thermal transmision via walls

Air conditioning, fans, and anything related to keeping it cool, such as insulation. This would include any posts generally discussing how to keep it cool, such as which types of blocks are better insulators.... ideal wall thickness for keeping an A/C house cool, etc.

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thermal transmision via walls

Postby geordie » Wed Jun 24, 2009 10:32 am

having been on the forum for six months and noted that several diferent methods of construction are available / used has anyone actually studied the advantages of say two qcon walls with a cavity over two concrete block walls with a cavity the adition of insulation or lack of ? is it better to go for a larger qcon block single wall or cavity concrete with maybe insulation within the cavity to stop radiant heat being transmitted or even the small red bricks used in some of the constructions are large polystyrene sheets available in Thailand now very common in uk for thermal breaks and can be purchased bonded to gyproc for dry lining basically what is the ultimate wall with an unlimited budget and what is an afordable alternative alot to ask and no doubt a lot of diferrent veiws but a serious consideration for someone starting a build
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Re: thermal transmision via walls

Postby Jack » Thu Jun 25, 2009 10:26 am

I went through this same decision process a couple of years ago when I was planning my house. I'd lived in a couple of houses in Thailand with red brick walls and knew I didn't want that. I lived in one house with QCon type block and it was much better so initially I thought that might be the way to go. But then I started looking at R values and prices and decided that for my budget a double thin breeze block wall with fiberglass in the cavity was the best choice. I've been extremely pleased with how things have turned out.

These are the R values I found from the tables (ignoring stucco/rendering)
single thin block - 0.8
double thin block with air cavity - 2.6 (a 1/2 to 4 inch void adds 1 to the R value)
single standard QCon block - 3.25
double standard Qcon block with air cavity - 7.5
30 cm thick Qcon block - 8.4
double thin block with fiberglass cavity - 9.3

So from the R values I saw I that with the double thin breeze block wall with fiberglass fill I could get better insulation than the large Qcon block and for significanly less money than even a standard single Qcon wall. So that's the way I went.

If you decide to go with a double wall I really think fiberglass insulation in the cavity is a much better option than air. The R value is nearly 8 times as high (7.7 vs 1) and it's not all that expensive. I got mine on sale at HomePro for 115 bt/2.4 sqm roll - around 6,000 bt for about 50 linear meters of wall.
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Re: thermal transmision via walls

Postby geordie » Thu Jun 25, 2009 2:51 pm

thanks jack informative and easy to understand so if money was no object a double qcon with an insulated cavity

i supose option two has to be the concrete 7.5 with a double layer/cavity /insulation option two being the more afordable

a third option i supose would be to double up on the walls that take the main heat of the sun

has any member tried remedial work or even new build with a fiberglass/cavity/and gyproc

is it possible to get the large polystyrene sheets over there ??
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Re: thermal transmision via walls

Postby Jack » Fri Jun 26, 2009 7:03 am

(Just saw a typo in my earlier post - it should have been 20 cm thick Qcon block - 8.4. Sorry)

I looked for the styrofoam sheets here in Udon and couldn't find them. They may be available some place else.

The double Qcon with an insulation cavity certainly gives you the highest R valve of the common wall systems. But I suspect that after you get to around R7 or R8 your return on investment with a much more expensive system decreases a lot since the temperature difference between inside and outside is not nearly as much here as in some of the colder climates. I didn't bother to try to calculate the decreased percentage of heat gain with higher R values like the double Qcon with insulation since my budget didn't stretch that far. But I'm guessing that with a temperature difference of, say, 10 degrees going from an R8 to R15 you're only decreasing heat gain by a few percent. It's harder to guess about the loading you'd get from the sun lit walls. But just with a "back of my hand" test with my walls I can't feel a temperature difference between a west wall with a couple of hours of sun exposure and an inside partition wall.

With an unlimited budget I'd have might have gone with the 20 cm Qcon since it's strong enough not to need columns, thick enough for alternative window treatments, and should have even better sound deadening properties than my walls (which do a good job on sound). But I'm more than happy with the walls I have so with the same budget I'd go that way again.
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Re: thermal transmision via walls

Postby geordie » Fri Jun 26, 2009 10:29 am

i suspect that the concrete double walled with the fiberglass would kill noise better than the qcon just judging it on a uk spec of cavity brick oposed to thermalite solid blocks the concrete is i think the more dense material

the point you made about air temperature is a valid one however wimp that i am air con will be in use the idea being to minimize the need / use of it

I am still a couple of years off building a home proper over there but intend to do it once only so its important to me to design right and make it afordable to maintain as well as comfortable to live in
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Re: thermal transmision via walls

Postby BKKBILL » Sat Jun 27, 2009 2:58 pm

Jack If I understand you

“With an unlimited budget I'd have might have gone with the 20 cm Qcon since it's strong enough not to need columns, thick enough for alternative window treatments, and should have even better sound deadening properties than my walls (which do a good job on sound). But I'm more than happy with the walls I have so with the same budget I'd go that way again.”

Does this mean on a single story house using steel on the perimeter at the roof line to support roof trusses the only pouring of concrete would be over windows and doors?
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Re: thermal transmision via walls

Postby MGV12 » Sat Jun 27, 2009 4:19 pm

BKKBILL wrote:Jack If I understand you

“With an unlimited budget I'd have might have gone with the 20 cm Qcon since it's strong enough not to need columns, thick enough for alternative window treatments, and should have even better sound deadening properties than my walls (which do a good job on sound). But I'm more than happy with the walls I have so with the same budget I'd go that way again.”

Does this mean on a single story house using steel on the perimeter at the roof line to support roof trusses the only pouring of concrete would be over windows and doors?



Correct -- 20cm AAC lightweight blocks are load bearing [single or two storey] and you just need a steel box wall plate [UK term] for the roof steel to sit on as you mentioned.

Concrete lintels wouldn't compromise the thermal resistance much as they would most likely be in the shade, otherwise you can buy Q-Con's own AAC lintel; many other makes of AAC block here but not aware of anyone else who does AAC lintels.

Be aware that 20cm AAC blocks weigh in the region of 18Kg a piece and so you may get the odd complaint of backache if you specify them; I am told that women on average suffer less as their lower back is stronger due to the child-bearing needs!!!!

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Re: thermal transmision via walls

Postby Jack » Sun Jun 28, 2009 9:58 am

Geordie, I think your comment about the concrete double wall being more sound proof, especially with the fiberglass, is correct. I looked at the sound transmission stuff a couple of years ago and decided that the Qcon type block would be quieter for the partition walls inside the house for things like closing doors, etc. Quiet and Qcon had stuck in my mind and that's why I made the comment.

After your comment I reviewed things a little and found that Smart block lists their block as having a Sound Transmission Class number of 43 but the STC for a normal weight concrete block the same thickness is 44. I don't know what the STC is for the thin blocks we use here but I would guess a little less than 44. This page has a good discussion of sound transmission and block walls. From it I gather that using thicker blocks to make the wall doesn't make the wall that much quieter. But using a double wall, especially with something like fiberglass in between, makes it a lot quieter.

I guess I ended up with the quieter wall after all. And since my double walls total 20 cm thick I don't have to see the columns and I could do my windows like I wanted them. And, of course, my wall has a good R value so I'm not sure I'd pick different walls if I ever, god forbid, build another house.

While looking around I found an interesting pdf on the Smart Block site. This pdf has a lot of specs for their AAC blocks and actually claims that it's only 2 baht per sqm (288.34 vs 286.50) more expensive to build a wall with their block than with red brick. The material costs that they use in their comparison look reasonable for the brick wall but I don't know about the labor costs.
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Re: thermal transmision via walls

Postby whatamut » Thu Feb 02, 2012 10:55 am

i was also thinking about double walls and will use whatever is available locally to supplement RF factor. but i am interested in perlite as a fill if it can be purchased
in los and the quantities and logistics are practical. i do know there is a perlite institute in thailand and there is a wholesaler in rayong but thats as far as I've gotten.
the perlite institute does have a detailed web site as to the thermal values as a fill or as a substitute for sand in creating a lite crete with thermal qualitys (recipe is
provided) anyone else interested, feed back is welcome.

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Re: thermal transmision via walls

Postby Andyfteeze » Sun Aug 31, 2014 2:00 am

One thing you guys havent been told is that fibreglass insulation absorbs moisture. Wet fibreglass is not a good insulator. So fibreglass in a very humid environment? Tontine or polyester is a much better idea here.
Tried rendered foam over Qcon? R 3.5-3.8. Australian ratings not american ratings. ( 1:4)
Just a couple of thoughts
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