Velox ICF external finish - bricks or slips... and tanking membrane details...

[AJPorter]

Hi folks,

 

I'm on a very protracted self build journey...

 

The main detail I'm struggling to satisfactorily resolve is thus...

 

Bricks or slips...

 

The building is partly below ground, built into the slope and the basement perimeter freely drains to the front corner... see attached 3D image for context... behind the car in the picture is a secret personnel door into the basement (it appears like black cladding under the single ground floor window - might be clearer on the architectural elevations)... regarding the basement classification I would prefer if it met the criteria for habitable space - ie dry and heated - whilst in reality remaining a workshop / hobby / storage space... nothing worse than putting a bike away in a cellar only to find a few months later its completely rusted (lived experience in an old farmhouse).

 

So... the conundrum... 

 

The tanking membrane needs to wrap around the outside of the Velox ICF below ground and terminates 150mm above the finished ground level. I know this is frequently a source of detailing headaches for ICF builds with basements... render needs to finish above the ground to prevent wicking... likewise brick slips... so whatever, there will be a tiny gap where the brickwork appears to float... something I'm not a fan of! You will see on the ATAL drawing that this remains a little open to interpretation - it simply states to 'render / cover the tanking membrane to prevent UV degradation' but that still doesn't seem to account for that little gap between the bottom of the render and the finished ground level...

 

Anyway... my preferred method is most definitely proper (full thickness) facing brickwork... this requires a foundation obviously... some other ICF systems suggest a cast in situ corbel on which to start that external brick wall but I think this poses a significant thermal bridge (and an unnecessarily complicated waterproofing / membrane wrapping detail)... the Velox detail I've attached shows the facing brick/block wall starting from a toe on the edge of the slab... this is fine (especially as its really only the North gable - the opposite end of the building to that shown in the picture) that will be affected - the 'long' sides will just be timber cladding sailing over the exposed tanking membrane in reality (as is correctly depicted on the architectural drawings)... the south gable is mostly above grade anyway - its only the corners that are affected (and besides the corners are mostly concealed by either steps on the South East corner and the retaining / landscaping wall on South West corner)... so, the point raised by ATAL is that wall ties pose a significant penetrative challenge to the tanking membrane - I have no intention of piercing the tanking membrane with anything... my point being why would wall ties even be necessary below grade (I've put this to the structural engineers too) - there are none mentioned on the Velox detail drawing and I would think that that wall is not subject to any unopposed outward force... the other question (since the change to basement regs in 2022) is how that build up would be classified / regarded by the regs... it is stated that sandwiched type A waterproofing is no longer recommended but it would seem that 'reverse external' type A water proofing is still acceptable - I think that pertains more to how the tanking membrane is reflected around the outside of the foundation rather than the position of the membrane within the wall buildup... and I would consider the detail shown by Velox to represent 'reverse external' type rather than sandwiched... Looking forward to the opinions of the group... 

 

 

d4.pdf ATAL5304-002A-Top of wall detail.pdf MOD - 141 - 03 Proposed Floor Plans.pdf MOD - 141 - 04 Proposed Elevations.pdf

[oldkettle]

These are questions I would love to know answers for, especially the two about covering the membrane around the gap and regs. Hopefully, someone will reply at some point. 

[liammcl]

I'm detailing my own ICF build now with a very similar problem regarding walkout basement, tanking and stone outer leaf.

 

Our basement is a walkout with the ground sloping down either side. Same as you, I didn't want to use a brick ledge as they're a nightmare to execute well so increasing the foundation width to take block/stone all the way up.

 

I've attached what I've drawn up so far. The guys at Newton are very helpful,  they're happy for the tanking to come through the outer leaf like I've drawn although it needs a protective layer before mortar bed and bricks/stone.

 

Also using Type B to some extent (waterproof concrete & injectable water-bar) + Type C internally.

 

Note: I am by no means an architect of any sort(I detail steel framed buildings) but have been involved with building & civils for long enough to have an decent understanding.

 

 

 

 

basement drg extract.pdf

Edited September 26 by liammcl
missing info

[Nickfromwales]

Why would anyone choose a woodcrete ICF systems when ANY part of the structure is below ground?

I have ‘experienced’ both Isotex and Velox, and compared to an EPS system they would have to come with free supply and fit for me to entertain ever using them. Sorry.

 

Make a better choice and reap the benefits, is my 2 cents.