ICF basement and 2 floor rear extension

[Osato]

Have planning permission for a basement and 2 floor rear extension 

[Nickfromwales]

1 hour ago, Osato said:

Have planning permission for a basement and 2 floor rear extension 

Then choosing ICF makes you a wise man, just stay away from woodcrete and defo go for EPS!

 

Can you anonymise your plans and upload them so we can pull them apart comment enthusiastically  

[Thorfun]

1 hour ago, Osato said:

Have planning permission for a basement and 2 floor rear extension 

nice! i lived in Epsom and Ewell most of my life before i had to head south to get more for my money.

 

we have a basement. built it using RC waterproof concrete with an external waterproof membrane and surrounded by and sat on 200mm EPS.

 

I put it up on a blog here if you're interested.

 

Edited January 21 by Thorfun

[mjc55]

On 21/01/2025 at 10:01, Nickfromwales said:

Then choosing ICF makes you a wise man, just stay away from woodcrete and defo go for EPS!

 

Can you anonymise your plans and upload them so we can pull them apart comment enthusiastically  

What are your issues with Woodcrete?

[Nickfromwales]

2 hours ago, mjc55 said:

What are your issues with Woodcrete?

I’ve worked on many EPS ICF builds and only 2 woodcrete ICF builds (1x Velox and 1x Isotex), so I can speak of both from hands on, literally, experience) and have had sufficient ‘contact’ to decide that I’d never use woodcrete over EPS, EVER.

 

Working on these 2 woodcrete jobs was painfully difficult, and eye-wateringly expensive for the clients, eg for us to go to the lengths that were necessary to achieve anything ‘great’ with it. 

 

I’m getting a headache just typing this, remembering back to these jobs! Sorry, it’s just horrible in comparison to an EPS system.
 

If you’re considering doing a basement, or anything sub or semi-subterranean with it, then I’d suggest having you sectioned. It’s porous for starters!

 

Just “no”. 
 

Getting my clients woodcrete projects airtight was just insanely and unnecessarily hard work, compared to the EPS ones, and keeping the weather out was horrendous too. Constantly ‘soggy’ with the Velox one literally having little rivers flowing across the downstairs floors when it rained for a few days or more; took forever to dry out afterwards too.
 

This is far worse on both counts with Isotex, as the blocks have a woodcrete bridge manufactured in to hold the inner and outer leafs together. These bridge both moisture and air, which makes problems you then have to pay again solve / resolve.

 

Velox don’t have these woodcrete bridges, thank feck, but instead you have to install hundreds (or thousands) of metal ‘forks’ (3 or 4 per block iirc) and it is these which hold each leaf of the system in position during construction. Total PITA as these need installing by hand vs being already inbuilt as they are in the majority (all?) of EPS blocks.
 

The builder on the Velox job was top of his game, and this saved the client a lot of time and money, on top of the ‘lot’ he had to charge to do it. Even he abandoned pumping concrete in eventually and went to hand balling buckets into the void; this was he needed to stop boards repeatedly breaking / blowing out during pours. If you asked him to do another Velox build, I’d keep just out of arms reach…. The amount of additional timber work / shoring / shuttering etc that the builders had to do was ‘significant’, adding even more time & cost.
 

Also, with the Velox project, they insisted on overselling the blocks at the point of order (20% iirc) just in case of blowouts or damage (blocks and boards breaking) during the build. This was, as it turns out, due to huge lead times to replace anything on warranty. So they paid in advance for the hypothetical warranty claims / product failures. You’d think if nothing out of the surplus was used you could of course ask for a refund, like these clients did, and they got told…. “nope”. They were then left to either sell it for pennies or pay to dispose of it, I cannot recall which they ended up doing but I got offered it and surmised that it just wasn’t worth the time / transport / storage, as there was a huge volume of it.

During the Velox build, before the pours began, the Velox rep was summoned to site by the builder and was shown the irregularities in the blocks, where there were gaps you could stick your little finger into. He simply said they would send a few cases of FM330 foam to squirt in all the gaps to stop the concrete escaping during the pour. 
 

Drumroll please…..

 

Then they sent the invoice for the foam. WTF 😳. 
 

Both systems needed parging, then repeated coats of a liquid airtightness membrane at corners and junctions where you can’t parge properly, and even then this still didn’t completely negate airflow through the entirety of the wall; the blocks are so porous the parge coats just sink in, shrink back and crack, meaning they were still permeable after all that huge effort! Then more AT membrane got painted on, and on, and on. 
 

The clients using Velox had to parge every single m2 of wall, and the client with the Isotex had to parge and then spray Passive Purple onto every wall and roof etc, the house looked like Barney at the end, and cost a fortune to do. After all that it still had an appalling airtightness score, that’s with me babysitting the builder and the client and then going back over things again in my own time when they’d both left site….  

 

The Velox build eventually returned a score of 0.88 at the first attempt, then I went around fine tuning, then it got 0.66, but the pain, suffering, time, labour, parge & AT products costs endured to get to that score ran well into into 5 figures. Not much change of £20k in total I’d bet.

 

Isotex build costs for same, again change of £20k. AT score of 3ACH for that one!? Completely soul-destroying tbh, and a shame to see good time and money gone to polish a turd of a product. 

So:

Woodcrete ICF is fine if you want to DIY a building regs home, eg particularly airtight etc, etc, but for anything else I’d implore you to use EPS; definitely avoid woodcrete if going anywhere near underground.

 

The end.

 

 

[JohnMo]

Another view

I did a self build with Durisol, never done it before, two of us did a 70m perimeter wall house up to 3.5m, plenty of internal and external corners etc. was very simple, took us 3 to 4 weeks. Total cost was about £7.5k in 2020 at the height of COVID.

 

An internal parge coat was applied over 2 days, joint between floor and wall sealed with liquid air seal.

 

No water leaks anywhere, even had an exposed external wall for a couple months after moving in - not a damp spot anywhere.

[Nickfromwales]

11 minutes ago, JohnMo said:

Another view

I did a self build with Durisol, never done it before, two of us did a 70m perimeter wall house up to 3.5m, plenty of internal and external corners etc. was very simple, took us 3 to 4 weeks. Total cost was about £7.5k in 2020 at the height of COVID.

 

An internal parge coat was applied over 2 days, joint between floor and wall sealed with liquid air seal.

 

No water leaks anywhere, even had an exposed external wall for a couple months after moving in - not a damp spot anywhere.

Yes, thanks, you’ve posted this previously and it’s good to hear. 
 

Odd how converse both my experiences were with woodcrete ICF, but I’ve not ‘done’ a Durisol build.
 

Durisol has the same manufactured-in bridges, so strange how zero rain penetrated. They have more internal

> external bridging than any other WC ICF too. 
 

I visited one in Poole, was passing so went to spec and price the heat pump and MVHR, but was there just in time to see the last of their pour going into a hastily organised skip. Bottom course blew out as they were trowelling off, must have been gutted, but the Durisol block looks to be the most robust tbh, with the 3 bridges per block so maybe DIY error played a part.

 

@JohnMo, did you do much bracing / shoring up? And did you screw each block to the last as you were going along?

 

Just seems, vs EPS ICF, to have a lot of woodcrete in with the concrete, so did you have to put any structural steel reinforcement in also?

[JohnMo]

15 minutes ago, Nickfromwales said:

@JohnMo, did you do much bracing / shoring up? And did you screw each block to the last as you were going along

The rule book said max 6 high then concrete fill to 5.5 block level. Only screws were used to part lengths blocks as belt and brace.

 

Bracing - Corners and all part block joints had 6mm OSB screwed to each block. Basically each sheet of OSB was made into 4 patch panels, 4 panels per corner (2 inside, two outside). That was all the bracing needed. No blow outs.

 

Rebar, above and to side of each opening, long rear wall had a rebar wind post formed midway along. But in general not much rebar.

 

Think the fill concrete was max stone size of 5 or 10mm, quite high strength concrete, but with a huge slump value, bit like cream. You can see the clear water free flow out the bottom blocks after the pour. I think this is what seals the blocks and the holes in the block become quite well sealed with concrete.