What’s an insulation material?
With more and more people talking about building energy efficiency and passive houses, it has become more and more common to hear about insulation.
In this article, we explain what an insulation material is, to try and shed some light on the topic, and bust some myths.
The energy efficiency of a building, as well as its comfort level, are based on the quality of its thermal envelope. This statement is valid for both winter heating, and summer cooling.
The best way to achieve that, is to decouple the indoor environment from the external conditions, so that the internal conditions (temperature and humidity) can be controlled with a minimum amount of energy.
Schematic diagram of an efficient thermal envelope, with the insulation layer (yellow) wrapping around the heated/cooled portion of the building
The compactness of the envelope remains of primary importance. Besides that, the decoupling of the inside from the outside is achieved by inserting one or more insulation layers within the structure of the envelope (walls, roof, openings and so on). The envelope needs to be airtight too.
WHAT ARE WE INSULATING FROM?
In the first place, you need to understand what you what to insulate from.
The main goals for insulation are:
– protection from cold weather;
– protection from hot weather;
– protection from noise.
To improve the energy efficiency of a building, the structures that require insulation are the ones that define the thermal envelope, which enclose the heated/cooled part of the building.
Andrew Michler’s passive house near Fort Collins, Colorado
In this article, we address the first point of the list: insulation to protect from cold weather. We’re going to address the issue of protection from hot weather and from noise in our future articles.
KINDS OF INSULATION MATERIALS
Insulation materials can be grouped into two families: materials that insulate via conduction (that is, materials that delay the heat transfer by having poor conduction level), and materials that insulate via radiation (materials that have low heat emission via radiation). This article is dedicated to the first group.
Insulated glass units (double-pane or triple pane glass) work in a quite different way, and we’re covering them in a separate article.
CONDUCTION INSULATION
Cellular glass insulates via conduction: as a panel (black, vertical), and gravel
In all materials that insulate via conduction, it’s not the material per se to insulate, but the air that is trapped in it (or the lack of air, in case of vacuum panels).
Overall speaking, an insulation material needs to be lightweight, because it has to contain a lot of air.
Heat transfer through a material, via a combination of conduction, convection and radiation (ANIT)
The “ability” of a material to insulate is described by its lambda value (which actually represents the opposite, that is, the ability of the material to conduct heat).
The insulative properties depend on the kind of material (cork, rock wool etc.), and on its density. This can range from 20 kg/m3 (1.25 lb/ft3) to up to 250 kg/m3 (15 lb/ft3), depending on the final use of the material.
The lambda value of EPS depending on its density (MAICO)
The lower the lambda value, the more insulative the material. Keeping this in mind, here are some typical lambda values (*) for insulation materials, ordered from the most performing to the least one:
PUR: 0,024 W/mK (0,014 BTU/h*ft*°F);
EPS with graphite: 0,031 W/mK (0,018 BTU/h*ft*°F);
Rock wool: 0,035 W/mK (0,020 BTU/h*ft*°F);
Wood fiber: 0,039 W/mK (0,023 BTU/h*ft*°F);
Cork: 0,045 W/mK (0,026 BTU/h*ft*°F).
(*) Please note that the values listed here are declared lambda values. We’ll have a chance to explain the difference between declared lambda value and design lambda value in a specific article.
COMMON MYTHS ON INSULATION
Generally speaking, a material is considered to be “insulation” if its lambda value is around 0,040 W/mK (0,023 BTU/h*ft*°F).
A common myth, widespread among non-professionals (at least in Italy), is that brick or stone masonry is per se insulative. With an equivalent lambda value of 1,4 W/mK (0,809 BTU/h*ft*°F), stone masonry “loses” 35 time more heat than an average insulation material.
Just to comply with current Italian energy requirements, the total thickness of such a stone masonry wall should be over four meters thick (13 feet); it should be over nine meters thick (29 feet) to meet passive house requirements.
With its very thick stone masonry walls, this prehistoric Nuraghe in Sardinia is probably one of the few stone buildings that can be considered “insulated”
IS WOOD AN INSULATION MATERIAL?
Another common myth, quite common also among industry professionals, is that wood is an insulation material. With an average lambda value of 0,13 W/mK (0,075 BTU/h*ft*°F, for fir or spruce wood), wood conducts heat three times better than an insulation material.
Wood is not an insulation material.
As a secondary myth, many believe that structural elements made of wood do not cause a thermal bridge when crossing an insulation layer.
The thermal bridge caused by a wooden balcony. On the right, the isotherms
Can you see the isotherms, on the right? Can you see how they bend where the wood slab crosses the insulation layer? That’s a thermal bridge.
As pictured in the finite element analysis above, a wood element crossing an insulation layer causes a thermal bridge. Sure, the entity of such a bridge is several times lower than it would be if the element was made of metal or concrete.
In case of highly efficient buildings and passive houses, however, you need to take all these thermal bridges into account: the more efficient the building, the more precise the calculation needs to be. The thermal bridge above does not cause any problems as far as internal temperatures (fRsi = 0,94); however its PSI value (0,0247 W/mK) is quite substantial in a context of energy efficient buildings, and cannot be overlooked in the energy balance.
Andrew Michler’s Passive House
During Enrico’s recent visit to Colorado, we finally had the chance to visit Andrew Michler’s passive house.
At about 2.000 m (6.400 ft), in the mountains near Fort Collins, Colorado, this building is capable of remaining comfortable even in case of a power outage, with an interior temperature of about 18°C (64°F) with no heating.
Certified construction system for Passive Houses
The construction system certification is possibly the least known certification offered by the Passivhaus Institut, and yet it can help spreading passive buildings all over the world.
We worked on the first system certification for passive houses in a warm climate: we try and explain what it’s all about.
Colorado: our work ties become permanent
With Mariana currently involved full time with Natural Capitalism Solutions and AE Building Systems, our professional ties with Colorado are now solid.
This allows us to have experience in highly efficient buildings on both sides of the Atlantic, with some initial interesting considerations.
PHPP 9: a misunderstanding?
At the 2015 International Passive House Conference in Leipzig, Germany, the Passivhaus Institut presented version 9 of PHPP, which includes many new features to design passive buildings.
Many articles have been written about the new primary energy method and the certification classes. In our mind, however, PHPP 9 has more important new features: we explain what they are.
Airtightness: why is it so important?
With this article, we address one of the most important topics in the field of energy efficiency: the airtightness of the thermal envelope.
Whether the building is a new construction or a renovation, its airtightness plays an important role for comfort, energy efficiency and durability of the structure.
Thermal bridges: the temperature factor fRsi
We continue our series of articles on the topic of thermal bridges: this time, we illustrate the fRsi value, which describes the thermal ”strenght” of a node under the point of view of internal surface temperatures.
As we have explained in a previous article, the PSI value describes a higher or lower heat flow caused by a discontinuity in the thermal envelope – a thermal bridge – the fRsi factor is of primary importance for health and comfort considerations.
Passive House Days in Cavriago: a great success
On Saturday 14th and Sunday 15th, our construction site in Cavriago was open to the public for the International Passive House Days. On Friday 13th, the local Scuola Edile visited us for a class on energy efficiency.
The event was a great success: the unexpected number of visitors (more than 100!) shows the great interest for Passive Houses in Italy.
In Cavriago, we’re currently building two certified Passive Houses, with a load bearing concrete frame and baked clay blocks as infill, and a wooden roof. For the first time in the world for a “warm” country, the whole construction system is being certified: we’re going to present it at the 2016 International Passive House Conference in Darmstadt, Germany.
A moment during the visit of the local Scuola Edile.
The event attracted over one hundred people, with a mixture of professionals and non professionals. We’d like to thank the visitors who came from Garfagnana and Faenza (over 100 km away!), as well as people from Reggio Emilia, Modena, Parma and Cremona.
We also would like to thank the local Architect’s Association, who attributed continued education credits to our event. Our site was visited by over twenty architects.
The construction site open to the public, on Saturday and Sunday.
The event was a success: one of its main goal was to locally share information about Passive Houses. For this reason, we are considering replicating the event later on, probably around February 2016.
We include here the photos of the information panels we prepared for the event.
Pre-existing building
Heath and comfort
The Passive House
The design of a Passive House
Construction details
Thermal bridges
Mechanical ventilation and airtightness
Construction photos
Costs of a Passive House
The most efficient solar panel: the window
On site verification
Thermal bridges: the PSI value
For new builds as well as energy retrofits, worldwide the construction industry is shifting more and more towards zero energy buildings and Passive Houses.
With the thermal envelope becoming more and more advanced, the correct evaluation of thermal bridges becomes critical: with this article, we explain the PSI value.
International Passive House Days in Cavriago, Italy
The International Passive House Days are an event organized by the Passivhaus Institut, to publicize what a passive house is, and to let people “touch” the state of the art of construction in terms of comfort and energy efficiency.
This year, we take part to the event with our Cavriago project, where we are currently building two single-family passive houses: our construction site is going to be open to the public on Saturday 14th and Sunday 15th.
