6 months on

It’s been 6 months since we’ve moved in. This period is way too short to write any definitive feedback, but nonetheless we’d like to share our findings so far.

To set the scene, we used to rent an uninsulated stone cottage over the other side of the hill for the past ten years. We loved the rural location and the quality of life, however we always dreaded the winter time. We used to spend about £1500 every winter on keeping the cottage warm(ish). The old oil boiler would break down regularly, leaving us with no hot water and struggling to keep the place comfortable. Naturally, we had big expectations for the new home.

We moved in last July. One of the early observations was the stable internal temperature of around 21°C, irrespective of what was going on outside. There was a spell of hot weather later in July with external temperatures reaching high 20s/ low 30s. In our previous cottage this would lead to overheating. We used to open the windows just to get a sense of air movement, but ultimately the internal temperatures would be uncomfortably high.

In the new house with the large roof overhang and some external blinds we managed to maintain the internal temperature below 23 degrees even during the hottest periods. The thermal mass of the concrete slab undoubtedly helped. Counterintuitively, we learned not to open windows during the highest outside temperatures, which makes sense if you really think about it. Bringing the warm air in doesn’t help to keep the house cool! At this point it is worth busting the old myth that you can’t open windows in a passivhaus – you absolutely can, and should. But think about the knock-on effects.

It’s all very well that the house is comfy in summer but what about when it gets cold out there? How are we going to cope with no radiators? Well, we needn’t have worried. As the season was turning colder, we were getting more and more ‘free’ solar gain from the lower sun, effectively balancing out slightly increased heat losses through the building fabric. It wasn’t until one evening in November when we lit the small wood stove for the first time. On average, we now light the stove for an hour or so every other evening, sometimes less often. As long as the sun is shining, the house maintains the temperature beautifully. It’s during the prolonged periods of overcast weather when we put the fire on more often. Having no radiators means the furthest parts of the house (bedrooms) do get a degree or two colder, but this works really well.

It’s worth mentioning the MVHR system does not have the capacity to even out the internal temperatures perfectly. It will constantly supply fresh air and extract used air, but there’s no active heating (or cooling) in the system to have a significant effect on internal temperatures. We have been monitoring the temperatures, humidity and CO2 and will share the data in summer 2018.

But it’s the other qualities of the house that we appreciate the most: the combination of open plan living and more intimate spaces, the sun rays shimmering on the soft clay plaster, the acoustics, the ability to accommodate big parties of friends, the luxury of being able to sit next to the large glazed window without feeling uncomfortable, the magnificent sunrises, the raindrops falling from the crinkly tin roof. We just love watching the world go by, whatever the weather.

6 months on

Summer comfort

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With the recent heat wave in UK, it’s been interesting to experience internal comfort in our house. Although we haven’t fully moved in yet, we’ve been spending considerable time inside doing various finishing tasks. Over the last few days the external daytime temperatures have been gradually rising, peaking at a scorching 30 degrees C today. Night time external temperatures have also been going up, last night levelling at 17.5 degrees C. This pattern is likely to carry on over the next few days.

We’re really impressed with how our house has been coping with the hot weather. Internal temperatures have been fairly steady, gradually rising from 18.5 to 21.5 degrees C. We’ve been keeping the windows & doors shut and the ventilation unit on. The MVHR unit has a built-in automatic summer bypass, which kicks in at 21 degrees C. We can contribute the comfortable internal temperatures to a number of design features:

  1. exposed concrete slab with its high thermal mass acting as a giant temperature regulator (warning: this can work both ways!)
  2. 1.5m roof overhang along the south verandah means no direct sun hits the big glass = zero unwanted heat gains
  3. external roller blinds to main bedroom (south facing), and two windows to east & west gables
  4. high levels of insulation & airtightness in walls & roof (thermos flask effect in reverse)
  5. fully vented facades & roofing. It is worth noting the facades and roofing are black colour, but the vented cavities help isolate the hot surfaces from the thermal envelope, slowing the heat flux down

We don’t have the hot water system installed yet and have not been cooking/ living in the house, so internal heat gains have been minimal (bar the dehumidifier which we’ve temporarily turned off). We’ll keep an eye on the temperatures & relative humidity and will start proper monitoring once we get connected to broadband. The initial impressions are very positive though and we can’t wait to move in!

Summer comfort