Cavity wall - leave to breathe or close?

[Bassosa]

The tops of my cavity walls were left open by my builder. Not sure why, see pic.

 

This is on the third floor and I'm basically in the attic looking down into the cavity. 

 

Should this be closed and what would be the best way? Access is now a problem because the ceilings are in. 

 

Thanks

 

 

[Artisi]

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

[evilebxxx]

4 minutes ago, Artisi said:

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

35% of heat lost from the home is through the walls.

[Bassosa]

Good discussion already, many thanks.

 

What about "open" cavity walls between rooms? This is a guesthouse and noise is a concern. Also, we have airconditioning in each room. Will in this scenario cool air escape?

[ThePioneer]

22 minutes ago, Artisi said:

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

 

How you would achieve to leave it open.

 

For strength of the construction there should be a concrete ring beam on top of the wall, and at least one ring beam somewhere half way the wall, spanning over both walls

 

Edit : at least that is how my house is built. My columns are the size of the whole cavity and both walls ( 25 cm ), and I have ring beams on top and half way my wall, connecting columns and walls.

 

 

 

 

[Bassosa]

There's a steel reinforced concrete beam about a meter down (horizontal), but obv not on top of the two rows of brick wall. The wall is however tied in on the sides.

 

Same wall, different angle, you can't see it but the horizontal reinforced concrete beam is right there about a meter down.

Looking in from the top.

[Artisi]

6 minutes ago, ThePioneer said:

 

How you would achieve to leave it open.

 

For strength of the construction there should be a concrete ring beam on top of the wall, and at least one ring beam somewhere half way the wall, spanning over both walls

 

Edit : at least that is how my house is built. My columns are the size of the whole cavity and both walls ( 25 cm ), and I have ring beams on top and half way my wall, connecting columns and walls.

 

 

 

 

For me, no ring beam at the top, 1 about half wall height - I had the builder place a number of 1" or 1,5" PVC pipe thru' the beam so the lower half communicates with the top half. I also put screened wall vent in all rooms to exit into the cavity.  

[Bassosa]

1 minute ago, mahjongguy said:

"There's a steel reinforced concrete beam about a meter down"

 

So, it seems that all but the very top bit of the wall is closed, right?

Correct.

[Bassosa]

7 minutes ago, Artisi said:

For me, no ring beam at the top, 1 about half wall height - I had the builder place a number of 1" or 1,5" PVC pipe thru' the beam so the lower half communicates with the top half. I also put screened wall vent in all rooms to exit into the cavity.  

Interesting!

 

Would you agree that the cavity also gets vented through the power sockets and power switches?

[kamalabob2]

Very interesting wall construction for 2019. What did your architect write on the plans?  Most plans I have seen are very clear on what size steel in a concrete reinforced ring beam. Your architect might also give you an opinion on the open cavity construction method. 

[Artisi]

18 minutes ago, Bassosa said:

Interesting!

 

Would you agree that the cavity also gets vented through the power sockets and power switches?

In theory yes, in fact - have not seen any sign that is happening - no tell-tale signs of dust accumulated in /on the wall plates. 

The wall vents are very effective, they are on a regular maintance schedule to be cleaned of crud collecting on the internal wire screen.

All early Australian cavity brick homes were built this way - so nothing new. 

[Farangwithaplan]

43 minutes ago, ThePioneer said:

For strength of the construction there should be a concrete ring beam on top of the wall, and at least one ring beam somewhere half way the wall, spanning over both walls

 

You are referring to a load bearing wall. The wall in question, based only on the photo available is simply a partition wall with no gravity loads on it other than self weight. It looks like a typical partition / infill wall. There will be some sort of reinforcing in a wall such as this to stop them toppling over. The steel sitting on the out skin will be designed to be supported at each end, not by the wall running under it. There is a vertical support sitting on the steel beam that might support roof rafters - not sure from the photos.

 

The OP has further mentioned in a later post that there is is a beam 1 metre below to brace the partition / infill wall..

 

OP you can leave the wall uncapped. What is your concern about it being uncapped if it in enclosed in the roof cavity?

 

 

 

 

 

 

[ThePioneer]

4 minutes ago, Farangwithaplan said:

You are referring to a load bearing wall. The wall in question, based only on the photo available is simply a partition wall with no gravity loads on it other than self weight.

 

In Thai construction walls are never load bearing, because they use column frame construction, and the walls are just to fill the space between columns and beams.

 

It is of course up to everyone's own preferences, but where the OP has 7cm  square columns and most likely footings sized accordingly, I feel safer with 25cm square columns and footings of 1 and 1.5 meters, and concrete ring beams of 25x25 cm covering both inner and outer walls.

[Bassosa]

17 minutes ago, Farangwithaplan said:

You are referring to a load bearing wall. The wall in question, based only on the photo available is simply a partition wall with no gravity loads on it other than self weight. It looks like a typical partition / infill wall. There will be some sort of reinforcing in a wall such as this to stop them toppling over. The steel sitting on the out skin will be designed to be supported at each end, not by the wall running under it. There is a vertical support sitting on the steel beam that might support roof rafters - not sure from the photos.

 

The OP has further mentioned in a later post that there is is a beam 1 metre below to brace the partition / infill wall..

 

OP you can leave the wall uncapped. What is your concern about it being uncapped if it in enclosed in the roof cavity? AC may perform better? Lower electricity bill?

 

 

 

 

 

 

 

Yeah you're right, infill wall, nothing structural. Thanks for clearing up the confusion.

I'm worried that soundproofing between rooms is compromised by having the cavity walls uncapped. By uncapping it, it's basically not a cavity wall anymore in my opinion?

 

In my condo we have noise issues with our neighbours, 90% of the sound travels over the wall, through the plasterboard ceiling.

 

Also, capping it may help with insulation? More efficient AC operation?

 

In any case you guys have confirmed that its not an issue either way, thanks.

 

 

 

 

 

 

[ThePioneer]

11 minutes ago, Bassosa said:

I'm worried that soundproofing between rooms

If you worried about sound proofing then fill the cavity with Styrofoam panels, or get those gyproc panels with Styrofoam attached and add them to the inner walls between rooms

[Bassosa]

52 minutes ago, ThePioneer said:

If you worried about sound proofing then fill the cavity with Styrofoam panels, or get those gyproc panels with Styrofoam attached and add them to the inner walls between rooms

 

Will look into it.

[eyecatcher]

Reasons to close the cavity.

1. It prevents the spread of fire into the roof space.

 

2. It prevents vermin scuttling about building nests which will drive you crazy.

 

3. The whole point about a cavity is to act as an insulating layer so anticipating heat is going to rise is just ridiculous....it doesnt matter!

 

4. Closing a cavity with masonry actually ties the top section of cavity wall together. Highly unlikely wall ties will be used correctly and steel trusses/rafters are exerting lateral pressures on those wall tops, even if the wall plate beam is being used.

 

5. Sound transmission from the roof, those rats again, maybe aeroplane noise, or those flying pigs

Yes I am now clutching at straws.

 

 

[Farangwithaplan]

4 hours ago, ThePioneer said:

 

In Thai construction walls are never load bearing, because they use column frame construction, and the walls are just to fill the space between columns and beams.

 

Yes, I realise they use a formed bond beam when the wall has supported either a wind up, down or gravity load as a standard practice. The bond beam is nothing more than a steel reinforced concrete lintel. The bond beam and piers form part of the wall hence the reason to refer to the structure as a load bearing wall. The point I was  making was that the wall in the photo has no bond beam because it is simply a partition.

[sometimewoodworker]

17 hours ago, Bassosa said:

The tops of my cavity walls were left open by my builder. Not sure why, see pic.

 

This is on the third floor and I'm basically in the attic looking down into the cavity. 

 

Should this be closed and what would be the best way? Access is now a problem because the ceilings are in. 

 

Thanks

 

My choice was to have all the cavities sealed. Leaving them open provides a place for the inevitable rodents to die, which provides a place for flys to ear, not to mention the amounts of gecko droppings that will accumulate.

 

If sealed there is less opportunity for any kind of organic material to enter. 

 

You can use a cement board and silicon or acrylic to easily seal the gaps and hold the boards down.

[Longcut]

17 hours ago, Bassosa said:

Good discussion already, many thanks.

 

What about "open" cavity walls between rooms? This is a guesthouse and noise is a concern. Also, we have airconditioning in each room. Will in this scenario cool air escape?

Cool air does not rise.

[TPI]

Mice live in cavity walls...snakes chase and eat mice in cavity walls...little furry animals live and die in cavity walls! Seal the top of cavity walls! Really!????

[Artisi]

18 hours ago, evilebxxx said:

35% of heat lost from the home is through the walls.

As this is Thailand, most would be more interested in reducing the external heat gain via the walls. 

[KKr]

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.

 

[chilly07]

You are very lucky to have cavities as most Thai houses don't. Hope you have cavity ties to bind the walls together. Never ever seal a cavity as it completely negates it's existence. Cavities should be vented top and bottom to the external air at regular intervals to keep air circulating thus allowing heat and moisture to escape. Hope you are lucky enough to have a damp proof course just above ground level. Thai houses tend not to have this.

[evilebxxx]

3 hours ago, Artisi said:

As this is Thailand, most would be more interested in reducing the external heat gain via the walls. 

cavity wall insulation may be likened to turning a house into a big thermos flask - if you do decide to have cavity wall insulation installed and start to experience condensation, damp or mould 

[Artisi]

15 minutes ago, evilebxxx said:

cavity wall insulation may be likened to turning a house into a big thermos flask - if you do decide to have cavity wall insulation installed and start to experience condensation, damp or mould 

Don't quote me out of context please, my comment was regarding a post talking about heat loss thru walls, my comment was about the heat gain thru wall in Thailand - - - nothing to do with cavity wall insulation. 

[Tanlic]

 

 

 

 

 

 

 

 

 

The idea of a cavity wall is not insulation at least not one with red bricks with a r value of .04.

 

The idea is to stop moisture reaching in inside skin and the only thing you should see inside a cavity is space and wall ties.

 

So you adding a bridge is as daft as it gets

 

Plus the cavity being filled like you seem to have done points to a Thai having no idea what he is doing

 

 

 

 

 

 

 

 

[Artisi]

15 minutes ago, Tanlic said:

 

 

 

 

 

 

 

 

 

The idea of a cavity wall is not insulation at least not one with red bricks with a r value of .04.

 

The idea is to stop moisture reaching in inside skin and the only thing you should see inside a cavity is space and wall ties.

 

So you adding a bridge is as daft as it gets

 

Plus the cavity being filled like you seem to have done points to a Thai having no idea what he is doing

 

 

 

 

 

 

 

 

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

 

Because  of the low R value of red brick, all the more reason for a cavity wall. 8

[natway09]

I would certainly leave it open.

Also air vent bricks to the outer wall are a good idea about 2 foot from the ground

Then the wall breaths

[The Theory]

“Would you agree that the cavity also gets vented through the power sockets and power switches?”

 

A vent must be a way to out, not to inner space. And a good vent will be at the top. It does not have to be open all the way at the top of walls. It could be only 3” PVC pipe at every few feet (pipes could be covered by PVC net to stop bugs.