Earth Floor (2 of 2)

humblebee hive - retrofit #11

The best laid floor plans...

A slight health warning here: this post is a bit long and "knotty" compared with my previous, more free-flowing posts, but I just wanted you to see the not so insta-perfect side, and so it may read like it's been hastily thrown together.

Challenges

Moving out of the ground floor was an operation in itself… we’d had the piano professionally removed and stored, paying a weekly charge, but the rest we either donated, stored in the garage or upstairs in everyone’s bedrooms and M's home "office" - it was chocka. Some of the “stuff” we’d thrown up there didn’t make its way down (or out on its ear) until this summer, so it was obvious that many items accumulated over the years were surplus to requirements – forced decluttering, now that’s a win! And proud to have kept the ground floor relatively junk-free since.

The team gutted the kitchen, and had taken the downstairs WC out which we haven’t yet reinstated - not great on our part as we only have one bathroom for the four of us! But when we moved back, one of the first things I needed to have operational was the washing machine, and I was adamant it wasn’t going back in the kitchen: it’s one of my pet hates, and taking it out allowed me to plan more effective kitchen storage, but it also meant the WC didn't fit anymore.

So the downstairs closet is now a mini utility room. We're looking at having one of those space and water saver combined WC and handwash basins, as soon as I can afford and find a plumber who’s happy to do small jobs. Anyone…?

Surprise!

Opening up the floor will always have a few surprises in store, as anyone in construction will tell you, like finding a concrete lump under the fireplace stone (now waiting to be made into a garden bench). When we lifted out the back door threshold, we realised the cavity wall insulation there hadn’t made its way into the section below the door…

Luckily the Retrofit Hub Team are never short of problem solving ideas. What does one do? Buy an old beanbag off Gumtree (second-hand buy and sell platform) for something like a fiver and empty its contents (polystyrene beads) into the cavity, what else. It did make me wonder if there were other areas below floor level that were missed, which wouldn't necessarily have shown up on thermal imaging...

It was also at this point we needed a plan for the services. Radiators were stripped out and redundant pipework was removed. We thought about sleeving the cabling from the consumer unit and the Solar PV, but there wasn't enough slack so they ended up safely buried. As the electrics were only a couple of years old, we didn't envisage any changes anytime soon, so that was fine.

Moving onto the next layer... because of the compaction of the foamglas aggregate, and some areas of deeper subfloor, the material volume was initially underestimated – don’t forget to use Tŷ-Mawr’s calculator form, for example – which led to the first programme hiccup with a few days' wait, and at £120/m3 it’s not a cheap material.

The job entailed lots of wheelbarrow loads of everything being carted around the site, which you would need to consider - the team had thought about this and constructed a ramp that wrapped around the house. And I've seen conveyor belts used on other projects, which is a shout if access is difficult.

The laying and compacting of the MOT Type 1, which had stones that were too large to flatten properly, also proved problematic, and a finer layer of granite had to be bought in to smooth the top layer out for the clay/sand mix to be applied.

Because of a misunderstanding we also ended up with a pile of cork insulation that wasn’t needed in the end. Very crumbly stuff, and not much use to us when we’ve already the insulated the life out of our home! Although C – who I recruited to fit the kitchen – got creative with a few pieces of it and insulated the pipework riser in the kitchen, with some left over cladding cedar over the top. The rest has been used for L's garden room, if I remember correctly.

Another thing that seemed to cause consternation was that I didn’t want any skirting boards. They are often used to cover up bad workmanship, they gather dust and grime, and I can think of more interesting or fun things to do with my time than go round wiping them down. And because R and I had discussed a parge coat of plaster connecting the wall finish to the ground level from an airtightness point of view, I thought we had it covered.

Unfortunately, with staggered summer holidays, the message hadn’t apparently got through to the installation team and we were left with a finished floor, but at the base of the walls it was a mess quite frankly.

Sequencing the remedial work was then a challenge. Because the earth floor has texture, and is finished with a wax, any flecks of anything would likely get embedded into the dimples, and painstaking to remove. Therefore any further plasterwork and painting needed doing before final waxing, and the floor had to be protected. We also needed to move back in as soon as the floor was oiled, as the school term had started and our generously free accommodation was coming to an end…

So we spent a bit of extra cash to get thin underlay boards – we were hoovering green fibres for months afterwards – topped with taped down OSB boards. (The OSB has since been put to use in the Retrofit Hub’s new training facility; the green fibreboards are piled up taking space in our garage, which I'm hoping we can use them as underlay for any marmoleum/cork/seagrass finishes we'll come to use for the upstairs floors).

Finishing Touches

We’d already partly moved back before the final wax and polish. Eventually the walls were finished down to the floor level with lime plaster - yay, no skirting boards, neat. You know we like to reference what was in the original building so the mini fireplace “alcove” was also plastered, a cute spot for a plant or a candle, or both, with a nod to its previous use.

And we loved reusing the old 90's kitchen tiles in the thresholds, set in a charcoal grey mortar - well done B. The demolition team had salvaged most of these duck-egg blue, green and turquoise squares, and at 15cm thick, they were sturdy enough to be used in this way. Over a few weekends we managed to repaint most of the ground floor walls and ceilings, including my office which really needed a lift.

Again some minor communication failure meant that Jamie (Jeffrey’s right hand man op North) arrived to wax and buff thinking he’d have a clear run, but we’d already started living in the space and with M away most of the week, I hadn’t been able to remove the heavy boards by myself so he needed more time than planned to complete the job.

We’d also had to get the piano back or it would have been weeks of paying out for storage. But my, it isn’t half heavy: even putting the floor protectors under the castors was tough (“just” lifting the ends one at a time), but moving it from the living room into the kitchen and back again without damaging the floor required Herculean strength - J might have been small in build, but he was mighty strong. A return visit was therefore also needed to get a second coat on with time to dry in between.

We started getting the kitchen cabinets built too so under there hasn’t been waxed.

Finally though, the walls were finished to the floor and we were able to move on and, as posted last time, we couldn’t be happier with the result, all our furniture safely padded, and strictly a no stiletto zone. In fact, "shoes off" is generally preferred. ;-)

Building Control

Would you be surprised to learn that the Building Control officer did not understand what we were doing. After we’d submitted the details, product information and U-value calculations they’d asked for, in typical we’re-too-stretched-to-deal-with-this manner, we got a letter saying we had to revert to the original construction or replace it with a DPM and concrete slab! More sleepless nights ensued…

They requested structural loading calculations, Part A 1(1)a): it helped that M was a structural engineer in a previous life so our note stated that the floor only supports itself and people load, that the limiting factor in our case was the ground itself, which has been supporting the house and these loads in a much more concentrated area around the perimeter, and that foamglas is used to support far bigger buildings than our little box, in the order of 50 x our domestic loads. With calculations to support it all.

Detail by Richard Shears at The Retrofit Hub

And then our detail didn’t quite match the approved LABC Geocell one due to the cavity wall, so they queried the damp proofing. My conversation with the BCO about Part C ([…] resistance to contaminants and moisture in buildings) quite literally ended with them saying “I’m going to have to read through the regulation and get back to you.” Needless to say we haven’t heard back. And the “enforcement” period has lapsed. Although it would be good to have sign off at some point…

Because our solution relies on vapour permeability to allow moisture that materialises in the fabric from its various sources (rain and snow, ground, people, cooking and washing, saturated outside air) it goes against the grain for “traditional” building people. And because there is an existing DPC in the cavity wall, we do have a bit of a hybrid situation.

Shout out here to Janna Laan Lomas, Marianne Heaslip and Gervase Mangwana for their input into what we needed to think about.

Ultimately, moisture in buildings is a weighing up of risk factors: in our case, flood risk is classed as very low (and radon is <1%), we have the French drain and external insulation plinth protecting the outer brickwork, the existing footings and DPC in the cavity, and, crucially, a dry subfloor to start with. Also the MVHR guarantees moisture is removed from internal spaces and keeps the air dryer than in most properties.

I would strongly advise putting some thought into it beforehand, especially putting it into context of your own risk factors and drawing up the detail.

Power consumption

The subfloor was so wet it took more than a week to dry out enough for the earth team to start, and plenty of fan power was required for the final lay, even in the warmer weather conditions (it was July/August after all). Our neighbours admitted to us a few weeks later that the house was literally humming overnight while the fans were running... humblebee HQ living up to its name!

And as you can see from the SolarEdge graph below, the blowers mainly, together with charging equipment for laying and drying out the floor (and possibly also an electric van) caused quite a spike in electrical consumption (!): more than a megawatt was used up that month alone, about 30% of our 2023 consumption.

So Flo... what about energy and comfort?

Well yes, fair question, the raison d’être of the earthfloor was to improve both the insulation and the airtightness of our floor, the last remaining heat loss element of our cosy box.

On the airtightness front, it’s definitely an improvement on the ventilated floor. But in terms of getting to EnerPHit – or even AECB Carbonlite levels – the jury’s still out as (because of the parge coat issue, and a bit of shrinkage at the perimeter). We haven’t completely sorted all the finishes so we’ve noticed a bit of leakage along the French door threshold for example.

We’re due an airtightness test before we embark on the final phase of this energy retrofit – the  advanced airtightness works to mainly the first floor ceiling – so I’ll certainly report back on this.

Insulation-wise the U-value has been improved from 1.25 W/m2K to 0.174 W/m2K, which using BR 443(2019) for ground floors is effectively going from 0.68 W/m2K for a ventilated floor to 0.09 W/m2K for a solid floor on ground.  It also has thermal mass which greatly helps with stabilizing temperatures.

Because the whole retrofit was going to make a significant difference, I only had two electric panel radiators installed downstairs for a total of 1kW. We still had a couple of radiators off the boiler upstairs.

I’m not gonna lie… I was disappointed at first as it ddidn't seem we'd achieved much higher comfort levels, and I was shocked at how much electrical energy we were using over the (bitterly cold and gloomy) winter, needing to borrow some portable electric rads from yet another set of lovely friends.  (It's frightening to see on the app, when you're not used to seeing your gas consumption in technicolour).

So much so, I contacted a heat pump installer to quote to install a heat pump and radiators instead, as well as the hot water tank… and then I went back to the calcs and, to be fair, the numbers roughly stacked up.

When the installer came round to assess, they saw what we’d done to the house and told me not to be so daft… ha! Their take: you’ve just had a wet construction laid – which will have been drying out all winter, increasing the heating load – and you’ve got your heat recovery*, so keep it simple. In new builds, they see heating bills go down from one year to the next for a good 2-3 years. Conclusion: trust your initial plan!

*So, funny story, in the meantime I’d been emailing back and forth with Airflow Developments about my unit (somehow I could never get to someone technical on the phone) because I was confused about the lack of temperature uplift. At first I’d put this down to the inefficiency of having the unit in the cold loft.

But when the temperature dropped below 3 oC outside – that’s when the post heater kicks in - we seemed to have astounding performance and the supply temperature shot up. And it was clearly heat recovery, not just the electric heater, because not only was the supply temperature close to indoor temperature, the exhaust air temperature was close to outdoor temperature. At one point I even wondered if the post heater was in fact a run-around coil!

I had another look at the controller's “expert” settings though, and I noticed there were two bypass settings… so I went to the manual… yep, you guessed it, we missed out on two years of heat recovery because of a flipping bypass control setting. Honestly, this is how systems the world-over fail: you can have intelligent professionals, competent installers, experienced commissioning agents, and things don’t work as they should because of a simple oversight or omission or miscommunication. Aaagh!

The upshot is, that we should be in for a better experience this winter… So, again, I’ll get back to you in 12 months' time!

This is an super long post so I’ll spare you the kitchen details for now, and wrap it all up in the next one, when we talk about our new smart hot water tank and finally get off gas. Whoop Whoop!

But here are the sub and earth floor costs.

Costs

Demolition and subfloor

£21,583.46, of which material costs £9,652.21

Earthfloor finish

£8,734.50

Total Floor: £30,317.96

Total Retrofit to date: £98,885.56 (£898.96/m2)

(Beanbag, cheap)

(Sweat and tears, some, not all mine)

(Gratitude gifts to friends: definitely not enough)

Target U-value: 0.174 W/m2K (effective U-value, slab on ground, 0.09 W/m2K)