It's cold outside...

... but fortunately seems to be ok on the inside even when the temperature drops to -5 on the outside.

Strange but true - at 19 degrees C, the house feels warm (whereas it felt much less comfortable at the same temperature before the insulation and draught-proofing).

The plaster is still drying out and the brickwork is still warming up after a year of exposure to the elements, so the gas boiler is working harder than it will need to next year, all other things being equal.

The 3 tiny radiators are not really enough to keep every room at 19 or 20 degrees C under these circumstances, but we are happy with bedrooms dropping to 17 or 18 degrees C at the coldest point in the night. (It beats the 8-12 degrees C that was the midwinter norm in 2010 and 2011).

The other striking difference for me is the complete absence of joint pain, which was a permanent feature for at least 4 months through previous winters. I had a hunch it was down to cold and damp in the house and I'm really delighted to experience such a spectacular difference this year. (Of course, for those who haven't got an extensive collection of injured joints, it won't make much difference).

The energy bills will also have a story to tell, but I don't have enough measurements yet (and there are further efficiency improvements to make anyway before the house reaches its "as designed" state).

One thing you do have to get used to is condensation or ice on the outside of the windows (because heat loss through the triple glazing is so low that the ice can still be found on the outside of the windows for hours - until the sun melts it off). I'm not complaining - so much nicer than having the ice on the inside as was the case for days on end in winter 2010 and 2011.

Moving in!

Finally, we have moved back in! There is still a fairly long list of things yet to be done (e.g. installing a kitchen) but great progress has been made in the plumbing department since moving in 2 weeks ago.

So what's it like? Thermally, it is fantastic - warm, comfortable, the temperature is stable, no hot and cold spots, no draughts. The thermometer sits around 19-20 degrees all the time. It is a completely different house from the one we moved out of a year ago.

We have 3 tiny radiators, which are currently on to help dry out the plaster, but we've had to turn some of them down or it gets too hot. So it looks as if the heating system is about right for the house. We'll know by the end of the winter if the system is adequate in really cold weather.

Since the MVHR was switched on, air quality has also been very pleasant (much better than having a window or two open, which did not promote air flow in every room).

It is still something of a DIY zone, but we are getting there. Not quite ready to commission the MVHR system and carry out the final air tightness test...

Open house visits in the Nottingham area

This house and other low energy new builds / refurbishments will open their doors to people who are interested during September.

For details, go to http://wbecohouses.co.uk/

Air tightness definitely heading in the right direction!

Now that the attic roof and the extension roof have been "taped and membraned" to the hilt, we've had an air tightness test to see whether we are anywhere near the EnerPHit target of 1 ACH @ 50 Pa.

The average of the de-pressurisation and pressurisation (sucking air out and blowing air in) values came out at 1.078 ACH @ 50 Pa, which is certainly cause for optimism! We are extremely grateful to our merry band of Eco House Group helpers who came along and tracked down draughts during de-pressurisation, or went round with tape and sealant blocking up the draughts identified. While some draughts are easy to spot and solve, it is truly amazing how some draughts can be felt, but no obvious hole or fault in the taping can be seen.

In the days following the test there were some worrying moments when the plasterboard went on as this can stretch or puncture the membrane if it is a little tight in places (almost inevitable in a complex roof structure like this one). However, improvements elsewhere cancelled out any small issues which we could not detect behind the plasterboard, so we are still on track.

As long as the remaining refurbishment work results in a few improvements and no mistakes, we should be able to get below the magic figure of 1. But success is by no means guaranteed so we'll be waiting until the very end to find out if we have made it.

For those more familiar with the other way of expressing air tightness (air permeability), Midland Energy Services has also provided that figure: 1.07 m³/h.m² @ 50 Pa.

Air Permeability and Air Changes per Hour do not necessarily match, but in a medium sized house like this one, they can do. For a small flat or a large hotel, the two figures would be very different.

Another little power station goes live in West Bridgford

Although I've been somewhat preoccupied with air tightness of late, other things are happening. Today, the new PVs were hooked up to the electricity meter and we are now generating energy and feeding it to the grid. Now all we need is some sun....

Compared with all the other work we've had done, the 2 visits from the team at Carbon Legacy to install the PVs have been most straightforward. What is there to say? Day one and the panels appear on the roof, day two and the cables link to the inverter and from there to consumer unit and meter.

The amount of electricity which we hope the system will produce in a year should be a little over 3,000 kWh.    This will hopefully equate to a significant proportion of our total annual energy use (electricity plus gas) once the low energy refurbishment is complete. (I'm expecting total energy use to be between 6,000 and 9,000 kWh a year - watch this space!)

For comparison, the original estimate for annual energy use in the "as bought" state (based on a SAP energy model) was 36,000 kWh. In fact, energy-saving habits meant that we only used about 24,000 kWh of gas + electricity in a year.

This is like a mini version of the UK's energy challenge. The Department of Energy and Climate Change anticipate that the UK could face energy shortages by 2015. Hence the interest in generating more renewable energy in one form or another. However, there's a very long way to go to meet ever-growing demand for energy, especially with certain older power stations reaching the end of their lives soon.

However, if homes, business etc. were very energy efficient and used MUCH LESS energy (through additional energy-saving habits, insulation, more efficient appliances and equipment, etc), then the scale of the challenge would be reduced - and the chance of power outages in 2015 would also be reduced.

The gentle art of extreme air tightness

Now that we have a roof, windows and externally insulated walls, it is time to tackle the air tightness to make sure that this low energy refurb really does end up with low energy bills.

For this refurb, the air tightness layer is on the inside: the plaster on the brick walls, tapes around the windows, and a breather membrane across the rafters in the attic.

Today I was most fortunate to have 2 volunteers to help me with taping up the joins in the Intello. (Thank you Debbie and Elaine!)

After a little trial and error, I think I have found a way round some of the more complicated details (with the help of the most flexible type of tape in my tool box).

The moment of truth will be the air tightness test that will follow in a week or two. The preliminary test (before the plastering and the internal tapes and membranes) was respectable - better than the average new build. But once the internal air tightness barrier is in place, we are aiming for a value below 1 ACH at 50 pascals. Will we manage it? Place your bets now....

Cold bridge detailing

Ultra-low energy refurbs should come with a health warning - you need lots of stamina to keep plodding on!

The insulation has taken longer than anticipated. This is largely because of the "complicated bits" which arise when trying to achieve a refurb at the passive house end of the spectrum. 

Installing a lesser thickness of insulation would normally be quicker and easier, but putting on 2 layers of boarding in most places and being extremely careful at junctions between wall and roof, window and wall, etc takes more time. 

(The greater the insulation thickness, the more any "thin" areas matter - hence places like our eaves junction have taken a lot of effort to achieve what we hope will be a good result).

This week, the boarding is finished and the render coats are well under-way - the end is in sight!

Already, it feels pleasantly warm inside - even with some windows open and no heating system installed. Of course, it should be warm in the house in July - but it has been a rather cold July so far, and it is noticeable that the house is warmer than it was before the insulation went on.