Two walls Vs Q-con blocks

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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Re: insulting rice husk?

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jazzman wrote:If the rice husk gets damp it will lose its insulting effect.

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Re: Two walls Vs Q-con blocks

Postby jazzman » Fri Aug 01, 2008 2:16 am

:mrgreen:
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Re: Two walls - and condensation problem?

Postby OlaF » Tue Jan 06, 2009 3:22 am

I consider a two layer Q-Con wall for my new 2-storey house (in Isaan).
I got good hints on this construction from Q-Con customer support.

One thing they pointed out, in particular if using insulation in the middle, was the importance of keeping a ventilated air interval to avoid moist problems from condensation.

Anybody have any experience (or opinions) with condensation problems inside double walls?

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Re: Two walls Vs Q-con blocks

Postby tung » Tue Jan 06, 2009 9:00 am

Planning on using a double qcon wall myself of 7.5mm blocks however I am not planning on putting anything in the cavity. I would think if the cavity is sealed then you should have no problems.
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Re: Two walls Vs Q-con blocks

Postby pklongball » Wed Jan 07, 2009 8:04 am

tung wrote:Planning on using a double qcon wall myself of 7.5mm blocks however I am not planning on putting anything in the cavity. I would think if the cavity is sealed then you should have no problems.


keep an eye on my build as we are also using double Qcon throughout the place.
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Re: Two walls Vs Q-con blocks

Postby OlaF » Fri Jan 09, 2009 4:28 am

tung wrote:
... I would think if the cavity is sealed then you should have no problems.

Maybe you’re right?
But I assume you have about the same air humidity in the cavity as ambient. Condensation comes from temperature differences between cavity air and wall surfaces - which might cause condensation when outside wall cools down during the night(?)
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Re: Two walls Vs Q-con blocks

Postby dooby » Sat Apr 11, 2009 5:19 pm

I'm with Olaf on this one.

Leave a cavity uninsulated..air is a very good insulator...and put a mortar fillet at the bottom of the "gap" and leave 1cm by 5cm gaps at 1,5 metre intervals.

This ensures that any water/moisture entering the cavity, be it condensation or capilliary action, runs down the inside of the external skin and leaves via the holes.

It also allows the movement of air within the cavity.

Make sure the cavity is free of all mortar to prevent bridging.
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Re: Two walls Vs Q-con blocks

Postby Jack » Sun Apr 12, 2009 5:09 pm

Wouldn't you be afraid of critters nesting in your walls if you vented them at the bottom like that? Ants if nothing else. With no vents but a big empty space between the walls I'd be afraid of convection currents in the air killing any insulation effect. There's also the radiant heat from the exterior wall to worry about. This r-value table lists a 1/2" to 4" air space as having an r-value of approximately 1 so I went with 2" insulation between my double concrete block walls when I built my house. I'm glad I used it because when we were building I checked out a section of the wall before the insulation went in. The interior side of the sun lit outer wall was quite hot and the facing interior side of the inner wall was pretty warm too. I couldn't stick my hand in very far but I would guess it was even hotter farther inside away from the opening.

A few posts back I described how I was building to keep the house reasonably cool. Basically a well ventilated and insulated roof space and double block walls. We've been in the house nearly 7 months now and the thermal performance of the house has been even better than I'd hoped. The house is built on what used to be a cassava field with no trees at all. And I've been a little lazy about doing any landscaping yet so the house is in full sun all day. This has been a pretty hot year up here with some days getting up to 37 or 38° outside but we haven't had to turn on the ACs yet. We cool off the house by opening the windows at night and close them around 7:30 or 8 in the morning before it warms up. The house stays cool all day.

On bright sunny days during the late afternoon it gets up to around 28° inside. With fans moving the air that's quite comfortable for my wife and I since we only set the AC to 27° when we do use it. When the house is closed up like that we seem to get about a 2 or 3° temperature rise inside during a sunny day. So as the nights get warmer and we can't cool off the house enough we will eventually have to start using the ACs.
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Re: Two walls Vs Q-con blocks

Postby pklongball » Mon Apr 13, 2009 7:42 am

Your house and the effects of the walls and roof are doing what you intended I think. I am trying to achieve the same sort of affect using the double Q-con walls and a very high well ventilated gable roof. In a couple of months when we finish I will find out how my extra expense for the block and roof work.
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Re: Two walls Vs Q-con blocks

Postby dooby » Mon Apr 13, 2009 11:58 pm

Jack,

That;s pretty impressive temperature's you are achieving. I, personally, would find 28 degs too high..[my wife wouldn't].

I set the AC's at 25 in summer but we get beyond 45degs in the daytime and 33 odd in the evenings.

The reason for the vent holes is more for the drainage of the moisture...I' ve had lots of problems with capilliary action on walls, especially those that don't face the sun and, as a result, don't dry out quickly.

I must admit that this only occurred with Face brick houses.

Obviously if the walls are rendered and have a good finishing coat this obviates just about all of that problem, except maybe at window cills areas..etc..

I also believe we use too much glass in our buildings.

I mean, it's not like we are on Mud Island where it is dark,cold and grey all the time.

Do you guys ever use a reflective..[aluminium] sheeting under the roof tiles as well as the normal insulation and vents.?
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Re: Two walls Vs Q-con blocks

Postby Jack » Tue Apr 14, 2009 7:49 am

Most of the posters on this site have gone with the aluminum radiant barrier under the roof tiles although there has been some "spirited" debate at times. I personally am sold on it and am sure that the roof system with it, vents, and fiberglass ceiling insulation is why my house works so well.

To revisit the insulated/uninsulated cavity question for a minute. This thread has gotten long enough that it's burdensome to go back and read it all but a few posts back I and more extensively Grant came up with some numbers for R values and heat transfer. My calculations from before I started building and Grants similar results later convinced me that adding fiberglass between the block walls would about triple the R value. The calculated R value was even higher than for the 20 cm single superblock walls. These were numbers pulled off the web and not measurements of the actual materials here so I treated them as ballpark figures but they were convincing for me.

My rough calculations using the pricing at the time of my build had the price of my wall system comparable to the price of a 7.5 cm superblock wall. But with the significantly better performance estimates I decided to go with the double block and insulation.

By the way, I had to break down and use the AC in my computer room last night for the first time this year. The night before wasn't very cool and I usually run my computer 24/7 so it stays warmer than the rest of the house. Oh well.
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Re: Two walls Vs Q-con blocks

Postby dooby » Wed Apr 15, 2009 5:07 pm

Jack,

I agree with you on the cavity walls with fibreglass insulation. I did a contract for one of South Africa's leading architects and Ove Arup in Soweto and they went with the same. This more to retain heat to keep the electricity bill down in winter.

I also agree with both the aluminium radiant sheeting [it also is a very effective dust excluder] and the insulation.
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Re: Two walls Vs Q-con blocks

Postby jazzman » Wed Apr 15, 2009 5:15 pm

dooby wrote:... I also agree with both the aluminium radiant sheeting [it also is a very effective dust excluder] and the insulation.

There is a long and detailed discussion on this board, together with technical research references, on the use of reflective aluminium foil. Some people don't agree with its use, but the results of scientific trials cannot be disputed.
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