Concrete Lego blocks and BC

[K78]

On 17/01/2020 at 08:41, Jeremy Harris said:

 

 

 

How would you deal with the big thermal bridge at the base of the blocks. though?

 

You could probably design a passive slab, with a reinforced ring beam around the edge, that would take the loading from the blocks.  That would then give you insulation under the floor slab, under the blocks and up around the edge ready to be continued with EWI up the walls, so no thermal bridging at all.  If you fitted UFH inside the concrete slab then you would effectively be warming/cooling the slab and the walls, like a giant storage heater/cooler.

 

I was thinking of using a similar approach to what I was going to use for a cavity build.

Your idea Is much better but I worry about the design costs. I’ve wasted so much money with SE’s and anything slightly unusual usually costs a fortune. 
 

I have emailed Olof at AFT to see what he thinks. 

 

Edited January 18, 2020 by K78

[Jeremy Harris]

Worth giving Hilliard Tanner a call, too.  He's been designing passive slabs for a decade or so now, and probably knows more about them than a lot of SEs.  He wrote this report for Kore, which is probably worth a read:  Kore Insulated Foundations Report.pdf

[Declan52]

If on your founds you build a few courses of thermal type blocks this could form your break and reduce the thermal bridge. Will also help you get it perfectly level.  You will obviously need to check the blocks are rated to a high enough N to withstand the weight that will be above. 

[CC45]

34 minutes ago, Jeremy Harris said:

Worth giving Hilliard Tanner a call, too.  He's been designing passive slabs for a decade or so now, and probably knows more about them than a lot of SEs.  He wrote this report for Kore, which is probably worth a read:  Kore Insulated Foundations Report.pdf

Hi Jeremy,

 

that report seems to be unavailable....

 

Interesting topic.

[Jeremy Harris]

39 minutes ago, CC45 said:

Hi Jeremy,

 

that report seems to be unavailable....

 

Interesting topic.

 

 

I've just fired up a laptop and it seems to download and open OK.  If you're having problems downloading it, and would like to see it, I can probably find another way to get it to you.

[Simplysimon]

downloads and opens in acrobat

[K78]

4 hours ago, Jeremy Harris said:

Worth giving Hilliard Tanner a call, too.  He's been designing passive slabs for a decade or so now, and probably knows more about them than a lot of SEs.  He wrote this report for Kore, which is probably worth a read:  Kore Insulated Foundations Report.pdf

 
Thanks Jeremy.
 

I’m also going to contact Jamie at insulhub. He’s a good guy and seemed confident his product was well priced. I didn’t discuss in detail as it was a ICF block course. 

[Stones]

14 hours ago, K78 said:

I was thinking of using a similar approach to what I was going to use for a cavity build.

Your idea Is much better but I worry about the design costs. I’ve wasted so much money with SE’s and anything slightly unusual usually costs a fortune. 
 

I have emailed Olof at AFT to see what he thinks. 

 

 

I think this is a very interesting idea, and given your proximity to the supplier (and the potential to negotiate a deal as they want to promote the product for housebuilding), worth serious consideration.  Personally, I wouldn't be too worried by the thermal bridge issue of using strip foundations.  Our house, (155sqm footprint) is built from ICF (280mm block, 150mm concrete core), the blocks sitting directly on the strip foundation without thermal break.  The slab is cast onto insulation but is (in contrast to the detail above) thermally broken from the ICF wall, i.e. it 'floats'. Cost wise we heat to 21C 24/7 and we spend £200 a year on heating, which given our rather exposed location, is IMHO, a pretty good result. 

 

Something to think about if you go down this route: the cost of fixings and labour to fit insulation and timber strapping.  ICF blocks generally have the benefit of plastic ties holding the two sides of insulation together to form the block, but they also perform another critical function - standardised fixing points into which fixings can be secured without having to drill hundreds if not thousands of holes into the concrete itself. You are going to have to mechanically fit a good depth of EWI, I assume some IWI, and then strap the walls inside to create a service void before you fit plasterboard.  That's a lot fixings and a lot of drilling, time and money.  Critical I think that you factor this in.  If you have a look at my blog there is some info and pictures on some of the fixings used in our build.

[PeterW]

In addition to what @Stones said - look at buying a very good SDS drill as you will need it..!! Concrete blocks like these will have some interesting grades of aggregate and you may need to get something such as a Bosch GBH SDS or similar as a normal SDS drill will just bounce off. Concrete screws would be useful but I don’t think you will get them to hold properly in this sort of material so you may have to drill and plug every hole for battens. 

[Jeremy Harris]

Just fixing some expanded mesh to the outside with big head Hilti nails would be a pretty quick and easy way to provide a secure attachment for EWI adhesive.  Hilti nails will drive into pretty much anything, just a matter of selecting the right ones for the type of concrete.  It would be easy enough to just use Hiltis to fix internal battens for an internal service void, too.

[scottishjohn]

heres your thinset mortar --in a can

 

Edited January 20, 2020 by scottishjohn

[K78]

7 hours ago, scottishjohn said:

heres your thinset mortar --in a can

 

That’s great although, I imagine that would not cheap.

[K78]

What would be the formula for calculating the u value of a 300mm wide block?

 

is it as simple as u value of a 100mm block x 3?

[Jeremy Harris]

14 minutes ago, K78 said:

What would be the formula for calculating the u value of a 300mm wide block?

 

is it as simple as u value of a 100mm block x 3?

 

The simple way is to use the λ value for the material plus the thickness, making allowance for the surface factors.  You can use this simple U value calculator, but it doesn't account for thermal bridging, geometric thermal bridging, or edge losses: Simple U value calculator.xls

[K78]

On 19/01/2020 at 09:44, Stones said:

 

I think this is a very interesting idea, and given your proximity to the supplier (and the potential to negotiate a deal as they want to promote the product for housebuilding), worth serious consideration.  Personally, I wouldn't be too worried by the thermal bridge issue of using strip foundations.  Our house, (155sqm footprint) is built from ICF (280mm block, 150mm concrete core), the blocks sitting directly on the strip foundation without thermal break.  The slab is cast onto insulation but is (in contrast to the detail above) thermally broken from the ICF wall, i.e. it 'floats'. Cost wise we heat to 21C 24/7 and we spend £200 a year on heating, which given our rather exposed location, is IMHO, a pretty good result. 

 

Something to think about if you go down this route: the cost of fixings and labour to fit insulation and timber strapping.  ICF blocks generally have the benefit of plastic ties holding the two sides of insulation together to form the block, but they also perform another critical function - standardised fixing points into which fixings can be secured without having to drill hundreds if not thousands of holes into the concrete itself. You are going to have to mechanically fit a good depth of EWI, I assume some IWI, and then strap the walls inside to create a service void before you fit plasterboard.  That's a lot fixings and a lot of drilling, time and money.  Critical I think that you factor this in.  If you have a look at my blog there is some info and pictures on some of the fixings used in our build.

I have just done a sketch of the wall build up I was thinking of using if I go with strip foundations. 
 

All the EWI and cladding would be DIY with skilled assistance. I think @Jeremy Harris suggestion of hilti nailing is the best option. 

[CC45]

On ‎18‎/‎01‎/‎2020 at 20:12, Jeremy Harris said:

 

 

I've just fired up a laptop and it seems to download and open OK.  If you're having problems downloading it, and would like to see it, I can probably find another way to get it to you.

I will give it another go now ....

[CC45]

3 minutes ago, CC45 said:

I will give it another go now ....

sorted - thanks Jeremy.

[K78]

On 20/01/2020 at 19:47, Jeremy Harris said:

 

The simple way is to use the λ value for the material plus the thickness, making allowance for the surface factors.  You can use this simple U value calculator, but it doesn't account for thermal bridging, geometric thermal bridging, or edge losses: Simple U value calculator.xls

So the uvalue of the 300mm block would be 1.5? (1.2 + 0.3)

 

Table is great resource. Thanks. 

[Jeremy Harris]

6 minutes ago, K78 said:

So the uvalue of the 300mm block would be 1.5? (1.2 + 0.3)

 

Table is great resource. Thanks. 

 

For just the concrete blocks on their own, as a single layer, with no insulation inside or out, then use the single layer option, enter the wall thickness (0.3m and the thermal conductivity (λ) for concrete (1.2 W/m.K), and this gives the basic U value for that layer, with normal internal/external surface thermal resistance values, of 2.38 W/m².K

 

For a two layer wall, use the next option down, for two layers.  If, say, the wall was 300mm of concrete, clad with 200mm of EPS as EWI, then the total U value would be 0.172 W/m².K

 

If PIR was used as EWI, then the same wall structure, but with 200mm of PIR as EWI, would give a total U value of 0.105 W/m².K

 

You could drop the EWI thickness down to 150mm with PIR as the EWI and still get a U value of 0.138 W/m².K, which is probably fine, especially as the U value will be improved slightly by having in internal service void, layer of plasterboard etc.

[Jeremy Harris]

Just done a quick and dirty run for the following build up:

 

12mm plasterboard

50mm service void

300mm concrete block

150mm PIR EWI

 

These are the results:

 

 

 

[K78]

3 hours ago, Jeremy Harris said:

Just done a quick and dirty run for the following build up:

 

12mm plasterboard

50mm service void

300mm concrete block

150mm PIR EWI

 

These are the results:

 

 

 

Thanks for that Jeremy. 
 

This is useful but a little dated. No PIR option. https://www.vesma.com/tutorial/uvalue01/uvalue01.htm

[Jeremy Harris]

7 hours ago, K78 said:

Thanks for that Jeremy. 
 

This is useful but a little dated. No PIR option. https://www.vesma.com/tutorial/uvalue01/uvalue01.htm

 

 

Use isocyanurate, as that's what PIR is.  There's no option for entering a service void, but a quick run on that with three layers, plasterboard, 300mm concrete and 150mm of isocyanurate gives a total U value of 0.13 W/m².K, so same ballpark.  The thermal resistance of concrete varies a fair bit with density (from about 0.6 W/m.K to about 1.8 W/m.K), and the value I chose (1.2 W/m.K) is around the middle of the range.  Using another value from the typical range of concrete thermal resistance would change things slightly.