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Who knew clay was so heavy?

Nelliekins

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Before I carry on, let's answer the question I posed in the last blog entry. I posted this picture of the basement rear wall, showing how we had joined the cross wall to the side wall (following the suggestion of the boss of Logix UK, who had attended site whilst the walls were being assembled (and even assembled some of them himself) as part of our on-site training:

 

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The problem here is that this wall is supposed to form part of the watertight barrier of the basement. The concrete had to be continuous. But of course, with this design it wasn't continuous - we only had pockets of concrete, 5" deep, every 16" up the wall. Structurally, it was more than up to the job. From a watertightness perspective, it was about as useful as a chocolate teapot.

 

But we didn't even think about this until much, much later. About 6 months after the concrete pour for the basement walls, in fact. By which time, remedial action became very complicated and very expensive.

 

Let's return to the blog timeline...

 

So, basement walls were constructed in about 8 elapsed days, which amounted to 5.5 days on-site. I was suitably impressed. 2 faces of steel rebar was set into the external walls, at 200mm centres vertically and horizontally. This was at the behest of our waterproofing specialist, who had overruled the SE. From a structural perspective, the SE had calculated that a single face of H12 rebar at 200mm centres was more than adequate to reinforce our 10" thick concrete walls and withhold the ground pressure. Our waterproofing guy said "the more steel the better, because it'll control the cracking better". So, with the steel not actually being that expensive, we ordered double the steel, and put 2 faces in.

 

Thank goodness we did. Remember the bank at the back that was propped on 4 acrows? They were rated at 1 tonne each. 3 days before the concrete pour, they failed overnight. A shelf of clay, weighing perhaps 6 tonnes, forced one of the acrows to deflect enough to destabilise the lot, and the shelf gave way, slid down the back of the excavation, and smashed into the polystyrene wall.

 

Unbelievably, the wall, supported by the ICF bracing system, held. Here's a photo of the damage:

 

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The bracing upright was bent to the tune of 10 degrees or so, and most of the studs that interlock the ICF blocks had sheared off. But because of that 2nd face of steel rebar, the wall resisted the impact, and the subsequent dead weight, of the clay against it. It took 2 hours and a few extra steel supports, but we managed to force the blocks back together, and brace it up sufficiently that it would take the concrete pour.

 

And a 3 days later, that's what we did. The concrete pour was moderately uneventful, as these things go.

 

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Apart from the pump getting blocked, because a piece of hardened concrete had made it into the mix in the batching plant, and then completely blocked the 3" reducer we were using:

 

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It took nearly an hour to dismantle the pump, knock that lump of concrete out, and reassemble the pump. The concrete firm said they'd have to charge us for the concrete wagon sitting outside doing nothing. I replied that was fine, but they were picking up the tab for the pump since they'd blocked it. They said for me not to worry, and apologised for any delays they had caused...

 

Oh, and one more problem - where the T-walls had been made, I hadn't braced the outside of the side walls sufficiently (or at all, truth be told!). This led to some substantial bulging of the side wall in a couple of places, which I had to shore up as a bit of an emergency 😟 The concrete was poured, and the walls started to harden pretty much as soon as it was poured. Here's the bulging:

 

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Ahem. Nothing to see here, move along. 😭

 

At least the shoring / bracing held.



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Can I ask a question about insulation?

 

What sort of U value are you achieving with that basement wall?  To me it looks mostly concrete with perhaps 50mm EPS inside and out. Or are the walls of the ICF blocks a lot thicker than that?

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I must admit I have thought the same, as the ICF EPS is only 70mm, thick, I believe, which is pretty marginal, even in terms of meeting building regs, I think.  A quick estimate, based on 300m thick concrete and two 70mm layers of EPS, seems to suggest the U value of the walls may only be around 0.22 W/m².K, not sure what the floor make up is.  I believe basement walls are treated as floors as far as the regs are concerned (not sure about this, I've not checked the most recent regs), so it looks like this build up may just meet the regs, which aren't exactly demanding in terms of thermal performance, plus I believe that just meeting the limiting fabric standards may well not meet the required TFEE/TER. 

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@Nelliekins  finding your blog very interesting (as another ICF builder). You've referenced on site training from the supplying ICF company. Can you quantify time wise how much training they provided, and can you give an indication of after support - could you pick up a phone and get help / advice etc?

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5 hours ago, ProDave said:

Can I ask a question about insulation?

 

What sort of U value are you achieving with that basement wall?  To me it looks mostly concrete with perhaps 50mm EPS inside and out. Or are the walls of the ICF blocks a lot thicker than that?

 

The walls are 70mm EPS on both faces. We are getting an effective 0.16/0.17 as the U value, thanks to the fact that we are underground, and have further layers that are added to the wall buildup (mainly due to the leak and subsequent remedial action). The concrete is 254mm thick, which makes the EPS) skinnier than it is. 

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5 hours ago, JSHarris said:

I must admit I have thought the same, as the ICF EPS is only 70mm, thick, I believe, which is pretty marginal, even in terms of meeting building regs, I think.  A quick estimate, based on 300m thick concrete and two 70mm layers of EPS, seems to suggest the U value of the walls may only be around 0.22 W/m².K, not sure what the floor make up is.  I believe basement walls are treated as floors as far as the regs are concerned (not sure about this, I've not checked the most recent regs), so it looks like this build up may just meet the regs, which aren't exactly demanding in terms of thermal performance, plus I believe that just meeting the limiting fabric standards may well not meet the required TFEE/TER. 

 

The earth sheltering and the moderate soil temp allow us quite an improvement over above ground walls. What would be 0.23 for above ground ends up at 0.17 for us (the increased depth over a regular basement helped here - the slab is 3.7m below ground level, so we would end up with 9' ceilings to improve the sense of space) 

 

Building control have already inspected that and signed off on our EPC side of things (although we haven't discharged it as a planning constraint yet...) 

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42 minutes ago, Stones said:

@Nelliekins  finding your blog very interesting (as another ICF builder). You've referenced on site training from the supplying ICF company. Can you quantify time wise how much training they provided, and can you give an indication of after support - could you pick up a phone and get help / advice etc?

 

Cheers for the nice comments 🙂

 

We had a total of 3 full days (8am-4pm) provided by logix UK. I am sure if I picked up the phone as a customer they would offer help if they could, although things between us and Logix UK went a little sour for a while... 

 

On a related matter, I can recommend another company much more wholeheartedly with regard to support and assistance. Perhaps a PM is a better way to provide that information, or do the mods not mind if I recommend companies here? I have no affiliation with them, in case it matters... 

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2 minutes ago, Nelliekins said:

 

The earth sheltering and the moderate soil temp allow us quite an improvement over above ground walls. What would be 0.23 for above ground ends up at 0.17 for us (the increased depth over a regular basement helped here - the slab is 3.7m below ground level, so we would end up with 9' ceilings to improve the sense of space) 

 

Building control have already inspected that and signed off on our EPC side of things (although we haven't discharged it as a planning constraint yet...) 

 

 

Why does the fabric U value change just because it's a basement?  All that changes is the temperature differential, with the ground being around 8 or 9 deg C or thereabouts all year around, so there is heat loss all year around too. 

 

A quick and dirty calc gives a U value of around 0.22 W/m².K.  If the room temperature in the basement is maintained at 20 deg C, and with a ground temperature of 9 deg C, that means the basement loses around 2.42 W/m² of wall area 365 days a year.  Not sure how much insulation you have under the floor, so I can't work out the floor heat loss per unit area.

 

We have 300mm of EPS under the floor, with a 200mm wide upstand around the edges of our slab, which is contiguous with the 300mm of insulation in the walls.  Our floor U value is 0.0975 W/m².K, and, because we have UFH, we still lose about 8.5% of the heating energy we put in down through the floor, rather than into the rooms.

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1 hour ago, JSHarris said:

Why does the fabric U value change just because it's a basement?  All that changes is the temperature differential, with the ground being around 8 or 9 deg C or thereabouts all year around, so there is heat loss all year around too

 

It doesn't, but an offset is applied by Building Control because of the ground temp. It equates to approx 0.06 improvement from memory. 

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As this is part of the SAP/EPC undertaken by an assessor, I'm not sure how, or why, building control can make any notional adjustment like this.  We have at least one assessor on here, who may be able to shed some light on this, but my experience was that building control required me to produce both a design EPC and get the as-built EPC lodged on the database; they had no involvement at all in ensuring compliance with Part L1a apart from getting the paperwork and checking that what was built matched the drawings and spec, although even then they didn't inspect the insulation level.

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5 hours ago, JSHarris said:

As this is part of the SAP/EPC undertaken by an assessor, I'm not sure how, or why, building control can make any notional adjustment like this.  We have at least one assessor on here, who may be able to shed some light on this, but my experience was that building control required me to produce both a design EPC and get the as-built EPC lodged on the database; they had no involvement at all in ensuring compliance with Part L1a apart from getting the paperwork and checking that what was built matched the drawings and spec, although even then they didn't inspect the insulation level.

 

There is apparently a different method to calculating the U value for basement walls when the basement (in particular the floor) is heated. The reference I found pointed me to BS EN ISO 13370 and also NHBC Approved Document Basements 

for Dwellings.

 

There is also an allowance made in the calculations for the insulative properties of the backfill and surrounding earth, both of which vary according to depth apparently. 

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Depends very much on the properties of the surrounding soil, though.  Some soils, like any very dry soil, are not very good thermal conductors, others, like any wet soil, usually are.  In general any wet soil will be a reasonably good thermal conductor (as borne out from experience with ground source heat pump collector loops), and anyway, there's no form of soil type adjustment allowable when calculating floor U values, AFAIK.  The assumption is that the ground temperature remains fairly constant, something that seems to be borne out by measurement.  We are on solid clay, and the ground temperature under our slab stays at a pretty constant 8 deg C all year around, not varying by more than about half a degree, if that.

 

The U value of the fabric is the U value of the fabric, and doesn't change just because of a change in the temperature on either side.  If the temperature differential changes then the heat loss rate for a given U value changes.  It would seem reasonable to use floor limiting and notional fabric U values from Part L1a for a basement wall, as the conditions are near-identical.  There's also the point that meeting the limiting fabric U values in Part L1a may well not result in an acceptable TFEE/TER.  That's one reason why there are also a set of notional fabric U values in Part L1a, to give a guide as to the sort of values that may be needed in order to get an acceptable TFEE/TER.

 

The actual values are:

Limiting fabric U values:

Wall = 0.30 W/m².K
Floor = 0.25 W/m².K
Roof = 0.20 W/m².K
Windows = 2.00 W/m².K


Notional fabric U values:

External walls = 0.18 W/m².K
Floor = 0.13 W/m².K
Roof = 0.13 W/m².K
Windows, roof windows, glazed rooflights and glazed doors = 1.4 W/m².K
Opaque doors = 1.0 W/m².K
Semi-glazed doors = 1.2 W/m².K

 

From the above I'd say that the target to just pass building regs requirements for a basement wall and floor should, perhaps, be the notional fabric U value for a floor, so around 0.13 W/m².K.  Having said that, most basements will be very airtight, so there is a margin to trade off the reduced ventilation heat loss against the fabric U value, in terms of meeting the TFEE/TER for the whole dwelling.

 

 

 

 

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Calculation of heat losses into he ground is covered in BS EN 13370 and covers normal ground floors (solid & suspended) and basement floors and walls.

 

Very simply for solid ground floors the U-value is dependent upon the P/A ratio and the the thickness/type of of insulation. With basement floors the depth of the the basement is also taken into account. In basement walls the heat loss is dependent upon the wall construction (including insulation), the depth of the basement but is is also linked to the basement floor P/A and insulation type & thickness. In solid floors/basement there is a correction factor for the ground type with an assumed conductivity of 1.5 W/mK for clay or silt, 2 W/mK for sand (these normally make little difference to the U-value), rising to 3.5 W/mK for rock (which can make a big difference to U-values).

 

At face value the above wall U-value (0.16) with 2 x 70mm EPS look to be of the right order of magnitude.

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