Most cost effective way to get to passive standard using block

[CalvinHobbes]

Hi, so if you have a 150mm cavity how can you get to passive standard? I realise we will need the triple glazing properly sealed and thermal bridging and air tightness is everything and wet plaster internally (no dot and dab).Would battens work to make it easier for services since labour or block & beam  floors? What about insulation? Eps in Cavity? What about outside? 

[Conor]

A few here have done it. Full fill insualtion and lightweight blocks for inner leaf will get you close. Or insualted plasterboard which is the common way down south for getting a traditional build to NZEB. But a 200mm cavity would make things much easier and give you more options.

 

Have a play around with this.

 

https://www.cba-blocks.org.uk/u-value-calculator/

 

 

Are you set on a traditional block build then? We're ICF with a total of 250mm of graphite  EPS insulation  (equiv to about 150mm PIR) that gets us well within passive standards.

 

PIR is still horribly expensive so you'll want to look at blown beads, mineral wool slabs etc.

 

For the foundations that largely depends on your ground conditions. Passive rafts from the likes of Kore in Monaghan are growing in popularity.

 

 

Your architect should be well up to speed on how to get the best U values for your build. Should be...

Edited October 21, 2021 by Conor

[joe90]

I have block and brick but with 200mm cavity. I used trench foundations but insulated, I guess with 150mm you might need to insulate/dry line.

 

[Declan52]

Def look towards a 200mm cavity of your going for EPs beads. Wet plaster is a massive help. Then it's just the simple things. No letter box, good quality 3g Windows, every light switch and socket conduit sealed up, ceiling lights covered over using thermal hoods or clay plant pots if your tight like me, airtightness tape from the blocks to your window and door frames. There's many tiny details that aren't expensive to do but will have a big impact on your houses heat loss. 

[Wumpus]

We are building with 215mm concrete block and 200mm eps external insulation. It has the benefit of being quite simple to manage the glazing installation and thermal bridges. The insulation is a continuous wrap around the floor, walls and roof.

[SteamyTea]

IWI and EWI.

And spend days sorting out all the places that air leaks will happen.

[CalvinHobbes]

12 hours ago, joe90 said:

I have block and brick but with 200mm cavity. I used trench foundations but insulated, I guess with 150mm you might need to insulate/dry line.

 

This looks good. We can go up to 200.So you are getting to passive standard with this? EWI is really expensive would like to skip it if we can. Are bricks better insulators than block?

[tonyshouse]

300 cavity for me ?.  Fibreglass batts, EPS below in cavity, 

 

cost effective compared to paying heating bills or retrofitting more insulation later 

[joe90]

4 hours ago, CalvinHobbes said:

This looks good. We can go up to 200.So you are getting to passive standard with this? EWI is really expensive would like to skip it if we can. Are bricks better insulators than block?

I didn’t bother with measuring my “passive” level just used passive principles. I don’t know if brick is a better insulator I just hate render and love bricks (of a cottage nature). The only thing we did differently is we lowered the DPC to floor level inside so that a slip plane was not created above skirting boards, as this then put the outside DPC at or below ground level (we do have a French drain all round the house) we installed a second DPC 150MM above ground level to stop rain bounce causing damp. My builder recommended this, he was well up on passive and “green” building techniques.

[SteamyTea]

3 minutes ago, joe90 said:

I don’t know if brick is a better insulator I just hate render and love bricks

https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

 

Easy to check out.

[CalvinHobbes]

Wow, some difference between the bricks. 

[Iceverge]

250mm eps blown bead cavity here. 0.31ach50.  wet plaster inside and out.

 

It’s certainly doable but there are easier ways to get to passive standard.

 

Look up the denby dale house on you tube and  @tonyshouse blog. I found them both very useful. 

 

 

[Rishard]

On 21/10/2021 at 16:02, joe90 said:

I have block and brick but with 200mm cavity. I used trench foundations but insulated, I guess with 150mm you might need to insulate/dry line.

 

I am building using this same method of insulating blocks for the inner leaf below dpc on my block-cavity-block house. My concrete footing is currently 900mm below ffl. Is there any merit in using the insulating blocks all the way down to the footing or just say 2 courses below ffl? Likewise with the xps insulation in the cavity. Is it better to go the full 900mm down with the xps or just the same 2 courses as the insulating blocks do you think? 

Edited September 5, 2023 by Rishard

[joe90]

29 minutes ago, Rishard said:

I am building using this same method of insulating blocks for the inner leaf below dpc on my block-cavity-block house. My concrete footing is currently 900mm below ffl. Is there any merit in using the insulating blocks all the way down to the footing or just say 2 courses below ffl? Likewise with the xps insulation in the cavity. Is it better to go the full 900mm down with the xps or just the same 2 courses as the insulating blocks do you think? 

My take on this is you might as well go down the full 900mm with both, belt and braces 👍

[Gus Potter]

1 hour ago, Rishard said:

I am building using this same method of insulating blocks for the inner leaf below dpc on my block-cavity-block house. My concrete footing is currently 900mm below ffl. Is there any merit in using the insulating blocks all the way down to the footing or just say 2 courses below ffl? Likewise with the xps insulation in the cavity. Is it better to go the full 900mm down with the xps or just the same 2 courses as the insulating blocks do you think? 

Good question.

 

There are not least two parts to this.

 

The first is structural. If you look at a lot of cavity wall construction you will see that below finished ground level the cavity is filled with lean mix concrete. One of the reasons for this is that the soil and hardcore inside when compacted exerts a lateral pressure on the walls.. they don't like that.

 

By all means take the insulating blocks down to top of found level. But one way of getting a lot of benefit is, if you have underfloor heating on a ground bearing slab, to carry 50mm of PIR down the inside of the inner leaf to the top of the found. This insulates the edges of the dumpling of soil under the floor slab.

 

 

 

 

 

 

 

 

 

 

[Iceverge]

1 hour ago, Rishard said:

I am building using this same method of insulating blocks for the inner leaf below dpc on my block-cavity-block house. My concrete footing is currently 900mm below ffl. Is there any merit in using the insulating blocks all the way down to the footing or just say 2 courses below ffl? Likewise with the xps insulation in the cavity. Is it better to go the full 900mm down with the xps or just the same 2 courses as the insulating blocks do you think? 

 

I played with THERM a bit modelling this and the end result is that adding lightweight blocks that are not inline with the insulation layer in the floor is of little benefit. 

 

In the above drawing if the floor insulation is 200mm thick then one 215mm block will perform almost the exact same as three of them ( in theory at least) 

 

 

 

 

[Iceverge]

As per Denby Dale. Full lightweight blocks to the foundation. No upstand to slab. 

 

Just aerated blocks inline with insulation + 25mm PIR upstand to slab.  It gives a better internal U Value. 

 

 

 

 

As above but with added lightweight blocks again.  Only about a 0.01W/m2K improvement. 

 

 

Finally an insulated raft which performs the best. 

 

 

 

 

 

 

 

 

[Gus Potter]

2 hours ago, Iceverge said:

I played with THERM a bit modelling this and the end result is that adding lightweight blocks that are not inline with the insulation layer in the floor is of little benefit. 

True enough as the aerated blocks still have less of an insulating effect but you should still get some improvement cf dense concrete blocks.

 

The big thing is your upstand around the edge of the slab. The old regs used to ask for 25mm thickness of upstand around the edge of the slab, I try and go for 50mm thick upstand around the slab perimeter and let the floor finish cantilever if need be. Usually you have skirting board or insulated plasteboard so no big deal with the flooring cantilevering 25mm or so.

 

Here is a question about the THERM software, can you see what value of thermal conductivity it is attributing to the soil?

 

The standard BRE guidance and Eurocodes goes for a default value of 1.5 λ (W/m.K) for clay soils

 

Can you change this value in the software?

 

The model output you show seems to correlate to an unheated ground floor slab where all the heat is coming from above. If you have UF it will be a diferent animal.

 

 

 

 

 

 

 

 

 

Edited September 6, 2023 by Gus Potter

[Dave Jones]

10 hours ago, Rishard said:

I am building using this same method of insulating blocks for the inner leaf below dpc on my block-cavity-block house. My concrete footing is currently 900mm below ffl. Is there any merit in using the insulating blocks all the way down to the footing or just say 2 courses below ffl? Likewise with the xps insulation in the cavity. Is it better to go the full 900mm down with the xps or just the same 2 courses as the insulating blocks do you think? 

 

joes buildup fails the new SAP due to cold bridging, you need this buildup using marmox blocks ideally. This shows the external door junction

 

 

 

 

[Rishard]

9 hours ago, Gus Potter said:

Good question.

 

There are not least two parts to this.

 

The first is structural. If you look at a lot of cavity wall construction you will see that below finished ground level the cavity is filled with lean mix concrete. One of the reasons for this is that the soil and hardcore inside when compacted exerts a lateral pressure on the walls.. they don't like that.

 

By all means take the insulating blocks down to top of found level. But one way of getting a lot of benefit is, if you have underfloor heating on a ground bearing slab, to carry 50mm of PIR down the inside of the inner leaf to the top of the found. This insulates the edges of the dumpling of soil under the floor slab.

 

 

 

 

 

 

 

 

 

 

Morning, you’re right regarding pressure on the cavity. I have my SE looking at this today to see if the insulation in the cavity is up to it or if we maybe need to use a block on its back to help be or partially fill the cavity up to a point.
 

Regarding the 50mm pir down to foundation, if the slab is suspended, like on the drawing, does the cavity insulation below dpc do a similar thing or is the 50mm pir reducing the heat loss up the insulating block to underside of slab? Mine will be a heated slab. 

[Rishard]

21 hours ago, Iceverge said:

 

I played with THERM a bit modelling this and the end result is that adding lightweight blocks that are not inline with the insulation layer in the floor is of little benefit. 

 

In the above drawing if the floor insulation is 200mm thick then one 215mm block will perform almost the exact same as three of them ( in theory at least) 

 

 

 

 

So I’m using 200mm pir insulation and have a suspended slab which loads onto the internal skin. It’s great to see some of your calculations, I wish it was something I was capable of or had access too. So from what you have said, there is little benefit in laying aerated blocks anything more than say 1 or 2 courses below my slab? Would you say to cavity fill with insulation down the whole 900mm to foundation top or would laying it down to say 600mm be adequate. My floor build up is, top down, 150mm slab, 200mm pir, 160mm void formers in some areas( ‘ground heave’) 150mm hardcore. 

[Rishard]

12 hours ago, Dave Jones said:

 

joes buildup fails the new SAP due to cold bridging, you need this buildup using marmox blocks ideally. This shows the external door junction

 

 

 

 

I know Marmox blocks are great for this kind of issue. In your drawing are they laid on the inner skin? They’re pretty dear, I know that much. 

[Iceverge]

20 hours ago, Gus Potter said:

I try and go for 50mm thick upstand around the slab perimeter and let the floor finish cantilever if need be. Usually you have skirting board or insulated plasterboard so no big deal with the flooring cantilevering 25mm or so.

Very wise.  25mm got lose under out inner layer of wet plaster. Too much may make it difficult to secure carpet at the perimeter however. 

 

20 hours ago, Gus Potter said:

Here is a question about the THERM software, can you see what value of thermal conductivity it is attributing to the soil?

 

The standard BRE guidance and Eurocodes goes for a default value of 1.5 λ (W/m.K) for clay soils

 

Can you change this value in the software?

 

Yes, i use 2.0 W/mK for sand and gravel soils. 

 

20 hours ago, Gus Potter said:

The model output you show seems to correlate to an unheated ground floor slab where all the heat is coming from above. If you have UF it will be a diferent animal.

 

Yes. 

[Iceverge]

2 hours ago, Rishard said:

So I’m using 200mm pir insulation and have a suspended slab which loads onto the internal skin. It’s great to see some of your calculations, I wish it was something I was capable of or had access too. So from what you have said, there is little benefit in laying aerated blocks anything more than say 1 or 2 courses below my slab? Would you say to cavity fill with insulation down the whole 900mm to foundation top or would laying it down to say 600mm be adequate. My floor build up is, top down, 150mm slab, 200mm pir, 160mm void formers in some areas( ‘ground heave’) 150mm hardcore. 

 

 

It's free. THERM Software Downloads | Windows & Daylighting (lbl.gov)

 

I used this PDF to get started. http://passivehouse.nz/wp-content/uploads/2018/07/ThermInstructions.pdf

 

I'll draw it and have a play.

 

 

[Iceverge]

1. Basic spec.

 

 

2. Add Lower cavity insulation.

 

3. Add second aerated block

 

 

4. Add 50mm PIR to the foundation 

 

 

5. Add more insulation lower in cavity

 

 

6. Add third aerated block