A pool of hot air

[bazza40]

Looking for some advice on the house roof space.

I've had 6" insulation, R factor 3.7 installed in the ceiling space, which has decreased heat transfer from the hot air to the living space quite considerably. However, there is still a pool of hot air above the insulation, because the roof is not ventilated.

I was thinking of having soffit vents in the eaves, with a short chimney and Dutch cap near the peak of the roof. I don't like the idea of whirlybirds, as I'm not sure they would not leak in the rainy season.

Any thoughts? Also, would there be an English-speaking builder in the Chiang Rai area who could quote on this?

[Kwasaki]

You want DIY forum. 

 

What you want can be easily achieved with eave and ridge venting which will cool it a bit better but there will always be heat in the roof area above insulated ceilings. 

 

If you have a gable ended roof you vent more with mesh louver openings at both ends.

[bazza40]

18 hours ago, Kwasaki said:

You want DIY forum. 

 

What you want can be easily achieved with eave and ridge venting which will cool it a bit better but there will always be heat in the roof area above insulated ceilings. 

 

If you have a gable ended roof you vent more with mesh louver openings at both ends.

Thank you

[sirineou]

I agree with Bazza 40 ,

install a vent at the highest possible location as close to the ridge, 

 and at your eves .or otherwise known soffits

Hot air will rise and exit from the gable vent and be replaced with cooler air from the soffit or eve vent creating a convection cycle and cooling the attic space.

Ridge vents are also available but are a major protect, the above configuration is something you can easily do your self.

[bankruatsteve]

Except when the ambient air is 40C.  There is no such thing as "cooler" to exchange.

 

[sirineou]

19 hours ago, bankruatsteve said:

Except when the ambient air is 40C.  There is no such thing as "cooler" to exchange.

 

Of course there is,

have you gone in an attic space in the middle of the summer? it is a lot warmer than outside, if you stayed there for any length of time you could die. Especially if you have a dark roof.

[Anythingleft?]

11 minutes ago, sirineou said:

19 hours ago, bankruatsteve said:

Except when the ambient air is 40C.  There is no such thing as "cooler" to exchange.

 

Of course there is,

have you gone in an attic space in the middle of the summer? it is a lot warmer than outside, if you stayed there for any length of time you could die. Especially if you have a dark roof.

True but I think he was on to the point of changing extremely hot air for hot air wasn't going to have a great deal of impact on what is trying to be achieved

[sirineou]

15 minutes ago, Anythingleft? said:

True but I think he was on to the point of changing extremely hot air for hot air wasn't going to have a great deal of impact on what is trying to be achieved

You could have a point, only the OP knows,

but the remedy is a simple and inexpensive one, a couple if gable vents and changing some sofits with the perforated ones , a day or two job for me, with plenty of beer brakes, not much more for some one else. And perhaps it could make a difference. It would certainly make it more comfortable  for the critters living in the attic.   

Edited September 4, 2016 by sirineou

[Kwasaki]

17 hours ago, sirineou said:

Of course there is,

have you gone in an attic space in the middle of the summer? it is a lot warmer than outside, if you stayed there for any length of time you could die. Especially if you have a dark roof.

 

A good place to create a free sauna.  

[Naam]

On 9/3/2016 at 10:45 PM, bankruatsteve said:

Except when the ambient air is 40C.  There is no such thing as "cooler" to exchange.

 

you'll be surprised how cool 40ºC is compared to the air in an unvented attic on  a sunny day! in Florida i was interested to find out, switched off all roof fans in the morning and measured at 15.00hrs 76ºC (ambient temperature was 36.5ºC).

 

reason for my test was a conversation with the chap who increased my R40 insulation to R60 with blown in material. when he mentioned "160ºF and above" i was laughing out loudly and asked him not to büllshyte me. even though he swore all holy oaths i didn't believe him till i ran my test a few days later.

[bankruatsteve]

18 minutes ago, Naam said:

you'll be surprised how cool 40ºC is compared to the air in an unvented attic on  a sunny day! in Florida i was interested to find out, switched off all roof fans in the morning and measured at 15.00hrs 76ºC (ambient temperature was 36.5ºC).

 

reason for my test was a conversation with the chap who increased my R40 insulation to R60 with blown in material. when he mentioned "160ºF and above" i was laughing out loudly and asked him not to büllshyte me. even though he swore all holy oaths i didn't believe him till i ran my test a few days later.

 

The point that i was attempting, is that when temperature reaches and then exceeds the really uncomfortable point (let's say 40C) then exchanging 76C with 40C is going to do nothing to help "cool" down anything especially the room underneath.  

 

Just curious though, what was your FL roof constructed from that it could make the attic that hot?  And how did you avoid death when you measured it?  

[sirineou]

4 hours ago, bankruatsteve said:

 

The point that i was attempting, is that when temperature reaches and then exceeds the really uncomfortable point (let's say 40C) then exchanging 76C with 40C is going to do nothing to help "cool" down anything especially the room underneath.  

 

Just curious though, what was your FL roof constructed from that it could make the attic that hot?  And how did you avoid death when you measured it?  

You make a good point, if the living space is insulated from the attic very well, then the increase of temperature in the attic space should not affect the living space below, though few houses are that well insulated, there are always gaps.  Naam mentioned R60, for florida where the temperatures are similar to Thailand. 

But even if the house is well insulated  heat transfer from the attic to the living space is not the only concern.

In Florida the roof truss system is constructed by 2x4 or 2x6 lumber, seethed with plywood, and the roofing singles are usually Asphalt composite. A poorly ventilated attic apace will bake the roof singles and eventually damage then, reducing their effective life.  I am not sure how roofing systems  in Thailand are affected by high heat , and or utilities, such as electrical, plumbing or mechanical  that might be located there, but I am willing to bet it is not a desirable situation. Perhaps some of you who know more about this can add their opinion. 

Anyway, conversations like this how we all learn, or consider things we might already know but have not considered.

[bankruatsteve]

I have said same on other threads:  IMO the best protection for the radiant heat from attic space is simply a reflective barrier.  You can put whatever insulation and "R" value but it's just a matter of time before the heat invades that.  Most reflective material will deflect 95% of radiant heat and there is no need for "insulation" otherwise.  Given that, I submit it doesn't matter what the temperature is in the attic.  Yes, it needs to be ventilated but going to extremes with fans, whirlybirds, whatever is superfluous to the root issue: keep the heat from penetrating below.  Reflective foil will do that and that is all that is needed.  Done.