ICF How much more expensive ?

[BotusBuild]

On 03/03/2025 at 08:41, Russell griffiths said:

the only reason I see the need for reinforcement of a basic straight short wall would be if it was holding back a load, like a semi basement, or any roof load pushing outwards onto it. 

What we had to do for ground floor because it was going to be a retaining wall part way round (horizontal and vertical). But the SE insisted on extending the horizontal rebar through the top floor as well

[Nick Laslett]

5 hours ago, Iceverge said:

Are those metal webs the same as the ones @Jenki has?

No, not really. Polysteel Block
 

 

Thermohouse block

 

 

The Thermohouse block flanges/webs are 40mm wide, spaced at 150mm centres.

[Iceverge]

Are those flanges strong enough to take a reasonable load like a big TV?

[Nickfromwales]

5 hours ago, Iceverge said:

Are those flanges strong enough to take a reasonable load like a big TV?

Easily! You can also rebate the insulation to fit plywood across multiples of them if you were looking to affix between or away from the flanges (where the fixing holes simply don't line up for eg). Exp foam behind the plywood and then fix that to the flanges, leave to cure for 24hrs, then crack on with plaster boarding. Much more flexibility if you make the plywood patch a lot bigger, so when the rooms finished and you think the TV's too high / low etc you have room to manoeuvre  

[Nick Laslett]

5 hours ago, Iceverge said:

Are those flanges strong enough to take a reasonable load like a big TV?

 

I'm not sure. They don't have any technical specs for the flanges. For internal finishing, you can either batten to the flanges, then fit plasterboard, or glue and screw the plasterboard directly to the blocks. When I finish the build, I might test the holding strength of the flange, but I would have thought it can hold 15kg on a single screw. The Fischer EPS fixings I use have a 10kg rating and they are just held in the eps.

 

 

 

 

Edited March 4 by Nick Laslett

[Nickfromwales]

16 minutes ago, Nickfromwales said:

Easily!

Obvs should have caveated by saying don’t hang an 80” TV off one fixing lol. 
 

200mm concrete screw for anything crazy. Happy days. 

[Nick Laslett]

I've watched a fews of these Youtube testing videos, and it is surprisingly how much weight plasterboard can take. (Obviously there are many different specs of plasterboard.)

 

This one tests a number of different fixings.

 

https://youtu.be/nfGG1Z5m-5A?si=tu70HP6OMuasUncK

 

DIYGuy Table

 

 

Gosforth Handyman has a load of testing videos, and he compared the Fisher Duo fixing in plasterboard and got good results, 27.8kg

 

Just as a point of reference the Samsung 98” Neo QLED 4K QN90D TV weighs 61.4kg. The Samsung 65” OLED S95D 4K TV weighs 18.9kg. TVs are just not that heavy these days. My old 60" Pioneer Kuro Plasma weighed 55.5kg.

Edited March 4 by Nick Laslett

[Chanmenie]

With my Beco blocks the inner insulation is only 55mm so for heavy stuff like radiators, TV and the doors I cut the insulation and bolted  4x2 timber to the concrete core, that gave a good base for fixing stuff 😀

 

this was for the TV Bracket, I took photos so I could remember where they were after I’d plasterboarded over them 

 

[SteamyTea]

With any fixing, it is not just static loads you need to consider.

Jerk is important.

[Iceverge]

1 hour ago, Nickfromwales said:

Obvs should have caveated by saying don’t hang an 80” TV off one fixing lol. 
 

200mm concrete screw for anything crazy. Happy days. 

 

 

BUT

 

I'M

 

LAZY..........

[Nickfromwales]

1 hour ago, Iceverge said:

 

 

BUT

 

I'M

 

LAZY..........

God dam-nit. 
 

Have you been speaking to my wife?

[ToughButterCup]

15 hours ago, SteamyTea said:

....

Jerk is important.

 

Oh how many times did that have to happen before someone enlightened me about shock-load? Hundreds.

 

From hand-held hammer drivers to dumping heavy objects on shelves, or being catapulted out of a mini-digger seat, or tapping a 'locked' nut, or opening a tight jam jar.

[ChrisJ]

How we get away without rebar throughout amazes me actually

 

Understanding what the rebar does would make you question - does the engineer understand it

 

The theory of we don't use it in block walls why would we put it in concrete walls then - is like comparing an engine on a 1992 Ford Escort and a 2025 BMW X5 

 

Concrete shrinks as it cures, the larger the concrete mass the more its pulling on itself and more chance of cracking. now granted its within the ICF form, the perfect cure environment as moisture is trapped, a typical concrete test is done at 28 days to ensure design strength has been achieved, in ICF I have had it fail many times at 28 days as the cure is so slow based on moisture being trapped, however at 56 days not only met the design strength but exceeded by 50% or more

 

Back to the rebar, the horizontal bar is to help with cracking, that's it, nothing more, nothing less, I'm referring to the horizontal in the main open part of the walls, above lintels is different. vertical rebar deals with loading, not just wind or backfill loads, but also point loads from above. how we set a steel beam into a pocket of the wall without vertical bar directly below amazes me as well

 

Does no one question why we do slabs and have mass amounts of rebar cages throughout and then the walls above have no rebar?

 

 

This post is to make you think and question nothing more

 

Edited March 27 by ChrisJ

[Nick Laslett]

Also on my build the vertical rebar connects the ground floor walls to the slab, then the first floor walls to the ground floor walls. 
 

[saveasteading]

3 hours ago, ChrisJ said:

why we do slabs and have mass amounts of rebar cages

We don't though.

Not on ground bearing slabs where crack control suffices.

 

[ChrisJ]

1 hour ago, saveasteading said:

We don't though.

Not on ground bearing slabs where crack control suffices.

 

Sure we do, rebar on the perimeter where the structure sits and then typically mesh across the top of everything

 

[ChrisJ]

1 hour ago, Nick Laslett said:

Also on my build the vertical rebar connects the ground floor walls to the slab, then the first floor walls to the ground floor walls. 
 

 

 

 

 

Is that DPM on top of the concrete slab separating the wall concrete from the slab, or placed prior to the slab concrete and just run over the top edge of the KORE?

 

 

Edited March 27 by ChrisJ

[Nick Laslett]

2 hours ago, ChrisJ said:

 

 

Is that DPM on top of the concrete slab separating the wall concrete from the slab, or placed prior to the slab concrete and just run over the top edge of the KORE?

 

 

Same spot on foundation pour day. 
 

 

You can see the DPM is still overhanging in this photo. According to my drawings you would put a second DPM strip under the ICF blocks before you start the wall. 
 

Not sure how necessary that is with ICF walls. Here is a close up.

 

 

Before the concrete. 
 

Edited March 27 by Nick Laslett

[Chanmenie]

5 minutes ago, Nick Laslett said:

Same spot on foundation pour day. 
 

 

You can see the DPM is still overhanging in this photo. According to my drawings you would put a second DPM strip under the ICF blocks before you start the wall. 
 

Not sure how necessary that is with ICF walls. 

I think it’s normal to just lay the ICF blocks on the overhanging DPM, why add another one ? 

[Nick Laslett]

19 minutes ago, Chanmenie said:

I think it’s normal to just lay the ICF blocks on the overhanging DPM, why add another one ? 

I agree, I don’t think it is critical. Here is the generic Kore construction detail, see the small green line for DPC under ICF block. 

 

 

[SteamyTea]

7 hours ago, ChrisJ said:

This post is to make you think and question nothing more

Does rebar help with catastrophic failure? i.e. holds chunks of concrete together.

 

When carbon fibre composites were first used as structural elements in vehicles, Kevlar was also put into the weave. Kevlar yield point was 'further up the scale' than CFs. 

Going back a bit further, when Kevlar was first used in composites, glass fibre was include.

There were times that a very flexible weave called Diolen was used to hold all the bits together when failures happened.

We had lots of failures when we first used more advanced composites back in the 1970 and early 1980s. Thankfully the knowledge base is huge now, back then there were only about 3 UK based companies doing it, and we're did not discuss our failures with each other.

[Chanmenie]

1 hour ago, Nick Laslett said:

I agree, I don’t think it is critical. Here is the generic Kore construction detail, see the small green line for DPC under ICF block. 

 

 

So how are you supposed to fold the DPC up into the ICF block ? Surely when you pour the concrete it’ll push it down. Seems overkill, especially with an EPS raft 

[Nick Laslett]

40 minutes ago, Chanmenie said:

So how are you supposed to fold the DPC up into the ICF block ? Surely when you pour the concrete it’ll push it down. Seems overkill, especially with an EPS raft 

I don’t know, made no sense to me. 

 

Here is my construction detail from Tanner, the DPS under the ICF is a little different. The MBC crew did my foundation, you can see from my photos what they did. 

This is Jeremy Harris construction detail, he had an MBC foundation and timber frame. You can see that the DPC is consistent with my photos. 

 

I’m not trying to confuse or mislead with my posts about DPC placement. Building controls seem to be very touchy about this requirement. Please seek professional advice, don’t take my posts as advice. 
 

@ChrisJ, sorry if I have made things more confusing. 

[Gus Potter]

On 02/03/2025 at 22:31, JohnMo said:

My rebar was limited to lintels at doorways and window plus vertically at doorways and a wind post rebar midway along back and end walls. So not much at all.

Much will depend on wall panel sizes and your attitude to shrinkage.

 

On 03/03/2025 at 08:41, Russell griffiths said:

my structural engineer said to me that you wouldn’t put re bar in a block built wall, so why is it needed in a concrete one with less joins. 

I suspect he maybe qualifed that statement. A masonry wall is more forgiving.. that is why we make the mortar weaker than the masonry units.

 

I'm assuming many here making comment are using ICF above ground and not using it to keep ground water out.

On 02/03/2025 at 22:31, JohnMo said:

My rebar was limited to lintels at doorways and window plus vertically at doorways and a wind post rebar midway along back and end walls. So not much at all.

Fair enough if your wall panels have a good aspect ratio and are not too large, it needs a lot of careful thought.

 

One of the biggies is not just what it looks like on paper / calcs but how you are going to execute the pours on site. Get this in the wrong order and your SE will not save your bacon!

 

To put this another way. If you ask me for the leanest design.. I'll maybe be able to give you that.. but then I'll say here is what you need to do on site and in this order. Your Contractor will say.. hey I'm going to have to make extra visits. The reality is that folk on BH will cut corners and think the can have their cake and eat it.. you can until something goes wrong and then you are STUFFED!

 

If you fail to follow my instructions then you are on you own. Ask me about the best and balanced risk way of building something and I'll support you to the hilt.. even if you get into a barny with your contractor.

 

Personally I'm ok with ICF. It's a concrete wall with permenant shuttering that is insulating. The shutters need tied together with insulating ties. The shuttering needs bracing more than traditional ply shuttering. If below ground we need to do some waterproofing detail.

 

Edited March 27 by Gus Potter

[ChrisJ]

@Nick Laslett Your drawing makes sense to me, couldn't tell from your photo 

 

I don't agree with the DPM between the top of the slab and the wall, may as well just slather some butter on there as the bond will be the same

 

@SteamyTea Yes rebar can help during catastrophic failure, I've seen it and allows time to safely secure and repair rather then no notice and someone die