How do I build this bit?

[willbish]

I need to work out how I am going to build the balustrade wall for my roof terrace.

 

It needs to have a rendered finish and look like a continuation of the house wall.

 

The easiest way would be to continue the ICF wall up and cap with a coping stone. However this would create a significant thermal bridge, the idea is to keep the concrete core of the ICF warm.

 

Now I could add additional insulation to what would have been the internal leaf of the ICF, and use a fillet of insulation on top of the core, this would be thermally acceptable (just!) I then would have a balustrade wall approx 560mm deep and this causes issues where the external stairs/bin store meets the balustrade wall. The stairs/bin store is a separate structure outside of the thermal envelope.

 

What I am wondering/asking, is there anyway I can build a 140mm block wall 1.1m high on top of my ICF EPS insulation?

My architect proposed laying a block on its belly for the first course (to increase the area) and then continue up normally. This creates an unsightly looking step and potential trip hazard.

 

Anyone have any alternative suggestions?

 

Some drawings & pictures, wall in question in yellow. The terrace will be a warm roof, GRP with pavers on pedestals.

 

 

[Mr Punter]

How does the render work with the ICF?  You could do the top bit in timber frame with an aluminium coping.

[PeterW]

Am I the only one not seeing the thermal bridge here..?? 

 

Bring the ICF up with a thinner inner, insert a timber wall plate in the top of the ICF to cap the concrete core flush with the last course. Secure this with anchors and then cap with a nice aluminum flashing. 

 

The bridge would be your core but tbh by the time you’ve come up through and insulated roof space, you will be at a negligable bridge point. 

[PeterW]

And lose the ridiculous hopper through the wall ..!!! Make the “flat roof” slope towards a natural exit, and then you’re not penetrating a decent wall and creating a potential damp issue. 

 

If  you want some advice on this - ask @jack

[Onoff]

Didn't @Barney12 do a hidden hopper on a flat roof in fibreglass that worked a treat?

[PeterW]

12 minutes ago, Onoff said:

Didn't @Barney12 do a hidden hopper on a flat roof in fibreglass that worked a treat?

 

It was from a flat roof into a gulley - this is through a parapet which is very different. Not difficult to design out this sort of stuff either ......

[Barney12]

2 hours ago, PeterW said:

And lose the ridiculous hopper through the wall ..!!! Make the “flat roof” slope towards a natural exit, and then you’re not penetrating a decent wall and creating a potential damp issue. 

 

If  you want some advice on this - ask @jack

 

Im not sur there is a natural exit looking st the drawing? The only exit point appears to be a set of steps and I wouldn’t want that as my exit point, well unless you’re trying to create a water feature!! 

[scottishjohn]

If you check out integraspec ICF they do end sections for window +door holes so you get complete insulating wrap,no wood  -- sono cold bridge anywhere --so maybe use something like that +dpc and then coping stone ?

[willbish]

Thanks for the feedback

 

12 hours ago, PeterW said:

Am I the only one not seeing the thermal bridge here..??

My intention was to find a solution where the balustrade wall could be built on top of the insulation. Either, the insulation of top of the roof terrace joists would extend on top of the concrete core and meet the outer ICF EPC or an EPC fillet placed onto the concrete core

 

12 hours ago, PeterW said:

Bring the ICF up with a thinner inner, insert a timber wall plate in the top of the ICF to cap the concrete core flush with the last course. Secure this with anchors and then cap with a nice aluminum flashing. 

That's a consideration, the core could be reduced from 158mm to 102mm.

 

12 hours ago, PeterW said:

And lose the ridiculous hopper through the wall ..!!! Make the “flat roof” slope towards a natural exit, and then you’re not penetrating a decent wall and creating a potential damp issue. 

Yeah, good point. As @Barney12 says no obvious exit for the water. What i could do is drain down into the bin store where there is a foul connection.

Drain indicated in red

 

 

[PeterW]

That would be preferable if nothing below as going through walls always causes problems. 

[Barney12]

I'd be tempted to put a roof drain of some sort in. If using fibreglass (which in my view is a very good option) then something like this:

 

https://www.roofinglines.co.uk/product/grp-rainwater-outlet-50mm?gclid=EAIaIQobChMI6qj_ntrO3gIVh9OyCh003QOgEAQYBSABEgIoi_D_BwE

 

You can get them with stainless grates or cowls.

 

EDIT:

 

You need to think carefully about the drain position and run off of the roof section.

 

IMO putting it in that corner where your bin store is would be 'less good' as your fall is still going to be towards the stairs. Equally any fall towards the house (and doors) is going to be bad. I hate to say it but where your gully is currently sat is probably the optimal position.

 

The wall around the stairs is also a real potential water trap even with the drain in its planned position.

Edited November 12, 2018 by Barney12

[PeterW]

Sloping it to the stairs at a day 1:40 GRP to give you a gully at the end would work and then just use slabs / porcelain on stands to level it and make it look good ..?? Could give a decent wash stop before the steps but hidden by the slabs ..? Thoughts..?

[willbish]

Remember the finish will be pavers on pedestals. Im hoping to have the pavers on pedestals level with the top step of the stairs. Therefore no water should be able to run off the terrace and down the stairs because there will be a GRP up-stand along the 'threshold' from terrace to stairs. So I could do a fall as pictured with drain as linked by @Barney12

 

Or perhaps instead of the original gully through the wall, it would be better to incorporate a drain near to the original gully. This could be sleeved through the ICF and link up to original downpipe.

[Barney12]

1 hour ago, willbish said:

Or perhaps instead of the original gully through the wall, it would be better to incorporate a drain near to the original gully. This could be sleeved through the ICF and link up to original downpipe.

 

That would be my preferred choice as you've got a downpipe anyway. Just make sure is roddable (is that a word?).

[willbish]

37 minutes ago, Barney12 said:

 

That would be my preferred choice as you've got a downpipe anyway. Just make sure is roddable (is that a word?).

Definitely a word in my dictionary.

Yes it would be preferable to send the rain water down that way rather than to a foul drain.

 

So back to the wall..

I'd like to build out of 140mm concrete blocks, bearing on the outer leaf of the ICF EPS (203mm deep).

The wall would be tied both ends and spans ~2.9m. 1.1m high.

 

Is this possible? Would it be liable to drop?

 

How about a section of RHS between the insulation and block work. There'd be nothing solid for the RHS to bear on but it could stop any sag

[Mr Punter]

Make sure that in the event of a blocked outlet the water will flow down the stairs, not through the doors.

[willbish]

32 minutes ago, Mr Punter said:

Make sure that in the event of a blocked outlet the water will flow down the stairs, not through the doors.

For sure. Door threshold 150mm above pavers.

[PeterW]

3 hours ago, willbish said:

like to build out of 140mm concrete blocks, bearing on the outer leaf of the ICF EPS (203mm deep).

 

You can’t do this as there is nothing tying the concrete core below to the wall above - there could be close on to a tonne of blocks up there and the EPS would give way. 

[willbish]

How's about 140mm block set back so it's above the concrete core? (with a 200mm EPS fillet between core and block)

 

I'd have to add additional EPS to the outside face of the block to have a flush finish for rendering with the rest of the house. A sort of pointless EWI!

 

[PeterW]

I’d just stick with the ICF and be done with it tbh as everything else will be a faff. Your core losses will be tiny compared to the windows. 

[willbish]

The ICF will also be faff, because I'll have to match the depth of the blocks used to build the bin store wall to the ICF.

 

Or put up with an odd return at the top of the stairs

 

[willbish]

Have now found a workable solution to this fiddler.

 

I will use a different grade of ICF and rip the inner leaf of EPS off.

A fillet on top of the lower warm core will minimise thermal losses. The ICF supplier recommend every 600mm leaving a 100mm gap in this fillet to take the weight and horizontal rebar to distribute the weight

 

Thanks to the crowd for your input.