Week 5 - Passivhaus Design Blog

Passive Design

External Envelope

This week, I had my presentation where I was able to show my final floor plan design, key considerations, the passivhaus principles I planned to address in my design and some concept sketches of the home. I received feedback in my WT4026 lab on my proposed design and it was mostly positive, and where I should start looking next. I was told to start looking at the benefits of open plan living as well as its health benefits and how it can effect your mood. Other areas I wanted to look at was my types of flooring, I have decided to go with polished concrete but I wanted to know how this was done and who could do it for me. I was also advised to begin looking at the external envelope of my house and start finalizing the details surrounding that. 

Foundations and Walls

The foundation I have decided to go with is the supergrund insulated foundation, with a wide cavity concrete block wall. Upon looking at the passivhaus principles it was clear that in order for my house to meet passivhaus standards I would require an energy-efficient insulated foundation to prevent heat loss. Traditional foundations rest directly on soil with no thermal break between the inner leaf of the concrete cavity wall and the ground. this allows for a significant amount of heat to be lost in the wall-floor junction. With an insulated foundation like the supergrund, it provides a continuous layer of insulation from wall to floor, with much thicker insulation than traditional systems. 

Supergrund is a system developed in Sweden and is manufactured in Co. Limerick by Aerobord Ltd, for our site this is great news as it means our foundations will be locally sourced reducing the buildings carbon footprint. The two main elements of the supergrund foundation are the perimeter ring beam, which supports the external load-bearing walls, and the floor slab. They are connected by stainless steel ties to prevent rotation of the ring beam. There are various shapes and sizes available which are determined by the type of material being used for the external wall, which in my case will be a concrete block, full fill cavity wall, which I will talk about later. 

The reasoning behind my choice is that supergrund foundation requires minimal excavation, having less impact on the landscape which is beneficial given that the site is so small. They use far less concrete and have a lower embodied energy compared to traditional foundation systems like strip foundations or stepped foundations. A big reason would be how supergrund prevents thermal bridging at the wall-floor junction, which allows it to meet passivhaus standards, added benefits to this would be how it will reduce energy bills and CO2 emissions. Finally this type of foundation is very quick to construct due to having allot less concrete and large lego like blocks of insulation that can be put together in minutes. However there are a few disadvantages to having this type of foundation, a high level of workmanship is needed and a great deal of attention is required to lay this foundation, while also having a specially trained team to install it. These disadvantages are minimal when it comes to having a energy efficient envelope to the home, granted costs may be higher but the occupants will save allot more money in the long run. Below you can see images I have taken from Trevors book on how supergrund foundations look and have completed my own detailed sketch on how my houses will be built using this foundation.

The external walls I have chosen for my design is a concrete block full fill insulated cavity wall. My reasoning for choosing this wall type is to do with my chosen passive house principles I wish to address in my build, as well as some of the 101 rules of good design that I would like to incorporate into my buildings. I discussed in last weeks blog under the subheading Rule 41 why I decided to go for concrete block wall over timber frame, but to briefly summaries it is to have as much thermal mass as possible in the wall that will work together with the insulation to ensure maximum heat retention and storage of heat that can be released slowly in the evening. Upon greater investigation into wall types I realised concrete block walls helped address problems I would have otherwise overlooked. This type of wall has a high level of structural stability due to its wall ties ensuring allowing the inner and outer leaves to act as one unit, it is sustainable due to the materials having a high level of embodied energy and it is also durable as concrete is very durable. Things like weather resistance, airtightness and moisture resistance are also huge factors I knew would be part of this system but ones I forgot about were its fire resistance, concrete is non-combustible and will resist collapse in a fire. Its high level thermal resistance was one I already explored and its ability to retain heat, but when I was thinking of heat passing through the wall I forgot to think about sound, concrete is quite acoustic resistant. The dense masonry is a good sound insulator which will be important to the occupants I have chosen to target which is post-grads and mature students, who will not want to listen to the load noises of students partying on the streets or the high volume of traffic on the main road.

Below is the images from Trevors book of a full fill cavity concrete block wall that meets passive house standard, I included this detail in my detailed sketch. 

In my house I will need to have some interior load bearing walls, I have a good idea where these will be but this will still have to be decided through weight distribution calculations. Below is a detail of how a load bearing wall will be laid in the foundations. 

Door detail

For my door details, which will be the same for front and back, the only difference will be the type of door installed. The back door will have to have a large fully glazed glass window in it to maximise solar gain since it will be south facing. The door detail must meet the passivhaus standard of having a U-value less then or equal to 0.80W/m²K which is the same for windows. Below you can see how the door sill and door head will be constructed in my houses, Next week I plan to finalise features like types of doors and my windows based off their U-value calculations, but for now, I plan to just finalise the external envelope details like this.

Window Details

The function of windows is to connect our indoor world to the outside by allowing natural light in and allow us to view the world outside from the comfort and warmth of our home. Windows are unfortunately the weak point of the building envelope and can become an area where not just heat energy, but also air and moisture can penetrate the building. If heat energy can penetrate through the window it can also escape through it, if not built correctly. The primary function of windows is to provide light but they should also prevent heat loss, protect us against the elements, prevent air movement when closed, and allow ventilation when open. 

Windows are actually quite amazing, as they have to meet the same performance criteria as the external envelope of the building while also serving their original functions. Next weeks blog will focus more on this, when I select the exact type of window I will be using, which will more then likely be a triple glazed window, looking at its benefits and at its U-Values. Below you can see my detail sketch and all the labelled parts of my window head and sill, these details will be the same throughout the house. The only thing that will change is their size, in the kitchen for example I will have a long narrow window like seen in the image from Trevors book below, and the living area will have the larger windows that have a sill closer to the ground to really open up the space and maximise the amount of natural light.

 

 

First Floor

  

Roof Details

The roof of my home is something I had not put much thought into yet, I knew my roof was going to be quite difficult to put together with the internal floor plan and still meet passivhaus standards. I have three different types of roof in my house design, one being a large monopitch roof, the next a low-slope roof, and there would also be a gable roof with a ridge and valley detail which you can see from my concept sketches below. However upon further research in trying to find a detail drawing of these rooves and how they join together I found out my roof detail is actually called a clerestory roofing system. I could not find any information on one that is built like mine and to passivhaus standard so I hope to ask Darren about this in my lab next week and see if I can get guidance from there, but for now I will focus on just the eaves detail. The problem I faced here was that my house is a story and a half so the roof trusts will not be resting on the wall but will be slightly higher up, below is an image that explains how my upstairs rooms will look and the type of eaves detail I will be using, labelled 2B, and the trusts labelled 2C. I also included an image of how the rafters will look and join to the monopitch side of the clerestory creating the valley roof.

I thought that slates would be the go to roof covering, but after researching different coverings I eventually decided to go with a zinc covering. Zinc is a naturally occuring metal that is mined in Navan, Kilkenny and Tipperary. The mine at Lisheen, Co. Tipperary is the second largest zinc mine in Europe and approximately 40% of Europe's zinc supplies come from Ireland. This is good for our site as it will not have to travel to far reducing the carbon footprint of the building, even though it is using up the earths resources, the benefits of having a zinc roof out way the negatives of using zinc, since we are still going to be exporting and mining it, at least it is locally sourced and a compromise sometimes has to made when it comes to passive house design and choosing materials. 

Zinc roofing is also extremely corrosion resistant, but will also offer further advantages over other metal rooves. Zinc roofing is self-healing, meaning given time any scratches it picks up will recover. It has a low maintenance regime and can last between 60 to 100 years. One problem with metal roofing that zinc roofing does not have is leaking, due to its standing seam joint crimping sequence which overlaps the sheets of metal and double locking them to avoid water seeping between the joints.

The issue I faced was trying to combine an eaves detail with the low slope roof detail of a zinc roof, I am not sure if my detail sketch is actually correct but I hope to find out off JJ in my Monday lab if it is right before I progress any further with my roofing, the detail sketch is seen below.

Next week after my presentation of my detail sketches I hope to have fully defined my external envelope of my house and be able to begin U-value calculations and detail drawings.