Is an Aerated Block cavity wall a better solution to a standard concrete wall?

bigdog

Hi,
I am trying to find out if aerated blocks(Ytong etc) and similar products are actually better to use than standard concrete block in constructing a house.
aslo would they be cheaper to use?

opinions greatly welcome.

Mazotasan

Not familiar with the said product but am using an aerated light block from an Irish manufacturer on our build shortly. We are using a std 4" block on external leaf, i think then its a 115mm cavity and then 6" aerated block on inner leaf.

When you say 'actually better' you need to check the actual specs of the product in terms of performance and structure etc whats the U values, what loading can they take, any special mortar mix etc. Can you use them in conjunction with std blocks etc etc. We are aiming to achieve a U value of below 0.2 for our external walls and after considering Insulated Concrete Foamwork and Insulated Concrete Panels etc we found the aerated blocks to be the best value for performance...they are not cheap, say 3-5 times cost of std blocks. But the actual block costs of a build are relative cheap. Work out the number of blocks required then work out the actual monetary difference...for us it was worth it.

It all depends on what how you want your walls/building to perform. I looked at the regs and said right I'd like to achieve 30% better performance then found a solution, priced it, moved spec again, priced it etc etc until I got the balance between performance and budget.

In general I think they are quite a good product...its mad the way you can actually cut them with a handsaw but at the same time they will take the loading of concrete slabs (work very well in compression). One thing I have heard (haven't seen acoustic data) is that for say internal walls they dont perform as well as the 4" standard block acoustically...!

bigdog

Do you mind if i ask what is name of block you intend to use, and where it is manufactured?

also you say the aerated block does not perform aswell accoustically, can you explain?

Mazotasan

Hi there, PM'd supplier website to you there so you can check them out.

Performing better acoustically means that sound will travel through the aerated blocks easier. There should be no problem with external walls but say you use the 4" aerated blocks for your internal walls there may be a difference.

We are using the Aerated blocks just on the external walls (building envelope) and std 4" on the internals...I would use the 4" aerated on the internal walls too but just cant stretch the budget.

The acoustics will probably be affected also by amount of plaster, plasterboard being applied or insulated plasterboard etc etc. I wouldn't get too hung up on it but try get some real actual data from suppliers if its an issue for you.

sydthebeat

personally, if i was using aac blocks (be they ytong, quinnlite etc) i would use the proprietory glueing system and not traditional 10mm mortar coursing. The traditional mortar coursing creates very significant thermal bridges in the block leaf and acts to significantly nullify the performance of the aac block.

This has add on effects. Your block courses will not be similar, therefore you will need, probably, to built the aac inner leaf first, fix wall ties to the external of the aac leaf (much like you would do with a TF build) to suit your insulation c/c and external leaf block courses. Opening areas would then have to be matched, probably by use of con saws.

Mazotasan

That is very true...the issue with the wall ties and the fact that I could only get one block layer (a Lithuanian guy who built in Germany using this method) to give me a price sent me in the direction of using the std mortar (weaker mix) road.

Again its back to specs, we can still achieve a good U value across the walls but a better one would've been achieved using the thin joint mortar system (the blocks were designed for). Ideally using the lite blocks on inner and outer leaves and using the thin joint mortar system you'd have a very high performing wall.

ardara1

Thin-Joint Aerated - great idea - leass thermal bridging
Normal bridging 8% of block bridged by mortar
Thin Joint less than 2% (Minimal thermal difference)
Wall Ties - can't use normal - use Helical fixing directly into block - not joins
Helical Ties -minimal area of S Steel - strength comes from helical shape.
Aerated block (A good one)- worth 20mm of PUR type insulation
Real benefit - thermal bridging detailing meeting Enhanced Accredited Standards Y-0.04 (If built right)
Difference between Y-0.15, Y-0.08 and Y-0.04?
Air permeability = 10/2/0.5

Try meeting an air permeabilty for 0.5@Q50!

My reckoning? - you CAN'T get an A rated house with a Y-value of 0.04

Go for it.

soldsold

Have you looked at a wide cavities?

I'm heading down the road of a 200mm cavity using 2 part ancon ties - allows standard 4" or 6" blocks on inner leaf and still very good u value.

Cheaper option I think than using aerated blocks.

Steve

ardara1

soldsold wrote: »

Have you looked at a wide cavities?

I'm heading down the road of a 200mm cavity using 2 part ancon ties - allows standard 4" or 6" blocks on inner leaf and still very good u value.

Cheaper option I think than using aerated blocks.

Steve

Your WORSENING thermnal bridging - how are you intending to tackle it?

sydthebeat

ardara1 wrote: »

Thin-Joint Aerated - great idea - leass thermal bridging
Normal bridging 8% of block bridged by mortar
Thin Joint less than 2% (Minimal thermal difference)
Wall Ties - can't use normal - use Helical fixing directly into block - not joins
Helical Ties -minimal area of S Steel - strength comes from helical shape.
Aerated block (A good one)- worth 20mm of PUR type insulation
Real benefit - thermal bridging detailing meeting Enhanced Accredited Standards Y-0.04 (If built right)
Difference between Y-0.15, Y-0.08 and Y-0.04?
Air permeability = 10/2/0.5

Try meeting an air permeabilty for 0.5@Q50!

My reckoning? - you CAN'T get an A rated house with a Y-value of 0.04

Go for it.

ardara, perhaps you can clear this up for me...

whats the co-relation between psi values and air infiltration.....????
are these two not separate factors determined independently and inputed independently into whatever software you're using???

ardara1

sydthebeat wrote: »

ardara, perhaps you can clear this up for me...

whats the co-relation between psi values and air infiltration.....????
are these two not separate factors determined independently and inputed independently into whatever software you're using???

You're right - there's no relation between the 2

The PSI value is a thermal transmittance across a junction (This deteriorates the BETTER the U-value is either side of the junction)

HOWEVER

Our ACCEPTABLE details - show detailing to improve thermal performance of the junction AND to improve the air peermeabilty of the house (The BLUE line)

Using the ACCEPTABLE DETAILS should result in an air permeability of around 7 - although the UK are finding a 4 is more common (TOO TIGHT - and finding remedial action needs to be taken to get fresh air in!) (PS - no tapes in UK details)

sydthebeat

ardara1 wrote: »

You're right - there's no relation between the 2

The PSI value is a thermal transmittance across a junction (This deteriorates the BETTER the U-value is either side of the junction)

HOWEVER

Our ACCEPTABLE details - show detailing to improve thermal performance of the junction AND to improve the air peermeabilty of the house (The BLUE line)

Using the ACCEPTABLE DETAILS should result in an air permeability of around 7 - although the UK are finding a 4 is more common (TOO TIGHT - and finding remedial action needs to be taken to get fresh air in!) (PS - no tapes in UK details)

are you referring to a requirement to increase 'designed' ventilation if the Q50 is low... something like what is proposed for our new part f??

im confused as to what you are referring to here:

ardara1 wrote: »

Air permeability = 10/2/0.5

Try meeting an air permeabilty for 0.5@Q50!

where does the Q50 = 0.5 come from... you're at passive levels there...
typical Q50 = 5 means 0.25 ac/h....

ardara1

sydthebeat wrote: »

are you referring to a requirement to increase 'designed' ventilation if the Q50 is low... something like what is proposed for our new part f??

im confused as to what you are referring to here:


where does the Q50 = 0.5 come from... you're at passive levels there...
typical Q50 = 5 means 0.25 ac/h....

Sorry Syd - It's figures I've played about with when taking the example 3 bed semi in the Acceptable details.

Take default themal bridging at Y=0.15 AND default permeability at 10.

Improve the Y to 0.08 and achieve an energy improvement by doing so.

Make the same gains by improve permeability only - you'll need to achieve 2

for Y@ 0.04 (Enhanced Detailing) = permeability imprved to 0.5

It demonstrates how critical detailing is - and yet it's mostly ignored!
Take the widening of a cavity to 200mm withour addressing the WORSENING bridging!

sydthebeat

ardara1 wrote: »

Sorry Syd - It's figures I've played about with when taking the example 3 bed semi in the Acceptable details.

Take default themal bridging at Y=0.15 AND default permeability at 10.

Improve the Y to 0.08 and achieve an energy improvement by doing so.

Make the same gains by improve permeability only - you'll need to achieve 2

for Y@ 0.04 (Enhanced Detailing) = permeability improved to 0.5

It demonstrates how critical detailing is - and yet it's mostly ignored!
Take the widening of a cavity to 200mm withour addressing the WORSENING bridging!

i understand now...

i suppose we need to see how different construction methods are fairing now that air tightness test is mainstream....

im still very doubtful that the ACCEPTABLE DETAILS we have been given actually do result in performance psi value of 0.08 that they purport... but thats another argument.

ardara1

sydthebeat wrote: »

i understand now...

i suppose we need to see how different construction methods are fairing now that air tightness test is mainstream....

im still very doubtful that the ACCEPTABLE DETAILS we have been given actually do result in performance psi value of 0.08 that they purport... but thats another argument.

The 0.08 is not a PSI value but a Y value - the Y value was based on 9 average house types and the length of each of the junctions averaged. These were multiplied up PSI x Length then totalled and total divided by the total ELEMENTAL HEATLOSS AREAS of the construction

On the contrary - the Y of 0.08 is probably on the cautious side.

d2ww

We had an extension done with Ytong 450mm blocks and 100mm for internal recently. The delivery was delayed by six weeks which really messed up the schedule and cost me money. There is no tech backup from either of the two suppliers here, so the builder had to figure things out himself. The other big thing was that every single one of the 450 blocks ended up chipped by the time the walls were finished, which made a mockery of the idea of easy plastering/rendering. The 100mm blocks which were a denser block were fine however.
Would I use them again? No.

d2ww

I think I should qualify my earlier comments by saying that if I was doing the actual building myself the blocks do have huge advantages in the physical labour involved, and the thin morter(sic) is very easy to handle. I would however, foresake a little thermal performance and use the medium density block to avoid the chipping problem.

soldsold

ardara1 wrote: »

Your WORSENING thermnal bridging - how are you intending to tackle it?

I have been assured that a thermal analysis was done on the effect of the wall ties and was found to be insignificant.

That may or may not be true, in any case I expect 200mm cavity full filled with minimal cold bridging at window details will be sufficient, I also have the option of dry lining internally to reduce the cold bridge from wall ties if needed.

sydthebeat

soldsold wrote: »

I have been assured that a thermal analysis was done on the effect of the wall ties and was found to be insignificant.

That may or may not be true, in any case I expect 200mm cavity full filled with minimal cold bridging at window details will be sufficient, I also have the option of dry lining internally to reduce the cold bridge from wall ties if needed.

have those ancon ties been certified fit for use?? they seem to only offer restriction to horizontal tension forces.... none against compressive forces or vertical movement.....

i think ardaras point may be that, when you are reaching low u values, the effect of thermal bridging materials increases.... not only will your wall tie frequency increase, but heat loss over these wall ties will increase....

soldsold

sydthebeat wrote: »

have those ancon ties been certified fit for use?? they seem to only offer restriction to horizontal tension forces.... none against compressive forces or vertical movement

From Ancon website:

"Ancon Two-Part Ties sustain loads which exceed the requirements for a Type 2 tie to BS 5628 for cavities up to 300mm."

Other than that, I dont know...

sydthebeat wrote: »

i think ardaras point may be that, when you are reaching low u values, the effect of thermal bridging materials increases.... not only will your wall tie frequency increase, but heat loss over these wall ties will increase....

Wall tie frequency (again from Ancon's website) is 450 vertical centres, 900mm horizontal centres for cavities of 150mm to 300mm, which seems ok to me.?

Its a fair point though, that the bridging effect becomes a higher % heat loss when the rest of the wall is insulated to high levels, but so do windows and doors, etc.

At some point I have to decide on a system to use to build, and every system has its potential issues whether risk of external insulation being blown over to scotland in a once in 80 year hurricane, Timberframe rotting and falling in on us, and so on. A 200mm cavity full filled with EPS is the cheapest option I can see to get to around passive levels (.17 u value) and I still have the option of drylining if needed, and using thermal mass of tiled floors, hollowcore first floor and block inner walls instead of the external wall thermal mass.

I know 200mm and 300mm wide cavity walls have been built successfully and I'll have the inner leaf on the flat so I'll just have to wager the banks money on it staying up.
:eek:

sydthebeat

how do you detail the massive thermal bridge at the rising walls if you are planning on passive levels??

soldsold

Still to be decideed and also some rising walls are supporting hollowcore slabs so I'm expecting:

1) Thickening the slab underneath the non loadbearing rising walls - they will only need to support their own weight (the slab will be sitting on 300mm EPS so may reduce to 200 or so here, as I say its still in the drawing stage)

and

2) For loadbearing walls on the flat will probably use quinnlite blocks for the courses that are in line with the underfloor insulation, with the quinnlites possibly wrapped in 20mm bitumen/ rubber but maybe not. This detail looks good for the foundations from the flux/ thermal analysis I have seen so would expect would also work well for simpler rising walls

Would appreciate opinions though, I originally planned timberframe internal walls and thats not off the agenda yet but the thermal mass would be lost.

Quinnlite internal walls would be a good way to reduce internal weight of the walls but price would go up and soundproofing would go down.

Will probably use 50mm edge insulation around the block inside walls to help the situation.

getting a PHPP analysis done at the moment so that should clarify a few of the above possibilities.

Maybe there are other options ye could suggest?