spray foam roof insulation

[mahjongguy]

Sorry, I know that insulation isn't a very fresh topic but I'd like to ask just one specific question:

 

I am having a house built in a development where the standard is to use little or no insulation on the ceilings nor under the roof tiles. Today I noticed that the underside of the roof a nearby half-finished house has been sprayed with a yellowish foam. So, whoever purchased that property seems to have insisted on bringing in a 3rd party to do the job.

 

Now, to the point. What is the safest product to use, one that won't burn too easily nor poison me even when it's not aflame? I have just enough time to arrange it before the gypsum goes up. Any tips or pros and cons would be appreciated, but I hope not to revive long-standing disagreements over ceiling vs. roof.

 

Cheers   

[Kwasaki]

Lots of pro's and con's on the internet.

Up to you. 

[sometimewoodworker]

1 hour ago, mahjongguy said:

Now, to the point. What is the safest product to use, one that won't burn too easily nor poison me even when it's not aflame? I have just enough time to arrange it before the gypsum goes up. Any tips or pros and cons would be appreciated, but I hope not to revive long-standing disagreements over ceiling vs. roof.

The most cost effective is PU foam stuck unde a steel roof. For tiles you have to use sprayed PU if you want foam on the underside of the tiles. However silver foil under the tiles and insulation on the ceiling are a cost effective.

[Encid]

46 minutes ago, sometimewoodworker said:

However silver foil under the tiles and insulation on the ceiling are a cost effective.

Probably the most cost effective but don't forget to ensure that the roof cavity is well ventilated.

Whirly-birds are good.

[unheard]

19 hours ago, Encid said:

Probably the most cost effective but don't forget to ensure that the roof cavity is well ventilated.

Whirly-birds are good.

Whirly birds are not that good.

They don't move significant volumes of air per unit - impossible to create a well ventilated roof without installing multiple units of them.

Very bad aesthetically.

But the long term leakage proofing is even bigger problem.

 

The amount of air they "move" would depend on each unit's opening cross section.

Their spinning action is just a marketing gimmick. It doesn't add any air velocity or create any additional suction.

Their venting value equals to the similarly sized hole in the roof.

[unheard]

20 hours ago, sometimewoodworker said:

The most cost effective is PU foam stuck unde a steel roof.

Steel, PU-insulated roof.

Simple to install, more durable than tile, less prone to leaks long term, lightweight etc, etc..

Yet tiles are so nice to look at.

So it's all about priorities.

[Kwasaki]

1 hour ago, unheard said:

Steel, PU-insulated roof.

Simple to install, more durable than tile, less prone to leaks long term, lightweight etc, etc..

Yet tiles are so nice to look at.

So it's all about priorities.

Good aesthetics can be achieved with a steel roof sheet that looks like a tiled roof.

[unheard]

15 minutes ago, Kwasaki said:

Good aesthetics can be achieved with a steel roof sheet that looks like a tiled roof.

Sure but that profile is not readily available with thick PU insulation as an option.

At least that was the case last time I shopped at my local BlueScope outlet.

That profile was only available with a very thin, silvery looking material as glued-on insulation.

[mahjongguy]

In my case, the roof tiles are in place. Beneath them is a thin metal film.

 

Soon the ceilings will go in so either I accept it as it is or I jump in asap with at least an inch of sprayed PU foam.

 

I thought that in this thread I'd be advised to use a specific brand/type of PU or strongly advised not to use it at all.

 

 

[unheard]

32 minutes ago, mahjongguy said:

I thought that in this thread I'd be advised to use a specific brand/type of PU or strongly advised not to use it at all.

There are some older threads with some reports on spray-on insulation.

You might try to locate them via common search engines since the forum search is not that great in comparison.

That said, I remember seeing only a few posters mentioning the practice.

It's uncommon for Thailand.

btw, if properly applied with a right mixture of ingredients it could be a really good option for the already installed tile roof.

Besides adding great insulating properties, PU insulation will also lock the tiles in place, preventing them from moving/sliding around due to the daily expansion/contraction thermal cycle - a common cause for leaks.

But then I think, the silver foil would need to be stripped off.

It sounds like it's already too late for you since the roof is done.

[nigelforbes]

1 hour ago, unheard said:

Whirly birds are not that good.

They don't move significant volumes of air per unit - impossible to create a well ventilated roof without installing multiple units of them.

Very bad aesthetically.

But the long term leakage proofing is even bigger problem.

 

The amount of air they "move" would depend on each unit's opening cross section.

Their spinning action is just a marketing gimmick. It doesn't add any air velocity or create any additional suction.

Their venting value equals to the similarly sized hole in the roof.

Exactly, the number of square centimetres of input air must be the same as the output, otherwise, output is limited to the smaller of the two numbers.

 

 

[Kwasaki]

29 minutes ago, mahjongguy said:

In my case, the roof tiles are in place. Beneath them is a thin metal film.

 

Soon the ceilings will go in so either I accept it as it is or I jump in asap with at least an inch of sprayed PU foam.

 

I thought that in this thread I'd be advised to use a specific brand/type of PU or strongly advised not to use it at all.

 

Well there's many way to insulate a roof under construction or after if need be.

[unheard]

double

[nigelforbes]

24 minutes ago, mahjongguy said:

In my case, the roof tiles are in place. Beneath them is a thin metal film.

 

Soon the ceilings will go in so either I accept it as it is or I jump in asap with at least an inch of sprayed PU foam.

 

I thought that in this thread I'd be advised to use a specific brand/type of PU or strongly advised not to use it at all.

 

 

The thin metal film is a radiant barrier, designed to stop heat from the tiles radiating onto the attic floor. In essence, that barrier converts radiated heat to convected heat, or hot air, which also must be dealt with by venting.

 

Sprayed on PU foam in your situation will only slow down the speed with which the roof tiles begin to create hot air in the attic. TBH, once you've got a radiant barrier installed, trying to install spray on foam is almost impossible. Ask me which is better, spray on foam or radiant barrier and radiant barrier wins every time. 

 

If me I would leave radiant barrier in place, forget PU foam and instal venting to manage the hot air. That might be vented or slotted eves boards which are easily retrofitted, or, vents in the ridge using bought in products to modify the ridge. Don't forget though, air out must equal air in or it doesn't work. Thai builders like to have slotted eves boards in the corner underside of the roof in the belief that the hot air will  overflow outside. That only works if the vents are higher than the attic floor/roofs of the rooms below which will suffer from heat penetration unless they are insulated with rolls of insulation.

 

[unheard]

4 minutes ago, nigelforbes said:

Thai builders like to have slotted eves boards in the corner underside of the roof in the belief that the hot air will  overflow outside.

I don't know what their belief is.

Slotted eves placed on every roof corner is a common practice over here.

They're being installed as fresh air intakes.

Their throughput is more than enough for any roof designed without exhaust openings.

[nigelforbes]

Just now, unheard said:

I don't know what their belief is.

Slotted eves placed on every roof corner is a common practice over here.

They're being installed as fresh air intakes.

Their throughput is more than enough for any roof designed without exhaust openings.

If they are fresh air intakes, where is the exhaust? And once again, the amount of air in must equal the amount of air out, otherwise air flow is limited to the smaller of the two numbers. A roof contains many cubic metres/feet of hot air, small vents in the corner of the eaves means that it will take a very very long time to replace all the attic air once. Ideally, for heat control, the air should be replaced three times per hour,which  means substantial venting in and out.

[unheard]

9 minutes ago, nigelforbes said:

Ask me which is better, spray on foam or radiant barrier and radiant barrier wins every time.

Don't know about that.

Have you ever tried to touch the radiant barrier layer under concrete tiles at the end of a hot, sunny day?

Isn't it scorching hot? (an honest question btw).

The radiant barrier will prevent re-radiated heat from heating up the ceiling, but it will surely heat up the attic air by convection.

The PU insulated metal (especially with thicker foams) feels barely warm to touch  in the open Sun.

[nigelforbes]

Some good basic principles of attic ventilation here:

 

https://snapzvent.com/post/the-why-and-how-of-proper-roof-ventilation/

 

Also, if you have a gable end(s) that helps, installing exit vents in them complements vented eaves boards.

[unheard]

14 minutes ago, nigelforbes said:

If they are fresh air intakes, where is the exhaust?

There are none - that's the problem.

Well there are normally some present, usually in the form of a traditional Thai gable vent.

But those are not effective in venting under all conditions.

In comparison, many roofs in the west are of the ventilated attic type - with intake and exhausts (e.g. vented ridges).

The intake must be sized to flow at least as much air as the exhaust does in order to be efficient.

[nigelforbes]

Just now, unheard said:

Don't know about that.

Have you ever tried to touch the radiant barrier layer under concrete tiles at the end of a hot, sunny day?

Isn't it scorching hot? (an honest question btw).

The radiant barrier will prevent re-radiated heat from heating up the ceiling, but it will surely heat up the attic air by convection.

The PU insulated metal (especially with thicker foams) feels barely warm to touch  in the open Sun.

Radiated heat means the heat contained in the heat store, eg your concrete roof tiles, is released over a long period in a directed stream. Convected heat means the air is heated which is then subject to the laws of air circulation. 

 

Yes, the radiant barrier will be very hot to the touch but because it is so thin it is unable to store heat, this means radiated heat that hits the barrier, stops it, the barrier then releases it immediately, into the air. The radiant barrier will be cool to the touch, 30 minutes after the radiated heat source is removed. Concrete tiles containing stored heat will continue to radiate heat for many hours after the sun goes down, easily until the small hours of the night.

 

You have to decide which you want to deal with first, radiated heat or convected heat, ideally you will deal with both but unless you dampen the source of the heat (from the tiles first) you can't win. Again, blocking the source of radiated heat and then managing heated air, should be your priority sequence. There's a ton of information on this subject on the internet, strongly suggest you look through some of it.

 

If it helps any, my roof was completely enclosed apart from small gable vents. I quadrupled the size of all four gable vents to where I have 3 square meters of out put air. I then replaced all the eves boards with slotted boards plus added other sources of cool air intake lower down. Next I added an exhaust fan behind one gable vent, that kicks in at 37 degrees and helps push air through. Lastly, I added almost a foot of rolled attic insulation on the attic floor. Today, my house is cold in the winter because I don't get any heat from the sun (the house is in the north). In the summer, even on the hottest days, we never use air con., only dehumidifiers.

[nigelforbes]

A basic law of physics that many forget is that heat only rises if there is cooler air to replace it, underneath. If you cut a hole in your roof and there's no cool air inlet below, the hot air wont rise and wont vent. That's why having the corner eaves vents are not effective because they allow cool air to sit under the hot air in the roof void but the hot air has nowhere to go.

 

Sounds to me like you have small gable vents, why not make them bigger and do as I did?

[unheard]

5 minutes ago, nigelforbes said:

You have to decide which you want to deal with first, radiated heat or convected heat, ideally you will deal with both but unless you dampen the source of the heat (from the tiles first) you can't win. Again, blocking the source of radiated heat and then managing heated air, should be your priority sequence.

OK

I still think I mis-understood what you meant under your prior statement: "spray on foam or radiant barrier and radiant barrier wins every time".

As in the cost and easiness of application?

Or as in the general contribution to the "hot attic" condition?

Spray on foam greatly reduces heat by convection and overall attic temperatures even without ventilation.

There's also a layer of a silvery foil (assuming for the purpose of a radiant barrier) applied on top of the sprayed on foam during production of the steel metal insulated sheets.

The radiant barrier technique does nothing for convective heating which leads to hot attic temps.

[mahjongguy]

I'm learning a lot and I appreciate it.

 

To clarify:  if the roof has already been built, with tiles in place overtop the metal foil, is it too late to spray PU foam?  Will it adhere to the foil or not?

[unheard]

2 minutes ago, mahjongguy said:

I'm learning a lot and I appreciate it.

 

To clarify:  if the roof has already been built, with tiles in place overtop the metal foil, is it too late to spray PU foam?  Will it adhere to the foil or not?

No, it will not adhere to foil.

The foil would need to be removed.

[nigelforbes]

Last point from me then I have to go:

 

Thai roofs are all steel and concrete, the steel runs down to the posts which contain steel rebar. Heat is conducted through the steel, into the posts and the walls, PU foam will not help prevent that. To stop that problem you would need a thermal break between the steel in the roof and the rest of the house.

 

If you can create  an air flow of cool air being drawn in at a low level and hot air being vented at a higher level, that helps cool not only the roof tiles but also the steel. Somebody, years ago described it to me as a sail of cool air and I thought he was mad. Actually what I have now in my attic is the bottom one foot of air is cool, and the hot air is just like a moving sail.

 

 

[unheard]

8 minutes ago, nigelforbes said:

Thai roofs are all steel and concrete, the steel runs down to the posts which contain steel rebar. Heat is conducted through the steel, into the posts and the walls, PU foam will not help prevent that. To stop that problem you would need a thermal break between the steel in the roof and the rest of the house.

That's how PU insulated steel roofs are constructed, with this thermal break present by design.

The metal roof sheets are not in contact with metal roof beams - they're separated by the insulation layer.

[nigelforbes]

3 minutes ago, unheard said:

OK

I still think I mis-understood what you meant under your prior statement: "spray on foam or radiant barrier and radiant barrier wins every time".

As in the cost and easiness of application?

Or as in the general contribution to the "hot attic" condition?

Spray on foam greatly reduces heat by convection and overall attic temperatures even without ventilation.

There's also a layer of a silvery foil (assuming for the purpose of a radiant barrier) applied on top of the sprayed on foam during production of the steel metal insulated sheets.

The radiant barrier technique does nothing for convective heating which leads to hot attic temps.

"spray on foam or radiant barrier and radiant barrier wins every time".

 

As in, effectiveness at reduced the radiated heat source. And since it also appears to already be there, cost also.

 

The PU foam and the radiant barrier (thin steel sheet) serve a very similar purpose, both eliminate radiated heat. BUT all insulation, be it PU foam or any other kind, can be defeated and bypassed/penetrated by heat, if the heat is strong enough  and enough time is allowed....this is basic physics. I suggest you put your hand on the underside of roof tiles that have been sprayed with PU foam, at about 4pm and tell me if it is not very very hot.

 

I agree, radiant barriers do absolutely nothing for convected heat.

 

But when you talk about the metal lining being applied to the underside of the insulation, do you have concrete or metal roof? I have assumed you have concrete tiles.

 

 

 

[unheard]

32 minutes ago, nigelforbes said:

BUT all insulation, be it PU foam or any other kind, can be defeated and bypassed/penetrated by heat, if the heat is strong enough  and enough time is allowed....this is basic physics. I suggest you put your hand on the underside of roof tiles that have been sprayed with PU foam, at about 4pm and tell me if it is not very very hot.

Well, that's why I have an insulated metal roof.

As I have previously mentioned, the steel roof sheet with a layer of 25mm of PU insulation feels barely warm to touch after many hours spent sitting under direct sunlight.

Don't have any experience with insulated concrete tiles.

But it shouldn't be drastically different.

Still...

The difference between concrete and metal is their thermal masses.

Metal is quick to heat but also quick to cool.

Concrete is the direct opposite - very slow to heat up but is also slow to cool down.

In addition to thermal mass, thermal inertia also plays a big role.

Concrete is obviously much higher on both compared to metal, thus making it a very hot material in the roof application.

[nigelforbes]

2 minutes ago, unheard said:

Well, that's why I have an insulated metal roof.

As I have previously mentioned, the steel roof sheet with a layer of 25mm of PU insulation feels barely warm to touch after many hours spent sitting under direct sunlight.

In your first post, you wrote:

 

"no insulation on the ceilings nor under the roof tiles". 

 

The discussion thereafter has been about the benefits of PU foam versus ventilation, along with radiant barriers. 

 

You now say that you have an insulated metal roof which is cool to the touch after many hours. 

 

It doesn't sound like you really need anything, if you do, I'm confused what it might be.

 

[Kwasaki]

19 minutes ago, mahjongguy said:

I'm learning a lot and I appreciate it.

 

To clarify:  if the roof has already been built, with tiles in place overtop the metal foil, is it too late to spray PU foam?  Will it adhere to the foil or not?

Learning is one thing what you do now is another, for flig sake stop worrying leave the roof as far as you have done already.

 

Just put 10 cm silver wrapped rockwool insulation over all ceiling areas, carefully placed without it going onto sofit areas.

 

If there are no vents in the roof then vent the sofits.