GREENACRE BUILDING FAQ
Frequently Asked Questions
Passive House
What is a Passive House?
‘Passive House’, or Passivhaus as it is called in its native Germany, is a low-energy building standard. For a building to be signed off as a Passive House it must have incredibly low heating and cooling needs - typically 90% less than non-Passive House buildings - while still maintaining an indoor air temperature of 20C degrees.
What is an MVHR?
MVHR stands for Mechanical Ventilation and Heat Recovery. In order not to need much heating or cooling Passive Houses must be incredibly well sealed - no draughts. A sealed building keeps the house a consistent temperature but doesn’t provide any passive ventilation. So an MVHR and a whole house ventilation system is used to bring fresh air into the building. The clever thing about an MVHR as compared to other ventilation systems is that it recovers the heat from the old air its pumping out and uses it to warm the fresh air thats being pumped in. This keeps the house perfectly ventilated without cooling the indoor air temperature.
Can I open the windows in a Passive House?
Yes! Not being able to open the windows is one of the longest enduring myths about Passive Houses and its absolutely not true. Just because you have a ventilation system doesn’t mean you can’t open the windows - you can open them as much as you want. What it means is that your house will be perfectly ventilated regardless of whether or not you open the windows.
Retrofit
What is retrofit? - is it different from renovation?
Retrofit is the word we use to describe construction works on an existing building to improve its energy use. In contrast to renovation, which is about changing how a building looks, retrofit is about changing how a building performs.
What does a retrofit involve?
This all depends on what challenges you’re facing with your building and what you want to achieve. Insulation is typically a key part of most retrofit projects. Roof, floors and walls (internally, externally or cavity) can all be insulated. Changes to heating, electricity, ventilation and water systems can also form part of a retrofit project.
If you’re not sure what you need don’t worry - thats what we’re here for. We always offer our retrofit clients a thorough assessment of their existing building to make sure we’re focusing on the right things in the right order.
What is ‘Ready for Retrofit’?
‘Ready for Retrofit’ in an industry term to describe construction works that need to be completed BEFORE any retrofit measures are undertaken. For example, in our Ready for Retrofit assessment we might identify a leaky pipe that is saturating one of your walls. You might have approached us to externally insulate that wall, but one of our Ready for Retrofit recommendations would be to first fix the leaky pipe and dry out the wall.
Although Ready for Retrofit works can feel frustrating or like a diversion, we can’t emphasise enough how important they are. In the example provided above for instance, that wet wall would be losing 40% more heat than if it were dry. No matter how you look at it, dealing with any existing problems first is simply the only thing to do.
What is ‘fabric first?’
‘Fabric first’ is a design and build approach which prioritises a consideration of what the building is made of, and how those materials will perform, over and above other ‘add on’ features such as solar panels.
Often people can think than an ‘eco building’ is one that generates its own electricity. While this is of course desirable, at Greenacre our primary focus will always be on the fabric of the building and making sure this is losing as little energy as possible. After all, the less energy your home needs, the less you have to generate.
Sustainable Building
What is sustainable building?
Sustainable or ‘eco’ building can mean different things to different people. For us at Greenacre Building it means prioritising the use of natural materials during construction and achieving a low-energy performance on all our projects.
What do you mean by ‘natural materials’?
Sustainably sourced timber, wood fibre board, WARMCELL blown newspaper insulation, lime plaster, clay paint and recycled glass are some of our most used natural materials.
Will my house be as warm as a modern house if it’s made out of natural materials?
Yes! Warmer, probably. We find that natural materials offer not just an adequate performance but a superior performance. Natural materials offer unique properties, like breathability and moisture management, that modern synthetic materials struggle to achieve. On solid wall retrofit projects natural materials work better with the buildings existing structure than their synthetic counterparts.
Energy-Use Design
What is Energy-Use Design?
Energy-Use Design is the term we use to describe how we assess and model the energy-use of your project. We use the Passive House Planning Package (PHPP) computer software to help us accurately quantify how much energy your house uses and loses.
I’m not aiming for Passive House certification - would my project still benefit from Energy-Use Design?
Definitely yes. The PHPP software was designed to support the design process for Passive Houses but we use it on almost all our projects regardless of Passive House certification as it gives us a solid baseline of data from which we can accurately advise you on your unique project. Without it, how does anyone know exactly how much insulation you need in your loft? Or just how much difference triple glazed windows will make on your house verses just getting modern double-glazed ones?
A PHPP model and an energy-use report will give you that information with no guessing. That way you can be sure you’re investing your money in the right things on your project and making the right design decisions at the earliest stages - while its still easy to change your mind.
Lime Plastering
How is lime different to normal plaster?
If you go to the building merchants to buy some plaster you’ll probably have two choices: cement (the grey stuff) or gypsum (the pink stuff). Both have their place in modern construction, and we use gypsum to plaster most of our internal walls in new builds. But we love lime…
Lime plaster is made from powdered limestone. Before WW2 every building would have used lime plasters, renders and mortars. Now its a specialist product, but one which offers a lot of benefits to modern as well as historic buildings.
What’s so good about lime?
So much! Here are a few things:
Lime plaster is brilliant at managing moisture. It can absorb and release moisture without cracking or failing. With a high PH, lime is also a natural fungicide, making it resistant to mould.
Lime plaster also has some flexibility, which means if you have a house which ‘moves’ with the seasons (building fabric expanding and contracting), the lime plaster can move with it - without cracking.
Lime plaster is relatively soft when set, so it can be removed fairly easily if needed for repairs or structural works without damaging the building fabric beneath.
Lime plaster and render is beautiful; it has a unique patina and texture to it that makes it very aesthetically pleasing. You can also easily add pigments to the lime before applying it to change the colour of the plaster or render without needing to paint.
I have a heritage/period property - should I be using lime?
Almost certainly yes. Unless your building is made out of cob, in which case you probably need clay plaster - luckily, we offer clay plastering too.
If you’re not sure what you need just get in touch and we’ll be able to advise you.