How To Properly Insulate & Ventilate Double Block/Brick Walls

[Artisi]

Doglover

Your question from another thread about internal wall vents.

"Posted 2011-03-05 19:14:17

Sorry Artisi, not sure where you would get them. But seeing as you are familiar with this venting system it would be great to hear some comments about it in the following thread. http://www.thaivisa....ockbrick-walls/

I keep hearing that some areas of AUS are very similar to LOS. That is why I would be interested to read about the method you are refering to if your care to type about it."

The older style houses in Aust. with double brick cavity walls which were open into the roof space were usually vented in a couple of ways. It was not unusual to have external wall vents into the cavity maybe 500 - 600 mm above ground level, there could also be vents high up just below the eaves. Likewise internallly there would be wall vents into the cavity high up and just below the cornice.

Of course this is no longer the case with the brick veneer construction currently the major build style for homes.

[doglover]

Doglover

Your question from another thread about internal wall vents.

"Posted 2011-03-05 19:14:17

Sorry Artisi, not sure where you would get them. But seeing as you are familiar with this venting system it would be great to hear some comments about it in the following thread. http://www.thaivisa....ockbrick-walls/

I keep hearing that some areas of AUS are very similar to LOS. That is why I would be interested to read about the method you are refering to if your care to type about it."

The older style houses in Aust. with double brick cavity walls which were open into the roof space were usually vented in a couple of ways. It was not unusual to have external wall vents into the cavity maybe 500 - 600 mm above ground level, there could also be vents high up just below the eaves. Likewise internallly there would be wall vents into the cavity high up and just below the cornice.

Of course this is no longer the case with the brick veneer construction currently the major build style for homes.

Thanks for taking the time to comment here Artisi. I think I am picturing what you are saying but now I don't understand why this is done. It sounds similar to older style UK double brick cavity construction and I get that part (along with the lower and upper exterior vents). Just not sure why the vent high up on the wall on the interior side of exterior walls. From what I picture the reason would be to vent hot air from the living space, up through the vent and into the attic via the opening at the top of the cavity. But it would be more effective to have a vent right in the ceiling some distance away from windows to allow this natural venting of hot air. Can an Aussie explain where I went wrong with my mental image of this? I grew up in an igloo in Canada so please pardon my ignorance.

[powderpuff]

I want to ask a question. Let's say I want to build a double QCON brick wall (non load bearing). What is the optimum gap between the 2 rows of bricks?

And should it be sealed or open at the top?

Thanks

[Artisi]

Doglover

Your question from another thread about internal wall vents.

"Posted 2011-03-05 19:14:17

Sorry Artisi, not sure where you would get them. But seeing as you are familiar with this venting system it would be great to hear some comments about it in the following thread. http://www.thaivisa....ockbrick-walls/

I keep hearing that some areas of AUS are very similar to LOS. That is why I would be interested to read about the method you are refering to if your care to type about it."

The older style houses in Aust. with double brick cavity walls which were open into the roof space were usually vented in a couple of ways. It was not unusual to have external wall vents into the cavity maybe 500 - 600 mm above ground level, there could also be vents high up just below the eaves. Likewise internallly there would be wall vents into the cavity high up and just below the cornice.

Of course this is no longer the case with the brick veneer construction currently the major build style for homes.

Thanks for taking the time to comment here Artisi. I think I am picturing what you are saying but now I don't understand why this is done. It sounds similar to older style UK double brick cavity construction and I get that part (along with the lower and upper exterior vents). Just not sure why the vent high up on the wall on the interior side of exterior walls. From what I picture the reason would be to vent hot air from the living space, up through the vent and into the attic via the opening at the top of the cavity. But it would be more effective to have a vent right in the ceiling some distance away from windows to allow this natural venting of hot air. Can an Aussie explain where I went wrong with my mental image of this? I grew up in an igloo in Canada so please pardon my ignorance.

I guess in the days of old they didn't have ceiling vents and figured that the ingres of dust was more likely with ceiling vents. Today you can buy ceiling vents with an upper dust cover to keep the dust out, actually I bought a couple from Aust. some years back and fitted them to the bedroom ceiling of the house I was living in, on a hot day the air flow up through the ceiling vents into a very hot roof space was quite amazing, was proven by a very scientific experiment using a smoky candle.

[Artisi]

I want to ask a question. Let's say I want to build a double QCON brick wall (non load bearing). What is the optimum gap between the 2 rows of bricks?

And should it be sealed or open at the top?

Thanks

The optimum gap is the width of a brickies trowel, assuming the Thai builders are even bothered to clean off any surplus concrete on the inside of the cavity. I would leave it open - but then I might be biased - see above posting re wall vents.

[doglover]

I want to ask a question. Let's say I want to build a double QCON brick wall (non load bearing). What is the optimum gap between the 2 rows of bricks?

I've heard the response that the optimum gap is the width of a brickies trowel a couple times myself. Optimum for him no doubt but how about the home owner? I hope someone will step forward with a more in depth explanation.

And should it be sealed or open at the top?

PP I know some of the posts are long, but if you read through this whole thread you find alot of discussion about your question. But if you choose, in the end, to leave your cavity open at the top I would just build the exterior wythe of the double wall out of red brick. It is stronger and cheaper than 'Q-cons' and you will have the same R-value of your wall system anyway with the cavity open. Personally, I would only make both wythes aerated concrete block if I was going to seal the cavity.

[klikster]

But if its a big area, do it right and hire an acoustic engineer (klikster?) to run sound tests in situ & design to the frequencies & sources present.

Klister is not an acoustical engineer.

I wouldn't even know how to effectively use a pink-noise generator. A 1/3 octave band analyzer is about my limit. The acoustic design on an auditorium? Not a chance!

For several years, I built portable and modularized industrial noise control structures and silencers. My experience is very narrowly limited to that field.

I probably understand noise better than most builders, but not nearly as well as said builders think they know.

[doglover]

I came across a very relevant thread to this topic (of wall construction) with some construction methods regarding keeping moisture out of the walls (not the cavity). Some of the posters used a combination of autoclaved aerated concrete block and red brick to better suit certain walls of the house. Apparently the aerated block has issues with soaking up water. Good idea to read before building.

http://www.thaivisa.com/forum/topic/322500-thai-red-brick-versus-autoclaved-aerated-concrete-block/

[bankruatsteve]

I want to ask a question. Let's say I want to build a double QCON brick wall (non load bearing). What is the optimum gap between the 2 rows of bricks?

And should it be sealed or open at the top?

Thanks

In my opinion, the optimum gap is zero with QCON (I like the Superblock). Why put a gap with aereated concrete? Those gaps just make places for ants and other critters to live. Any additional insulative value or vapor lock is just good imagination.

[doglover]

But if you choose, in the end, to leave your cavity open at the top I would just build the exterior wythe of the double wall out of red brick. It is stronger and cheaper than 'Q-cons' and you will have the same R-value of your wall system anyway with the cavity open.

A quote from myself in post #36. It actually is not cheaper at the end of the day. So I take that back :jap: .

[powderpuff]

PP I know some of the posts are long, but if you read through this whole thread you find alot of discussion about your question. But if you choose, in the end, to leave your cavity open at the top I would just build the exterior wythe of the double wall out of red brick. It is stronger and cheaper than 'Q-cons' and you will have the same R-value of your wall system anyway with the cavity open. Personally, I would only make both wythes aerated concrete block if I was going to seal the cavity.

Good response. I personally see no reason to seal the gap. I think I would use maybe 3 cm. Thinking about it now the outer wall provides shade for the inner.

I have no worries about water where I live & would never ever install "venting bricks". So thanks for that answer. Makes me think about it a different way. I have no concerns about ants either. They go after food; nothing else.

[doglover]

Good response. I personally see no reason to seal the gap. I think I would use maybe 3 cm.

I didn't say that I wouldn't seal the gap. Personally I would (if I even built with a cavity) seal it and use double wall of aerated blocks. The reason I would do so as trapped uncirculating air has some insulation value (that is one reason why double pane windows are sealed). But the idea of mold in the walls may have others decide to leave it open at the top (a very valid concern). As far as the gap goes I would just flush up both whythes of wall to the outside edges of the columns in the house and whatever the gap ends up being it ends up being. That way you won't have the corners of your columns jutting out where the walls meet together. Much easier to install your floor and ceiling trim this way as well. Also if the gap is too narrow heat will radiate from the outer whythe to the inner (more so with red bricks and especially with typical concrete blocks)

Thinking about it now the outer wall provides shade for the inner. I have no worries about water where I live & would never ever install "venting bricks". So thanks for that answer. Makes me think about it a different way.

It sure does shade the walls which is really the reason for the double wall with cavity. So if your exterior whythe does not have a descent R-value (the new aerated concrete blocks or insulation) the cavity should really be vented as heat will build up to intense levels. And to vent effectively you require some 'venting bricks' at the bottom (with the top of the cavity open) so that when the heat rises it will draw in cooler air (cooler than the air in the cavity) to replace it. Same idea as venting your attic to lessen the heat that enters your living space through the ceiling. This venting will also take care of any moisture that will be in the cavity.

I have no concerns about ants either. They go after food; nothing else.

Yes, but where do they make their homes? If one opted for no cavity at all and just chose a thick aerated concrete block (say 20 - 30 cm) then they have no concerns of ants or termites (plus geckos and spiders if open cavity) utilizing the cavity as a base for their war efforts. And no concern about mold issues. Which, after learning from the responders to this thread, is exactly what I would do. No cavity. After all if there are complications with any services inside the cavity one of the whythes will still have to be demolished to access the problem area. With the services cut in to a single (extra thick) wythe the issue may even be easier to locate and certainly easier to access.

Of course this is only my opinion and I'm only a novice in this area. This response is only with good intentions to have you (and others) end up with a wall system you are a happy with and not to 'correct you'. I personally built (3 years ago) my exterior walls from a double whythe of typical concrete block with a 1 - 2 cm gap and sealed the cavity. I regret my choices and am just trying to help others not regret their choices. The reason I started this thread was so I could get it right the next time and assist others in getting it right the first time.

Edited March 11, 2011 by doglover

[powderpuff]

Spot on DL. I liked what you said about making the inner wall & outer wall flush to the posts & beams. Makes a nice smooth finish.

We are all learning together. DIY forum rocks.

Edited March 11, 2011 by powderpuff

[Naam]

I want to ask a question. Let's say I want to build a double QCON brick wall (non load bearing). What is the optimum gap between the 2 rows of bricks?

And should it be sealed or open at the top?

Thanks

In my opinion, the optimum gap is zero with QCON (I like the Superblock). Why put a gap with aereated concrete? Those gaps just make places for ants and other critters to live. Any additional insulative value or vapor lock is just good imagination.

no it's not good imagination but a fact. think of a regular thermos flask! the gap between the two containers provides the main insulation factor to keep liquids hot or cold. this gap is sealed as should be the top of a double wall to prevent any air movement which would reduce the insulation factor by up to 80%. simple physics says ideal would be an air gap as big as possible. but that would not be convenient for most buildings. no ants or other critters can access a properly built closed double wall.

another example what an air gap does for insulation are double or nowadays in continental Europe triple and even quadruple glazed windows and glass doors where in top quality products the air is replaced by Argon gas.

case closed... next!

[Langsuan Man]

next.....

What is the cost factor in % in building double block walls versus "super block " single wall ?

[doglover]

next.....

What is the cost factor in % in building double block walls versus "super block " single wall ?

Can it be assumed that you mean the following?

......What is the cost factor in % in building a double block wall from typical concrete blocks versus a single wall of autoclaved aerated concrete blocks?

You will have to also specify what thickness of aerated blocks you plan to use for your comparison. If my above assumption is correct and you used a thickness of the aerated blocks equal to the thickness of two typical blocks for example.... The single wall of aerated blocks will be cheaper and more effective at the end of the day. I cannot give you a % difference though.

[Langsuan Man]

Fair enough, how much more would it have cost me to use these blocks in a double walled configuration

,

[doglover]

Now that's specific! And a good question so one may attain a ballpark figure for that area of the building costs. Anyone have some data on costs per square metre of a single wall that has been rendered on both sides constructed from the following?

1. typical concrete block
2. red brick
3. autoclaved aerated concrete block (say 7cm thickness)

I sure don't, but I do know the labour time involved from least to most is 3, 1, 2. And I would hazard a guess that final wall weight from lightest to heaviest is 3, 2, 1.

Edited March 12, 2011 by doglover

[KunMatt]

I did start another thread before which has been mostly answered in here, but just to reassure my paranoid mind before we lay down the final plans...

I have the choice of using a single wall of 8" Q-Cons or 2x 3" Q-Cons with a 2" gap. This is because the support columns are 8" and I don't want them sticking out along the walls.

The price is roughly the same, about an increase of 50 Baht/m2 if I use the 8" bricks compared to 2x3" all in, but I believe I will get a much better insulating factor by using a 2" air gap compared to a 'solid' (albeit aereated) 8" brick.

Of course I am worried about any damp in the gap as it hammers down with rain frequently where the house is being built, but if the gap is left unsealed at the top I believe it won't be such a problem(?).

Any advice will be greatly appreciated.

[bankruatsteve]

Consider this... the price would NOT be the same for the labor: you would be building 2 walls vs. 1. R value of air greater than Qcon? I don't think so.

[KunMatt]

Consider this... the price would NOT be the same for the labor: you would be building 2 walls vs. 1. R value of air greater than Qcon? I don't think so.

Trust me, I've already got the quote. Anyways, I'm not asking about the cost

What I am concerned about is if it is a good idea to use a dual wall of 7.5cm Q-Con bricks with a 2" gap, or to just use a single wall of 20cm Q-Cons? I'm most concerned about keeping my house cool.

Thanks.

[bankruatsteve]

I'm pretty sure the answer is the 20cm block vs a gap within the same dimension. The block, with the same dimension as an air gap, will have better insulative property. Having an air gap is not what you want, in my opinion.

And, why somebody would be willing to build 2 walls for the same price as 1 sounds amazing. But, TIT.

[KunMatt]

I'm pretty sure the answer is the 20cm block vs a gap within the same dimension. The block, with the same dimension as an air gap, will have better insulative property. Having an air gap is not what you want, in my opinion.

I read that even using 2x 7.5cm bricks right next to each other gives a better R value than using a solid 15cm brick. Ideally I'd like to use one solid brick wall but if there is a lot of difference using any gap then I would do that. Can anyone with experience in this subject please advise me about this?

And, why somebody would be willing to build 2 walls for the same price as 1 sounds amazing. But, TIT.

Because of 2 factors:

1. The 20cm brick costs 33% more than the 15cm. You also need more of the cement.

2. There is an extra labour charge for building the single wall with much bigger bricks.

Currently my quote is for a single 7.5cm wall. If I want to change this the extra labour charge to build anoter wall with 7.5cm brick is 180B/m2. The extra labour charge for using the 20cm brick in a single wall is 100B/m2, but I have already asked him to re-negotiate this cost so I think they will work out about equal when you factor the costs of the bricks and extra cement in.

Edited April 11, 2011 by UKMatt

[KunMatt]

I read that even using 2x 7.5cm bricks right next to each other gives a better R value than using a solid 15cm brick. Ideally I'd like to use one solid brick wall but if there is a lot of difference using any gap then I would do that. Can anyone with experience in this subject please advise me about this?

Can anyone give me a definite answer to this yet? We start building real soon and whether we have walls or not is quite an important factor for the house!

TIA.

[trogers]

I read that even using 2x 7.5cm bricks right next to each other gives a better R value than using a solid 15cm brick. Ideally I'd like to use one solid brick wall but if there is a lot of difference using any gap then I would do that. Can anyone with experience in this subject please advise me about this?

Can anyone give me a definite answer to this yet? We start building real soon and whether we have walls or not is quite an important factor for the house!

TIA.

Using a 20cm thick solid brick will not give you better insulation against heat. A cavity wall is better. But I do not understand your concern on this matter. I would use a 15cm single block, and on the side(s) facing the afternoon sun, I can later add a cavity effect using Viva boards fixed on to the outside surface of the finished wall with a 50mm cavity between. This have the effect of shading your block wall with an umbrella.

Edited April 18, 2011 by trogers

[kamalabob2]

If you were in Bangkok between May 4 to May 8th you could ask in person to many genuine experts of building materials at Impact Convention Center at the free annual Architect Expo which is called BuildTech 2011. You can register for free admission at the door. This is not a lame sales Expo such as a HomePro Expo or HomeWorks Expo, but really a LARGE exhibition with all the major players in Thailand Building materials and quite a few smaller vendors with innovative and/or new to Thailand building products. No coyote dancers, no hard sell booth staff, but often the top technical people from CPAC, COTO, WEBER, all the cement companies, most every paint vendor, all the roof tile companies, pipes you never imagined were actually for sale in Thailand, etc..

The web site is not real good, but the Expo is excellent based on my attended the three previous years. http://buildtechexpo.com/ There will be full page advertisements for this Expo in many Thai language newspapers in late April and perhaps in the two English language newspapers. You are able to meet face to face with staff who UNDERSTAND your questions in English, they will always give you their personal business card and are not put off by Expats asking detailed questions.

I have no affiliation what so ever with this event. They offer a free shuttle from and back to Mo Chit BTS and their are plenty of metered taxis at this venue. They are not stingy with brochures, more often bi-lingual, and the booths are laid out by building materials.

[rijb]

Is there any downside to using foil-backed gypsum panels on a ceiling, with a well-ventilated roof?

[doglover]

Is there any downside to using foil-backed gypsum panels on a ceiling, with a well-ventilated roof?

....the non-shiny side