Which concrete blocks?

[flanagaj]

15 minutes ago, Mr Punter said:

 

Unless this is a strict planning condition you may find render is more acceptable to future purchasers and lenders.  Probably cheaper and quicker as well.

The cladding is something we don't want to change.

[Iceverge]

1 hour ago, flanagaj said:

I have put the numbers into the knauf calc and I end up at 0.19.  The other issue is that I am using timber clad and not render.

 

Change that to medium blocks inside and outside and you get to 0.18. That's a nice calculator actually by Knauf. It is fairly optimistic with the values it's allowing for the airspace behind the plasterboard though but it'll get you through regs which I'm getting the impression is the aim.  

 

 

 

Hemelite blocks are a small bit cheaper too. 

 

 

 

 

 

Superglass is a bit cheaper again than Knauf.  

 

 

 

 

 

£51.37 inc VAT per m2 for the blocks and insulation.

 

Edited 17 hours ago by Iceverge
Correcting mistakes made again!!

[Mr Punter]

10 hours ago, Iceverge said:

it's allowing for the airspace behind the plasterboard though but it'll get you through regs

 

In reality this is more likely to lose heat v solid plaster, as it can allow cold outside air to circulate behind the plasterboard.  This can be very significant and difficult to resolve.  Another failing of SAP.

[FarmerN]

No mention of thermal bridging in this discussion of blocks

Is it important , especially through foundations?

Should different blocks be used in foundations?

 

Our build was all masonry construction , and due to ground conditions ended up with a beam and block construction. This meant all masonry walls were thermal bridges, more so than on ordinary foundations. I keep meaning to get a thermal imaging camera to see just how bad it is, and compare internal to external walls.

 

 

[ADLIan]

Aircrete block will generally give a much better psi-value than a medium or dense block (in the same detail). In a typical ground floor/wall junction expect the psi-value with dense block to be approx 3 times higher than with an aircrete block.

[ADLIan]

3 hours ago, Mr Punter said:

 

In reality this is more likely to lose heat v solid plaster, as it can allow cold outside air to circulate behind the plasterboard.  This can be very significant and difficult to resolve.  Another failing of SAP.

Nothing to do with SAP - its a perfectly acceptable inclusion in the U-value calculation and is covered in the U-value conventions document that supports the Bldg Regs/Appr Docs. Done correctly, to MIs, mass air movement behind the plasterboard will not occur.

[MikeGrahamT21]

If you are wanting to go high performance, something like Marmox Thermoblocks can be used at the wall/floor level to prevent thermal bridging, much better than aircrete, but for the rest of the construction go with dense blocks, they're robust, don't crack easily, no silly rules for wet plastering, and also keep the temperature balanced out over the year (thermal mass! yes i said it!)

Edited 3 hours ago by MikeGrahamT21

[Mr Punter]

17 minutes ago, ADLIan said:

Done correctly, to MIs, mass air movement behind the plasterboard will not occur.

 

OK in theory but this never ever happens on site, which is why the "plasterboard tents" are notoriously freezing.

[Nickfromwales]

31 minutes ago, ADLIan said:

Done correctly, to MIs, mass air movement behind the plasterboard will not occur.

Something as simple as a continuous bead of expanding foam at the foot of the plasterboard, before fitting skirtings, will make a huge difference; this prevents air being sucked in at the bottom of the wall preventing convection airflow / travel around blobs of adhesive when dot and dabbing the boards on.

 

11 minutes ago, Mr Punter said:

 

OK in theory but this never ever happens on site, which is why the "plasterboard tents" are notoriously freezing.

Anything done poorly will always perform poorly, as with everything. Other notorious failures are sealing the slab around rising services such as SVP's when there's a cold ventilated void under block & beam. Heating bills go sky-high when you add all these things together.

 

Edit to add, if you're D & D in an airtight house then this is moot.

[Iceverge]

Has anyone got examples of Dot and Dab blowerdoor tests(not gamed!)? Did anyone get below 2ACH ?

 

When it comes to passivhaus airtightness the build types I've seen to have achieved those levels are wet plaster, tapes membranes/boards in timberframe, ICF, SIPS. 

 

 

Two one offs were @Gone Wests Icynene TF and an archive building somewhere in England that used Passive purple paint. 

 

I haven't come across any dot and dab getting below 0.6ACH. 

 

 

 

 

 

 

[flanagaj]

15 hours ago, Iceverge said:

 

Change that to medium blocks inside and outside and you get to 0.18. That's a nice calculator actually by Knauf. It is fairly optimistic with the values it's allowing for the airspace behind the plasterboard though but it'll get you through regs which I'm getting the impression is the aim.  

 

 

 

Hemelite blocks are a small bit cheaper too. 

 

 

 

 

 

Superglass is a bit cheaper again than Knauf.  

 

 

 

 

 

£51.37 inc VAT per m2 for the blocks and insulation.

 

Thanks @Iceverge!  That is perfect and you have listed suitable materials that come in cheaper than my estimators quote too 🙂  If we had a bigger budget then I'd look to improve the U value further, but if I don't keep costs down, we'll have to sell when we have finished the build.

[Gone West]

51 minutes ago, Iceverge said:

Two one offs were @Gone Wests Icynene TF and an archive building somewhere in England that used Passive purple paint. 

Yes, we achieved 0.47ACH with only the Icynene, combined with the 15mm OSB3 exterior racking, as the airtightness. We didn't use any tapes or membranes in the structure at all. The windows and doors were sealed using two strips of Compriband and the Soudal SWS system.