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I decided to do the refurb on the house for several reasons. While I suppose I’m environmentally-minded, I guess a large part of why I did the refurb was that the house was damp and dark when I bought it, and parts of the house (e.g. the bathroom) were freezing in cold weather, and I decided that I didn’t want to live in a place like that. In any case, I had to do a certain amount of things anyway since the house was in a fairly bad state (e.g. window frames were rotten), so I found that this was a good time to try to make it better while I was at it. The only thing was that I didn’t know much about energy efficiency or in what order to do things, so I spent some cash on a few books and read up about what I should do, after which I made a do-list and decided roughly in what order things should be done.
• 28mm gap, argon filled double glazing, U value 1.5
• 70mm thick friction-fitted foil-backed Kingspan internal insulation, U value 0.37
• 270mm thick Carbon Zero mineral wool added to loft space, U value 0.16
• 100mm thick foil-backed Kingspan friction-fitted between joists (floor insulation), U value 0.24
• 120mm thick friction-fitted foil-backed Kingspan fitted to bathroom ceiling, U value 0.12
• Ventilation test done and the result was 7.85 m3/hour/m2 before final draught-proofing was completed so the result should be better- update coming soon
• MVHR installed (Xpelair Xcell-300) with extraction from kitchen & bathroom, 91% recovery
• Remeha Condensing boiler with room Stat Programmer & TRVs
• 90% of light bulbs are energy efficiency
• Added wood burning stove downstairs in one of the fireplaces
• Water saving devices include; Ifö sink, toilet & bath which are designed to save water by design (toilet flush 2 or 4 litres)
The main improvements have been a reduction in humidity, a warmer house and better air quality. I had an injected damp course done on the whole ground floor, but what made most difference to the humidity (measured by how much condensation was on the windows) was dealing with the evaporation of water from muddy ground below the ground floor (through putting a type of gravel down, covered with plastic) – this cleared up the condensation overnight. In addition to that, I draught-proofed the whole ground floor to prevent air leaking from the crawl space into the living areas. Humidity from other sources (e.g. bathroom, breathing, cooking) is now also kept in check also by the ventilation system that extracts moist stale air and replenishes with air from outside. The humidity in the house now averages between 40 and 60% and I find that in winter when temperatures outside are lower, the system gets more efficient at reducing humidity in the house compared to summer. Regarding temperature, the house is much quicker to heat up than before due to the wall & floor insulation and draught-proofing – meaning I don’t spend much on gas.
I have three favourite parts rather than just one, since I know that these aspects go together to be effective: insulation, draught-proofing and ventilation.
I didn’t do a final air test, but had one done once most insulation and airtightness was done, and the result was 7.85 m3/m2/hour (that is the UK method for measuring leakiness) which translates to about 9.3 air changes/hour (m3 of air compared to volume of house, which is the Passive House method). This was still leaky because there was a large leak from an open chimney flue and a few other places, so if I redid it, I reckon I’d be somewhere around 3-5 air changes – which isn’t enough. I now know you really need to be somewhere around 1.5 air changes an hour for the MVHR unit to operate efficiently. So my air tightness wouldn’t have been good enough, it needs a lot of attention to detail.
Xpelair Xcell300. Wouldn’t do that again – hopeless technical help and fan speeds cut out once you reduce to its minimum, which is still too fast for my house volume. You need fully programmable fan speeds ideally as well as one that is efficient etc.
No it draws air from inside the house, which works well as air comes in via ventilation system, so there doesn’t seem to be a problem in terms of O2 levels.
I’d recommend doing an energy analysis on the house first and then fit the wall insulation work into a retrofit project that might include other measures while you’re at it. This is because wall insulation of external-facing walls will most likely be a major contributor of heat loss and carbon emissions, but it might not be the biggest factor. If space heating demand or carbon emissions are your main driver for wanting to do the work, then you need to be sure you’re targeting the right thing(s). Also depending what your goals are, if comfort is a big driver for you wanting to do this work, then airtightness and ventilation will be a major contribution to feeling comfortable, not insulation alone.
Also if you’re doing internal wall insulation, you really need to get the airtightness right on the internal face – any gaps will mean moisture can get through and cause interstitial condensation on the cold original wall surface leading to mould (e.g. from modeling and field tests, we know that a typical 1mm gap in air membrane that is 1m long can allow 360g of water to condense – this is with conditions of 20 deg C inside and 50% relative humidity, and 0 deg C outside with 80% relative humidity). So it really kind of links in to other parts of a retrofit and I’m not sure it should be done in isolation without airtightness/ventilation.
The gravel was called ‘MOT’ – don’t know what it stands for but you get it from builder merchants like Travis Perkins. I put down about 5cm depth all over the crawl space, which equated to about 4.5 metric tones! I don’t know exactly what type of infill it is, but it tends to soak up moisture a bit, so it helped to make a dry-ish base on which to stand and sort out my joists before putting the DPM down.
The humidity was sorted overnight after the plastic sheet went down, even with all the floorboards up and joists exposed. I know this because I’d get condensation on the windows every morning and the morning after there was none. It just showed that a lot of moisture was coming from evaporation from the ground. Also I know this because the underside of the original chipboard floor was covered in white mould except for the place where it went over the base of the hearth – here there was no mould. Again confirming that evaporation from ground was a big issue.