Sunday, 16 June 2013

Hints and tips from Open Eco Homes: aerogel, lime plaster and more.

I visited three homes yesterday through Open Eco Homes - an annual event in Cambridge organised by Cambridge Carbon Footprint. The idea is to look at what people have done to their homes to make them more energy efficient and sustainable, and ask them about having it done - who did it, what was it like, how do they like it now, what would they have done differently and so on. Of the three houses I saw yesterday two were retrofits with solid wall  insulation. Here are some of the tips I picked up.

Aerogel has it's uses.

Airogel is nearly twice as insulating as the same thickness of PIR foam (such as cellotex, kingspan and so on) but it costs several times as much. It is beyond most budgets for normal situations but it is extremely useful when there isn't room for the conventional choices. I saw a house (Ross  Street) where it was used on a side wall in the rear corner very close to a window facing the garden. They could not insulate this wall on the outside because it would mean encroaching on a shared alley. On the other hand conventional insulation on the inside would encroach on the window and replacing that with a smaller one would also be expensive.. It worked out cheaper to leave the window where it was and use aerogel instead: they used an aerogel/plaster board composite (10mm aerogel bonded to 9mm of plaster board called Magnaline Superslim from In another house (Richmond Road) they used arogel in a similar situation to avoid moving a door. They used aerogel blanket from 10mm of aerogel is not as good as 100mm PIR but by my calculation they will still have cut their heat loss by more than half (solid brick U-value initially about 2.0 reduced to 0.8).

NB. Aerogel is difficult to work with and cutting it produces a fine dust which is unpleasant, though nothing like as toxic as conventional silica dust (because it is not crystalline so the dust does not have sharp edges).

Draught stripping a suspended floor works wonders.

Both houses had insulated under their suspended wooden floors and then found they still were not very warm because of draughts between the boards and under the skirting boards. When you insulate under your floor you still have to leave a void for ventilation and if there are gaps in your insulation then the cold air gets in. You can think of your house as a giant chimney because unless you have it really airtight, which is virtually impossible in an old house, warm air inside rises and sucks cold in at the bottom. Anway, having insulated your floor the air underneath is even colder and if it doesn't come up between the boards it will sneak in around the edge and under your skirting boards. The lady in Ross Street fixed this herself using Draughtex and she said it was quite straightforward to use.

Honeycomb blinds look great and help to insulate too

Ordinary window blinds give you only one layer of material but honeycomb blinds open out into small hexagonal cells which help to trap the air. There are lots of brands but this web page has a good picture showing the hexagonal structure.

Obviously if the blinds are not fitted well in the window frame then air can leak around the edges but they are still more insulating than venetian or roman blinds.

Put your combi boiler in the kitchen

I have written before about the issue of long pipe runs between your hot water source (tank or combi boiler) and your taps (How to save on hot water). You can have several litres of water sitting in the pipe that you have to run through before you can get any hot to your sink - this water has been heated once and now gone cold. I measured how much cold water I had to throw away before the kitchen tap got hot in our house and it was 4 litres. In the winter that heat may still be useful but it certainly isn't in the summer. The Ross Street house had a combi boiler right next to the kitchen sink and on other side there was a washing machine with a hot water feed. You can't do better than that.

Lime plaster is difficult to work with

Unlike ordinary gypsum plaster, lime plaster can let the material underneath breathe. This means if you are using organic insulation such as wood fibre it can help to manage humidity in the room. However, handling lime plaster is very different from normal plaster and most plasterers won't have experience with it -  so do warn them before you start and try to find one who has used it before.  Also you may not get quite such a perfect finish as we are use to.

Open Eco homes events are always interesting and good fun too. You meet some lovely people and come away with lots of ideas. Also, you can learn lessons from other people's experience, which is much more pleasant than learning from your own. The Cambridge one is running next weekend too so it is not too late for this year but if you don't live here there may be something similar near you.  There are lots around the country such as Bristol Green Doors, and others in Stroud and Lewes - if there is one near you do take a look.

Also, if you are near Cambridge come to the Transition Cambridge Energy Group forum on insulating solid walls on 27th June.


  1. I wonder how Draughtex compares with this:
    Either way both seem alarmingly expensive given how simple they are!

  2. The old fashioned way to fix draughts was using papier mache. The modern products are easier to use but they do cost more. There is more information about draught stripping here:

  3. Thanks for providing very helpful piece of allocation regarding open eco homes. I enjoyed learning through and most importantly glad to learn new modern products to fix draughts though it's fixing process pretty costly.