Don’t play with radon!

Our house, built into a slope and on a rock seam, also lies within a medium-high radon risk area, according to PHE/UKradon. A while back, I applied to UKradon for a home testing kit, which comprised three dosimeters: one for each floor. When the results came back in from the laboratory, some of my fears were confirmed. Ideally, levels should be below 100 (Bq/m³), but not exceed 200.

Our results were as follows:

  • Bedroom (top floor): 37
  • Living Room (ground floor): 85
  • Kitchen/diner: 290!

I suspected the source to be ground radon. The kitchen/diner and extension is built on a new slab with a gas-proof barrier (see earlier post). But, the undercroft beneath the original house simply has a concrete slurry cap (nominal 4in thick) poured on top of the subsoil – I believe the radon is permeating through this cap. The section below has been highlighted to show the suspected radon source (red):

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Indoor Air Quality: VOCs

This first article on the topic of IAQ reports on the results from enhanced monitoring and air sampling, which took place during the winter (2015/16) to evaluate the levels of volatile organic compound (VOCs) pollutants inside the home, and the potential increase of these pollutants when the ventilation rate was reduced.

The chart shows the results of samples taken from the main bedroom and living room over two 7-day periods. The first set of samples were taken with the MVHR ventilation running continuously (i.e. as normal) delivering 220 m³/hour (approximately 0.5 air changes). The second set of samples were taken with the ventilation set to unoccupied mode, which delivers 140 m³/hour for 15 minutes in every hour (less than 0.1 air changes) – show as ‘ventilation off’ on the chart. Activities and occupancy were similar, and there was a two-week interval between the samples being taken.

According to the performance criteria in Approved Document F, exposure to TVOCs should not exceed 300 μg/m³ averaged over an 8-hour period. It is clearly evident that, whilst the ventilation is running normally, both the living room and main bedroom fall well within this threshold value, measuring 80 and 90 μg/m³ respectively, averaged over the 7-days. However, the repeat measurement with the reduced ventilation rate shows and increase to 340 and 370 μg/m³ receptively for these rooms – an increase of around 75%. The ventilation rate was reduced at the beginning of the sampling, so the observed concentration would likely be higher still if the sampling commenced at a later point.

Whilst TVOCs do not give an indication of the ‘toxicity’ of the air, analysis of the chromatograms identified chemicals, which included: 2-chloropropane – a chemical used as a blowing agent in some phenolic insulants; α-pinene and 3-carene – naturally occurring, derived from oils in woods, but still can cause skin irritation at higher concentrations; texanol – a solvent used in paints. In the lower ventilation (2nd) sample the same chemicals were observed, but at higher concentrations.

This experiment demonstrates the importance in the use of purpose-provided ventilation. Without ventilation, and within an airtight property, the concentration levels of pollutants inside seem set to rise – who knows how high these concentrations would have risen to if the experiment continued for longer than 7 days.

More IAQ stuff to come.

featured in passivehouse+ magazine


We are pleased to be featured in this month’s passivehouse+ magazine. The article has given me a bit of a jab in the arm to do further updates on this blog. So upcoming themes will include:

  • Indoor Air Quality – we have recently monitored the home (winter 2015/16) for a range of pollutants: VOCs; formaldehyde, nitrogen dioxide and radon.
  • Water use – have we managed to reduce our water use as well as our energy use?
  • Energy use – comparison of the last three heating seasons, and further interventions made to further optimise our gas and electricity use

Check back soon for these updates.

a good morning for more thermal imaging

Front 2 Jan 2015

Perfect conditions this morning for some more thermal images. The house is still performing well, and as these images show, there is quite a contrasting heat loss between us and neighbouring properties (which have cavity wall insulation). The temperatures across the front elevation show good uniformity, and the triple-glazed windows are approximately the same temperature at centre pane point (spot temperatures on image below: Sp1 = minus 6.5°C and Sp2 = minus 6.2°C). As highlighted in the the posting for last year’s survey, there is some thermal bridging around the top of the windows, but budget restrictions meant that we didn’t invest in the best thermal performers. Still quite pleased with with their overall performance.

Front 1 Jan 2015

It’s not all good news however. Around the back, some problems are coming to light (in the IR spectrum). This is where the first lot of external wall insulation was applied, and it looks like we have some thermal bypass – possibly air gaps beneath the first insulation layer.

Temperatures on the spots below are: Sp1 = minus 5.0°C, Sp2 = minus 2.1°C, Sp3 – minus 2.8°CRear Flank Wall

Temperatures on the spots below are: Sp1 = minus 5.0°C, Sp2 = minus 3.4°C, Sp3 – minus 2.0°C, Sp4 = minus 2.7°C, Sp5 = minus 5.0°CRear Flank Wall Low

There’s not a lot we can do about this, unless a problem arises in the future. The internal scan showed good uniformity, and checks with a moisture meter do not suggest anything sinister. Not sure why this didn’t show up on last years survey – perhaps some de-lamination has occurred over the last year? It was the wettest point, I recall, so may be the adhesive has de-bonded – this is why mechanical fixings are also required. I will, at some point, do in-situ U-value measurements. If I apply heat flux plates around here then I can compare with a ‘good’ section and see what the difference is. When I know more, I’ll post. As always, I welcome comments.

we are now a SuperHome

front completed

After demonstrating that our retrofit has achieved 69% carbon emission reduction, compared to its pre-retrofit state, we are very pleased to announce that our home has been accepted onto the SuperHomes network. The 69% reduction, which is based upon calculation, compares very well with our measured reduction of 71%, both in carbon emission terms (kgCO2/m²/yr) and primary energy (kWh/m²/yr). This reduction  has been achieved even though the treated floor area of the house has increased by more than 20%.

Read more on our listing page on the SuperHomes website. You may also be interested to read our entry on the Low Energy Buildings Platform, which gives more technical information.

monitoring data: winter comfort

I have taken a closer look at the monthly data for temperature, relative humidity and CO2 concentrations. The previous post considered mean monthly values, whereas the charts in this posting give the hourly averages during February 2014. In addition to the mean value, I have also charted the 10th and 90th percentile values to illustrate the ‘bandwidth’ for the observed conditions.

Feb T_RH_CO2

This chart shows the mean hourly conditions in the bedroom in February. The temperature (blue) has a mean of 18.2ºC, with a very small mean deviation of +/-0.6ºC between 10th and 90th percentile. This constant temperature means the comfort conditions are excellent – no more waking up feeling cold in the middle of the night.

Relative humidity is also near optimal with a mean of 52% (should ideally be between 40 and 60%). Again, there is a small mean deviation of +/-3%, indicating that the ventilation in the bedroom is sufficient for managing metabolic moisture levels. Note, that the ‘blip’ that occurs at around 0900hrs (and on temperature) is when the sun passes over the sensor.

The CO2 levels show that the bedroom is in use typically from 11pm through to 7am. The mean values for daytime are from 7am through to 7pm and show that the mean CO2 concentration is 737ppm. During the night (7pm to 7am) the mean is 995ppm. The 24hr mean is 865ppm and is within guideline values of 800-1000ppm (mean) and 1500ppm peak. The 90th percentile shows a peak of approximately 1500ppm at around 3am. This may be the cause for some debate amongst my contemporaries, but I don’t believe that a 1500ppm peak in a bedroom is a problem. Many bedrooms concentrations that I have seen elsewhere peak well above 2500ppm. At 5000ppm, CO2 concentrations are likely to lead to drowsiness, but the longer-term risk is that other, more toxic, pollutants will also increase. But, in reality, I am not too bothered if the 1500ppm peak CO2 makes me drowsier at 3am. I would add that, since the ventilation system has been commissioned (and fine tuned), the conditions in the bedroom in the morning are ‘fresh’. Before the renovation, and particularly in winter when the windows were closed, it was notably ‘stuffy’ and stale in the mornings. Not any more.

Feb T_RH_CO2 Lounge

Feb T_RH_CO2 Kitchen

The kitchen and living room charts are posted here too. They too show the performance is doing well. But, for brevity, I won’t go into too much detail with these charts – they tell their own story in a way. But briefly, the living room shows a slightly warmer temperature, compared to the bedroom and kitchen. This is due, in part, to the occasional use of the wood burner. The 90th percentile indicates the wood burner benefit from 8pm onward. CO2 levels in the kitchen show when we are preparing meals for breakfast, lunch and dinner, with concentration levels peaking at around 1400ppm.

Do drop me a line if you have queries. I plan to post more on comfort conditions through the year, so keep checking back.

first monitoring results: comfort

I have now analysed the comfort data for the winter. The monitoring started in November 2013, although some data was collected in October. The chart below shows the mean temperatures, relative humidity and carbon dioxide concentrations for the three rooms being monitored. I have only posted the charts for the first part of the winter here (I am analysing in quarters Nov-Jan; Feb-April; etc).T_RH_CO2 Nov2013_Jan14

The mean temperatures for November to January show a fairly even distribution across the house. The living room has a slightly warmer mean, probably due to the occasional use of the wood burner. Our thermostats for the heating are set at 18°C on each floor – this being our preferred temperature, not an attempt to be frugal.

Relative humidity (RH) was a bit of a problem, causing some localised mould growth for the first few months after completion. I have attributed this to the drying out of the wet construction and finishes (mortar, plaster, etc), and because the house was becoming increasingly airtight with late commissioning of the ventilation system (switch on mid-September 2013). The mean RH should be between 40 and 60%, and the monitoring shows a steady decrease from November through to January. It is slightly higher in the kitchen, due to cooking activities. The RH has continued to drop in February and March (check back later for an update). The initial problem with mould has now disappeared.

To maintain good indoor air quality, CO2 concentrations should average between 800 to 1000ppm. By keeping below or within this band, other (more serious) pollutants, such as VOCs, are kept within safe levels. The measured CO2 levels are higher in the bedroom, as this is where we spend more time than any other room (that is being monitored). I have carried out some fine tuning to the ventilation in February and the average has dropped to below 1000ppm. However, I feel that reporting monthly averages for CO2 concentrations is not particularly representative, and therefore useful. CO2 concentration levels are only of interest when rooms are occupied. So, I will provide further analysis on CO2 in future posts, but what this overview shows is that we have no real concerns about indoor air quality.

fabric performance – thermography

front LHS2 IR

The fist thermal images of the finished house were taken very early in the morning at the end of January. The results are very encouraging and show, as expected, that the insulation measures are working well, and that we have significantly reduced the amount of thermal bridges, particularly for the concrete gutters. The image above shows our house in the foreground with our neighbours’ houses beyond. The temperatures of the outside of our house are the same as unheated surroundings: vehicles, plants, etc. Compared to neighbouring houses, not only are the surfaces cooler (less heat escaping), but the temperatures are more uniform, showing good insulation continuity.

front LHS IR

The image above was taken further up the street, with our house now in the background. Our neighbour’s house in the foreground has the same thermal properties as our house did when we moved in, i.e. no cavity wall insulation. The difference is quite striking between our properties.

rear IR

From the rear, the house appears to be performing well too. The wall insulation is continuous and the thermal bridging relating to the concrete gutters (as shown in an earlier post) have been eliminated. There is a small amount of thermal bridging around the new window frames, but this is expected given that we opted for less expensive windows that do not have thermal breaks in the core of the frame.

rear neighbour IR

By contrast, our neighbour’s house is losing more heat, as shown in the image above. The thermal bridges from the concrete gutters and the single leaf masonry panel beneath the windows are quite evident.

wemico trays

We have introduced some bridges that we hadn’t thought about. Ironically, it is from the steel trays that carry the external wall insulation panels that are conducting heat. These are fixed to the masonry (warm side of the insulation) and some of this heat is clearly coming through. Perhaps plastic trays would have been better. In the grand scheme of things, this is relatively minor stuff.

green roof installation

Finished sedum roof

There has been a bit of a pause in the postings to this blog, mostly because we are busy decorating, which is a little boring to do, let alone write about. One thing that we have had done lately is the sedum roof over the extension and the porch.

The sedum layer has been laid by the original single-ply roofing installer, who now specialises in sedum and wild flower roofs. Before the sedum is laid, a geotextile membrane is laid on top of the water proof layer of the roof and the sedum drainage layer is placed on top as shown in the photo below. The drainage layer is made from recycled plastic and also contains a network of cups to store water and keep the sedum happy during dry weather. The organic substrate is applied on top of the drainage layer and the sedum is rolled out across this.

Drainage layer Substrate layer

The sedum was installed about three weeks ago now and has taken well (thanks to the break in the dry weather). The addition of the sedum roof should offer a number of benefits, which include: extending the roof life (less exposed to UV); reduce summer overheating in the studio space below; and reduce surface water run-off. Most of all it looks great.