Cavity wall - leave to breathe or close?

[eyecatcher]

Cavities should never be vented, this fans any fire.

Cavities can be totally filled with insulation or partial fill as long as that material does not transmit moisture to the inner skin or timber frame.

A cavity wall was always designed for insulation purposes, and empty cavity is actually an insulant.

Air bricks in cavity walls have one purpose that is to ventilate a timber floor to stop it rotting. Air bricks always have a sleeve so they seal the cavity aswell as penetrating the inner skin.

 

Just saying..but not guessing. 

[sandyf]

On 9/9/2019 at 3:54 PM, Artisi said:

Leave open, heat passing the first wall will rise up and exit into the roof space 

In theory yes. but for that to happen you need lower vents, I had that in mind but decided against it would lead to unwanted residents.

Cavity walls should be tied and my window frames serve that purpose. I do not have any internal cavity walls but again if I did the door frames and pillars would probably make ties unnecessary. Insulation against sound would be improved by injected foam but the cost/benefit ratio is debatable.

The cavity on my walls is also open along the top and after 10 years has never posed a problem. Having the cavity has been quite effective, in the warmer weather we have the AC on in the bedroom overnight and that keeps the internal temperature comfortable during the day until the following night.

[sandyf]

21 hours ago, KKr said:

I have heard some people say that due to the high temperatures under roofs Rockwool kinda evaporates (no physically plausible explanation was offered )

Any informed opinion on durability of insulation materials will, I think, benefit all on this discussion.

 

That is absolute rubbish. i used to design industrial ovens and genuine Rockwool was the preferred insulation, used it both in batt for the lower temps and loose fibre form for temps up to 600 degrees C. I have seen ovens getting on for 20 years old that have come back for repair and shown very little sign of deterioration in the insulation.

Rockwool is a lot denser than fibreglass and safer to handle, the fibre length being less of a health issue.

[KKr]

5 hours ago, sandyf said:

That is absolute rubbish. i used to design industrial ovens and genuine Rockwool was the preferred insulation, used it both in batt for the lower temps and loose fibre form for temps up to 600 degrees C. I have seen ovens getting on for 20 years old that have come back for repair and shown very little sign of deterioration in the insulation.

Rockwool is a lot denser than fibreglass and safer to handle, the fibre length being less of a health issue.

Thank you for clarifying, appreciated.

[carlyai]

as I remember, there are two types of sound problems.
Contact sound and Air sound
1) Contact sound travels primarily through floors, ceilings, and through connections between the two partitions, hence a beam half way the wall greatly reduces the effectiveness of the sound proofing of the partitions.
2) air sound travels, you guessed it, through air, electrical and antenna sockets are famous for that, so should not be opposite each other and preferably covered on the back with 5 cm of rock wool or something like that.
3) ventilation vents let air flow and that is great, but  also let sound through. Hence, we used to put a 10 cm sewage pipe into the cavity what not only enhanced suction, but sticking that pipe up a meter or two into a common ventilation channel also inhibited back flow of air, thus smell and sound, from other rooms or apartments on other floors as the case may be, and lessened sound transfer.

As for an open cavity, we used to fill those with Glassfibre or rock wool, very effective. Styropor one would have to glue two overlapping layers to ensure airtightness.
Leaving the cavity open, I agree, in a lively nature like in Thailand is not an option really. personally I'd use boards of "cement wood" that seem more durable and tooth proof then gypsum to close the top of the wall cavity yet leave the option to add, or fish for, cables.

In moderate and cold climates, we would even retroactively fill wall cavities with foam, but I am not sure how long the various spray foams will last in 40 plus, and moreover, I have heard some people say that due to the high temperatures under roofs Rockwool kinda evaporates (no physically plausible explanation was offered )

Any informed opinion on durability of insulation materials will, I think, benefit all on this discussion.
 

We are visiting our Pattaya home after many years. We had the roof foam sprayed about 15 years ago and the house is still cool compared to other similar houses in the area. People have been inspecting the house (as it's for sale), and they all comment how cool it is compared to theirs. I would say foam spray is good value for insulation, sound proofing and keeping the roof enyering theives out.

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[carlyai]

@Tanlic When I built my home with all red brick cavities, red bricks were all the workers knew how to lay, so red bricks it was. Don't forget that the outer and inner red brick layers have a good inch (guess) of render on them.

Regardless if the r factor, the solar flares, the coeficient of certain things or the specific gravity of Leo beer, if you put your hand on an outside sun exposed wall it is very hot. Put your hand on the inside wall and it is cool. Pub test QED.
No wall ties. I think it was just as well as was a never ending battle to get the brick layers not to throw the excess mortar in the cavitys. If wall ties are not supervised correctly the dropped mortar forms a bridge between the walls and water migrates across the bridge to the inside walls.


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[Artisi]

22 minutes ago, carlyai said:

@Tanlic When I built my home with all red brick cavities, red bricks were all the workers knew how to lay, so red bricks it was. Don't forget that the outer and inner red brick layers have a good inch (guess) of render on them.

Regardless if the r factor, the solar flares, the coeficient of certain things or the specific gravity of Leo beer, if you put your hand on an outside sun exposed wall it is very hot. Put your hand on the inside wall and it is cool. Pub test QED.
No wall ties. I think it was just as well as was a never ending battle to get the brick layers not to throw the excess mortar in the cavitys. If wall ties are not supervised correctly the dropped mortar forms a bridge between the walls and water migrates across the bridge to the inside walls.


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Some good advice there for anyone interested 

 

[Tanlic]

You couldn't buy a bottle of Leo with what you will save these days..........a single layer of aac block have 4 times the insulation value and will work out about the same cost

Edited September 14, 2019 by Tanlic

[Artisi]

17 minutes ago, Tanlic said:

You couldn't buy a bottle of Leo with what you will save these days..........a single layer of aac block have 4 times the insulation value and will work out about the same cost

The cavities in my construct served 2 purposes, 1, to exclude external heat rise and 2. No inside columns sticking out like dog's-balls into the rooms and in the corners. 

[carlyai]

You couldn't buy a bottle of Leo with what you will save these days..........a single layer of aac block have 4 times the insulation value and will work out about the same cost

@Tanlic you are right about the blocks. if I did it again I would use 2 layers of QCon blocks. Or a cavity of AAC blocks but I didn't have the choice, it was red bricks or red bricks.

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[carlyai]

The cavities in my construct served 2 purposes, 1, to exclude external heat rise and 2. No inside columns sticking out like dog's-balls into the rooms and in the corners. 

Good no.2 point as well Artisi. All my internal walls are cavity as well and nice neat walls.

Off topic but in the Pattaya house I made a feature of the dogballs columns. Pic.



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[canopy]

Taking a step back I've never understood the fascination of building a cavity wall. I guess if all you have to choose from are poorly performing red bricks then ok it makes sense. But it's not the 1950's anymore--we have other materials and wall systems here. For example AAC has been invented and used for a long time now. Other countries in the world build using a single row of thick load bearing AAC blocks and thus no longer need columns which helps with time and cost and such houses are quite strong and have excellent thermal performance. The house goes up quick and cheap because one block is equivalent to dozens of red bricks and you don't waste money and time on a reinforced concrete structure. So that's the way I went and couldn't be happier and there is just no way you could ever convince me to build a cavity wall in the 21st century. Old habits die hard I guess.

 

[Artisi]

1 hour ago, canopy said:

Taking a step back I've never understood the fascination of building a cavity wall. I guess if all you have to choose from are poorly performing red bricks then ok it makes sense. But it's not the 1950's anymore--we have other materials and wall systems here. For example AAC has been invented and used for a long time now. Other countries in the world build using a single row of thick load bearing AAC blocks and thus no longer need columns which helps with time and cost and such houses are quite strong and have excellent thermal performance. The house goes up quick and cheap because one block is equivalent to dozens of red bricks and you don't waste money and time on a reinforced concrete structure. So that's the way I went and couldn't be happier and there is just no way you could ever convince me to build a cavity wall in the 21st century. Old habits die hard I guess.

 

I don't think there is any fascination in the building of cavity walls, it comes down to the best system to used based on the experience of the builder you are using. 

The builder I used was top of the league in the "old habits" but wasn't interested in changing his build method, which I can understand (to a point) so had to go with the flow or look around and contract an unknown quality builder. 

At the end of the day the result was 100% so no complaints. 

[Bassosa]

1 hour ago, Artisi said:

I don't think there is any fascination in the building of cavity walls, it comes down to the best system to used based on the experience of the builder you are using. 

The builder I used was top of the league in the "old habits" but wasn't interested in changing his build method, which I can understand (to a point) so had to go with the flow or look around and contract an unknown quality builder. 

At the end of the day the result was 100% so no complaints. 

Same here. Red bricks or red bricks.

 

In our case there might have been an ulterior motive because our contractor earns money on his guys' labour. Every single dividing wall in our building is a double red brick wall, so it takes ages to lay. Then, because the bricks have been laid in the shoddiest way possible, you need 2.5 centimeters of render. Imagine how long that takes.

Our is a renovation project and we deal with uneven surfaces a lot. That may be a reason to use red brick because I imagine it gives you a little more versatility.

Next project AAC all the way.

 

Edited September 15, 2019 by Bassosa

[canopy]

5 hours ago, Artisi said:

it comes down to the best system to used based on the experience of the builder

That is true, but the thing is I don't sense even the tiniest bit of change towards doing things any different. Once upon a time every builder built with wood in Thailand. In the 20th century they all switched to red bricks like we see today which was an absolutely huge night and day change. Now AAC has been in Thailand for 30 years and I don't get the impression there is any change whatsoever coming as far as building houses without columns. In Thailand they may substitute AAC for red bricks; that's about it. Ironically developed countries always use AAC without columns. I don't think load bearing AAC is too technical for the builders here. Making a concrete frame like they do is no picnic; lots of rebar work, forms, heavy machinery, and such and it all adds substantial cost.

 

[notrub]

For any house built with 'hard' materials the buildings I have seen start with concrete columns on a pad maybe with driven piles too, depending on where you are.  Then there is a ring beam on grade with another at 3 meters or so.  Whatever you put in to form the curtain wall is not usually structural, even if it could be.  I use siporex or expanded cement blocks.  A beam between the columns 1/2 way up is normal and of course lintels over doors, windows and other openings.  Do NOT use red terra cotta brick as they are small, take a lot of time to place and are fragile to fasten to for kitchen cupboards (or anything) and are basically <deleted>.   

 

Contractors know how to build this way and all the equipment is owned or easily rented by the contractor.  All the rebar cages can be bought cheaply already made up.  Be careful to wrap the columns in plastic wrap, cling film, that is sold everywhere.  Get 50 cm rolls and wrap around the column horizontally.  

 

The contractor knows how to do this and how to price it and employees know what to do too.

 

I us a fairly shallow pad 40cm thick 120x120 or so and the grade beam rests to the pad and buts into the columns.  I use a floating slab that must be poured on top of the gb and tied into it with rebar connection.  this is not so common in Thailand and they tend to pour the slab on grade between the grade beam and not keyed in by much.  Stupid.

 

A cavity wall is not common here and will not function as a cavity if it is filled in.  They are a bit good in the UK but there is no point to them here.

[Artisi]

1 hour ago, notrub said:

For any house built with 'hard' materials the buildings I have seen start with concrete columns on a pad maybe with driven piles too, depending on where you are.  Then there is a ring beam on grade with another at 3 meters or so.  Whatever you put in to form the curtain wall is not usually structural, even if it could be.  I use siporex or expanded cement blocks.  A beam between the columns 1/2 way up is normal and of course lintels over doors, windows and other openings.  Do NOT use red terra cotta brick as they are small, take a lot of time to place and are fragile to fasten to for kitchen cupboards (or anything) and are basically <deleted>.   

 

Contractors know how to build this way and all the equipment is owned or easily rented by the contractor.  All the rebar cages can be bought cheaply already made up.  Be careful to wrap the columns in plastic wrap, cling film, that is sold everywhere.  Get 50 cm rolls and wrap around the column horizontally.  

 

The contractor knows how to do this and how to price it and employees know what to do too.

 

I us a fairly shallow pad 40cm thick 120x120 or so and the grade beam rests to the pad and buts into the columns.  I use a floating slab that must be poured on top of the gb and tied into it with rebar connection.  this is not so common in Thailand and they tend to pour the slab on grade between the grade beam and not keyed in by much.  Stupid.

 

A cavity wall is not common here and will not function as a cavity if it is filled in.  They are a bit good in the UK but there is no point to them here.

It will function as a cavity wall if designed as a cavity, as mine are with internal screened wall vents into the cavity. 

[notrub]

 

Sandyf, If the picture posted of the wall with siporex (aerated cement) blocks faced off with quality red brick and cavity between is yours, congratulations!  What a nice neat job that is.

 

I am still not a fan of cavity walls but if you want to construct that way you have shown an excellent example of how to do it correctly.

 

The red brick that I referred to are 4x4x10 cm approximately and are commonly used here in my corner of Isaan as infill between load bearing frames.  They are very bad for lots of reasons.  Nothing like the quality bricks shown in your photo.

 

I like siporex blocks the best and they can be used as a load bearing wall, although I have never seen it here.  They are completely inert and do not suffer from condensation or insect infestation and I have never seen a mouse attempting to chew through my walls (why bother, they use the door).

 

They are lightweight and easy to build with.  They are ready to take a render (use the correct product) and are easy to fasten to with simple nylon inserts or various expanding bolts.  They are easy to cut through if you want a new door etc..  If you make a ring beam at window/door lintel height it makes that job even easier.  Lintels are supplied made of the same product but it is easier and much (much) cheaper just to form and pour concrete lintels.  With this climate there is not the same problem with a thermal bridge that you would find in colder countries.

 

Rockwool is a good product and the compressed version is easy to use.  It can be load bearing on a roof and put down (onto sheets of some product) as a single matt with metal frames (to fix the roof cover) laid on top screwed down to the structure below. This is called built up roofing.  

 

It is so easy to build here without the freeze thaw cycle to take into worry about.  I know there are other problems but freezing is not one of them. 

 

       

[notrub]

On 9/11/2019 at 9:25 AM, sandyf said:

In theory yes. but for that to happen you need lower vents, I had that in mind but decided against it would lead to unwanted residents.

Cavity walls should be tied and my window frames serve that purpose. I do not have any internal cavity walls but again if I did the door frames and pillars would probably make ties unnecessary. Insulation against sound would be improved by injected foam but the cost/benefit ratio is debatable.

The cavity on my walls is also open along the top and after 10 years has never posed a problem. Having the cavity has been quite effective, in the warmer weather we have the AC on in the bedroom overnight and that keeps the internal temperature comfortable during the day until the following night.

Great looking construction!

[sandyf]

47 minutes ago, notrub said:

Great looking construction!

Thanks, my own design. I drew up some sketches and got someone to draw up the plans. Apart from some of the finishing off, the builders and the electrician did a great job.

[Chazar]

On 9/10/2019 at 4:22 PM, Artisi said:

Wall ties in Thailand, now that Is a big ask. 

no  pompem ,  make  yer  own, galvanised and  dipped in red  oxide, just buy them for the normal blocks and bend to shape, failing that steel wire   galvanised and bend to shape, I sealed  my  walls due to having aircon on  almost 24/7

Edited September 24, 2019 by Chazar

[Artisi]

5 minutes ago, Chazar said:

no  pompem ,  make  yer  own, galvanised and  dipped in red  oxide, just buy them for the normal blocks and bend to shape, failing that steel wire   galvanised and bend to shape, I sealed  my  walls

I was really asking about the use of wall ties as being a big ask. 

[Chazar]

1 minute ago, Artisi said:

I was really asking about the use of wall ties as being a big ask. 

diy =no pompem

[JimShortz]

I used solid (no holes) Lightweight Concrete Blocks in place of AAC because you can use regular render on them, and this is a massive saving, especially where thick render is required to deal with posts, etc - and it allows Thai builders to work the way they know, albeit having to wet the bricks before laying, and again before rendering. I also like the hard concrete render coat as it makes wall fixings a breeze. These LCBs are available from several companies in Chiang Mai and I paid B17 per block (20x60x7). They have something like 85% of the thermal efficiency of AAC without the special render drawback.

To deal with the wall tie issue I had my walls set out to total 20cm width then had every 2 or 3 courses laid on their side. This creates a good thermally efficient wall that is tied together, is strong, has closed cavities, and works just great for me - and no metal ties to rust out!

 

 

Edited September 24, 2019 by JimShortz

[JimShortz]

Actually, on checking, it seems my blocks were 7.5cm wide.

For anyone interested to know more, we bought SLP blocks directly from the factory where they are made (we went and saw this happening - very cool, at least for me!). If you are interested, Google SLP Chiang Mai you will find some Facebook links to get you on the right track  ????  There are several manufacturers in Chiang Mai but I found zero information about them in English - my wife tracked them pown for us in Thai.

[sometimewoodworker]

2 hours ago, JimShortz said:

I used solid (no holes) Lightweight Concrete Blocks in place of AAC because you can use regular render on them, and this is a massive saving

No saving at all as the AAC render is cheaper than the render for cinder blocks.

[JimShortz]

By the bag maybe, but given that it isn't mixed with sand, but just mixedd with water like a western plaster, regular sand and cement render is much cheaper. It also allows for Thai style thick render and associated strong surface for fixings. It has worked out great for me... 

[canopy]

Also remember AAC mortar comes out cheaper because it is laid thin and the blocks are longer and taller. That also means speed which saves labor cost and improves build time. But you have to look at the whole picture. A builder told me AAC, breeze blocks, or red bricks really has no effect on the final cost of a house. It just comes down to personal preference.

 

I love the qualities of AAC render. It can be easily sanded smooth or into bull nose corners. With AAC you do need to use approved fasteners for furnishings and results will be as good as any other.

 

[Artisi]

The material and construction method really becomes a secondary consideration unless there is a considerable price advantage when the initial aim is to construct a well insulated house. 

My home is cavity wall of double red brick rendered on both side - well below the outside temp. even on the hottest days in Phitsanulok - which can be bloody hot - as mentioned in other posts, after many days and nights of hot weather, the inside temp. will gradually increase but that is from other factors not necessarily thru' the cavity walls. 

 

[JimShortz]

2 hours ago, canopy said:

Also remember AAC mortar comes out cheaper because it is laid thin and the blocks are longer and taller. That also means speed which saves labor cost and improves build time. But you have to look at the whole picture. A builder told me AAC, breeze blocks, or red bricks really has no effect on the final cost of a house. It just comes down to personal preference.

 

I love the qualities of AAC render. It can be easily sanded smooth or into bull nose corners. With AAC you do need to use approved fasteners for furnishings and results will be as good as any other.

 

I very much agree, in theory, and have a 4m "cube" workshop with Sala on top built from AAC. I guess it depends how you are building, and who your builders are, but the "thin" part works not so well where there are cast concrete lintels, strengthening beams, etc. and the result for me was less "sharp/precise" rendering than is commonly achieved with sand and cement render. I'm pleaseed that I built this before the house. It was a good learning experience for me.

I am super pleased with the sand and cement rendering that I have on the 60x20x7.5 LCBs (same size and dimensional accuracy as AAC blocks) on my main house. This type of rendering is something that Thai builders are often familiar with and very good at, and the strength it gives to otherwise quite weak walls is a real advantage imho (especially on the interior walls which are single skin in my case). I know that if you use the AAC blocks with precise laying, the proper AAC lintels, etc. and have the right builders, a single 5mm skim of AAC render is possible - it's just not what happened for me.

Both options can work well. I'm pleased the AAC worked well for you. The LCBs have worked out much better for me. Each to their own, I guess, I just wanted to share what had worked well for me. The LCBs are a great choice for people with "village builders" - it isn't too much of a stretch for them, and a great improvement in thermal insulation over the other regular "Thai" block/brick options  ????

 

Edited September 25, 2019 by JimShortz