makes a huge difference.

[wgdanson]

15 minutes ago, Kwasaki said:

Yeah sometimes to improve things take time and money even football teams. ???? 

Are the window frames a type that could be secondary glaze with mirror glass. 

Is there room in the windows glass frame to double glaze with mirror glass.

Banana trees grow quick with thick leaves, your have plenty of space to see either side em.

 

 

 

Yeh, I see what you are saying, and of course, plenty of bananas for brekky. The whole front faces South West.

Edited May 5, 2019 by wgdanson

[wgdanson]

4 minutes ago, sometimewoodworker said:

That will work, but the good stuff isn't cheap. Why not replace the glass with Low-E glass it makes a huge difference.

I think that's what we have. Problem really is IT'S TOO EFFIN'HOT.

[Fruit Trader]

20 hours ago, sometimewoodworker said:

in the example the reflective film will reflect heat back to the tiles. It will also prevent almost all heat inside the roof from escaping towards the tiles.

Only one side of the foil has a air gap. The guys sales pitch uses the fact that the foil will reflect some radiant heat. No snake oil no missing physics lessons.   

[CGW]

20 hours ago, wgdanson said:

I think that's what we have. Problem really is IT'S TOO EFFIN'HOT.

Eloquently put Sir! there comes a time to close the curtains put the AC on and hide! The floors in my house where the AC is not run are 32.5c, they have a 1m airgap under them, not like the heat is being transferred, we have double glazing, maybe it helps? not a lot though! The rains will be here soon ???? 

[sometimewoodworker]

3 hours ago, Fruit Trader said:

Only one side of the foil has a air gap. The guys sales pitch uses the fact that the foil will reflect some radiant heat. No snake oil no missing physics lessons.   

So do you think that as it will act to retain heat in the roof space (not mentioned) that talking about it as a radiant barrier when it is clear that it is being sold as a way to stop heat from the tiles and possibly as a water proofing layer is as clear as it should be?

 

Most of the videos from them are as bad.

[Fruit Trader]

44 minutes ago, sometimewoodworker said:

So do you think that as it will act to retain heat in the roof space (not mentioned) that talking about it as a radiant barrier when it is clear that it is being sold as a way to stop heat from the tiles and possibly as a water proofing layer is as clear as it should be?

 

Most of the videos from them are as bad.

In the video, foil is sandwiched with the timber board and they become a mixed conductor. I do not know how much this would change the timber boards ability to conduct heat from inside the roof space.

 

The best but impractical location for a radiant barrier would be on the outside of roof material.

[Enki]

Well, for the physics noobs:

The silver just works like a mirror. And the silver is silver on both sides of the mirror ... wow that was the easy part.

If you don't have the "insulation" then the roof gets hot and radiates in infra red "heat" down to the floor. 

From the point of view of the floor or the roof, it actually does not mater at all which side points up and which down, as: both sides are silver.

 

So: insulation like that *also* acts as typical insulation as in "heat transfer" via "heat conduction". So the "insulating cloth/fabric" is sided to the roof. And the reflecting side is inside the house. The fabric works in both cases, outside cold and you like it warm inside. And in that case, warm inside also means: reflect heat inside.

However: the other side of that silver is reflecting, too. So I guess the compromise of having the fabric outside and the silver inside is just a proven concept of better over all performance.

 

Anyway: from the point of view of the silver alone, it makes no difference how you turn the foil. The silver layer is silver on both sides ... and reflects just the same on both sides.

[sometimewoodworker]

57 minutes ago, Enki said:

Well, for the physics noobs:

The silver just works like a mirror. And the silver is silver on both sides of the mirror ... wow that was the easy part.

If you don't have the "insulation" then the roof gets hot and radiates in infra red "heat" down to the floor. 

From the point of view of the floor or the roof, it actually does not mater at all which side points up and which down, as: both sides are silver.

There we have an example of confusing the purpose of a radiant barrier. Also the confusion between reflection and radiation.

 

Physics 101

A polished cube of metal with a silver surface at 300 degrees C will feel significantly cooler if you hold your hand near but not touching the surface than a similar cube at the same temperature but with a black surface.

 

Try this simple experiment in your kitchen. Heat a baking sheet to around 200C~300C one half black the other half with kitchen foil in as close contact as you can.

Hold your hand as close as you can without touching the surface.

 

You will be able hold your hand very much closer to the kitchen foil covered half.

[sometimewoodworker]

1 hour ago, Fruit Trader said:

In the video, foil is sandwiched with the timber board and they become a mixed conductor. I do not know how much this would change the timber boards ability to conduct heat from inside the roof space.

It doesn't affect the ability of the timber boards to conduct heat from inside the roof space at all, but it reduces the ability of the hot boards to radiate that heat by around 97%

 

1 hour ago, Fruit Trader said:

The best but impractical location for a radiant barrier would be on the outside of roof material.

A radiant barrier (used as a radiant barrier) on the outside of the roof would only be useful in very cold climates, as it would prevent the roof from radiating heat from the house.

 

In hot climates a reflective surface on the outside of the roof is effective.

 

 

Edited May 6, 2019 by sometimewoodworker

[Fruit Trader]

7 minutes ago, sometimewoodworker said:

In hot climates a reflective surface on the outside of the roof is effective.

Which would make it a radiant barrier.

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

[sometimewoodworker]

2 minutes ago, Fruit Trader said:

 

10 minutes ago, sometimewoodworker said:

In hot climates a reflective surface on the outside of the roof is effective.

Which would make it a radiant barrier.

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

 

No it doesn't.

 

 

1:58

[Fruit Trader]

1 minute ago, sometimewoodworker said:

No it doesn't.

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

[Enki]

11 hours ago, sometimewoodworker said:

There we have an example of confusing the purpose of a radiant barrier. Also the confusion between reflection and radiation.

 

Physics 101

A polished cube of metal with a silver surface at 300 degrees C will feel significantly cooler if you hold your hand near but not touching the surface than a similar cube at the same temperature but with a black surface.

 

Try this simple experiment in your kitchen. Heat a baking sheet to around 200C~300C one half black the other half with kitchen foil in as close contact as you can.

Hold your hand as close as you can without touching the surface.

 

You will be able hold your hand very much closer to the kitchen foil covered half.

Seems you answered to the wrong person.

[sometimewoodworker]

1 hour ago, Enki said:

Seems you answered to the wrong person.

It was your post that I replied to. So unless someone else is using your account I don't think so.

[Enki]

Then your answer makes no sense at all, what do you want to say?