For anyone involved in the world of building or DIY we are always being told that solid walled houses are really bad insulators. Certainly compared to modern theoretical standards of building the computer programmes tell us that old solid walls perform really badly on this score. However times are changing and people are actually doing some real-life testing on old houses to see if the assumptions built into the computer models are OK. Lo and behold where we have been told that all solid walls have an U value of 2.1 what we actually find in the real world is that they are generally between 0.7 and 1.6 (the lower the U the better the insulation value). This is still higher than modern building regulations (these require a typical U value of 0.3 for a wall), but also a lot better than we were led to believe.
So we find that solid walls actually perform much better than thought. Research is also now looking at thermal mass. This is the capacity of a material to absorb heat in times when the temperature of the air is higher than the temperature of the material and also its ability to release heat into a room when the temperature of the material exceeds the temperature of the air. Thermal mass can also work by absorbing the heat from the sun when in direct sunlight (passive solar gain) and releasing it when the air is cooler.
This ability to retain heat for long periods of time can help to smooth out the temperature fluctuations in a room / house, thus making it cooler in the heat of the day and warmer in the cool of the night. This is great in the summer (as long as you don’t get too much passive solar gain as this can cause overheating), but still has the disadvantage of keeping a house cool in the winter (unless passive solar gain is used wisely).
So is there a way of having the best of both worlds?
Yes. Ideally solid walls are insulated (using a breathable insulation) on the outside, thus keeping the thermal mass inside and active whilst slowing the heat loss during the winter months. Wood fibre boards are excellent for this, as are thick insulating lime based renders.
Wood fibre boards are widely used on the continent and are readily available in the UK (if you know where to look). Contact the Eco Home Centre for access to these products. They are finished with a lime render and a suitable breathable paint (limewash / silicate paint) so in many instances the appearance of an already rendered / painted building will not change too much.
Insulating breathable plasters are more interesting. Just by using the right aggregate you can change the insulating value of a render. This is why we always recommend NOT using sand. Sand / crushed glass is a good conductor of heat and so doesn’t really give you any added insulation value, however, by using a crushed limestone, a volcanic rock or an air filled aggregate you can improve the thermal performance. So think about an InsOwall plaster or a Lime product from the Eco Home Centre.
If you cannot insulate the outer walls then you can look at insulating the inner walls of the house.
Many people make the mistake here of using insulating plaster boards. Please do not! The alternatives are:
1. Use Hemp Lime plaster (this is a coat of render / plaster that has hemp fibres in them that act as a insulator)
Pros: follows the wall to give an original feel to the walls; cheap to buy; can be applied as a DIY product or by professionals; highly breathable (if using a lime putty mix); does not isolate the underlying structure; no void for flora or fauna to exploit; decrement value
Cons: Not a brilliant insulator so depth required to get a good insulation
2. Use InsOwall plaster
Pros: follows the wall to give an original feel to the walls; cheap-ish to buy; can be applied as a DIY product or by professionals; breathable; does not isolate the underlying structure; no void for flora or fauna to exploit; decrement value
Cons: Good but not brilliant insulator
3. Calcium silicate boards
Pros: Can be applied as a DIY product or by professionals; breathable; does not isolate the underlying structure; no void for flora or fauna to exploit; decrement value
Cons: Good but not brilliant insulator; cost; does not follow walls and so needs a regularising coat first
4. Wood fibre boards
Pros: Can be applied as a DIY product or by professionals; breathable; does not isolate the underlying structure; no void for flora or fauna to exploit; decrement value; variety of thicknesses to suit needs; can follow existing surface to a large extent
Cons: Good insulator; requires a flat surface ideally, or a regularising coat is needed
5. Stud wall with breathable insulation infill
Pros: Can be applied as a DIY product or by professionals; breathable; creates a new wall so does not need to follow existing wall
Cons: Very good insulator; cost; isolates the underlying structure; void for flora or fauna to potentially exploit; lower decrement value
So, overall solid walls are undervalued for the advantages that they bring, but they can still be improved upon to bring them into the 21st century. For more advice on this vital area of refurbishment please contact the Eco Home Centre.
