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What do you mean by long term sustainability?

Whilst we appreciate the need and rush to reduce our impact upon the planet we believe that we also need consider the implications of our actions.

Ok, so what do you mean by that?

When we 'retrofit'/add insulation, reduce 'draughts' or 'air-leakage', or use materials with different properties than the ones previously used, we physically change the way a building will function. We believe that this should be understood and appreciated before undertaking any works which may have detrimental consequences to a building. After all, the most sustainable building is usually one that is already built.

You warn of detrimental consequences, can you give some examples?

Using a 'non-pervious' or 'waterproof' paint or render on an older building is one of the most common 'good intentions' that usually have detrimental consequences. If a 'waterproofing' paint or hard cement render is used to try and keep moisture out, by their very nature it means that any water that is already inside or seeps in later (through cracks in the paint/render, gutters that are blocked and over-flowing, blocked/in-adequate drainage causing moisture to rise up within the walls) can't escape (be evaporated away) and are trapped in.

Why are wet walls a problem?

They are more thermally conductive, hence why you should never use a wet towel to remove something hot from the oven as you will probably burn yourself! Wet walls can loose heat 25 times faster than dry ones, so the simplest way to improve the energy efficiency of walls is to make sure they can dry. Obviously the wet walls will be cold as a result, making for an uncomfortable and unpleasant internal environment, but can often lead to mould issues and even to decay of the building fabric/structure. There are other less obvious costs, cold homes are not only reported to increase the likelihood of minor illness such as cold and flu, but also mental health issues, respiratory and cardiovascular issues, and can cause excess winter deaths when compared to more energy efficient homes. Warmer housing has been attributed to 38% less sick days, 50% less missed school days, and even saving the NHS £0.42 for every £1 spent on keeping homes warm (Department of Health, 2009). Studies in England have suggested that England’s poor housing stock costs the NHS between £600 million and £2.5billion annually.

So you are not a fan of cement then?

If cement was a country it would be the 3rd largest emitter of CO2 in the world. That is not to say that it is inherently evil, just maybe we need to consider why we are using it and where do we actually need to use it. But no, not really a fan of cement. Probably due to spending far too much of our time hacking it off buildings where it should not have been applied, and is subsequently causing issues.

What about insulation, surely we need to be adding this at a great rate if we are to improve the energy efficiency of our building stock and meet our legally binding climate change targets?

Possibly, but only if we are consistent in our approach, understand what we are adding and how that will impact upon how the rest of the building functions. For example, when large amounts of 'impervious' foam and foil insulation are added to walls internally it reduces (or at least attempts to) any heat getting 'lost' into the the wall itself. It may do this, but if it does, then it will also increase the risks of problems with moisture in any place the the insulation is not continuous (think of a floor joist penetrating in to the wall etc.), or, by preventing moisture from being able to get out (evaporate) of the wall internally (ideally most of this should happen externally), or by reducing the temperature on the outside of the wall which then increases the risk of frost damage.

Insulation Vs Ventilation, which is more important?

Without adequate ventilation not only would we struggle to survive but so would our buildings as they would be stale, damp and mouldy places. People seem to care a great deal about outdoor air pollution but seldom even give indoor air quality a thought, we think this is wrong, particularly if we seem to spend more time indoors now than ever before. Yes we need to be insulating, but not without 1st making sure ventilation is sorted.

What is the difference between lime and cement?

Cement is harder and more vapour resistant (waterproof), whereas lime is softer, and allows for more moisture to pass though. So unlike a cement based render, a lime render can allow water into a wall when it rains but importantly, it will then let the moisture out (to be evaporated away) when it stops. 

Soft mortar sounds worrying but you suggest it's a good thing, why?

The mortar is there to keep the stones or bricks apart, and should usually be weaker than the bricks/stones used. When buildings move and crack (which they do over time) it's preferable to have the mortar crack and not the bricks/stones as it is far easier to rake out and re-point mortar than it is to replace the bricks/stones. Traditional lime mortars are often the main method used to help aid the drying out of solid wall buildings, it does this by drawing moisture out from within a wall to be evaporated though the pervious (not waterproof) pointing. When harder cement mortars are used it is usually quite easy to tell (if it has been there for a while) and the stones/bricks will of started to crack and deteriorate, far too many examples of this can be seen in and around Aberystwyth, please stop!

I live in a exposed area and have been told I need to use a cement render, is it true?

That line of thinking relies on the walls being dry in the first place, the cement render never cracking, failing, or being compromised, which might be true when installed but doesn't usually take long for someplace to let in water. Our line of thinking admits that the wall will get wet and our job is to use materials and traditional techniques that will help it to dry out. One such technique is to apply a lime-based "roughcast" or "Tyrolean" textured finish that drastically increases the surface area of the wall which allows for faster rates of evaporation and subsequent drying.

The building inspector tells me we need to meet a certain U-value in the building regulations, is this true?

That depends. The Welsh Government "Approved document part L1B - Conservation of Fuel and Power in existing dwellings" is there to "provide guidance" on requirements for "reasonable provision" in "ordinary circumstances".  The document specifically states that special considerations apply to buildings "of traditional construction with permeable fabric that both absorbs and readily allows the evaporation of moisture". So it depends upon the type, age, location, etc. of the building in question. For example, in older buildings it is often not possible to add wall insulation where it's most effective (on the outside), and risky to apply lots of it on the inside (particularly when using the wrong type of insulation and not providing adequate ventilation), so a balance has to be struck. 

My old single-glazed wooden windows are cold and draughty, should I just replace them with double glazing or fit secondary glazing?

Why not start by just repairing them and fitting the brushes that help to minimise draughts? Or by hanging curtains? Both of these interventions will usually help and they are far cheaper and less risky than replacement. A common problem found in older buildings that have had the windows replaced with double-glazed UPVC is that it moves the condensation (that would of once formed on the glass) to the now colder surface that is the wall reveal. To make things worse, by reducing the draught (or passive ventilation as sometimes known) it will exacerbate the problem of stale moist air increasing the amount of condensation on the cold reveal. We visit a lot of houses which have had their beautiful old wooden sash windows ripped out to be replaced with the soulless (and often short lived) modern plastic ones that over time may have caused just as many issues as they sought to solve. Once they are gone, they are gone.

You do lectures, teaching and training, what sort of thing?

Steve has been an external lecturer and practical teacher at the Centre for Alternative Technology in Machynlleth for a couple of years now, focusing on building with lime and plant based fibres and the realities of retrofit. We believe in what we do and believe that we also need a shift in mindset about how we view construction and our wider built environment. We seek to engage, listen, discuss and inform, whether that be to home owners, school kids, tradespeople, apprentices, landlords, or local government. Why, what, and how we do our work is important to us. We also realise that many people who own their own homes wish to try and undertake works themselves, as always we do recommend using trained and competent professionals but if you do insist then we do ask that you employ the services of someone to offer training, guidance, and some form of quality insurance to the work you are undertaking. 

Questions and Answers