Cavity Wall with PU Foam Insulation - Pros and Cons

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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Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Khunchai » Mon Sep 08, 2014 5:27 pm

We are building a 2-storey house in Thailand and while the structural frame of the house is being built, we have about 1 month to decide what kind of walls to make.

The structural columns are 20 cm thick.

The wall options I am considering are as follows:
  • 20 cm thick AAC blocks, just a single layer without air cavity
  • 7.5 cm thick AAC blocks with 5 cm cavity between 2 layers of blocks filled with some kind of PU foam
Is the second option more efficient in terms of external heat isolation and electric energy saving to keep the house cool at lower AC power consumption?

What is the best material to fill the air gap of a cavity wall between 2 layers of AAC blocks?

How to prevent dew condensation on the internal wall surface resulting in potential mold formation?

Any comments will be appreciated.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby fredlk » Mon Sep 08, 2014 5:32 pm

You will be wasting your money filling the cavity because the windows and doors will leak some cool air while the air-conditioning is on.
I have 20 centimetre q-con blocks and they insulate very well while I've heard that 10 centimetre thick q-con are just as good.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Khunchai » Mon Sep 08, 2014 5:40 pm

Thank you for your comment.

fredlk wrote:You will be wasting your money filling the cavity because the windows and doors will leak some cool air while the air-conditioning is on.
I have 20 centimetre q-con blocks and they insulate very well while I've heard that 10 centimetre thick q-con are just as good.


In this case one may want to install double glazed UPVC windows.

I wonder if double glazed UPVC windows are available in Thailand?

uPVC-Double-Glazed-Window.jpg
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Andyfteeze » Thu Sep 11, 2014 7:40 pm

How is this for a solution. 75mm extruded foam fixed to qcon 75mm blocks. You then render both sides. A quick calculation and the walls then have an r rating of at least 3.5. Compared to single brick of 0.5. This will be my solution. The more insulation and the lower the mass of your walls the better. Double glazing is available in thailand. Not from Windsor, lol.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Andyfteeze » Thu Sep 11, 2014 7:44 pm

I think that any suggestion to not worry about the cavity wall is missguided. Anything extra you do is not wasted. Everylittle bit counts. But obviously there is a good way , a better way and a very good way of detailing these things.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Andyfteeze » Thu Sep 11, 2014 7:48 pm

You can get very good information on r ratings and ways of doing things on the. HEBEL site (australia). You can down load various pdf files with how to and other specifications.
Read the available literature and work it out for your self, not hard.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Andyfteeze » Thu Sep 11, 2014 7:49 pm

Most countries with extreeme weather have already pioneered rendered foam walls. No reason why it cant be used here too.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Khunchai » Sat Sep 13, 2014 12:13 pm

I found that at present 7.5 cm Q-CON blocks are very cheap in Thailand, according to this website the price is only 16 Baht per piece.

At the same time 15 cm. and 20 cm. Q-CON blocks are priced 43 and 60 Baht respectively.

It means that it is much more cost efficient to use 7.5 cm. Q-CON blocks to have the same wall volume, isn't it?

For example the estimated total wall surface area of my future house is approximately 338 sq.m. (excluding doors and windows).

If I want to build a 15 cm. thick wall there are 2 options:
  • Use 3,000 pcs of 15 cm. Q-CON blocks (the total block cost : 3,000 x 43 = 129,000 Baht)
  • Use 6,000 pcs of 7.5 cm. Q-CON blocks (the total block cost : 6,000 x 16 = 96,000 Baht)

Using double quantity of 7.5 cm. Q-CON blocks instead of 15 cm. blocks will result in a huge saving of 33,000 Baht to achieve the same result: 338 sq.m. of Q-CON wall with the thickness of 15 cm.

Is my calculation correct or not :?:
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby fredlk » Sat Sep 13, 2014 1:20 pm

Khunchai wrote:Is my calculation correct or not :?:

You forgot to calculate double the labour plus double the rebar ties into the columns.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Khunchai » Sat Sep 13, 2014 1:46 pm

I wonder if anybody has experience with the so-called "Cool Blocks" made in Thailand: Cool Blocks :?:
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Sometimewoodworker » Sat Sep 13, 2014 8:49 pm

Khunchai wrote:I wonder if anybody has experience with the so-called "Cool Blocks" made in Thailand: Cool Blocks :?:

Have you seen any prices? They don't look very strong, similar to the usual Thai cement block but with much better insulation.

The only problem, as Fred will tell you, is that if the fill is polystyrene the rats like it.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Andyfteeze » Sat Sep 13, 2014 11:37 pm

Thanks for the info on the rats. They like render too! Just patched up some holes in a wall over a roof- rats getting inside the ceiling. I checked my handy work after a couple of days to find some dickhead rodent tried to chew through an inch of render. It gave up after 1/4 inch. A day later tooth marks in the same area. And a week later, i hear the frantic scramble of a rodent in the ceiling again! Guess i have to find the other holes, lol.
Anyone else have issues with rodents chewing through foam? Probably another topic
These blocks look interesting. I will try to get some info and post it.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Khunchai » Sun Sep 14, 2014 8:47 am

The isolating material is called Expanded Polystyrene Foam.

Cool Blocks come in 4 different kinds:
  • 19 x 39 x 7 cm, THB 26.00
  • 19 x 39 x 9 cm, THB 32.00
  • 19 x 39 x 15 cm, THB 48.00
  • 19 x 39 x 19 cm, THB 58.00

It takes 13 pcs per square meter of a wall.

Cool Block 7cm, 9cm.png
Cool Block 15cm, 19cm.png
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Sometimewoodworker » Sun Sep 14, 2014 9:41 am

Khunchai wrote:The isolating material is called Expanded Polystyrene Foam.

Cool Blocks come in 4 different kinds:
  • 19 x 39 x 7 cm, THB 26.00
  • 19 x 39 x 9 cm, THB 32.00
  • 19 x 39 x 15 cm, THB 48.00
  • 19 x 39 x 19 cm, THB 58.00

It takes 13 pcs per square meter of a wall.

Cool Block 7cm, 9cm.png
Cool Block 15cm, 19cm.png

At those prices AAC blocks are much better, cheaper and rodent proof.
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Re: Cavity Wall with PU Foam Insulation - Pros and Cons

Postby Khunchai » Sun Sep 14, 2014 9:43 am

Sometimewoodworker wrote:The only problem, as Fred will tell you, is that if the fill is polystyrene the rats like it.


We definitely do not want rats to come to the cavity between 2 layers of our cavity wall.

The questions arise:
  • Are the rats capable of gnawing holes through 7.5 cm. AAC block wall?
  • Do the rats like to gnaw Polyurethane?
  • How to stop rats from invading the cavity in a cavity wall?
  • Is it a good option to fill the cavity with PU foam?

:?:
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