Remember that once you have a "very good" detail you can spend a lot of money to get to an "excellent" detail for little benefit. 

 

I would use number 4.  The benefit at the junction to increase to option 6 is only 0.0034 W/mK.  For a freezing day with a house of perimeter of 50m you would only be using an extra 3.4W to heat the house. Even for passivhaus it's off the scale of a small difference. 

 

 

 

Out of interest, here is what would happen if you took a more BREGS approach to the junction and forgot to use Aerated Concrete blocks and put in standard dense blocks everywhere. About a 100w difference in heating the house on a freezing day. 

 

 

 

 

11 hours ago, Rishard said:

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. 

 

inner skin for internal walls, outer skin for doors. They are expensive but so is 4x2 its all relative.

@Iceverge Thanks for doing that, and making it so easy to understand. It's funny how so many people state that if you don't do it a certain way, your bills are going to be through the roof, and the planet will explode. So with using number 4, and actually getting my wife to turn the odd light off, i would be doing just as well as all the Greens ? Obviously, they would still be doing better than me, because they would never leave a light on. Thanks again, great to see it actually worked out. 

1 hour ago, Big Jimbo said:

actually getting my wife to turn the odd light off, i would be doing just as well as all the Greens

Change the bulb to a 3W one.

So if this detail fails SAP then it only leaves marmox blocks right? Does this mean everyone is going to be doing this detail? 

The detailing of the floor/wall junction does not give a SAP 'fail'. Some details will be better than others but this is only one of many (40+) linear thermal bridges that must be accounted for within SAP.

It’s very helpful to see the small increments in improvement and its relative impact on the watts. If I use 60m of insulating blocks for 2 courses it still comes in at under half the cost of the marmox blocks. Would the £600 difference pay itself off in energy saved? If not then I may be happy with using detail 4 and move on to other decisions. 

 

11 hours ago, Rishard said:

So if this detail fails SAP then it only leaves marmox blocks right? Does this mean everyone is going to be doing this detail? 

 

no you dont have to use marmox but not aware of any other products that achieve the same results at same cost. Stricter Regs  new this year so expect more materials to come to market as eveyone has the same issue to overcome.

 

 

On 06/09/2023 at 23:16, Iceverge said:

 

Out of interest, here is what would happen if you took a more BREGS approach to the junction and forgot to use Aerated Concrete blocks and put in standard dense blocks everywhere. About a 100w difference in heating the house on a freezing day. 

 

 

 

 

 

depends on the perimter size really. could be 2kw.

My perimeter is 50m so assume it’s closer to what iceverge suggested. Although I’m not the best at working these things out…. Yet 

So which is it ? 3.4w for 50 meter perimeter, or 2kw ? These can't both be right unless the 2kw represents a house with a perimeter of a mile ?

In my head there also has to be a big difference when using either a floor slab on ground, or a block and beam floor. On a block and beam floor, the "marmox" block would be in a dry zone, ie: DPC under block and beam. However, slab on ground the DPC would be below DPC. So if you are going to use either lightweight block, or marmox, in One situation, the block is going to be in the wet, in the other it's not. Perhaps the super block has less need, or use, if doing block and beam ?

I would assume on that drawing the exposed area is, a block width X perimeter X temperature difference so say 35 (if UFH) less 6.

 

0.1x50x29x0.2568 so 375kW for building regs 

Edited September 8, 20233 yr by JohnMo

Just now, Big Jimbo said:

In my head there also has to be a big difference when using either a floor slab on ground, or a block and beam floor. On a block and beam floor, the "marmox" block would be in a dry zone, ie: DPC under block and beam. However, slab on ground the DPC would be below DPC. So if you are going to use either lightweight block, or marmox, in One situation, the block is going to be in the wet, in the other it's not. Perhaps the super block has less need, or use, if doing block and beam ?

Sorry, slab on ground, the DPC would be above the marmox, and in the wet

1 minute ago, JohnMo said:

I would assume on that drawing the exposed area is, a block width X perimeter X temperature difference so say 35 (if UFH) less 6.

 

0.1x50x29, so 1.45kW for building regs 

So the 3.4w is what. Loss per meter ? And what about block in wet , or dry zone ? would that make a difference ?

On 06/09/2023 at 00:19, Iceverge said:

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

 

 

 

For this one 208w. I used something like this but with a 70mm upstand.

 

Joes detail which is taken from the golcar house has a dpm wrapped around the top block to try avoid it being ‘wet’ as you describe. 

Blinking heck, i'm still confused. (Not hard) So is it, big loss, or little loss ? When looking at everything, which you are when building a house, there is always a question of cost verses benefit. I was reading something last night about full fill cavity. It said that the blockwork outside should not be bucket handle pointed, but packed, and scraped off flush. according to the article, the bucket handle finish losses were considerable. I know we should all be looking at fabric first, but you can get tied in knots if you are that way inclined.

23 minutes ago, JohnMo said:

For this one 208w. I used something like this but with a 70mm upstand.

 

Can i ask. Over what distance ?

23 minutes ago, Big Jimbo said:

Can i ask. Over what distance ?

Not sure how I calculated the previous posts. Must have had a decimal place wrong or something. But also the floor temp would be closer to say 23 at the perimeter not UFH flow temp.

 

So for a building regs detail, with a 50m perimeter. The heat loss is for the total perimeter.

 

0.1 X 50 x 17 x 0.2568 = 22W or 0.5kWh per day.

 

For other detail I referenced

 

0.1 X 50 x 17 x 0.1435 = 12W or 0.3kWh per day.

Edited September 8, 20233 yr by JohnMo

If we assume a floor with perimeter 50m and area 100m2 with a U-value of 0.15 W/m2K. The rate of heat loss associated with the floor and perimeter would be as follows;

 

Floor only = 100 x 0.15 = 15 W/K

 

Perimeter heat loss(using SAP default psi-value) = 50 x 0.32 = 16 W/K

 

Perimeter heat loss(using dense block psi-value, insulated cavity) = 50 x 0.17 = 8.5 W/K

 

Perimeter heat loss(using enhanced psi-value, with aircrete block inner, insulated cavity) = 50 x 0.08 = 4 W/K

 

The exact geometry of the floor/wall junction may change the psi-values but above are the right order of magnitude.

6 hours ago, Dave Jones said:

 

depends on the perimter size really. could be 2kw.

 

Sorry, I was working on a basic assumption of a 50m perimeter and a 20deg delta just to get a feel for the difference. 

5 hours ago, Big Jimbo said:

Blinking heck, i'm still confused. (Not hard) So is it, big loss, or little loss ? When looking at everything, which you are when building a house, there is always a question of cost verses benefit. I was reading something last night about full fill cavity. It said that the blockwork outside should not be bucket handle pointed, but packed, and scraped off flush. according to the article, the bucket handle finish losses were considerable. I know we should all be looking at fabric first, but you can get tied in knots if you are that way inclined.

 

Can I ask have you a design of the floor and wall currently or are you yet to get that far? 

 

What kind of performance are you targeting?

8 hours ago, Big Jimbo said:

Sorry, slab on ground, the DPC would be above the marmox, and in the wet

 

marmox go above the beams not below. and below the dpc. doesnt matter if they get wet they immune to moisture its just UV they need protection from.